VSR-411
(2+2)
General Veterinary Surgery, Anaesthesiology and Diagnostic Imaging.
SYLLABUS GENERAL SURGERY- THEORY Introduction history classification surgical terminology and development of veterinary surgery. Asepsis antisepsis, their application in Vety.Surgery. Surgical Risk & Surgical judgement. Management of shock, haemorrhage & its management. Principle of fluid therapy in surgical patients. Differential diagnosis and surgical treatment of abscess, tumors cyst, haematoma, necrosis, gangrene burn, wound, classification, symptoms, diagnosis and treatment & complication ,their treatment and prevention. PRACTICALSSurgical instruments and equipment. Operation theatre routines. Surgical pack: Preparation, sterilization and handling. Familiarisation with suture materials, surgical knots, suture patterns and their use. Familiarisation to live surgery haemostatsis.
ANAESTHESIOLOGY- THEORY (Region specific) Preanaesthetic consideration and preanaesthetics. Aneasthesi, local analgesia / anesthesia, general anesthesia, anesthestic agents (like barbiturates, dissociative agents) inhalation anaesthesia and agents, maintenance and monitoring of general anaesthesia, aneasthestic emergencies and their management. Only awareness of neuroleptanalgesia, electro-anesthesia, acupuncture, hypothermia, muscle relaxants. Post operative pain management. General principle of chemical restraint of wild / zoo
animals and aneasthesia, of lab animals.
PRACTICALSFamiliarisation with aneasthetic, apparatus, endotracheal tubes. Laryngoscope, gadgets for monitoring pre aneasthetic preparation, induction of general aneasthesia, in small and large animals and endotracheal intubations in dogs. Demonstration of inhalant anaesthesia monitoring of general aneasthesia, and the management of aneasthestic emergencies. Use of artificial / assisted respiration. Various methods of local infiltration aneasthesia, and regional block, for surgical procedures of different regions of body in Large and small animals. Chemical restraint of lab animals. (Visit of a wild animals facility and audiovisual aids)
DIAGNOSTIC IMAGING –THEORY Production and properties of X-rays. Factors influencing production of X-ray. Principles of viewing and interpreting X-ray films, classification of radiographic lesions, Contrast radiography: classification, materials, uses, indications and contra indications. Biological effects of radiation, radiation hazards and their prevention by adoption of safety measures. Principles of ultrasonography and its applications in veterinary practice. Awareness on principles of radiation therapy, Isotopes and their uses in diagnosis and therapy; Principles and application of CT scan, MRI, echocardiography, scintigraphy, gamma camera, xeroradiography and Doppler.
PRACTICALFamiliarization with operation of the X-ray equipment, X-ray accessories and adoption of safety measures in radiography. Dark room equipments, X-ray film and its processing. Intensifying screen and its uses. Radiographic technique-positioning of small and large animals. Handling, viewing and interpretation of X-ray films. Familiarization with film contrasts, density and detail, common defects of X-ray films. Radiographic anatomy and interpretation of radiographic lesions. Demonstration of contrast technique in small animals. Familiarization with ultrasonography of small and large animals
PART- I (General Veterinary Surgery )
COURSE OVERVIEW This course is designed to teach students the general veterinary surgery, general anaesthesia and radiology. The objectives of this course are,
To assist undergraduate students in understanding o the pathophysiology, differential diagnosis and surgical treatment thorough knowledge of this subject help the student to develop the skill to diagnose and perform surgery. o the various disease conditions are enumerated system wise with etiology, clinical signs , and diagnostic methods enumerated in a sequential way. o monitoring of anaesthesia o anaesthetic emergencies and their management o production and properties of X-rays Illustrations added will aid the student to give quick rememberence of the disease process. View vidieo procedures by clicking on the icon. Applied knowledge of this course information with analytical thinking will facilitate the understanding of the differential diagnosis. Overall knowledge gained from this course will help the student to develop skill ability to approach surgical cases in a systematic manner.
LEARNING OBJECTIVES
History of surgery Classification General surgery principles Pre and post-operative considerations History and Development of Veterinary Surgery
Module-1 =
History and Development of Veterinary Surgery HISTORY OF ANAESTHESIA
300 B.C. Juice of mandrake plant was used during Alexandrian period. Egyptians induced unconsciousness by compression of the carotid arteries. In following centuries various plants containing opium and atropine likecompounds were used. 1540, Paracelsus administered ether to chickens. 1771, Joseph Priestley isolated and identified depholgisticated airoxygen and depholgisticated Nitrous oxide. 1825, Hentry Hill Hickman performed surgeries on experimental animals by inducing asphyxiation using carbon dioxide. 1831, Chloroform was discovered independently by Von Liebig, Souberian and Guthrie. 1846 William Thomas Green Morton (1819-1868) demonstrated the use of ether as anaesthetic for the removal of tumor in humans. Later ether was patented as Lethon. Morton deserves the chief credit for the introduction of ether as anaesthetic agent. 1846, Chloroform was used first in animals by Flourens. 1847, Horace Wells (1815-1848) though lived only a for short duration, published valuable information through his news letter “A History of the discovery of the application of Nitrous oxide gas, Ether and other vapours to surgical operations”. 1857, John Snow administered chloroform to Queen Victoria during the delivery of her eighth son Prince Leopold and later it became popular.
Sir William Macewen (1847-1924) Pioneer of oral and nasolaryngeal intubation in diphtheria patients as an alternative to tracheotomy using rubber, gum elastic catheters and metal and flexometalic tubes. Later he administered chloroform and air through the tubes for induction of anaesthesia. William Stewart Halsted (1852-1922) Famous surgeon proposed the “Principles of Surgery” originated nerve block techniques like blocking brachial plexus, nerves of the face, internal pudental nerve and posterior tibital nerve using cocaine in 1886. Classification of surgeryDEFINITION
Surgery is a branch of Medicine, in which manipulative and other modalities are used in treating injuries, deformities and diseases. The word surgery originated from a Greek word “CHEIR” meaning “HAND”, and “ERGON” meaning “WORK” German language it is called CHIRURGIA. FUNCTIONS OF A SURGEON
A surgeon mainly deal)s with o Repair of tissues. Example: Treating a lacerated wound. o Reconstruction of tissues. Example: Suturing divided tendons and nerves. o Control of infection. Example: Post pharyngeal abscess. o Prevent spread of malignancy. Example: Tumours of lung. o Alter or correct structural and functional disorders.Example: Correction of knuckling of fetlocks (Structural disorder). o Removal of harmful or useless parts. Example:Gangrenous limb, gangrenous bowel. REASONS FOR SURGERY
To save life of an animal. To prolong life of an animal. To hasten recovery from an injury. For elimination of disease process. Example: removal of a benign tumour. For cosmetic reasons. For correction of deformities. For replacement of a part by an artificial one. To make an animal sociality acceptable. Example: Castration in a male cat. To aid in diagnosis. Example: Exploratory laparotomy. For investigation in research work. Example: Rumen fistulation.
OBJECTIVES OF SURGERY
Restoration of functions to as near normalcy as possible. To eliminate life threating maladies (choke, intestinal obstruction). Removal of diseased part - gangrenous tail Removal of foreign bodies - rumenotomy To hasten recovery process - wounds and fractures To make the animals to less dangerous - debudding For economic reasons - e.g.,castration in pigs, cattle etc.,to improve the live body weight For aesthetic purposes - removal of supernumerary teat To replace the organs - Organ transplantation For confirming diagnosis - exploratory laparotomy . BASED ON NATURE OF SURGERY
General surgery: Is carried out to restore the normal function of the body without substituting or discarding any part of the body. (Restorative Surgery) Extirpative surgery: Involves removal of a part e.g.,ovariohysterectomy, eyeball Plastic surgery: To restore the destructive part which includes reconstructive surgery (a structure is reconstructed) e.g., skin grafting and cosmetic surgery (which improves appearance) e.g. docking, ear cropping etc. Replacement surgery Physiological surgery - Portosystemic shunt Diagnostic surgery Exploratory surgery
CLASSIFICATION BASED ON REGIONS/SYSTEMS INVOLVED
Specialization on particular system examples o Thoracic surgery o Cardiovascular surgery o Orthopaedic surgery o Ophthalmic surgery o Neuro surgery o Urogenital surgery
CLASSIFICATION BASED ON INSTRUMENT/APPLIANCES USED
General surgery - Is used when in a procedure common surgical instruments are used Micro surgery - Magnification facilities are used for specialized surgical procedures.
Cryosurgery - Involves controlled use of substances like liquid nitrogen which produces freezing temperatures to destroyed abnormal tissues. Electro surgery - Electricity is converted into heat to incise tissue. Laser surgery - Laser beams are used to cut or destroy diseased tissue Ultra sonic surgery - High frequency waves are used to destroy particular tissue or a substance (lithotripsy) Endoscopic surgery - involves use of rigid and flexible scope e.g., laparoscope, arthroscope, bronchoscope TENETS OF HALSTED
HALSTED described certain essential principles for wound healing. These include:
Gentle handling of tissues to avoid unnecessary trauma Aseptic procedures to control infection Anatomical dissection of tissues with sharp instruments. Avoid damage to major blood vessels and nerves Control haemorrhage with fine, non-irritating suture material in small quantities Obliteration of dead spaces to avoid accumulation of blood and exudates which favour pus formation Use of Minimum suture material Avoidance of suture Tension Immobilisation - Give rest to the operated part and to the patient G A A C O M T I - accronymn CLASSIFICATION OF PHYSICAL STATUS
It reflects an attempt to define the condition of the animal and thereby surgeon becomes alert to problems which may occur during anesthesia and surgery. Physical status may be of o Good o Fair o Poor o Extremely poor o Emergency good o Emergency poor o Moribund condition The patient -> Identification History Preparation of patient .
IDENTIFICATION
Identification is important due to veterolegal cases Extension of preoperative medication when owner is not available To prepare operative site To avoid chances of wrong animal being operated To avoid mixing of radiographs HISTORY
Information provided by the owner may prove highly beneficial since an animal cannot describe the ailment. A surgeon should have experience and analytical power to extract valuable information as an owner may provide misleading history. A simple language without technical terms should be used while extracting information. An approach of through questioning with tact and generation without irritating the owner may provide better results. Clinical signs recorded by owner, probable duration of the disease, status of pregnancy , date of last parturition and status of milk yield should be recorded. Information should also be gained regarding the treatment previously received by the animal The conflicting points of history should be sorted out logically to gather reliable information. Even though history provided by the owner may be useful it is not a substitute for careful clinical examination. If history and clinical examination are at variance, it is better to depend upon the examination. PREPARATION OF PATIENT
Make the patient an indoor one to accustom with the environment of ward In ruminants rest for couple of hours lowers the stress(Travel of animal long distances on feet) Emergency case should be attempted immediately General physical examinations should be carried to assess prognosis. Severe dehydration and debilitation with prominent ribs indicate poor prognosis if general anaesthesia or major surgery is indicated. Rough and hard coat . Sunken eyes Prolonged lateral recumbency o Colour of the mucous membrane and capillary refill time are the o useful aids in dealing seriously ill patients Rectal temperature, pulse and respirations should be recorded Palpation, percussion and auscultation help to arrive diagnosis
In a febrile state surgery should be postponed Paracentesis of swelling and cavities for differential diagnosis Laboratory procedures – Pathological tests and their correction for treatment Radiography Fluid therapy particularly in case of dehydrated and worm infested animals. With holding of feed and water Large animals: 24 - 48 Hrs ; 12 - 24 hrs Small animals : 12 Hrs ; 4 - 6 hrs Administration of laxative, purgative or enema for 2-3 days before operation to evacuate the bowels and fit for general anesthesia (not recommended in Ruminants) Preparation of operation site -> Day before operation Day of operation Preparation of the surgeon Location Planning Maintenance of records . DAY BEFORE OPERATION
Clipping of long hairs by scissors or by shaving the animals. Before shaving some soapy solution should be used Washing the area by non-irritant antiseptic lotion like Savlon liquid Washing by plain water and rubbing gently by cotton or swab gauge Again washing by running water Evaporative type of antiseptic wash or lotion should be applied locally Covering the site by sterile gauge and bandage for the next day of operation DAY OF OPERATION
Again wash with antisepti clotion and shaving Application of alcohol At the time of operation the animal should be brought to the operation table PREPARATION OF THE SURGEON
Surgeon dresses should be changed in preparation room
Infection from the nose and mouth should be prevented by using caps and musk Shoes of surgical team should be changed Hands upto elbow should be scrubbed for at least 5 minutes with soap and running water. Nails should be cut and scrubbed with nail brush or gauge. Hands should be immersed in cetrimide solution or rinse with surgical spirit (70% alcohol) While putting on gloves the outer surface of the gloves should not touch with the hands . LOCATION
It is always preferable to do surgery in an operation theater if feasibility exists where routine professional and manual help in and equally available. PLANNING
A surgeon must know the structure to be incised and handled in any surgical procedure and so be thoroughly familier with surgical anatomy. If doubt, available literature should be consulted. Anatomical structure should be reviewed on a cadaver. (Major surgery) The surgeon should also ensure that the equipments, instruments, drugs and other items required during an operation have been arranged properly. A better approach is to mentally visualize the operation to be done and make a check list of all items required. Necessary assistance required for restraint of the animal should be arranged. Getting a risk note signed from the owner even for a simple operation is essential. A proper planning avoids wastage of time and energy immediately, before and during surgery. MAINTENANCE OF RECORDS
A surgeon must keep records of each and every aspects of a case. The case sheets should be such that there can be stored for future reference and use. Description of the patient identification marks, owners name and address, history of the case clinical findings type of surgical and postoperative treatment and the outcome should be recorded. Records can be analyzed to work out incidence of various diseases in an area and also to judge the efficany of the treatment measures adopted. Records will help to identity the technical areas of difficulty Post operative care and management -
Shifting of patient in the ward Post-operative medication Post-operative diet Post-operative exercise Post-operative dressing Release from the ward Followed by check up – SHIFTING OF PATIENT IN THE WARD
Immediately after major operation, the patient should be gently removed from operation table. Unconscious patient should be placed in the bed of surgical ward with slightly lowered down the head except in brain surgery operation cases. It prevents cerebral ischemia, vomition and helps to remove tracheobronchial secretion. POST-OPERATIVE MEDICATION
According to severity of pain, analgesic drugs should be given to control pain which may originate from the operation site. Restlessness can be controlled by the application of sedative or tranquilizer. Routine broad or narrow spectrum antibiotic should be given. Antiemetics may be given to prevent vomition. Supportive therapy with fluid and vitamins should be resorted too. o Oral intake of food and fluid is restricted for 12-24 hours after major operation. o Liquid diet should be given at second day. o Semisolid food should be given from forth day. o Solid food should be given after 8th day of operation. o Food must be free from fat and some vitamins, enzymes should be added. POST-OPERATIVE DIET
Oral intake of food and fluid is restricted for 12-24 hours after major operation. Liquid diet should be given at second day. Semisolid food should be given from forth day. Solid food should be given after 8th day of operation. Food must be free from fat and some vitamins, enzymes should be added.
POST-OPERATIVE EXCERCISE
Exercise means walking which should be accomplished for 2-3 hours per day. The time and distance of walking depend upon the severity of patient. POST-OPERATIVE DRESSING
Dressing should be done on 3rd, 5th and 7th post-operative days to visualize the condition of operative site. The area should be washed with antiseptic lotion and rebandaged for proper healing. RELEASE FROM THE WARD
Skin sutures should be removed between 8-10th day of post-operative days according to the condition. Operative site should be treated with topical antibiotics and covered by light bandages. FOLLOWED BY CHECK UP
The surgeon advised the attendants that the patients must be checked by him for a certain days. Module – 2 = ASEPSIS, ANTISEPSIS & THEIR APPLICATIONS IN VETY. SURGERY. TERMINOLOGY
Asepsis - being free of disease-producing microorganisms. Contaminated - dirty, unclean, soiled with germs. Disinfection - the process of destroying most, but not all, pathogenic organisms. Medical Asepsis - the practice used to remove or destroy pathogens and to prevent their spread from one person or place to another person or place, clean technique. Microorganism - a living body so small that it can only be seen with the aid of a microscope. Sterilize - to kill all microorganisms including spores.
Antisepsis: is the destruction of micro organisms but not bacterial spores on living tissue. Antibiotic: A substance derived from mould or bacteria that inhibit the growth of other micro-organisms. Astringent: Causes contraction of tissues and so arrests haemorrhage. Styptic: Astringent, haemostatic agent used externally to stop flow of blood. Haemostatic: Arresting flow of blood within a vessel. Sterilization: Complete elimination of microbial viability including both the vegetative forms of bacteria and spores process by which an article can be rendered free from all forms of living microbes including bacteria, fungi and their spores and viruses.
STERILIZATION TECHNIQUES FOR SURGICAL MATERIALS AND INSTRUMENTS
Two general categories of sterilization methods can be grouped under. o Physical sterilization Thermal Filtration Radiation o Chemical sterilization Germicidal solutions Glutral dehyde, Beta propiolactone Ethylene oxide THERMAL
Steam sterilization is the most commonly employed method of sterilization of instruments and equipment. Different types of autoclaves are o pressure steam sterilizer o steam pressure sterilizer o vacuum steam sterilizer o dressing sterilizer o gravity displacement sterilizer
Points to be considered
Instrument packs are positioned vertically (on edge ) and longitudinally in autoclave A 13 minutes sterilizing cycle (exposure to saturated stem at 1210C) is a safe minimum required Large linen packs require 30 minutes at 1210C Once sterilized, sterile packs should be stored in closed cabinets. All packs should be dated.
Sharp instruments ¾ scissors, needles; surgical instruments can be sterilized by this method.
Dry heat sterilization
Dry heat destroys microorganisms primarily by oxidation process. It is used to sterilize those materials for which moist heat cannot be used either due to deleterious effects on the material or material being impermeable to steam e.g: oils, powders, glass surgicals etc. Slow process and long exposure time at a high temperature is required as spores are relatively resistance to dry heat.
Methods
Direct exposure of instruments to flame – not reliable. Hot air oven – most common method. An exposure to dry heat at a temperature of 1600C for 60 min will achieve sterilization equal to that of moist heat at 1210C for 15 min, at 151 lbs pressure.
Temperature time combinations for dry heat sterilization
1200c for 8.0 hours 1400c for 2.5 hours 1600c for 60 minutes 1700c for 40 minutes Exposure time relates to the time after specific temperature has been achieved and don’t include heating lags. Clean gowns, paper wrapped material, swabs, Petridis – 1200c for 8 hours Stainless steel lens and glass ware – 1600c for 60 min FILTRATION
Filtration is used in air conditioning system to remove particles as small as 0.3 µm in diameter and also used to filter-sterilize heat labile solutions. RADIATION
Ultraviolet light is used for surface sterilization. Ionizing radiations, Beta and cathode rays are used to sterilize heat sensitive prepackaged surgical materials. Example: Surgical mask - to produce two fold effect. CHEMICAL AGENT
An ideal chemical agent should have following properties o kill all pathogenic microorganism o work effectively in short period of time o exert residual action o not corrode, dry or stain o be stable, odorless, non toxic o be effective in presence of organic matter o not be inactivated by other concurrently used chemicals
Agents in solution form Alcohol
Ethyl alcohol (70%), Isopropyl alcohol (90%) are commonly used Presence of water easily denatures the protein. o 70% alcohol is more qermicidal than absolute alcohol. o Isoprophyl alcohol is more bacterial than ethyl alcohol Sterilization can be done by immensities continuously. Eg: Needles.
Aldehyde
Formaldehyde and flutasaldehyde (cidex, parvo cide )
Formaldehyde
Available as formalin 37% solution of formaldehyde and water. Used as gas for fumigation. Irritant to skin and mucous membranes. o Oxidizing agent e.g. Halogens Inorganic Iodine compounds Organic Iodine compounds o Surfactants – Soaps, detergents, o Phenolic derivatives - carbolic acid
Chemical sterilization by gases
Ethylene oxide acts by inactivating the DNA molecules in the microbial cells thus preventing cell reproduction. Temperature - 120 to 140F Eg: ethylene oxide, formal dehyde and beta propiolatone (generally used) Sharp edged instruments – Scalpel blades, hypodermic needles. PREOPERATIVE CONSIDERATIONS
A surgeon must keep certain considerations in mind before undertaking surgery.
Preoperative considerations may relate to the owner, patient and Surgeon. THE OWNER
Owner is the custodian and provider of the animals need and therefore he has a legal right over his animal. A veterinarian is legally answerable to the owner. The owner must be well informed about the diseases, proposed surgical treatment and the possible outcome. The owner must be convinced that every thing being done is in the interest of the animal patient. Owner – patient – Surgeon relationship becomes very important in veterinary profession to maintain a good rapport. The whole approach towards the owner should be based on the logic and sound reasoning. In Eastern countries the relationship may at times be more influenced by personnel & religious sentiments of the owner, the myths of taboos of the region. Incertain instances the owner may strictly forbid the use of a knife or other cutting instrument on the animal. A surgeon may be approached for surgery when it is not feasible. Ex. Multiple fractue of pelvis. A surgeon must also consider 1. Economic aspects of the case 2. Surgical risk involved 3.Ethics and centiments of the owner. After weighing each aspect carefully, the surgeon should make a decision and communicate the same to the owner in a confident and convincing tone. It is the ethical and legal duty of the surgeon to inform the owner about surgical risk in advance. SURGICAL RISK
The term risk is used to describe the animal’s potentiality for surviving anesthesia and surgery. To reduce the risk to minimum is of surgeons concern and alert to problems that may arise during anesthesia and surgery. FACTORS INFLUENCING SURGICAL RISK
Haemorrage and shock Fluid and electrolyte imbalances Acidosis and alkalosis Anemia and hypovolaemia Malnutrition and hypoproteinemia Pulmonary and cardiovascular complication
Hepatic insufficiency Renal and adrenal diseases Obesity of the patient Extreme of age - complication in both very old and very young animals HOW SURGICAL RISK IS DETERMINED
Detailed history of animals Physical status and condition of animal Individuality Clinical examination of the patient including general, systemic and special examination Essential laboratory examination including routine examination of stool, urine and blood (clotting time, bleeding time, total count, differential lecucocytic count, hemoglobin %, packed cell volume) On the basis of magnitude of operation, nature of aliment with foresaid findings, the risk of patient is evaluated ADJUNCTS AND SAFEGAURDS
These are o Evaluation of operative risk o Recognition and correction of preoperative deficits o Prevention of intra-operative and postoperative complication before they develop o Resuscitation and after care of surgical patient SURGICAL JUDGEMENT
Surgical judgment is something that can be developed only over a period of time, the length of time depending on the surgeon’s exposure to many and varied cases. A Surgeon who continuously makes the same errors can never develop sound judgment. When examination and diagnosis favours or indication for surgical treatment then decision must be made about: o Feasibility of performing surgery in consideration to the animal’s condition. o When to under take surgery Feasibility of performing surgery entirely depends of the evaluation of the patient but the proper timing of operation is more of a problem in clinical judgment then the decision as to performance. The decision must be based on the circumstances and the optimum condition of the patient for surgery. Such type of decision as to wheather and when to undertake surgery is applicable both for emergency and elective surgery.
In elective surgery certain preoperative schedule should be carefully followed and evaluated. o Careful recorded history o Detailed physical examination o Essential laboratory test o Radiographic study where necessary Other diagnostic test like ultrasonography, computed tomography, doppler study, magnetic resonance imaging etc., wherever required Emergency surgical operations are those where there is serious injury or massive internal hemorrhage which may endanger the life of the patient. In such cases the preoperative preparation must be limited to be rare essential. It is never justified to omit the details of a careful recorded history and careful physical examination treatment of preoperative preparation of emergency cases. Resuscitation, emptying of stomach, empting of bladder by catheterization should be considered as general rule, if necessary.
Module -3 SHOCK & ITS MANAGEMENT – DEFINITION
A recent veterinary textbook defines shock as "the clinical state resulting from an inadequate supply of oxygen to the tissues or an inability of the tissues to properly use oxygen." This deprives the organs and tissues of oxygen (carried in the blood) and allows the buildup of waste products. Shock can result in serious damage or even death. Many attempts have been made to define shock, but because it is such a complex disorder, no single definition has been successful. CLASSIFICATION
There are four general categories of shock: hypovolemic, cardiogenic, septic and vasogenic shock.
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Hypovolemic shock is the result of inadequate intravascular circulatory volume commonly resulting from haemorrhage, fluid loss in excess of intake, or third spacing of body fluids. A. Acute blood loss: - Major laceration, ruptured abdominal or thoracic organs, surgical procedures. B. Fluid loss:- Severe vomiting, diarrhea, burns C. Fluid sequestration: - Massive tissue trauma, especially crushing injuries. Cardiogenic shock occurs from cardiac insufficiency with lowered cardiac output. It may result from: · Inherent heart diseases such as arrhythmias, myocardial trauma etc. · Extracardiac diseases such as cardiac tamponade, tension pneumothorax. The circulatory failure is central in origin. Septic or endotoxic shock occurs from massive infection caused by gram negative microbes. Various diseases which can cause this type of shock are peritonitis, pyometra, haemorrhagic gastroenteritis, intestinal strangulation, or volvulus, pericarditis, mastitis, osteomyelitis etc. Vasogenic shock occurs either due to extensive vasoconstriction or extensive vasodilatation. Direct action of toxic substance on blood vessels produces dilatation of blood vessels. It leads to decreased resistance and increased capacity of vascular bed. Pain or extensive handling and traction of the viscera – massive vasoconstriction Deep anaesthesia or spinal injury – extensive vasodilatation Anaphylactic shock occurs due to antigen-antibody reaction and resultant histamine release. Histamine leads to increased permeability and massive vasodilatation. PATHOPHYSIOLOGY OF SHOCK
Although the nature of shock vary, the fundamental sequence of events is essentially the same in all forms of shock: o Some precipitating cause decreases cardiac output and blood pressure o Stimulation of sympathoadrenal system leads to peripheral vasoconstriction and shunting of blood away from the skin and intestinal viscera o Heart rate and myocardial contractility increases, leading to cardiac output o Simultaneously there is increased release of ADH, activation of rennin-angiotensin system and release of aldosterone which
ultimately helps to conserve water and sodium through the kidneys. In microvascular level certain compensatory changes become less reversible as shock persists and provide a positive feedback. o There is lowered oxygen delivery to tissue due to sympathetic constriction of arteriole and pre-capillary sphincters. o Development of cellular anoxia with release of lactic acid. o Permeability of cell membrane increases with release of lysozymes o Capillary stasis and decreased capillary pH triggers vascular pulling and decreased venous return to heart. o Hypercoagulability also occurs, which may leads to disseminated intravascular coagulopathy (DIC). The end result in all forms of shock is cardiac failure ultimately leading to death. Click here to view the flow diagram of the Pathophysiology of shock SYMPTOMS OF SHOCK
It is easy to recognize fully established shock; but it is difficult in early or compensated shock. Shock is dynamic and not a static process. Physical examination findings associated with hypovolemic and cardiogenic shock include: o Tachycardia o Tachypnea o Pallor of mucous membrane o Prolongation of the capillary refill time and decrease pulse quality o Heart murmurs or arrhythmias (not absolute) Laboratory findings during shock shows lowered red blood cells, haematocrit and plasma proteins; and elevated blood urea nitrogen (BUN). Other signs include weakness, restlessness, and depression, reduced urine output, coma and dilation of pupils. TREATMENT
The most important goals in the treatment of shock include: o quickly diagnosing the patient's state of shock; o quickly intervening to halt the underlying condition (stopping bleeding, re-starting the heart, giving antibiotics to combat an infection, etc.); o treating the effects of shock (low oxygen, increased acid in the blood, activation of the blood clotting system); o and supporting vital functions (blood pressure, urine flow, heart function).
Patent airway should be ensured by intubating animal if collapsed or comatose. Oxygen should be delivered via musk, cannula or endotracheal tube. Haemorrhage, if any, should be controlled by direct pressure, bandages, tourniquet or ligation. Fluid theraphy: A multi electrolyte, sodium containing crystalloid replacement solution is usually the fluid of choice; plasma and whole blood have obvious advantages. TYPES OF INTRAVENOUS FLUIDS
Crystalloid: Dextrose or electrolyte solutions increase intravascular and interstitial fluid volume: Isotonic .9% NaCl, lactated Ringers Hypotonic (5% dextrose in water, 45% NaCl). Colloids: Do not diffuse easily through capillary walls Fluids stay in vascular compartment; increase osmotic pressure: albumin, plasma protein and dextran. Blood and blood products: Treatment of hemorrhage Restore coagulation properties. Glucocorticoid: the role of glucocorticoid in shock state has remained debatable even in man and small animal. Beneficial effects (dexamethasone @10mg/kg, prednisolone @ 30mg/kg) include: increase in cardiac output, decrease in peripheral resistance, increase in metabolism of lactic acid, improved efficiency of glycolytic enzymes, stabilization of lysosomal enzymes and interference with endotoxininduced immune reaction. Vasoactive drugs are used to modify sympathetic and adrenal responses. Dopamine is most popular vasoactive drugs used in shock. Sodium bicarbonate is indicated to counteract metabolic acidosis caused by accumulation of lactic acid in shock state. Broad spectrum antibiotics are indicated to combat wide-ranging secondary bacterial infection and diuretics for over dehydration or poor urine output. Drugs acting on cardiovascular system are also indicated to improve blood pressure and to stimulate blood flow. Digitalis and adrenaline are drug of choice in this case. The animal should be kept in a warm and well ventilated room without exposing direct heat. Thrombolytic therapy (drugs that dissolve clots as they form) may be considered in the case of myocardial infarction or pulmonary embolism. Treatment with antioxidants that help rid the body of free radicals (harmful by-products of the oxidative process) may protect against some types of shock. o Carnitine may be helpful in treating cardiogenic, septic, and hypovolemic shock. o Coenzyme Q10 (CoQ10), an antioxidant, may be beneficial in treating hypovolemic and septic shock.
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Glutamine added to parenteral nutrition may protect the intestines and prevent complications from septic shock. N-acetylcysteine (NAC) improved the immune system response in septic shock caused by endotoxins (toxins released from bacterial cells). Omega-3 fatty acids compared with omega-6 fatty acids may protect against the harmful effects of septic shock. Vitamins B3 and B 12 -nicotinamide (a form of vitamin B3) may help protect against bacterial endotoxin that causes septic shock. MODULE-4=
HAEMORRAGE & ITS MANAGEMENT
HAEMORRHAGE
Haemorrhage means escape of blood from an artery, vein or capillary to extravascular space. The complete loss of blood is referred to as exsanguination. CLASSIFICATION
External haemorrhage Internal haemorrhage Depending on the time of occurrence Depending on the source of haemorrhage o External haemorrhage occurs from open wounds or cut wounds that is visible on the outside of the body o Example Epistaxis – bleeding from nose. Haematuria: Blood in urine. Haematemesis- vomiting fresh blood . Haemoptysis – coughing up blood from the lungs . Melena - presence of blood in faeces. o Internal haemorrhage is bleeding occurring inside the body . It may be caused by high blood pressure (by causing blood vessel rupture) or other forms of injury, especially high speed deceleration occurring during an automobile accident , which can cause organ rupture. When blood is collected in a newly formed cavity called as Haematoma. o Example: Haemometra - haemorrhage into uterus Haemopleura - haemorrhage into pleural cavity Haemoperitoneum - haemorrhage into peritoneal cavity
Haematocele - haemorrhage in to tunica vaginalis Haemarthrosis - haemorrhage into a joint Haematomyelia - haemorrhage into spinal cord Petechiae - Pinpoint haemorrhages on skin and subcutis Ecchymosis - haemorrhagic spots on skin and subcutis. Depending on the time of occurrence Primary haemorrhage occurs immediately after injury. Reactionary haemorrhage occurs within 24hours after the primary bleeding has been arrested due to mechanical disturbance of clot in vessel or due to slipping of the ligature. Secondary haemorrhage occurs after about a week or more due to septic disintegration of clot or due to sloughing of portion of vessel because of a septic or gangrenous lesion. Depending on the source of haemorrhage: Arterial, Venous and Capillary
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ETIOLOGY
Trauma - blunt trauma (e.g. fall, motor vehicle accident), laceration, or penetrating trauma (e.g. knife or gun). Necrosis and ulcerations of blood vessel wall Infection and subsequent release of toxins of microorganism Aneurysm ( weaknesses in blood vessels ) Increased blood pressure Lack of oxygen and nutrition. Anaphylactic shock Deficiencies of coagulation factors. Deficiency diseases o Haemophilia o Thrombocytopenia o Deficiency of vitamin C, vitamin K o Plant toxins (sweat Clover) SYMPTOMS
Bleeding from injured blood vessel Skin and mucous membrane become pale, cold and moist Patient feels thirsty Air hunger Thready pulse Hypotension Low hemoglobin and red blood cells
HAEMOSTASIS
Haemostasis may be defined as complex interaction between vessels, platelets, coagulation factors, coagulation inhibitors and fibrinolytic proteins to maintain the blood within the vascular compartment in a fluid state.
Methods of haemostasis
Bleeding should be addressed in calm and controlled manner. Gentle digital pressure on the point of haemorrhage provides an extremely effective temporary haemostasis in minor bleeding. Pressure haemostasis: A dressing, typically made of gauze, should be applied. The tissue should be gently blotted rather than wiped (Wiping causes abrasion and dislodges blood clots that have formed). Haemostatic forceps: Crushing of tissues at the point of application leads to clot formation inside the vessel adjoining the ruptured ends of the inner coats. This can be done using artery forceps. Diathermy: Cauterization of vessel is usually performed by Mono polar coagulation and bipolar coagulation. Arteries less than 1mm and veins 2mm diameter causes vessel wall to shrink and lumen occlude by thrombosis. Ligation is the ideal method of controlling bleeding from a vessel which can be accomplished first by grasping the vessel followed by putting a ligature. Vascular clips made of titanium or stainless steel is also used for ligation. Tourniquet: A cord should be tied around an extremity (limb, tail, penis etc.) and proximal to bleeding area to control bleeding (not more than one hour 20 to 60 minutes). The use of a tourniquet is not advised in most cases, as it can lead to unnecessary necrosis or even loss of a limb. Topical agents like Fibrin adhesives, oxidized cellulose (regenerated), absorbable collagen fibrils, and gelatin sponge with or without thrombus are also helpful for arresting bleeding from small vessels. Bleeding from drilled cut or chipped edges of bone can be controlled by using bone wax plugs physically. Application of Tr. Benzoin, Liq. Ferri perchlor, collodion, ice, cold water etc. can be successfully used for controlling bleeding from small vessels. Bleeding from unidentified points of vessels in a wound cavity can be controlled by packing or plugging the cavity with sterilized gauze pieces (tampon). Tamponing favours coagulation of blood by exerting pressure in the area. Adrenalin, a vasoconstrictor agent when applied topically controls bleeding especially from a small bleeding vessel. Administration of vitamin K (Kapillin), calcium and other coagulation factors may have remarkable effect in controlling haemorrhage.
Module -5 = FLUID THERAPY IN SURGICAL PATIENT FLUID INFUSION Fluids
Routine administration of multielectrolyte containing crystalloid replacement solutions at the rate of 10 ml/kg/hr plus 2 to 3 times the volume of estimated blood loss will satisfy the requirement during surgery. During major procedures it can be increased upto 20 ml/kg. Lactated Ringer’s is preferred over other solutions during shock.
During anaemia
If the PCV less than 20% blood transfusion is indicated and if the serum protein is less than 3 to 3.5 g/dl further volume replacement is done using plasma or synthetic colloidal is administered. Blood volume is calculated as 8 to 10% of the body weight in dogs (45% cells and 55% plasma) and 6% in cats(36% cells and 64% plasma). Blood transfusion is indicated in dogs whose preanaesthetic haemtocrit is less than 30 to 34% and in cats less than 25 to 29%. If the blood loss is more than 10% during surgery blood transfusion is necessary. Blood and plasma transfusion is done based on the following formula. o Amount of donor blood needed (ml) = Recipient blood volume in ml x ((Desired PCV - Patient PCV) / PCV of donar blood) o Amount of donor plasma needed (ml) = Recipient plasma volume in ml x ((Desired TSP - Patient TSP) / TSP of donar blood) FLUIDS AND THEIR USE
Isotonic crystalloids
Indications o To maintain plasma volume in uncomplicated anaesthetized cases. o To replace deficits in dehydration o To restore interstitial fluid status o To promote diuresis Disadvantages o Large volume of administration coupled with migration into interstitial spaces may result in oedema o Produce haemodilution in anaemic patients
Hypertonic crystalloids
Indications o Expansion of plasma volume o Used in the intial treatment of shock o Administered intraoperatively during cardiac surgery o To prevent tissue oedema from the conventional therapy o These agents increase the plasma volume; cardiac output and improves the blood pressure. They increase the myocardial contractility o Improve the microcirculatory blood flow by decreasing the systemic vascular resistance, lowering the blood viscosity and reducing the size of the endothelial cells. Disadvantages o Induce hypernatraemia, hyperchloraemia, hypdokalaemia, hypermolarity and metabolic acidosis o May induce mild cellular dehydration o Uncontrolled bleeding will become worsen due to the rapid increase in blood pressure.
Synthetic colloid solution
Indications o Hypoproteinemia and hypoalbuminemia o Blood loss o Hypovolemia o Sepsis o Persistent hypotension o Does not cross the capillary walls hence will have sustained effect o No risk of transmission of infectious diseases as compared with plasma and less expensive Disadvantages o Induce pulmonary oedema in patients with permeable capillaries o May induce circulatory over load
o
May induce coagulation disorders due to dilution of platelets, precipitation of coagulation factors, increased fibrinolytic activity and decreased functional von willebrand factor.
Module -6 DIFFERENTIAL DIAGNOSIS & SURGICAL TREATMENT OF ABSCESS, TUMOUR, CYST , HAEMATOMA=> ABSCESS -
DEFINITION
Abscesses are circumscribed collections of purulent material (pus) in a cavity, found in several species of animals in a variety of locations. This purulent inflammation is usually caused by one of four pyogenic (pus producing) bacteria: Corynebacterium, Pseudomonas, Streptococcus and Staphylococcus. PARTS OF AN ABSCESS
Abscess consists of a wall, pyogenic membrane and pus (Liquor puris). The pyogenic membrane that lies between the wall and pus, controls spread of infection, and helps in phagocytosis and granulation tissue formation. CONTENTS OF PUS AND ITS CHARACTER
Pus contains necrosed tissue, dead bacteria, leukocytes and proteins of blood and tissues. Pus cells mainly consist of polymorphonuclear leukocytes along with a few mononuclear cells. Pus is alkaline in nature and yellow in colour.
Pus serum will not clot, since the fibrin of exudates is digested by the proteolytic enzymes of the leukocytes. CLASSIFICATION OF ABSCESS
Abscess may be classified as: o Acute Abscess (Hot abscess): Inflammatory symptoms are more active. o Chronic Abscess (Cold abscess): Inflammatory symptoms are less active. Chronic abscess may be: Hard with inspissated pus,or Soft with liquid pus and thin abscess wall. o Superficial or deep abscess: based on location. ETIOLOGY OF ABSCESS
Pyogenic organisms like Staphylococci, Streptococci, Escherichia coli and Pseudomonas aeruginosa. Specific organisms like Corynebacterium pyogenes, Actinomyces bovis etc. Chemicals like mercuric chloride and Zinc chloride. COMMON SEATS OF ABSCESS FORMATION
Cattle: Yoke, udder and prominences Horses: Shoulders, sub-maxillary and post pharyngeal lymph nodes. Dogs: Anal region, and mammary glands. ACUTE ABSCESS
Acute abscess forms in 3 to 5 days following infection.
In long duration abscess, the liquid part is absorbed and the solid part is left. This is called Inspissated Pus.
Symptoms
Acute superficial abscess appears as a local painful swelling. The dead tissues and dead inflammatory cells are continuously thrown into the cavity which leads to a gradual increase in the amount of pus. Thus the abscess enlarges till it reaches the surface of skin or mucous membrane. The center of abscess becomes soft (pointing) and later ruptures, discharging pus. Local acute inflammatory symptoms without fever are observed in superficial abscess.
Deep abscess has no local symptoms, but fever and pain on manipulation of the part are evident. CHRONIC ABSCESS (Cold abscess)
A chronic abscess develops slowly without any inflammatory symptoms. It may be painless or slightly painful. Primary chronic abscess usually occurs from repeated injuries and observed on the prominences of limbs and ribs due to bed sores. Secondary chronic abscess develops in the course of various local affections. Chronic abscess may be hard in consistency surrounded by fibrous tissue and containing small amount of pus or it may be soft and thin walled with comparatively larger amount of pus. TREATMENT
Treatment should correspond to the stage of development of an abscess. In time, abscesses may become inactive or enclosed (sterile); the body defenses having killed all of the causative bacteria. The accumulated pus, with no route of escape, will slowly become liquefied and be absorbed. o Measures to accelerate maturation of abscess by using liniments, fomentations and mild blisters. o Once mature, abscess must be early cleared up of pus by aspiration and subsequent washing of the purulent cavity. o The abscess should be opened by syme’s abscess knife or a scalpel at the place of pointing. The pus should be drained and the cavity is to be irrigated with a mild antiseptic lotion. In cases where the pointing of abscess is not at a dependent Part, then drainage will not be perfect. A counter opening is made at the most ventral part (dependent Part) of the abscess. o Tincture of Iodine soaked gauge is be packed to keep the openings patent. This should be changed once in 24 hours. The quantity of gauze used to pack the abscess cavity has to be reduced daily as the cavity is being filled up by granulation tissue. Gauze soaked with 0.5% silver nitrate is best against most of the micro-organisms. o Further therapy is the same as that of a granulating wound. o A chronic abscess is converted into an acute abscess by applying blisters, and then treated as acute abscess. Sometimes the chronic abscess is enucleated under local infiltration analgesia, and the skin is sutured. Cellulitis or Phlegmon is diffuse, suppurative spreading inflammation of loose connective tissue, with predominance of necrotic events over suppurative. Pustule is a circumscribed cavity with pus, situated in epidermis.
Furuncle or Boil is suppurative inflammation of hair follicle or a sebaceous gland due to Staphylococcus aureus. A group of furuncles is called Furunculosis. Carbuncle is small boil, which drains to outside by multiple small openings. It is caused by Streptococci and Staphylococci. Acne is an abscess of sebaceous gland. It appears as single or multiple pustules containing grayish white pus. Antiseptic ointments externally and systemic penicillin gives good relief. Empyema is collection of pus in a body cavity. Example: Empyema of frontal sinus, empyema of joint. Antibioma is a clinical condition resulting from improper treatment of an abscess. TUMORS (Neoplasm)
The term neoplasm is a Greek word used primarily for new formations or new growths. Tumour may be defined as “an abnormal mass of tissue, the growth of which extends uncontrolled, in comparison to the normal tissue and persists in the same excess even after cessation of the stimuli which evoked the change.”
TYPES OF TUMOR Benign
Malignant
Grow slowly
Grow rapidly
Locally grow to great size
Create metastases
Don’t invade the neighboring tissue
Invade and destroy neighboring tissues.
Usually do not return after surgical removal Recurrence after surgical removal
INCIDENCE
Tumors are more common in canines. o Skin - Common in older dogs (often benign) but much less common in cats (malignant).
Breast - Fifty percent of all breast tumors in dogs and 85% of all breast tumors in cats are malignant. o Testicles - Testicular tumors are rare in cats and common in dogs, especially those with retained testes. o Bone - Bone tumors are most commonly observed in large breed dogs and rarely in cats. The most common sites are leg bones, near joints. o Head and Neck - Cancer of the mouth is common in dogs and less common in cats. A mass on the gums, bleeding, odor, or difficult eating are signs to watch for. Horse and cattle are more often affected than sheep, pig and goat. o Fibropapillomatosis of the skin, mucosa of mouth, esophagus and urogenital organs are often seen in domestic animals. Fibroma is more common in horses, cattle and dogs. Old animals are affected more commonly than young ones. o
VARIETIES OF TUMORS Tissue of origin Mesenchymal tumors
Epithelial tumors
Name of tumor
Cell type
Fibroma
Fibrous connective tissue
Chondroma
Cartilaginous tissue
Osteoma
Bony tissue
Odontoma
Tooth substances
Myoma
muscular tissue
Myxoma
Cardiac skeleton
Lipoma
Adipose tissue
Neuroma
Nerve cells and fibers
Leiomyoma
Smooth muscle
Rhabdomyoma
Skeletal tissue
Haemangioma
Blood vessels
Meningioma
Meninges
Teratoma
Germ cells
Papilloma
Skin or mucous membrane
Adenoma
Glandular epithelium
Basal cell tumour
Basal cell of skin
Hepatocellur adenoma
Hepatocytes
Glomus tumour
Melanocytes
Blood cells
Non-Hodgkin lymphoma and Hodgkin lymphoma
Lymphoid cells
Leukemia
Hematopoietic cells
DIAGNOSIS
Clinical examination – location, size and consistency Radiography – bones and vascular organs. Biopsy – exploratory cytology TREATMENT
Prophylactic treatment is undertaken either to reduce the anticipated incidence rate of a particular tumor type or the rate of recurrence of a neoplastic disease after therapy. o Mammary tumors in bitch – Spaying between 6 and 12 months of age will greatly reduce the risk of breast cancer. Surgery is the treatment of choice for this type of cancer. o Benign vaginal tumor – ovariotomy o Testicular tumors (Seminoma and sertole cell tumour) - Castration Definitive excision refers to use of surgery as the sole treatment procedure without adjunctive radiotherapy or chemotherapy. o Local excision: The removal of a neoplastic mass with the minimal amount of surrounding normal tissue. o Wide local excision: Removal of a significant predetermined margin of surrounding tissues together with the primary mass. o Radical local excision: Removes of a tumor with anatomically extensive margins of tissue extending into fasuil planes which are wndistrubed by the primary growth of the tumor us termed radical local excision or compartmental excision. Eg: sarcomas. Palliative treatment: A procedure that remarkably improves an animal’s quality of life by providing pain relief, or relieving poor function, despite the presence of unsolved systemic neoplastic disease. o Eg: Limb amputation – osteosarcoma o Spleenectomy – Bleeding haemorrhage of sarcoma
Apart from surgery and chemotherapy, radiation, cryosurgery (freezing), hyperthermia (heating) or immunotherapy can be effectively used to treat cancers. Combination therapy is commonly employed. CYST
A cyst is a closed sac having a distinct inner lining of secreting membrane. They may contain air, fluids, or semi-solid material. Cyst may contain a solid structure like tooth (dentigerous cyst) or hair (dermoid cyst) also. The outer wall of a cyst is called as ‘capsule’. Most of the cysts are benign in nature, but some may produce symptoms due to their size and /or location. Size of a cyst may vary from a small grape to a football. Cysts can arise anywhere in the body, o Common example listed below: Chalazion cyst (eyelid) Retention Cyst (gland like salivary cyst) Dentigerous Cyst (associated with the crowns of non-erupted teeth) Exudation Cyst (Hydrocoele). Dermoid (misplaced embryonic tissue). Encapsulation cyst (around foreign bodies and parasites. Ex: Cystecercosis) Neoplastic (Cyst adenoma). Ganglion cyst (hand/foot joints and tendons) Glial Cyst (in the brain) Distension cyst: (Follicular cyst of ovary, cystic distension of a joint bursa). Meibomian cyst (eyelid) Ovarian cyst (ovaries, functional and pathological) Renal cyst (kidneys) Sebaceous cyst (sac below skin) DIAGNOSIS
Cysts are generally non-inflammatory in nature and develop slowly with well defined periphery. On palpation fluid filled cyst fluctuates uniformly while cysts with solid mass fluctuates en-masse. TREATMENT
Puncture and evacuate the contents of cyst and inject an irritant solution like Tr. iodine to destroy the smooth lining membrane and setting up inflammation. Use of setton to drain cyst is a good practice.
Surgical excision of the cyst is the preferred option. Intact cyst is carefully dissected and removed from the surrounding tissue in possible cases.
DIFFERENTIAL DIAGNOSIS An abscess must be differentiated from the following conditions:
Cyst Slow in development as compared to an abscess. o Soft and fluctuates uniformly, but not hard at periphery. o No inflammatory symptoms. o No pain sensation. Haematoma o Forms due to coagulation of blood or serum. o Doughy on palpation and forms immediately following an injury. o Does not point like an abscess. o No pain sensation. Hernia o History of recent injury and swelling. o Hernial ring can be palpated. Tumour o Uniformly hard in consistency. o Exploratory puncture with needle may reveal blood. o No pain sensation. o Does not point like an abscess. o
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MODULE-7 NECROSIS, GANGRENE & BURNS – SCALD. NECROSIS
Necrosis means death of tissue in the body. This occurs when enough blood is not supplied to the tissue, whether from injury, radiation, or chemicals. Necrosis is not reversible. CLASSIFICATION
Avascular necrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones. Without blood, the bone tissue dies and causes the bone to collapse. This disease also is known as osteonecrosis, aseptic necrosis, and ischemic bone necrosis Coagulative necrosis is typically seen in hypoxic environments (e.g. myocardial infarction , infarct of the spleen ). Liquefactive necrosis is usually associated with cellular destruction and pus formation (e.g. pneumonia ). Haemorrhagic necrosis is due to blockage of the venous drainage of an organ or tissue (e.g. in testicular torsion ). Caseous necrosis is a specific form of coagulation necrosis typically caused by mycobacteria (e.g. tuberculosis ). Fatty necrosis results from the action of lipases on fatty tissues (e.g. acute pancreatitis , mammary tissue necrosis). Fibrinoid necrosis is caused by immune -mediated vascular damage. It is marked by deposition of fibrin -like proteinaceous material in arterial walls. ETIOLOGY
There are many causes of necrosis including injury, infection, cancer, infarction, toxins and inflammation . Severe damage to one essential system in the cell leads to secondary damage to other systems, a so-called "cascade of effects". Necrosis can arise from lack of proper care to a wound site. o Physical agents like excessive heat or cold. o Mechanical injuries that crush or cut off blood supply. o Loss of blood supply cuts off oxygen may be due to passive hyperemia with sluggish flow of nutrients and deficient oxygenation (volvulus, strangulated hernia) and ischemia ( decreased blood supply to a part) due to thrombus or embolism; compression of an artery, and ergot poisoning GANGRENE
Gangrene is necrosis and subsequent decay of body tissues caused by infection or thrombosis or lack of blood flow. It is usually the result of critically insufficient blood supply sometimes caused by injury and subsequent contamination with bacteria. This condition is most common in the extremities . ETIOLOGY
The main factors in gangrene are loss of blood supply, and later invasion of the part by micro-organisms. Gangrene may be caused by: o Direct damage to tissues which include:
o
Mechanical compression or interference with blood and nerve supply to a part of the body or an organ while lying on a hard floor. Example: bed-sores; sit-fast. Physical agents like application of heat and cold. Example: burns, frost-bite. Action of acids, alkali and other chemicals producing dry gangrene and moist gangrene. Impaction of intestine in the hernial ring and infestation with pathogenic microbes especially with anaerobic infection. Indirect changes in tissues due to cardiac, venous, arterial or nervous affections like: Ergot intoxication, which causes spasmodic narrowing of arterioles and leads to dry gangrene of extremities. It is commonly seen in feet of cattle. Diabetic gangrene narrows arteries and sugar in tissues, favours bacterial growth. Senile gangrene i.e. arteriosclerosis in old age, which narrows lumen of blood vessels.
COMMON SITES OF AFFECTION
Extremities like legs, ears, tail, wattle and combs. It is mostly due to freezing or ergot poisoning. Mammary gland: Staphylococcal mastitis produces necrosis due to toxins or thrombosis of mammary vessels. Involvement of lung due to wrong drenching of medicines, improper passage of stomach tube or severe lung infection. Intestines in equines are commonly involved either with infarction due to verminous thrombosis of anterior mesenteric artery; or due to acute, local passive hyperaemia produced by intestinal torsion, volvulus or intussusceptions.
CLASSIFICATION, ETIOLOGY AND SIGNS OF GANGRENE Type Wet gangrene, or moist gangrene
Etiology Sudden interruption of blood flow such as due to burns, freezing, injury or blood clot. Wet gangrene spreads very quickly and can be fatal.
Characteristic signs
Affected tissue may appear badly bruised, swollen or blistered. May also become infected.
Dry gangrene
Insufficient blood flow through the arteries such as due to atherosclerosis or blood clots. It usually doesn't involve bacterial infection.
No clear line between healthy and affected tissue.
Affected tissue becomes shriveled, dry and blackish or greenish colour. cold to touch
Gas gangrene
Infection with certain types of bacteria, such as clostridium. It typically occurs at the site of a recent injury or surgery. The bacteria rapidly destroy muscle and surrounding tissue.
Swelling around skin due to exudates and gas formation. Skin initially looks pale and then turns dark red or purple in color. Offensive odour of exudates.
DIAGNOSIS
Diagnosis of gangrene will be based on a combination of o History (recent trauma, surgery, cancer, or chronic disease). o Physical examination o Results of blood and other laboratory tests (presence and extent of infection). TREATMENT
Treatment should be directed to:Prevention of cause and extension of gangrene.
Debridement: Removal of dead, damaged, or infected tissue to improve the healing potential of the remaining healthy tissue. Application of warm antiseptic fomentations to relieve pain. Surgical excision or amputation of a limb or organ. Antibiotics alone are not effective because they do not penetrate ischemic muscles sufficiently. However, penicillin is given as an adjuvant treatment to surgery. In addition to surgery and antibiotics, hyperbaric oxygen therapy (HBOT) is used that inhibit the growth and kill the anaerobic organisms. ULCER
An ulcer is a localised defect in the continuity of an epithelial surface without any tendency to heal. It is usually associated with an inflamed base of granulation tissue with or without necrotic slough. The majority is chronically inflamed; the slough at their base represents inadequate drainage. Acutely inflamed ulcers may have an outer rim of cellulitis. Ulcer must be differentiated from erosion which is an epithelial defect with loss of superficial layers, but the basal layers are intact. CLASSIFICATION
Iatrogenic ulcers: wound breakdown post-operatively and in irritant fluid extravasating. Non-specific ulcers: Ex; Traumatic ulcers including secondary stress ulcers. Specific ulcers: as observed in tuberculosis, ulcerative lymphangitis, and glanders. Malignant ulcers observed in skin and gastrointestinal tract. Ischemic ulcers or Decubitus ulcers: These are due to continuous pressure which interferes with supply of nutrition to local tissues leading to pressure or bed sores. Infective ulcers: primary e.g. viral, tuberculosis, and secondary e.g. due to drainage of deep focus. Neuropathic ulcer e.g. in diabetes ETIOLOGY
Repeated and continuous irritation of wound. Example: Traumatic ulcer, bed sore. Secondary infection of the site by bacteria, fungus or virus with which the tissues cannot effectively combat. Insufficiency of nerve and blood supply to the part. Presence of necrotic tissue or foreign body in a wound. Specific diseases like tuberculosis, glanders, and ulcerative lymphangitis. Presence of neoplasm. Example: Rodent ulcer. COMMON SITES OF ULCERATION
Cattle: yoke Horse: saddle place, elbow, limbs. Dog: root of tail, tip of ears, and cornea of eye. SYMPTOMS
The edge of ulcer may be raised or in level with the surrounding skin and rugged.
The center of the lesion may be flat or concave, and may show necrotic spots. Granulations are pale or blue in colour depending upon the form. The discharge may be serous, purulent or grayish. TREATMENT
The specific treatment of an ulcer is dependent on the subtype.
Elimination of the cause adversely affecting the course of ulcerative disease and stimulation of regenerative processes at the affected site. Astringent or caustic applications for ulcers with excessive or unhealthy granulations. E.g. copper sulphate, silver nitrate, carbolic acid. Thermo-cautery with red hot iron to destroy unhealthy tissue which promotes granulation and cicatrisation. Bier’s hyperaemic treatment. Antibiotics are only indicated for infected ulcers in which there is evidence of spread around the margin e.g. a cellulitic rim and there may be ongoing systemic infection e.g. tuberculosis. Exposure to ultra – violet rays to stimulate circulation and to destroy microorganisms. For large deficits or prolonged ulcers with little evidence of healing, further surgical intervention may be indicated e.g. skin grafts and rotational flaps. BURN AND SCALD
Burn is an injury of integuments and underlying tissues, occurring due to high temperature or chemical substances. Burn may be defined as tissue changes that occur on excessive absorption of heat by skin. Scald is an injury caused by hot liquids or stream. Scald is likely to be more injurious than because of the hot liquid may penetrate into the deeper part of tissues. CLASSIFICATION
According to the depth and severity of burn:
First Degree (Superficial): epidermis is affected and transient erythema, sometimes vesicle formation and desquamation of the epidermis occurs. Epidermal burns look red, are painful and heal rapidly. Second degree burn (partial thickness burn): Here, depth extends to the mid dermis. Loss of epidermis is complete. Capillaries and venules in the dermis is dilated, congested and exude plasma. There is erythema, coagulative necrosis of epidermal cells and vesicle formation. Healing is rapid and complete by the regeneration of epithelium unless there is involvement of secondary infection.
Third degree burn (Full thickness): is characterized by coagulation of epidermis and dermis. Severe edema of the sub cutis develops and dry gangrene of the damaged tissue occurs. The epidermis is desiccated and charred with presence of black layer in skin. Permanent scarring occurs due to healing by granulation. Full thickness burn is insensitive to pain because of damage of cutaneous nerve endings. Fourth degree: Here, subcutaneous fascia and deeper tissue like muscles, bones etc are involved. The clinical features are similar to those described in third degree burn. Repair is by scar formation preceded by sloughing of the necrotic tissue. CAUSES
The following may cause burn:
Thermal injuries o Direct heat o Flame o Scalding Electrical burns o Electrical cord exposure o Lightning
Chemical burns
Injuries caused by chemicals like strong acids and alkalis, solvents, petroleum distillates and hot tars are referred to as chemical burns. The chemical produces localized necrosis of skin and deeper tissues with which it comes in contact. The degree of tissue destruction depends on the strength of the chemical and the duration of contact. Chemical causes local coagulation of proteins and necrosis. CLINICAL SIGNS
Thermal burns
Superficial-hyperemia, desquamation and pain. Partial thickness- exudation, pain, decreased sensitivity. Full thickness- White, black or brown, leathery escher, subcutaneous edema and little or no pain.
Electrical burns
No pain
Well-circumscribed cold, blood less, pale yellow lesion.
Chemical burns
Line of demarcation between dead and healthy tissue Devitalized tissues may get infected Formation of ulcer which heals gradually TREATMENT
The therapeutic measures must be aimed at o termination of painful stimuli and improvement of the nervous system function for avoiding shock; o reduction of autointoxication; o prevention of infection; o promotion of rejection of coagulated Skin and tissues; o creation of favorable conditions for regeneration of skin Anti-shock measures are to be provided to prevent shock that may arise as burn complication. Burn may lead to renal failure and fatty infiltration of liver thus appropriate care should be extended to combat the complication. Local treatment of burns should include: o Application of ice (3-17ºc) pack wrapped in a soft towel and cold water for 30 minutes or covers it with wet towels. This also helps to remove caustic substances (acid or alkali) if these are the cause. o Hair should be removed and gently clean from the site. Necrotic tissue should be debrided. The area should be swabbed with weak vinegar (half water, half vinegar) using cotton wool or cloth. o Topical antibacterial ointments may be applied to prevent the animal from post burn sepsis. Several topical commercial products like Aloevera cream, Silver sulphadiazine cream (Indo-Pharma), Silver nitrate 0.5% Solution, chlorhexidine 0.5% Solution, gentamycin sulphate 0.1% cream, povidone iodine cream can be used. Soothing and protective preparations like Badional gel (Bayer), Caladryl cream (Park Davis), Burnol (Knoll) may be used as burn dressing. o Drugs like gentian violet, picric acid, acriflavin and tannic acid should not be used as far as possible as they delay the healing process by damaging the living cells. o Analgesic should be given to reduce pain. o Hypovolemic shock and acidosis are to be prevented by supplementation of large quantities of fluid (Dextrose 5%) including 4% sodium bicarbonate. o The treatment in chemical burns should include washing with lots of plain water and neutralization of the offending chemicals. Acids can be neutralized with 2-3% solution of sodium carbonate or milk, while alkali with 2% vinegar, citric or boric acid. Finally soothing ointment like
olive oil may be applied. If shock occurs, keep the animal warm with heating pads or hot water bottles and a blanket of heavy coat. A burn patient (pet) should be provided with ample warm fluids to drink and this may be given in the form of milk or glucose water.
FROST BITE
Frost bite is injury of tissues due to the action of a low temperature on them. The condition is rare in animals because they can withstand cold temperature due to their hairy coats and will instinctively seek shelter from inclement weather. Udder and teats are commonly frozen in cows during exercise on frosty winter days. Besides the prepuce, penis and scrotum in horses, snout of pig, comb and wattles of birds, tip of the ear and scrotum of dogs, tail and distal extremities in other animals are commonly affected. It usually occurs in a low temperature but it can also ensue in prolonged action of wet moderate above zero temperature (3-7ºc) since heat conductance of the skin is increased and heat emission is intensified by it. CAUSES
Exposure to cold or chilling environment. Contact with cold metal, glass, and liquids. Iatrogenic freezing with cryogens like liquid nitrogen and nitrous oxide etc. CLASSIFICATION AND PATHOPHYSIOLOGY
Various degrees of frost bite recognized are: o Mild: contraction of blood vessels (parts appear white) —> paralytic dilatation of blood vessels —> engorgement of vessels —> parts appear red and swollen —> thawing —> severe pain o Moderately severe: Below 0oC temperature for longer period than mild —> injury of Blood vessels —> inflammation of the tissues —> redness of epidermis together with certain amount of necrosis and blister formation —> desquamation o Severe: Temperature falls for lower than freezing point —> impaired circulation of blood and lymph —> parts undergoes necrosis and gangrene may ensue CLINICAL SIGNS
Loss of sensation in the affected part.
Cyanotic or pale appearance of frozen part. Moderate edemas, pain and very cold to touch. Shivering. In neglected cases, necrosis and sloughing of skin. TREATMENT
Withdrawal from cold Warming of frost bitten extremities, and restoration of blood and lymph circulation: Frozen animals must be immediately put in a warm housing to restore body core temperature. Hot water bag or hot pad may be used for warming; frozen parts should be bathed in increasingly warm water until pink colour is restored. DRUGS
Prevention of infection with systemic antibiotics Fluid therapy with dextrose should be considered. Analgesics may be provided to prevent self-trauma. Artificial respiration should be provided to frozen animals. The frozen tissue should not be massaged. Necrosed tissue if there should be removed. Amputation of frozen part if necessary should be carried out Diet: High protein, high caloric diet and vitamins should be instituted.
MODULE-8:
WOUND –
CLASSIFICATION, SYMPTOMS, DIAGNOSIS AND TREATMENT Learning objectives This module deals with
Wound and its classification Symptoms of wound Phases of wound healing Factors affecting wound healing
INTRODUCTION
A wound is a separation or discontinuity of soft tissues caused by trauma, surgery or noxious physical agents.
CLASSIFICATION OF WOUND Open or external wound
There is discontinuity in the skin and other covering tissues to a varying depth. In closed or interstitial wound, only deeper tissues, barring the skin or mucous membrane are damaged.
Closed wound/ internal wound
Contusion is injury to the skin without any break in the continuity of tissue surface. It is caused by blunt objects and the subcutaneous tissues, muscles; nerves are damaged to a varying degree. According to the severity and extent of tissue damage it may be of: o First degree with rupture of capillary vessels of the skin and subcutaneous tissue. o Second degree with rupture of larger vessels leading to haematoma formation. o Third degree with major damage of tissues leading to gangrene formation.
Open wounds
Incised wounds are caused by sharp cutting instruments such as knives, scalpels, fragments of glass etc with minimum loss to tissue, edges are regular, bleeds freely and painful. Lacerated wounds are caused by tearing of tissues with torn and uneven edges. Wounds have irregular jagged borders and loss of tissue is limited to skin and subcutaneous tissue e.g.: barbed wire. Penetrating wounds are types of deep wounds communicating with cavities like abdomen, thorax, and joints etc. e.g.: stab wounds. Perforating wound is having two opening, one of entrance and other of exit. Punctured wound are caused by sharp pointed objects like nails relatively with a small opening. There might be presence of infection/
foreign particles deep into the wound with inadequate opening for drainage. Ex: Stab wounds. Gunshot wound is produced by various forms of firearms e.g. injuries caused by bullet. Abrasions are superficial damage to the skin, generally not deeper than the epidermis. Avulsion occurs when an entire structure or part of it is forcibly pulled away. Explosions, gunshots, and animal bites may cause avulsions. Bite wounds are caused by snake; dog or wild animals bite with significant degree of tissue damage. Virulent wounds are caused by bacteria or virus leading to formation of pustules or vesicles e.g.: FMD, anthrax. Granulating wound is one in which there is a tendency to heal within expected time. Aseptic wound is surgical wound made under aseptic conditions where chances of bacterial contamination are negligible. Contaminated wound is one where there is presence of micro organisms. Infected/ septic wound: A contaminated wound may become infected after a period of 6 -8 hours where bacterial multiplication may occur and liberation of their toxin.
SYMPTOMS OF WOUND
Localized pain and bleeding. Gaping of the lips of wound. Weakness, paralysis or a loss of function in a dependent portion. Febrile disturbances in severe septic wound. Neuritis extending along the course of the nerve involved in the wound. PHASES OF WOUND HEALING
Wound healing involves a complex series of interactions between different cell types, cytokine mediators, and the extracellular matrix. The phases of normal wound healing include hemostasis, inflammation, proliferation, and remodeling. Each phase of wound healing is distinct, although the wound healing process is continuous, with each phase overlapping the next. Before the advent of modern veterinary practice, many soft tissue injuries healed with time. The difference that the modern veterinary practice has made is that the more severe injuries that would have killed the animal are now
manageable; the deformity and infection that often accompanies natural unaided tissue healing can be avoided or minimized. The Four phases of wound healing are o Haemostasis o Inflammatory phase o Proliferative phase o Wound remodeling
HAEMOSTASIS
Tissue injury initiates a response that first clears the wound of devitalized tissue and foreign material, setting the stage for subsequent tissue healing and regeneration. The initial vascular response involves a brief and transient period of vasoconstriction and hemostasis. A 5-10 minute period of intense vasoconstriction is followed by active vasodilatation accompanied by an increase in capillary permeability. Platelets aggregated within a fibrin clot secrete a variety of growth factors and cytokines that set the stage for an orderly series of events leading to tissue repair.
INFLAMMATORY PHASE
The second phase of wound healing i.e. the inflammatory phase lasts for 1-3 days in uninfected wounds. o Classic signs include the following: Redness (rubor) Swelling (tumor) Pain ( dolor) Heat (calor) Loss of function (function laesa) o Process The inflammatory response increases vascular permeability, resulting in migration of neutrophils and monocytes into the surrounding tissue. The neutrophils engulf debris and microorganisms, providing the first line of defense against infection. Neutrophil migration ceases after the first few days post-injury if the wound is not contaminated. If this acute inflammatory phase persists, due to wound hypoxia, infection, nutritional deficiencies, medication use, or other factors related to the patient’s
immune response, it can interfere with the late inflammatory phase. In the late inflammatory phase, monocytes converted in the tissue to macrophages, which digest and kill bacterial pathogens, scavenge tissue debris and destroy remaining neutrophils. Macrophages begin the transition from wound inflammation to wound repair by secreting a variety of chemotactic and growth factors that stimulate cell migration, proliferation, and formation of the tissue matrix.
PROLIFERATIVE PHASE
The subsequent proliferative phase is dominated by the formation of granulation tissue and epithelialization. o Its duration is dependent on the size of the wound. o Chemotactic and growth factors released from platelets and macrophages stimulate the migration and activation of wound fibroblasts that produce a variety of substances essential to wound repair, including glycosaminoglycans (mainly hyaluronic acid, chondroitin-4-sulfate, dermatan sulfate, and heparan sulfate) and collagen. o These form an amorphous, gel-like connective tissue matrix necessary for cell migration. New capillary growth must accompany the advancing fibroblasts into the wound to provide metabolic needs. o Collagen synthesis and cross-linkage is responsible for vascular integrity and strength of new capillary beds. o Improper cross-linkage of collagen fibers has been responsible for nonspecific post-operative bleeding in patients with normal coagulation parameters. o Early in the proliferation phase fibroblast activity is limited to cellular replication and migration. o Around the third day after wounding the growing mass of fibroblast cells begin to synthesize and secrete measurable amounts of collagen. o Collagen levels rise continually for approximately three weeks. o The amount of collagen secreted during this period determines the tensile strength of the wound.
WOUND REMODELING
The final phase of wound healing i.e. remodeling develops 3 weeks following injury and continues up to two years, achieving 40-70 percent of the strength of undamaged tissue at four weeks. This phase is characterized by reorganization of new collagen fibers, forming a more organized lattice structure that progressively continues to increase wound tensile strength. The strength of scar tissue formed in this phase is less than the surrounding normal tissue.
COMPLICATIONS OF WOUND HEALING
Wound dehiscence is the splitting and separation of previously closed wound layers. Evisceration is protrusion of viscera through the wound. Eventration is protrusion of the bowels from the abdomen. The main causes responsible for these conditions include improper surgical technique and the local and systemic factors described below. Dehiscence usually occurs 3-5 days after surgery before collagen deposition. The characteristics features include incisional swelling, discolouration, necrosis and unusual exudation. Haemorrhage due to rupture of blood vessels can lead to development of hemorrhagic shock and ultimately death. Traumatic neuralgia is the pain perceived at or around the vicinity of wound. Primary traumatic neuralgia persist for prolong period whereas secondary one appear during cicatrisation. Septicemia and pyemia are the common complications of wound healing cause by the bacterial toxins due to massive infection and may lead to endotoxic shock. Traumatic fever is the resultant of pyrogen release from neutrophils and injured body tissue. Haematoma (accumulation of blood in the Subcutis) or seroma (accumulation of serum in the dead space) may occur due to rupture of blood vessels following injury. Sinus (draining tract from a suppurative cavity to the surface) may develop due to presence of necrotic tissue debris and foreign bodies. Fistula (abnormal passage between two internal organs) may develop due to paucity of drainage from a purulent cavity. Cellulitis is inflammation of the connective tissues presenting as oedema, redness, pain and heat often with hardness. Exuberant granulation tissue (proud flesh) is granulation tissue which grows above the level of the surrounding skin (overgranulation), preventing epithelial cells from growing across the wound.
Tetanus may develop due to Clostridium tetani infection particularly in deep penetrating and punctured wound. Caprine, equine and camalidae are more susceptible to tetanus. Adhesions are the major post-operative complication following abdominal surgery due to rough handling of viscera. Traumatic emphysema arises due to punctured wounds of the respiratory or gastrointestinal tract where gas or air accumulate in and around the wound area. Venous thrombosis and embolism may occur when fat tissue accidentally entered in the circulation. Gas gangrene may develop.
FACTORS AFFECTING WOUND HEALING
Local factors Systemic factors Medication Systemic diseases LOCAL FACTORS
Good surgical technique is warranted for proper wound healing if Halsted’s principles are followed. The principles include: o Gentle handling of tissue. o Aseptic surgical technique o Perfect hemostasis and preservation of blood supply to the wound area. o Close tissue approximation and obliteration of dead space o Removal of necrotic and devitalized tissue. Tissue vascularity ensures oxygenation and nutrients which is essential for wound healing. Oxygen influences angiogenesis, epithelialization and resistance to infection. Infection is one of the major factors which retard the wound healing significantly as it prolongs the inflammatory phase, disrupts the normal clotting mechanisms, promotes disordered leukocyte function and ultimately prevents the development of new blood vessels and formation of granulation tissue. Topical medications promote wound healing by minimizing bacterial infection. However, certain antimicrobial agents and local anesthetics delay the healing process by destroying cellular elements of wound. Lavage and dressings accelerate wound healing by protecting healing tissue. Lavage with sterile isotonic solutions like normal saline decreases the concentration of the microorganisms mechanically and aids in healing process. Nonadherent, moist dressing triggers
epithelisation whereas adherent gauge dressing mechanically debride the contaminated wound. Presence of foreign bodies such as tissue debris, dirt, soil, sequestrum, or nonabsorbable braided suture materials delay the healing process by exacerbating the inflammatory response and inciting infection. Obliteration of dead space and prevention of fluid accumulation promote migration of reparative cells and minimizing the risk of infection during wound healing. Ionizing radiation retards wound healing by decreasing fibroblast formation, collagen synthesis and neovascularisation within fortnight of surgery. Movement of the wound site prolongs the healing process as movement can disrupt cell migration, neovascularisation and formation of early ground substances of the wound. Mutilation of the wound not only disturbs the healing but also complicate by creating evisceration like condition. SYSTEMIC FACTORS
Advanced age retards healing because of reduced skin elasticity and collagen replacement. The immune system also declines with age making patients more susceptible to infection. Older animals are also susceptible to other chronic diseases, which affect their circulation and oxygenation to the wound bed as compared to young. Nutrition plays a pivotal role in wound healing process. Protein is required for all the phases of wound healing, particularly important for collagen synthesis. Hypoproteinemia slows healing by decreasing wound tensile strength, delaying fibroplasia and producing edema. Glucose balance is essential for wound healing. Hyperglycemia delay wound healing. Iron is required to transport oxygen. Minerals like zinc, copper are important for enzyme systems and immune systems. Zinc deficiency contributes to delay epithelisation and disruption in granulation tissue formation by inhibiting fibroblastic cellular proliferation. Vitamins A and B complex are responsible for supporting epithelialization and collagen formation. It is also important for the inflammatory phase of wound healing. Vitamin C is essential for formation of intercellular cementing substances as it is needed for hydroxylation of the lysine and proline moieties of collagen. Carbohydrates and fats: These provide the energy required for cell function. When the patient does not have enough, the body breaks down protein to meet the energy needs. Fatty acids are essential for wound healing.
MEDICATION
Anti-inflammatory, cytotoxic, immunosuppressive and anticoagulant drugs all reduce healing rates. o Anti-inflammatory drugs like corticosteroids if used in long term and at higher doses impair the inflammatory phase, decrease fibroplasia, collagen synthesis and neovascularisation. o Chemotherapeutic agents like methotrexate, doxorubicin and cyclophosphamide delay the wound healing process by inhibiting cell division or collagen synthesis. In addition, healing process is adversely affected by depressing immune function, epithelialization and contraction. o Anticoagulant drugs retard the healing by interrupting clotting mechanism and thus making a wound more prone to infection due to presence of blood clots. o Most NSAIDs lower resistance to infection and ultimately delay healing. SYSTEMIC DISEASES
Systemic diseases like malignancy, uncontrolled diabetes, renal and hepatic disturbances delay healing process. A malignancy in the body retards wound healing by altering metabolism, producing chachexia, and minimizing inflammatory cell division. Uremia delays fibroblastic proliferation, granulation tissue formation, epithelial proliferation and subsequently strength of healing wund. In patients with uncontrolled diabetes, there is delayed healing as hyperglycemia impairs collagen formation, neovascularisation, granulocytes cell functions and ultimately leading to wound dehiscence.
CLINICAL SIGNS OF INFECTION
Local pain/tenderness Local swelling/oedema Increased exudate Frank pus Wound breakdown Pyrexia Delayed healing Change in appearance of granulation tissue
Bridging of epithelial tissue Abnormal smell
MANAGEMENT OF WOUNDS
Humans have always been faced with the dilemma of how to treat wounds. Many diverse and interesting approaches to wound management have been applied throughout medical history. Thirty years ago physicians believed pus in a wound was laudable and anxiously awaited its arrival; surgeons today attempt every conceivable means to prevent its presence. o Contusions: are treated with cold and astringent applications to minimize extravasation. o Haematomas: when small get absorbed other wise they may have to be opened and treated. o Open wounds: surgical or aseptic wound, contaminated and septic wound or infected wounds.
Surgical or aseptic wounds
A surgical wound made with all aseptic precautions in a non infected tissue is an aseptic wound. Surgeon should avoid drying of the tissue, excessive trauma and haemorrhage – lower the wound infection. Prophylaxis against tetanus. Dependent drainage should be provided if haemotoma or seroma formation is expected. Suture should be supported upto healing time 8 -14 days Systemic use of specific antibiotics as a therapeutic or prophylactic measure. Local application of Fly repellents – hot summer months. The patient and the affected injured part should be kept at rest.
Contaminated wound
A fresh wound gets contaminated when it is more than 4 -5 days old. The principal therapeutic strategies of the open and contaminated wound are to convert it into a clean closed wound.
WOUND CLEANSING PROTOCOL
Wound cleansing is a clean - not sterile – procedure. Not all wounds require cleaning.
Reasons to clean a wound
Presence of: o Foreign bodies o Debris e.g. slough, residue from hydrocolloid dressings o Purulent exudate i.e. infection
EQUIPMENT
Clean basin - basin for this purpose must be washed with soapy water, rinsed and dried before use. Warm tap water is required otherwise cold water may reduce the temperature of the wound surface to a degree where cell mitosis will not recommence for up to 4 hours. Gauze / soft wash cloth: Contaminated wound, where possible, immerse and clean. Otherwise, the soaked wash cloth must be squeezed over it allowing the water to wash over it. Non-fiber shedding gauze should be used where foreign bodies remain. This is not a routine practice as it redistributes bacteria, is painful and causes trauma to healing cells Disposable gloves (clean but not sterile) o The following procedures should be meticulously adhered: A sterile gauze pad should be placed over the wound followed by shaving the surrounding skin and finally, cleaning the edges of wound with a detergent soap and water. The surrounding area should be draped with a sterile one. The wound area should be prepared for surgical debridement by gentle irrigation with lukewarm isotonic saline solution. Devitalized and ragged skin edges, nonviable and heavily contaminated tissues should be removed. Again the wound area should be exposed by gentle traction and carefully irrigated.
After cleansing, dry surrounding skin but not the wound itself. The operative field should be again prepared by placing sterile gauze over the wound and redraping the surrounding area. Capillary and venous oozing should be controlled by gentle pressure and ligating blood vessels if necessary. Wound closure should be done either by suture without drainage or placing a small rubber drain into the depths of the wound and other end in the skin margin. The wound may be loosely packed with petrolatumimpregnated gauze and sutured at a later date (delayed primary closure).
SEPTIC WOUND OR INFECTED WOUND Basic principles of infected wound treatment strategies
Debridement: Thorough debridement is most essential to manage septic wounds which will provide easy access to the wound depth. o All necrotic tissue debris and foreign materials should be removed until clean, healthy tissue margin of the wound are achieved. o Infected wound should not be plugged or closed unless infection is well controlled for primary healing but should be left to heal by secondary healing. Lavage: after removal of the necrotic debris, the wound and its periphery should be copiously irrigated with warm normal saline or water and soap or 2% hydrogen per oxide. o Volume and nature of lavage fluid depends on the degree of gross contamination and size of the wound. o Addition of antibiotics or antiseptics is not required when large volume of fluid is used as improper concentrations of such drugs may have deleterious effect to the wound healing process. Wound drainage can be achieved by using Penrose drains, plastic or rubber tubes or open drainage with bandage support. The aim is to reduce fluid accumulation, dead space, hematoma and seroma. The following guidelines should be observed: o Dependent drainage of wound exudate should be provided if possible so that gravity will aid drainage of the exudate. o The incision for drainage should be placed in the most direct route possible and away from anastomotic sites, tendon and major vessels. They may cause pressure necrosis.
Soft, petrolatum based antiseptic gauze should be used to keep the wound edges apart. o Incision to place the drain should be made within the zone of reaction; avoid cutting into non-infected areas. The drain exit site should be prepared in an aseptic manner and should be covered with sterile bandages to prevent premature removal or loss of the drain and to access the nature of the exudate. o Through and through drainage should not be used. o Usually drain should be removed after 24-48 hrs. ( insert picture). Antimicrobial therapy: Selection of the antimicrobial agent should be based on culture and antibiotic sensitivity test. However, empirical antimicrobial agents should be advocated in life–threatening infections that exists or develops while awaiting culture and sensitivity results (4872 hrs). In most cases, animals with existing wound infection are treated initially with loading dose of intravenous medication. Antimicrobial therapy should be continued for 10-14 days. Sterile protective bandaging is a good practice to avoid hospital infection, colonization of the wound by opportunistic organisms and to prevent environmental contamination with the infective agent. o
PART – II ANAESTHESIOLOGY --------------------------------------------Module – 9 PREANAESTHETIC CONSIDERATION & PREANESTHETICSPREMEDICATION
Premedication and selection of premedicants are important components of safe anaesthetic protocol in tailoring anaesthetic regimen suitable for species, breeds, age and disease status.
Aims of premedication
To reduce fear and calm the patient, To reduce distress during restraining and minor manipulations like placement of catheters, To produce pre, intra and post operative analgesia, To reduce salivary secretion and airway secretion, To decrease the total quantity or amount of the major anaesthetic drug, To reduce the delecterious side effects of the major anaesthetic drug, To provide smooth induction, To reduce intra operative complications like vomiting and regurgitation and
To provide safe and smooth recovery.
CLASSIFICATION OF PREMEDICAMENTS
The premedicants used in veterinary anaesthesia are classified as follows based on their properties.
S.No. Premedicaments
Examples
1
Anticholinergics
Atropine sulphate, Glycopyrrolate
2
Transquilizers or neuroleptics
Chlorpromazine, Acepromazine, trith promaziae promethorine
Phenothiazine derivatives Butyrophenones Benzodiazepines
Droperidol, Azaperone Diazepam, Medazolam, Zaazepur clamazolam
3
Sedatives Alpha 2 adrenergic agonist Chloral hydrate
4
Opioid agents
Xylazine, Detomidine,Meditomedine Ranifidiae
Morphine, Meperidine
Agonists
Pentazocaine, Butorphenol
Partial Agonists/Antagonists
ANTICHOLINERGICS
Anticholinergic premedicants are atropine sulphate, scopolamine and glycopyrrolate. Atropine sulphate is a natural product widely available invarious plants like Atropa belladonna. It is also found in Jimson weed. Scopolamine is not used in veterinary practice. Glylcopyrrolate is a synthetic quaternary ammonium compound. These agents are competitive of acetylcholine (Ach) hence attenuate the physiological responses of parasympathetic nerve impules. CLINICAL PROPERTIES AND USES
These agents are administered to o suppress the vagal tone o reduce salivary and bronchial secretions. Anticholinergic premedication is contraindicated in ruminants as the salivary and bronchial secretions will become more viscid and block the airway. They also induce ruminal atony. But their use is justified and recommended along with anaesthetics and adjuncts, which cause excessive salivation and bradycardia (eg. Xylazine). Though the routine use of these drugs has decreased in anaesthetic protocols, their use is still recommended in patients with preexciting bradycardia or in combination with drugs anticipated to cause bradycardia. In animals with preexciting bradycardia they increase the cardiac out put. Herbivores are more resistant to anticholinergics. They increase the heart rate by blocking vagal tone on S.A node. The increase in heart rate is associated with increased myocardial oxygen consumption, hence contraindicated in animals with pre exciting tachycardia, heart failure and cardomyopathies. Large dose of atropine may cause dilatation of cutaneous vessels due to the effect on the cholinergic receptors of the vascular smooth muscles (Atropine flush). Decrease salivary secretion, gastric acid secretion and gastrointestinal motility.
Decrease bronchial secretion, dilate bronchi and increase the pulmonary dead space. Induce mydriasis due to the cholinergic blockade of iris and ciliary body and paralyze accommodation reflex (cycloplegia) resulting in photophobia and blurred vision. Indicated in eye surgeries whether performed under local or general anaesthesia to prevent oculo-cardiac reflex. Relax the urinary tract smooth muscles and tend to cause urinary retention. Excessive dose of atropine and scopolamine may induce hallucination, excitement and seizures. And this central stimulation is not noticed after administration of glycopyrrolate, as it does not cross the bloodbrain barrier. Due to this property glycopyrrolate is considered as a usefulo premedicant in equine anaesthesia. The undesirable effects of atropine and glycopyrrolate can be reversed with neostigmine or physostigmine.
ADVANTAGE AND DISADVANTAGES OF ATROPINE AND GLYCOPYRROLATEDrug Atropine sulphate
Advantages Disadvantages Less expensive, may induce Tachycardia is not extreme variety of cardia as in glycopyrrolate arrythmias if Indicated in animals myocardial requiring immediate oxygen demand is treatment for bradycardia not satisfied. due to its quick action. Iduces bradycardia initially if administered through intravenous route due to the stimulation of vagal nuclei in the medulla: hence intravenous administration is contraindicated for caesarian
section in bitches. Glycopyrrolate
Less dose (0.44 mg of Not completely effective atropine is equivalent to in preventing sialorrhea 0.11 mg of glycopyrrolate in intravenous route). Controls bradycardia effectively. Indicated in caesarian section as it does not cross the placental barrier and causes excessive increase in the heart rate of neonates. Effectively controls gastric acidic pH and avoids aspiration of gastric acidic secretion. Causes less intestinal stasis hence indicated in equine anaesthetic regimen to reduce the incidences of post anaesthetic colic due to ileus.
CLINICAL DOSES Species
Atropine
Glycopyrrolate
Horses
0.02 – 0.05 mg/kg S.C/I.M 0.02 mg/kg S.C/IM
Goats
0.20 mg/kg I.M
Pigs
0.3—1.8 mg total dose
Dogs
0.01 mg/kg I.M
0.02—0.05 mg/kg S.C/I.M 0.01—0.02 mg/kg S.C/I.M/I.V 0.02 – 0.02 mg/kg I.V
Cats
0.02 – 0.1 mg/kg S.C/I.V
0.02—0.02 mg/kg S.C/I.M./I.V
0.01 – 0.02 mg/kg I.V
Last modified: Saturday, 9 October 2010, 06:32 AM
PHENOTHIAZINE DERIVATIVES
Phenothiazine derivatives are basically three ring structures in which two benzene rings are linked by a sulphur and nitrogen atom. The steriochemical model of phenothiazine derivatives is similar to epinephrine, norepinephrine and dopamine. They act on the central nervous system by depressing the brain stem and connections of the cerebral cortex. These agents increase the dopamine and norepinephrine turn over in the brain and block the peripheral actions of catecholamines at alpha 1 receptors. These agents are weak anticholinergics and have extrapyramidal stimulating properties. Acepromazine maleate, triflupromazine hydrochloride, chlorpromazine, promazine, promethazine and methotrimeprazine are the commonly used phenothiazines. Among these agents acepromazine, triflupromazine and chlorpromazine are used in veterinary anaesthesia. CLINICAL PROPERTIES AND USES
Produce sedation, general calming and reduction in motor activity Antagonize dopamine excitatory chemoceptors and suppress vomiting. At high doses and some times in clinical doses induce extrapyramidal signs such as rigidity, tremors and catalepsy. Hence contraindicated in patients; o With the previous history of epilepsy, o Undergoing myelographic procedures o With the history of recent intake of organophophorus drugs or toxicity Pulmonary functions are maintained following the administration of phenothiazines except slight depression in respiratory rate Induce urine production due to the suppression of antidiuretic hormone Animals undergoing intradermal allergic tests should not be administered with phenothiazines as they are potent antihistaninics Depletes catecholamines of the thermoregulatory center and render the animal’s body temperature susceptible to the changes in the environmental temperature. Tranquilization with phenothiazines is contraindicated in animals undergoing epidural, spinal or segmental anaesthesia. Following
induction of regional anaesthesia there will be vasodilation in the anaesthestised part of the body and this effect is compensated by the vasoconstriction in the unanaesthetized parts of the body to maintain cardiac out put. This response is abolished by the generalized vasodilationinduced by phenothiazines.
CLINICAL DOSES Drug Acepromazine
Dose Dogs = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.05 mg/kg I.M. Cats = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.1 mg/kg I.M. Horses = 0.02 – 0.05 mg/kg I.V, 0.04 – 0.09 mg/kg I.M. Cattle = 0.02 – 0.05 mg/kg i.V, 0.04 – 0.09 mg/kg I.M. Pigs = 0.1 mg/kg I.M.
Chlorpromazine Dogs = 0.55 – 4.4 mg/kg I.V, 1.1 – 6.6 mg/kg I.M. Cats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M Horses = 1.1 – 2.2 mg/kg I.M. Cattle = 0.2 – 1.1 mg/kg I.V, 0.2 – 2.2 mg/kg I.M. Sheep = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M. Goats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M. Pigs = 1.0 – 2.0 mg/kg I.M. Promazine
Horses = 0.44 – 1.1 mg/kg I.V/I.M. Cattle = 0.44 – 1.1 mg/kg I.V/I.M.
Goats = 0.44 – 1.1 mg/kg I.V/I.M. Sheep = 0.44 – 1.1 mg/kg I.V/I.M. Pigs = 0.44 – 1.1 mg/kg I.V, 0.44 – 4.0 mg/kg I.M. Triflupromazine Dogs = 1.00 mg/kg
BUTYROPHENONES
Butyrophenones have similar properties like phenothiazines. They block the central actions of dopamine and norepinephrine. They are more likely to produce extrapyramidal signs like tremors, rigidity and catalepsy in clinical doses hence not popular. Droperidol, fluanisone, azaperone and lenperone are the butyrophenones used in anaesthesia. They are potent antiemetics and even prevent drug induced vomiting produced by opioid analgesics by acting on the chemoemetic trigger zone. Hence used as neuroleptic analgesics in anaesthetic regimen. Butyrophenones have less cardiac depressive effects and the hypotension produced by the agents can easily be reversed with phenylephrine. They induce minimal changes in respiratory parameters. DRUGS AND DOSES
Droperidol o It is available in combination with an opioid analgesic, fentanyl citrate. (0.4 mg of fentanyl citrate and 20 mg of droperidol per ml = Innovar vet) This combination produces profound analgesia for 30 minutes and sedation for a considerable time in dogs. o In cats it may induce undesirable central nervous system stimulation. o Other effects noticed after administration are panting, aggression upto 48 hours after recovery, defecation and salivation. Naloxone - 0.04 mg/kg mixed with 4- aminopyridine - 0.5 mg/kg intravenously reverse the side effects of droperidol-fentanyl combination. o Clinical dose Dogs 0.05 – 0.1 mg/kg I.M Cats 0.10 – 0.11 mg/kg S.C Pigs 0.10 – 0.4 mg/kg I.M Azaperone o It is widely used in pigs for control and transportation. In pigs it is administered prior to metomidate. Azaperone sometimes produce
muscle tremors, sweating and excitement in horses hence it is unsuitable for equine anaesthesia. o Clinical dose - Pigs = 0.4 – 1.2 mg/kg I.M (low dose),2.0 mg/kg I.M (medium dose), 4.0 mg/kg I.M (high dose) Fluanisone o It is available in combination with fentanyl citrate. (0.315 mg of fentanyl and 10 mg of fluanisone = Hypnorm). o This combination is contraindicated in patients with respiratory, renal and hepatic diseases. Naloxone is the reversal agent for this combination. o Clinical dose - Dogs = 5 mg/kg along with 0.1 mg/kg of fentanyl citrate (neuroleptanalgesia). BENZODIAZEPINES
Benzodiazepines exerts their effects by binding to a specific binding site on aminobutyric acid (GABA) receptor. They do not have analgesic property. These agents are good anxiolytics, hypnotics and anticovulsants. They have minimal respiratory and cardiovascular depression. These agents produce muscle relaxation. Diazepam, midazolam, climazolam and zolazepam are the commonly used benzodiazepines. These agents are combined with opioid analgesics and dissociative anaesthetics. DIAZEPAM
Diazepam is used to treat status epilepticus in dogs, cats and human. It can not be used as a sole sedative agent in dogs and cats. In horses it produces excitation if used as a sole sedative premedicant hence combined with xylazine. It decreases the release of catecholamines and act as antidysrhythmic agent. It is used as an effective appetite stimulant in dogs and cats at the dose of 0.05 – 0.40 mg/kg Oral/I.M. In human it causes congenital anomalies if administered during the first trimester of pregnancy. And the significance of this is not clear in veterinary practice. It is absorbed by plastic materials hence storage in plastic syringes, infusion bags and infusion tubes are not advisable. Rapid intravenous injection may cause thrombosis. Dose o Dogs 0.1 – 0.5 mg/kg I.V, 0.3 – 0.5 mg/kg I.M. o Cats 0.05 – 0.4 mg/kg I.V, 0.3 – 1.0 mg/kg I.M. o Horses 0.02 – 0.04 mg/kg I.V
o o o o
Foals 0.1 – 0.2 mg/kg I.V Cattle 0.1 mg/kg I.V Goat 0.1 – 0.1 mg/kg I.V Pigs 1.0 mg/kg I.V MIDAZOLAM AND CLIMAZOLAM
Midazolam o It is twice as potent as diazepam. o Can be administered as premedicant to thiopentone, ketamine and propofol anaesthesia. o It is metabolized in the liver rapidly hence less cumulative can be stored in aquane solution in plastic container upto 100 hours without loss of potency. o Dose - Dogs & cats = 0.07 – 0.22 mg/kg I.M/I.V Climazolam o It is a potent benzodiazepine, has variety of use in cattle, sheep, horses and dogs. o In horses the drug is combined with other premedicants and anaesthetics as it may produce excitement and muscle weakness. o Dose Dogs = 1.0 – 1.5 mg/kg in combination with 5.15 mg/kg of fentanyl I.V Horses 0.05 – 0.2 mg/kg I.V Cattle 0.5 – 1.1 mg/kg I.M Sheep & goats 0.5 – 1.1 mg/kg I.M Pigs 0.5 – 1.0 mg/kg I.M Chicken 5.5 – 11.0 mg/kg I.M
ZOLAZEPAM AND FLUMAZENIL
Zolazepam o It is marketed in combination with dissociative drugs like tiletamine (250 mgs of tiletamine and250 mgs of zolazepam in lyophilized form). For dose calculation the two drugs are considered as one product (500 mg). o Dose Dogs 6.6 - 9.9 mg/kg I.M, 2.0 - 43 mg/kg I.V Cats 6.0 - 11.9 mg/kg.I.M. Flumazenil
o
The actions of all benzodiazepines can be reversed or antagonized with flumazenil at the dose of 0.1 mg/kg I.V. ALPHA 2 ADRENERGIC AGONIST
Alpha 2 adrenergic agonists are referred as sedative analgesics. The popular agents are xylazine hydrochloride, detomidine, meditomidine and romifidine.
XYLAZINE HYDROCHLORIDE
Xylazine is a sedative analgestic having alpha 2 adrenergic agonist activity. It produces dose-related depression of the central nervous system. The duration of analgesic activity is 15 – 30 minutes and the sedation is for 1-2 hours. Ruminants are more sensitive to xylazine. One tenth of the dose used in horses and dogs induce sedation and recumbency in cattle. In horses it is a reliable sedative and the horse will be in standing position in clinical doses. Drooping of head and buckling of hind limbs are commonly noticed in horses. The clinical dose through intravenous route is 1.1 mg/kg. Further increase in the dose will not increase the intensity of sedation, only the duration will be increased. Emesis is common in dogs and cats after xylazine injection due to the stimulation of central emetic center. Produces muscle relaxation, which is attributed to decrease in intraneural and synaptic transmission in the central nervous system. Xylazine is used in the treatment of equine colic for pain relief. But it must be used with caution as it may mask the clinical signs and may aggravate ileus. Xylazine induce profound depression of cardiovascular system. Bradycardia, decreased cardiac out put, hypotension and and increase in central venous pressure are noticed. It also often produces A.V block. Intravenous administration causes a transient increase in blood pressure. Administration of anticholinergies as premedicants reduce the incidence of bradycardia and even the bradycardia that occurs after administration of xylazine can be reversed with atropine (0.045 mg/kg initially and followed by 0.01 mg/kg intravenously). It is contraindicated in branchycephalic breeds, older dogs and in intestinal obstruction.
It increases the sensitivity of myocardium to the circulating catecholamines. Cardiac dysrhythmias may occur if used along with halothane. In ruminants it reduces the gastrointestinal and ruminal motility with relaxation of cardia oesophageal sphincter. This favors ruminal tympany and regurgitation. Xylazine has oxytocic property and increase the intrauterine pressure hence it may induce abortion in pregnant animals. Increase in intrauterine pressure may cause embryo/ovum ejection if administered in embryo/ovum transplantation. Thermoregulation is depressed following xylazine administration and the animal may become hypothermic or hyperthermic depending on the ambient temperature. Xylazine is used as epidural anaesthetic because of the presence of alpha receptors in the spinal cord and its structural similarity with lidocaine. Other effects o Excessive urine production because of the suppression of antidiuretic hormone o Salivation o Hyperglycemia Dose o Horse 1.1 mg/kg I.V/IM o Dogs & cats 0.2 --- 1.1 mg/kg I.V/I.M/.S.C o Cattle, sheep & goats 0.05 – 0.08 mg/kg I.M. standing restraint 0.1 – 0.3 mg/kg I.M. recumbency and prolonged 0.1 – 0.2 mg/kg I.V recumbency o Pigs 1.0 – 2.0 mg/kg I.V Upto 4.0 mg/kg I.M. o Epidural 0.07 – 0.17 mg/kg in 5.0 to 10.0 ml of saline OTHER AGENTS
Detomidine
Detomidine is a potent alpha 2-adrenaergic agonist mainly used in horses and cattle. Advantages of these drugs o Does not stimulate pituitary adrenocortical adrenocortical axis hence stress is less. o Can be administered in pregnant animals o Can be administered in animals which are not fasted o It is very effective in relieving pain from colic in horses. o Provides standing restrain in cattle at the dose of 10 to 20 µg/kg I.V
o
Dose (not recommended in dogs cats and wild felines): Horse, Cattle, Sheep & Goats 10 - 40 µg/kg I.V
Meditomidine
It is a potent alpha 2 adrenergic agonist used in small animal anaesthesia. The other properties are similar to xylazine. Dose o Dogs 0.01 - 0.04 mg/kg I.V/I.M/S.C o Cats 0.04 - 0.08 mg/kg I.V/I.M/S.C o Cattle 0.01 - 0.02 mg/kg I.V
Romifidine (Sedivet)
It is developed from clonidine and has alpha 2 adrenergic agonistic action. Used in horses and maximum sedation is achieved at the dose of 80 µg/kg I.V SPECIFIC REVERSAL AGENTS
Alpha 2 antagonists
Yohimbine hydrochloride o It is a specific reversal agent for xylazine and detomidine. o It is an alpha 2 adrenergic blocking agent used at the dose of 0.1 mg/kg I.V. o It is often combined with 4-aminopyridine (0.04 mg/kg) for better results. o Yohimbine is used in the treatment of equine colic due to ileus. o It reverses the gastrointestinal stasis produced by xylazine. Atipamezole o It is used to reverse the effects of meditomidine at the dose of 0.04 – 0.5 mg/kg I.V. Doxapram o It is not a specific reversal agent to alpha 2 adrenergic agonists but offer certain beneficial effects due to its central nervous system stimulation and respiratory stimulation. CHLORAL HYDRATE
Chloral hydrate is used as a reliable sedative hypnotic in cattle and horses. It is less expensive and still perfectly acceptable sedative agent. It has deeply penetrating aromatic odour and is bitter in taste. The central nervous system depression is due to its metabolic product namely 2,2,2 trichloro ethanol, hence the sedative effect is prolonged even after cessation of administration.
It does not have analgesic property. Trichloro ethanol conjucates with glucuronic acid to urochloralic acid and excreted. Chloral hydrate depresses the motor and sensory responses at sedative dose and produces cerebral and medullary center depression at anaesthetic dose resulting in muscle relaxation and depression of cardiac and respiratory system. In cattle it can be drenched preferably through stomach tube, at the dose of 30 to 120 grams dissolved as 1 in 20 solution in water. Bullls that are uncontrollable and free in the yard can be controlled by water deprivation for brief period and allowing them to drink chloral hydrate dissolved water (90 to 120 grams in 12 litres of water). Chloral hydrate is administered as 10% solution intravenously in cattle at the dose of 80 to 90 mg/kg. Chloral hydrate is combined with magnesium sulphate at 2:1 or 3:1 ratio (weight) and administered in cattle. It is combined with magnesium sulphate and pentobarbital and administered to horses (Equithesin mixture). Intravenous dose of chloral hydrate in horses o Chloral hydrate alone 5 to 10 mg/kg for mild sedation and hypnosis, 20 to 40 mg/kg for moderate sedation and hypnosis, 50 to 75 mg/kg for profound sedation and hypnosis and 150 to 250 mg/kg for anaesthesia. o Chloral hydrate 100 mg/kg and thiopentone 1.5 to 2 mg/kg o Chloral hydrate 100 mg/kg and ketamine 1.5 to 2 mg/kg o Promazine 0.6 to 0.8 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiopentone 5 to 7 mg/kg o Acepromazine 0.04 to 0.08 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiamylal 2 to 4 mg/kg. o Xylazine 0.4 to 0.6 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiamylal 1 to 2 mg/kg. Disadvantages of chloral hydrate o Prolonged hangover with ataxia and stupor o Perivascular administration causes pain, swelling and necrosis o Induces abortion in mares
Opioids Derivatives -
Pure agonists-
Morphine
Pathadine,meperidine and oxymorphone -
Fentanyl citrate and etorphine -
Partial agonists
Partial agonists (agonists/antagonistics)
Pure Antagonist PURE AGONISTS
MORPHINE
Morphine o Morphine is derived from the dried milky exudates of the unripe seed capsules of the opium poppy (Papaver somniferum). o The exudates contains 3-25% of morphine, 5% noscapine and 0.8% papaverine. o The laboratory synthesis of morphine is different hence still it is derived from opium poppy. The laboratory synthetic agents are codeine, heroin (dimorphine = diacetylmorphine) and oxymorphine. o Morphine acts and produces Analgesia Drowsiness Produce nausea and vomiting by stimulating chemoceptor trigger zone for vomiting. It induces dopaminergic excitement in cats, horses, pigs, dogs and cattle. Induce respiratory depression Depress cough The effects on myocardium are not significant; but produce increase in vagal tone and slowing of heart. Morphine is used as a postoperative analgesic for pain relief in veterinary practice. Morphine decreases motility of stomach with increase of antral portion. Initial use may cause defecation and chronic use will result in constipation. It is absorbed from the gut and oral mucosa. It is used in the treatment of congestive heart failure to relieve pain and decrease after load. Preservative free morphine can be administered epidurally to relieve pain. Dose o Horses Morphine gives good results in horses if administered after xylazine sedation. Xylazine 1.0 mg/kg I.V and morphine 0.6 mg/kg I.V o Dogs 0.2 – 0.5 mg/kg ( total dose not exceeding 10 mg ) I.M/I.V o Cats 0.05 – 0.1 mg/kg S.C/I.M. must be administered with caution because it may induce CNS stimulation. Hence must be used with suitable tranquilizer.
o
Morphine is administered after administration of Acepromazine. Acepromazine 0.1 mg/kg I.M. and Morphine 0.6 mg/kg I.M. PATHADINE, MEPERIDINE AND OXYMORPHONE
Pathadine o Pathadine is a vagolytic and negative inotropic drug at clinical doses. o It reduces salivation and respiratory secretion without inducing vomiting and defecation. o Pathadine induces histamine release if administered through intravenous route. o Dose Dogs = 2 - 6.5 mg/kg S.C/I.M Catls = 2 - 4.4 mg/kg S.C/I.M Meperidine o It is a synthetic product, less potent (one tenth of morphine) and used in dogs and cats. o Intravenous administration causes release of histamine hence most often used along with acepromazine. (Phenothiazines are potent antihistaminics) o Dose: Dogs and Cats 2-5 mg/kg I.M Oxymorphone o Oxymorphone is a synthetic derivative having 10 times greater potency than morphine. o It is widely used in dogs and cats for its analgesic property. Analgesia lasts for 4 hours. o It does not cause histamine release as meperidine. o It is used popularly in small animal anaesthesia due to its analgesic and lack of release of histamine. o The only limitation with drug is stimulation of vagus leading to bradyarrhythmias and it can be reduced or prevented with the use of antichlinergic agents in the protocol. o It is also administered epiduraly to control pain in the hindquarters (0.025 - 0.05 mg/kg). o Dose Dogs 0.05 - 0.2 mg/kg I.V/I.M/S.C (total dose not exceeding 4.5 mg) Cats 0.05 - 0.4 mg/kg I.V/I.M/S.C Horses 0.02 - 0.03 mg/kg I.V/I.M. FENTANYL CITRATE AND ETORPHINE
Fentanyl citrate
Fentanyl is a synthetic opioid product related to phenylpiperidines. Its analgesic property is 80 times greater than morphine.
Cardiac out put, heart rate, respiratory rate and arterial oxygen tension (PaO2) are reduced following administration of fentanyl. Fentanyl citrate is available alone, or in combination with droperidol (Innovar vet contains 0.4 mg of fentanyl and 20 mg of droperidol per milliliter) or fluanisone. (Hypnorm contains 0.315 mg of fentanyl and 10 mg of fluanisone per milliliter) Fentanyl combinations provides good intra operative analgesia. In dogs and primates it produces sedation and myosis whereas in horses it produces excitement and mydriasis. It is not recommended in cats. Dose - Dogs 0.01 - 0.02 mg/kg I.M/I.V. (see butyrophenones for other doses). The other synthetic pure agonists are afentanil, sufentanil, lofentanil and carfentanil.
Etorphine
Etorphine is a potent synthetic morphine derivative. Its general properties are similar to morphine. The dose of etorphine is 0.5 mg/500 g B.W Etorphine is an extremely long acting agent whose effects are maintained by enterohepatic recycling. The action of this drug can only be terminated by the administration of the specific antagonist Diprenorphine. In clinical dose etorphine along may produce initial excitement hence it is marketed in combination with phenothiazine derivatives. Separate combinations are available for large and small animals. Each pack of the marketed drug will be having two components. 1-Immobilon and 2-Revivon. Preparation Immobilon L A contains Etorphine 2.45 mg/ml and acepromazine 10 mg/ml Immobilon S A contains Etorphine 0.074 mg/ml and Methotrimeprazine 18 mg/ml Revivon L A contains Diprenorphine 3.0 mg/ml Revivon S A contains Diprenorphine 0.272 mg/ml This mixture is popularly used to capture elephants and giraffes Not recommended for domesticated and wild felines Etorphine is extremely potent in human and any accidental injection may cause death if not treated with naloxone or diprenorphine.
PENTAZOCAINE, BUTORPHENOL TARTRATE AND BUPRENORPHINE Pentazocaine
It is used as an analgesic. In human it causes dysphoria and hallucination and pentazocaine is developed to prevent drug abuse. In clinical doses it produces pulmonary vascular resistance.
In horses it is used in the treatment of colic and administered at the rate of 0.33 mg/kg I.V. Dose -3 mg/kg for 1 to 3 hours of analgesia. Penlog -Duration of analgesia 3-4 hour . Onset 1 min – one hour
Butorphenol tartrate
Butorphenol is used in horses, cats and dogs. It produces sedation, analgesia and increase in pulmonary vascular resistance. Dose o Horse = 0.1 mg/kg I.V o Dogs = 0.2 – 0.8 mg/kg I.M/S.C o Cats = 0.2 – 0.4 mg/kg I.V/I.M/S.C o Onset 1 mint – 15 mint I.V. rapid
Buprenorphine
Respiratory depression is more and often treated with intermittent positive pressure ventilation. Dose o Horses = 6 - 10 µg/kg o Dogs = 0.01 - 0.02 mg/kg S.C/I.M/I.V o Cats = 0.005 - 0.02 mg/kg S.C/I.M PURE ANTAGONISTS
Naloxone hydrochloride, nalorphine hydrochloride and diprenoorphine are the opioid pure antagonists used for the reversal of the effects of pure agonists and partial agonists. In horses naloxone is used in the control of crib biting. o Dose Naloxone Dogs and cats = 0.04 - 0.1 mg/kg I.V/I.M/S.C Horses 0.005 = 0.2 mg/kg I.V Diprenorphin-Dogs & Cats = 0.0272 mg/kg I.V Horse = 0.02 - 0.03 mg/kg I.V Module- 10 => LOCAL ANAESTHESIA (Introduction)
Varieties of minor and major surgical procedures canbe accomplished in domestic animals under local and regional anaesthesia, depending on the species, breed, temperament of the animal, health status of the animal and magnitude of the procedures. LOCAL ANAESTHETICS
Cocaine
It is an extract from the leaves of Erythroxylon coca. It is an irritant and toxic in small doses. The toxic manifestations include clonic convulsions, loss of consciousness and paralysis of medullary centres. The maximum dose is 780 mg in horses, 120mg in large dogs, 45 mg in small dogs and 15 mg in cats. Cocaine was used as a doping agent in horses. The lethal dose is 15 mg/kg. Cocaine is withdrawn from the injectable forms due to its toxicity. Only topical preparations are available for eye(4% solution) and nasal and laryngeal areas (10 to 20% solutions).
Procaine hydrochloride
It is a short acting local anaesthetic derived from ester. It is detoxified in the blood and liver rapidly. The margin of safety is high in terms of convulsive dose (35 mg/kg in cats). In clinical practice it is administered intravenously to relieve pain in fire injured patients. It is also used as adjunct to thiopentone sodium to maintain anaesthesia. Procaine is combined with adrenaline 1 in 100000 to potentiate its anaesthetic action.
Lidocaine hydrochloride
It is a fast acting amide local anaesthetic detoxified in the liver. The convulsive dose is 15 mg/kg in cats. Goats are extremely sensitive to lignocaine. The total dose should never be exceeded 10 mg/kg in any route. The toxic manifestations in goats are excitation, tonic clonic convulsions, opisthotonus, respiratory depression, cardiac arrest and death. Lignocaine is combined with general anaesthetics, which does not posses convulsive properties as an ajunct (See injectable anaesthetics). It is often combined with thiopentone due to its dysrhythmic property and protective action on myocardium. In clinical practice adrenaline free lignocaine is administered intravenously at the rate of 0.25 mg/kg in cats and 2 mg/kg in dogs to control cardiac arrhythmia due to myocardial ischemia. The local anaesthetic preparationis marketed in combination with adrenaline 1 in 200000. It is also available as 2% jelly and 2.5% and 5% viscous ointments. The duration of action is two hours.
Bupivacaine hydrochloride
Bupivacaine is a fast and long acting amide derivative. Its margin of safety is less. The convulsive dose in cats is 3.4 to 5 mg/kg. Intravenous administration induces mdyocardial depression. Bupivacaine associated ventricular dysrhythmia are due to prolonged inhibition of sedum conductance in the cardiac muscles. It is not combined with general anaesthetics. High molecular weight substance like dextran is added to prolong the duration of action in obstetrical anaesthesia. POTENTIATION OF LOCAL ANAESTHETICS
Epinephrine/Adrenaline - 1 in 1000000 or 1 in 200000 is added to increase the intensity and duration of action. Hyaluronidase - It increases the diffusion of local anaesthetics and favours quick onset of action. It is added at the rate of 150 TRU (Turbidity reducing unit) Addition of hyaluronidase will reduce the duration of action. Dextran - High molecular weight substance is added to reduce the rate of absorption and increase the duration of action. TYPE OF NERVE BLOCKS SURFACE ANALGESIA
Surface anaesthesia includes topical analgesia of skin, eye and mucous membrane of nose, mouth, penis,vulva, urethra and rectum and intra – synovial analgesia. TOPICAL ANALGESIA
Ice, ethyl chloride spray, ether spray and carbonic acid snow are used to achieve superficial analgesia of the skin. Absorbent cotton or gauze soaked in 4% procaine or 2% lignocaine is often used on superficial aberrations of the skin and eczematous lesions to alleviate pain. Lignocaine 4% and proxymetacaine 5% (Ophthaine) are used as topical anaesthetics for eye. Analgesia of mucous membrane is induced for examination, catheterization or intubation. The commercial preparation containing lignocaine with carboxymethyl cellulose is applied on mucous membrane. This preparation is also used to lubricate catheters and endotracheal tubes. Lignocaine 4% is sprayed on nasal or oral mucous membrane to achieve analgesia. In horses 60 ml of lignocaine 1% can be administered intra rectally to reduce the discomfort during examination.
INTRA-SYNOVIAL ANALGESIA
Intra-synovial analgesia is induced to relieve pain arising from the joint and tendon sheath. Often it is used in the diagnosis of lameness in horses. Strict aseptic precautions muse bt adopted prior to injection. Inadvertent introduction of infection will be disastrous. If the needle is placed into the synovial cavity one can notice synovial fluid at the hub of the needle. Some quantity of synovial fluid is aspirated before injection into a distended synovial cavity. The intra-synovial injection techniques in horses are
Distal interphalangeal (coffin) joint
Site - in the midline approximately one centimeter proximal to the coronary band with the needle angled slightly steeply than at right angles to the skin. Needle and volume 19 G x1”, 5 - 8 ml.
Proximal interphalangeal (pastern) joint
Site - Pastern joint is situated approximately 1 cm below an imaginary line through the attachment of the collateral ligaments to the first phalanx. The joint is entered near the midpoint on the dorsal midline approximately 3 cm proximal to the coronary band with the needle pointing obliquely downwards and inwards. Needle and volume 20 Gx 1”, 5 - 8 ml
Metacarpophalangeal (fetlock) joint
Site - The fetlock joint is entered in the triangular space formed by the third metacarpal bone, the proximal sesamoid bone and the suspensory ligament. Can be performed with the limb weight bearing. Needle and volume 20 G x 1”, 10 ml
Digital flexor tendor sheath
Site - Usually performed onlyd in the presence of synovival distension. The site of injection is the most prominent distended part of the sheath on the lateral aspect of the digital flex or tendons just proximal to the fetlock. Needle and volume 20G x 1”, 10ml
Carpal joints
Site - The two carpal joints into which inje3ction can be performed. (mid carpal joint and antebranchiocarpal joint). The mid carpal joint opens with the proximal (antebrachiocarpal joint) between the third and and fourth carpal bones hence does not require separate injection. The joints can be entered on the dorsal aspect of the flexed limb just lateral to the extensor carpiradialis tendon. Needle and volume 20G x 1”, 10 ml.
Elbow joint
Site - The elbow joint can be entered either in front or behind its lateral ligament. To enter in front of the ligament the needle is inserted just under themargin of the lateral condyle of the humerus. Needle and volume 19G x 2”, 15 ml.
Shoulder joint
Site - The shoulder joint is entered horizontally between the anterior and posterior part of lateral tuberosity of the humerous. Needle and volume 19G x 3.5”, 20 ml
Tarsometatarsal joint
Site - Over the head of the fourth metactarsal bone and fourth tarsal bone Needle and volume 20G x 1”, 5 ml
Stifle joint
Site -This joint has three synovial sacs, one in the femoropatellararticulation and two, one medial and one lateral in the femoro-tibial artibulation. Femoro-patellar sac can be entered on either side of the middle patellar ligament. Medial sac of the femoro-tibial articulation can be entered between the patellar ligament and the medial femoro-tibhial ligament. Lateral sac of the femoro-tibial articulation can be entered behind the lateral patellar ligament. Another route is between the lateral femoro-tibial ligament and the common tendon of the long digital extensor and the peroneus tertius. Needle and volume 18G x 2”, 20 ml each sac.
Hip joint
Site - Can be performed in standing horse. The needle is inserted between the anterior and posterior parts of the trochantger major. Needle and volume 2 mm x 15 cm
INFILTRATION ANAESTHESIA
In this procedure the nerve ending is desensitized at the actual site of operation. Depending on the duration one can use procaine, lignocaine or bupivacaine. This form of analgesia is useful in the treatment of wound, skin incision, extirpation of superficial tumors. Following disinfection of the skin 0.5 to 1 ml of local anaesthetic is injected intradermally before injecting into deeper tissues. This called as an intradermal skin wheal. Small circular wheals are created for catheterization of vessesl. A linear continuous wheal can be produced by the use of a longer needle with single prick and it reduces the number of pricks in case of paravertibral nerve block. There are two types of infilteration anaesthesia o Line block o Field block LINE BLOCK
The needle is inserted parallel to the skin incision and for every 1 cm area of incision 1 ml of the local anaesthetic solution is deposited. The needle is withdrawn gently as the solution is deposited. If the length of the incision is longer than the length of the needle the needle can be inserted at the mid point of incision to preent multiple pricks. FIELD BLOCK
Field block
Making walls of desensitized areas enclosing the operation or incisional site.
Production of a cup
A cup of desensitized area is produced by making fan wise injection.
Inveted “L” block
Two lenior infiltration at right angle in the form of an inverted “L” desensitizes the flank region in cattle.
Ring block
Used in the extremities like limb for amputation of digit in cattle or in teat for teat surgery. Infiltration is done proximal to the site of operation.
Inverted “V” block
This is an another alternative method for ring block normally done in teat for the repair of teat fistula.
Local anaesthesia of fracture
Lignocaine is directly injected into the haematoma of fracture site with through aseptic precautions to relieve pain and favours closed method of reduction. REGIONAL INTRAVENOUS ANAESTHESIA
This technique is used for amputation of limbs and digits. A tight tourniquet or blood pressure measuring cuff is placed proximal to the site of operation to block venous drainage. Procaine or lignocaine is injected into the engorged superficial vein so as to facilitiate the retrograde flow of blood and deposition and infiltration of local anaesthetic into the tissues. Bupivaccaine is not normally used in this technique due to its myocardial effects. Analgesia lasts as long as the cuff or tourniquet is in place and maintains the pressure above the systolic blood pressure. INFRA ORBITAL NERVE BLOCK
Nerve
Infra orbital nerve is the division of trigeminal nerve. It supplies sensory nerve to the first and second molar (PM 1 & 2), canine and incisors as it passes the canal. After emerging from the canal it supplies sensory fibres to the upper lip, cheek, nostrils and lower part of the face.
Site and technique
The nerve can be blocked either as it passes the canal or after emerging from the canal using a 19 G x 5 cm needle. The infra orbital foramen is located about one half the distance and 2.5 cm dorsal to a line connecting the nasomaxillary notch and the rostral end of the facial crest in horse. In dogs the infra orbital foramen is situated in front of the anterior margin of the PM 4 where it can be palpated.
Its better to have the tip of the needle slightly curved to enter into the canal, 0.5 to 2 ml may be required in dogs and 10 ml in large animals.
Area desensitized
The skin of the lip, face of the side upto the level of the foramen is desensitized if blocked at the level of the foramen. If it is blocked in side the canal in addition to the above structures PM 1 & 2, canine, and incisors with their alveoli and gum and the skin upto the inner canthus of the eye. MANDIBULAR NERVE BLOCK
Nerve
Mandibular nerve is the alveolar branch of mandibular division of the 5th cranial nerve. It enters the mandibular foramen at the medial aspect of the vertical ramus of the mandible. Then it passes through the mandibular canal and supplies sensory dental and alveolar branches to the side. After emerging out it is called as mental nerve and it supplies to the lower lip.
Site and technique
The nerve can be blocked as it enters the mandibular foramen or as it emerges out from the mental foramen. Mandibular block: The mandibular foramen is located opposite to the point of intersection of a line passing vertically downwards from the lateral canthus of the eye and another line extending backward from the tables of the mandibular teeth. The site is selected medially 3 cm below the temperomandibular articulation on the posterior boarder of the mandible. 4 to 6 ml of the solution is deposited using along spinal needle. Mental block: Mental foramen is easily located on the lateral aspect of the jaw below the angle of the lip (in the middle of the interdental space) 3 to 5 ml of the solution is deposited. SUPRA ORBITAL NERVE BLOCK
Nerve
Supra orbital nerve (frontal nerve) is a sensory terminal branch of the ophthalmic division of 5th cranial nerve. It emerges from the orbit through the foramen accompanied with the artery. It supplies sensory fibres to the upper lip andpartof the skin on the forehead.
Site and technique
The foramen is palpated as a pit like depression midway between the upper and lower borders of the supra orbital process close to the frontal bone (about 6-cm dorsal to the medial canthus) 5 ml of the solution is injected with 19G x 2.5 cm needle. Successful block desensitizes the upper eyelid and the frontal region. Dogs do not have supra orbital foramen. The frontal nerve leaves the orbit medial to the ligament. CORNUAL NERVE BLOCK
Cattle
Cornual nerve is a branch of lacrimal (zygomaticotemporal) division of ophthalmic division of trigeminal nerve. It supplies sensory fibres to the horn corium and the skin around the base of the horn. The nerve passes through the periorbital tissues dorsally and then runs along the frontal crest to the base of the horn.
Goats
In goats the horn is supplied by the corneal branch of lacrimal (zygomaticotemporal) nerve and corneal branch of infratrochlear nerve. The infratrochlear nerve emerges from the orbit dorsomedially. SITE AND TECHNIQUE
Cattle
As the nerve run from the orbit to the base of the horn it becomes more and more superficial. The block is done more easily 2 to 3 cm below the base of the horn with 5 to 10 ml of 2% lignocaine. In cattle with large horn a second injection is given about 1 cm behind the first to block the posterior division of the nerve.
Goats
The lacrimal branch can be blocked half way between the lateral canthus and the lateral base of the horn. The infratrochlear branch can be blocked half way between the medial canthus and the medial base of the horn. To amputate the horn at the base it is better to provide sedation, as this block will not desensitize the perostium and sinus mucous membrane.
RETROBULBAR NERVE BLOCK
Auriculopalpebral branch of the facial nerve - motor nerve (VII) Oculomotor (III), trochlear (IV), and abducens (VI) nerves – motor innervation to the ocular muscles Maxillary branch of the trigeminal nerve (V) - sensory innervation to lower eyelid, soft palate, the nasal cavity, maxilla maxillary sinus and adjoining bones and the region supplied by the infraorbital nerve. Ophthalmic branch of the trigeminal nerve - sensory innervation to the upper eye lid, third eyelid, medial canthus, caudal part of nasal septum, cornea and sclera and the frontal sinus Optic nerve (II) For enucleation of eyeball all these nerves are blocked to achieve analgesia of the eye and orbit and immobilization of the globe. SITE AND TECHNIQUE
All these nerves except the optic nerve pass through foramen orbital. Anaesthetic solution is deposited anterior to the foramen. The notch formed by the supraorbital process, zygomatic arch and the coronoid process of the mandible is located and a 18G x 7 to 11 cm needle is inserted directed towards the opposite side last upper premolar until it reaches the pterygopalatine fossa. Deposit 15 ml of the solution. An additional 10 to 15 ml can be deposited slightly caudodorsally as the needle is withdrawn. This block does not provide desensitization of eyelids, hence for extirpation of eye ball in addition to this the auriculopalpebral nerve block and infiltration of eyelids mut be carried out. PARAVERTIBRAL NERVE BLOCK
This regional anaesthesia is very important for bovine laparotomy. The dorsal and ventral nerve roots of last thoracic (T13) and first and second lumbar (L 1 & 2) spinal nerves are blocked as they emerge from the intervertibral foramen. If analgesia of caudal paralumbar area is required additionally the third lumbar (L3) is blocked which result in weakness of the hind limb. SITE AND TECHNIQUE
Each nerve is blocked immediately in front of the cranial border of the transverse process of the succeeding lumbar vertebra. The last thoracic nerve is blocked half way between the last rib and the transverse process of the first lumbar vertebra about 5 cm from mid line.
The first and second lumbar nerves can be blocked at the posterior edge of the transverse process of the corresponding vertebrae about 5 cm from the mid line. The needle pricks are made through the subcutaneous wheals, to penetrate the intertransverse ligaments and 15 ml of local anaesthetic is deposited below the ligament and another 5 ml above the ligament. Successful block shows analgesia of flank, paralysis of flank muscles, increase in the temperature of flank, and scoliosis towards the desensitized side. In horses the block is performed on T 18, L1 and L2. EPIDURAL ANALGESIA
Epidural space is that compartment between the duramater and the bony and ligamentous wall of the spinal canal. This space is filled with extradural fat, internal vertebral plexus of veins and the spinal nerves. Injection of local anaesthetics will desensitize the nerves. Normally the site is preferred after the end of cona medularis of the spinal cord. SITE OF INJECTION IN DIFFERENT SPECIES Bovine - Sacrococcygeal junction between I & II coccygeal vertebrae Equine - Between I & II coccygeal vertebrae o Canine - Lumbosacral space o Swine - Lumbosacral space o Sheep and Goats - Lumbosacral space The terms high (anterior) and low (posterior) are often used to describe the level of block. If the block extends the segment from where the sciatic nerves arises (second sacral and more cranial segments) the block is termed as anterior epidural. The anterior epidural is achieved by increasing the volume of local anaesthetic injected. In high epidural or anterior epidural the animal will be recumbent and the motor functions will be lost. o o
TECHNIQUE Cattle and horse
The exact position of the sacrococcygeal junction or the space between the first and second coccygeal vertebrae cn be located by palpating the borders with simultaneous pumping of the tail. 3 ml of 2% lignocaine with epinephrine is injected in cows for low epidural which will induce paralysis of tail, and analgesia of perineum rectum, and the inner aspect of the thigh.
Higher dose upto 120 ml of 2% lignocaine is administered in adult cow to achieve high epidural in which the cow will be recumbent for more than 4 hours. Sympathetic blockade and hypotension are common in high epidural. In horses low epidural is induced using 5 to 7 ml of 2% lignocaine. Analgesia of rectum tail, distal colon, bladder, and reproductive organs are produced.
Swine
The site of needle placement is on the midline, just caudal to the transverse line between the cranial prominences of the wing of the ilium on either side. A 20G x 8 cm needle is inserted caudal to this line at an angle of 20 caudal to the perpendicular. Local anaesthetic is injected at the rate of 1 dml for every 10 kg. Hypotension and death are more common in pigs following epidural analgesia.
Dogs
The site of injection is lumbosacral space which is located in the middle just behind the line joining the highest points of these crests. Some time the local anaesthetic is administered between sacrococcygeal or I and II coccygeal vertebrae for docking. The compliation of epidural anaesthesia includes hypotension, respiratory collapse due to the block on higher levels, clonic spasms, convulsions (goats are more sensitive), pareses or paralyses due to infection and fistula formation. INTERNAL PUDENTAL NERVE BLOCK
This block is commonly done to induce relaxation and analgesia of penis to aid in examination and treatment in cattle. The lesser sciatic foramen is located by rectal palpation as a circumscribed depression in the sciatic ligament. The internal pudental nerve is found a finger width dorsal to the pulsating pudental artery. The block is done bilaterally on both the sides. The ischorectal fossa is prepared aseptically and an 18G x 8 to 10 cm needle is inserted and directed towards the nerve under rectal guidance 20 to 25 ml of local anaesthetic is deposited and the process is repeated on the other side. Penile relaxation and cutaneous analgesia over the anus, perineum, posterior medial thigh and urethral opening are achieved. ANALGESIA FOR CASTRATION
Analgesia can be provided by injecting local anaesthetic into the spermatic cord or directly into the testicle. The incisional site must be infiltrated subcutaneously on the scrotum. BRANCHIAL PLEXUS BLOCK
This block is mainly induced in dogs. Successful analgesia will show all the symptoms of radial paralysis. The brachial plexus in the dog is best blocked on its lateral recumbancy. First the costochondral junction of the first rib is located by moving the upper limb. An 8 to 10 cm long needle is inserted towards the costochondral junction. If the leg is held, as in the normal positionthe correct site of needle insertion will be medial to the shoulder joint directed parallel to the vertebral column. After reaching the costochondral junction the needle is withdrawn 0.5 to 1 cm, then aspirated to ascertain that no blood vessel is punctured. 1 to 10 ml of 2%lignocaine is injected depending on the size of the dog. MEDIAN AND ULNAR NERVE BLOCK
Median and ulnar nerve block will desensitize the carpus and structure distal to it. Median nerve is blocked at the caudomedial borner of the radius just distal to the superficial pectoral muscle. The nerve lies cranial to the median artery and vein. Skin desensitization involves only the medial aspect of the pasern. Ulnar nerve is blocked in the groove on the palmar aspect of the antebrachium between the ulnaris lateralis and the flexor carpi ulnaris muscles, 10 cm proximal to the accessory carpal bone at a depth of 1 to 2 cm. Skin desensitization occurs on the dorsal aspect of the proximal metacarpus. Needle and volume 20G x 1”, 10 to 15 ml on each site. TIBIAL AND PERONEAL NERVE BLOCK
Tibial and peroneal nerve block will eliminate deep sensation from the hock and structures distal to it. Tibial nerve is blocked just caudal to the deep digital flexor tendon and cranial to the Achilles tendon about 10 cm proximal to the top of the tuber calcis on the medial aspect of the limb beneath the fascia. Skin sensation is usually lost between the bulb of the heel. Peroneal nerve is blocked between the long and lateral digital extensor tendons on the lateral aspect of the crust, 10 cm proximal to the lateral malleolus. The peroneal nerve has deep and superficial branches. 10-ml of 2% lignocaine is injected around the deep branch and 5 ml around the superficial branch as the needle is withdrawn. Needle and volume 19G x 2”, 20 ml on each site.
PALMAR/PLANTAR DIGITAL NERVE BLOCK
The palmar/plantar nerve is desensitized in the palmar region of the pastern joint medially and laterally. Palmar nerve is formed by the fusion of the terminal branch of ulnar nerve and the terminal branch of median nerve Plantar nerve is the result of bifurcation of the tibial nerve. Needle and volume 20 to 25 G x 2.5 cm, 2 ml on each site. The area of desensitization includes pastern and one third of the hoof with portions of navicular area.
MODULE-11: GENERAL ANAESTHESIA - INJECTABLE AGENTS Learning objectives This module deals with
Introduction to injectable anaesthetics Routes of administration Advantages and disadvantages of injectable anaesthetics Classification of injectable anaesthetics INTRODUCTION
Injectable anaesthetics can be administered through various routes. The equipment required for administration of injectable anaesthetics is minimal. Following are the commonly used equipments o Syringes o Needles o Butterfly needles o Intravenous catheters. Two types of intravenous catheters are available; they are Through the needle catheters
Over the needle catheters. Through the needle catheters are long and used for long term administration of fluids. 12 to 16 gauge 5¼ inch catheters are used in large animals and 18 to 22 gauge catheters are used in small animals. (Refer Anaesthetic equipment) Infusion controllers and Syringe devises (refer Anaesthetic Equipment).
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ROUTES OF ADMINISTRATION
Intravenous e.g. thiopentone in horses Intramuscular e.g. ketamine in dogs Intraperitonial e.g. thiopentone in cats Intrathoracic e.g. thiopentone in cats Intratesticular e.g. pentobarbitone in pigs for castration Subcutaneous e.g. droperidol – fentanyl in cats ADVANTAGE AND DISADVANTAGE
Advantages
Simple to administer Have rapid onset of action Useful as induction agents Does not irritate the airways Non explosive and inflammable Does not pollute the theatre
Controls convulsions
Disadvantages
May induce tissue damage if not injected through appropriate route (thiopentone if administered perivascularly induce severe tissue reaction and accidental administration of xylazine through carotid artery may cause fatal). Excess dose administered without calculating the dose or patient evaluation may cause toxicity. It may not be possible to recover the patient without the use of specific reversal/antagonistic agents, oxygen supplementation, intermittent positive pressure ventilation and other life saving supports.
CLASSIFICATION OF INJECTABLE ANAESTHETICS Main category
Examples
Barbiturates
Dissociative anaesthetics
Thiobarbiturate e.g. thiopentone sodium, thiamylal sodium Methylated oxybarbiturate e.g. methohexitone sodium Oxybarbiturate e.g. phentobarbital sodium Ketamine hydrochloride Titatamine Phencylidine
Steroid anaesthetics
Combination of Alphaxalone and alphadolone e.g. Saffan, Althesin
Imidazole derivatives
Etomidate Metomidate
Alkylphenols
Propofol
Opioid synthetic analgesics
Fentanyl citrate Alfentanil Sufentanil Lofentanil Etorphine
Neuroleptanaesthetic mixture
Centrally acting muscle relaxants Chloral hydrate
Droperidol and Fentanyl Fluanisone and Fentanyl Etorphine combinations
Glyceryl Quaiacolate -
ULTRA SHORT ACTING— BARBITURATE= > The commonly used ultra short acting barbiturates are thiopentone sodium , thiamylol sodium and methohexitone sodium. o Thiopentone and thiamylal - thiobarbiturates o Methohexitone - oxybarbiturate. These agents are strong alkalies (11 -12 pH) and the alkalinity is due to the addition of sodium carbonate. Following administration, the blood buffers neutralize the sodium carbonate. Thiopental and thiamylal are converted into acid form, which bind with the plasma protein particularly with albumin fraction. The narcotic and anaesthetic action is induced by the unbound fraction. These agents produce dose dependent action varyhing from hypnosis to general anaesthesia. o Binding with protein depends on the drug concentration and the ptotein level. Hence care must be taken in calculating the dose of thiopentone,
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thiamylal and methohexitone for hypoprotinemic animals. Unbound fractions will be more and may cause profound depression. These agents produce unconsciousness in 30 to 90 seconds as they cross the blood-brain barrier in one arm-brain circulation. The duration of anaesthesia varies from 5 to 15 minutes. The recovery from anaesthesia is not due to the detoxification, biotransformation and elimination, it is due to distribution. From the blood it moves to the highly vascularised tissues and from there slowly redistributed to less vascularised tissues. Initially the concentration in the fat will be more. If fluids are administered during recovery the redistributed fractions may be mobilized into the circulation resulting in further deepening of anaesthesia. The distribution depends on the speed and quantity injected. A small quantity injected rapidly as a bolus will produce high plasma and brain concentration resulting in narcosis and the recovery will be faster. The amount of thiopentone and thiamylal required to produce anaesthesia vary from 10 to 18 mg/kg in small animals and 6 to 10 mg/kg in large animals. Anaesthesia is induced by administering half of the calculated as a bolus followed by slow incremental doses to abolish pedal reflex. Thiopentone and thiamylal are administered as 1 to 5% solutions in dogs and cats and 5 to 10% solutions in horses and cattle. Methohexitone is administered as 1% solution in small animals and as 6% in large animals. The dose is 3 to 5 mg/kg intravenously. CARDIOVASCULAR AND RESPIRATORY EFFECTS
Cardiovascular effects o Barbiturates are potent cardiovascular depressants. o They increase the heart rate and peripheral resistance with reduction in cardiac out put and increasein central venous pressure. o These actions are due to the reflex action secondary to the stimulation of baroreceptors and chemoreceptors and myocardial hypoxia. o Myocardial hypoxia may result in cardiac arrhythmia, bigeminy, premature ventricular contraction and depression/elevation/slurring of ST segment. o Administration of oxygen will prevent further manifestations. o Lidocaine can be administered to control ventricular arrhythmia and it can act as a useful adjunct if incorporated in the anaesthetic regimen. o It prevents and corrects ventricular arrhythmia and reduce the requirement of barbiturates. Separate syringes must be used for administration to prevent the formation of precipitation. Respiratory effects o Ultrashort acting barbiturates induce severe respiratory depression even at clinical doses. o Rapid administration results in apnea during induction.
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The changes are reduction in respiratory volume, tidal and minute volume. If respiratory arrest is noticed it must be managed with oxygen supplementation and mechnical ventilation. Artificial respiration by compressing the chest and stimulation of respiratory reflex may help to over come apnea but may not be as effective as oxygen supplementation. Thiopentone protects the ischemic brain hence used in patients with brain injury and in cardiopulmonary bypass anaesthesia. Thiopentone is used as an induction agent in patients suffering from epilepsy. These agents are metabolized in the liver and to a less extend in kidney, brain and in other tissues. They are eliminated as alcohols, ketones, phenols and carboxylic acids through urine. Microsomal enzymes of the liver get elevated following administration of barbiturates. These agents do not cause prolonged decrease in gastrointestinal motility. They produce sufficient muscle relaxation required for minor surgery. Barbiturates readily cross the placental barrier and depress fetus. However the amount of thiopentone transferred is not large enough to be detrimental to the neonate at birth.
CONCURRENT USE OF OTHER DRUGS AND BENEFITS
Antichlolinergics o Anticholinergics are administered to reduce salivation and prevent bradycardia. In horses anticholinergics can be administered if they are fasted for 6 to 8 hours. o Atropine sulphate - Dogs & Cats = 0.044 mg/kg S.C/I.M, 0.022 mg/kg I.V o Glycopyrorolate - Dogs & Cats = 0.011 mg/kg I.M. Tranquilizers o Tranquilizers are administered to reduce the anxiety and the dose of the anaesthetic drugs o Triflupromazine - Dogs & Cats = 1.0 mg/kg I.V o Acepromazine - Dogs & Cats = 0.1 - 0.2 mg/kg I.M., Horses = 0.06 0.1 mg/kg I.V/I.M. o Chlorpromazine - Dogs & Cats = 1.1 - 2.2 mg/kg I.V/I.M. o Xylazine Dogs = 0.22 - 1.1 mg/kg I.V, 0.55—2.2 mg/kg I.M. Cats = 0.5 - 1.1 mg/kg I.M. Horses = 0.5 - 1.0 mg/kg I.V Cattle 0.1 – 0.2 mg/kg I.V (combine anticholinergics) o Diazepam - Dogs & Cats 0.04 mg/kg I.V Neuraleptanalgesics o Not safe to combine with barbiturates as the combined effects will be extreme bradycardia, hypotension and cardiac arrest. Narcotics
Narcotics markedly reduce the dose of barbiturates. o Morphine - Dogs 0.11 – 0.66 mg/kg S.C, Cats not recommended o Methadone - Dogs 0.11 – 0.55 mg/kg I.M/I.V, Cats not recommended o Oxymorphine - Dogs 0.22 mg/kg I.V/I.M/S.C, Cats 0.88 --- 3.3 mg total dose I.V/I.M/S.C o Pentozocaine - Dogs & Cats 2.2 – 3.3 mg/kg I.M./S.C o Innovar vet - Dogs 1 ml/7 to 9 kg I.M. , Cats not recommended Muscle relaxants o In large animals centrally acting muscle relaxant glyceryl quaiacolate (Guaifenisin) is combined with barbiturates. 2 to 3 grams of thiopentone is added to 50 grams of glyceryl guaiacolate and 5% solution of glyceryl quaiacolate is prepared using 5% dextrose solution. Anaesthesia can be induced by the intravenous administration of the solution at the rate of 1 to 2 ml/kg in horses. o In dogs - succinyl choline, pancuronium, gallamine and other products can be combined with barbiturates. Oxygen administration and intermittent positive pressure ventilation are essential to maintain respiratory and cardiovascular functions. Procaine and lidocaine o Procaine hydrochloride and lidocaine hydrochloride can be combined with thiopentone and thiamylol. They should not be mixed in the same syringe because the local anaesthetics are acidic and barbiturates are alkaline. Every time the needle or the catheter must be flushed with normal saline before administration of each agent. o Advantages Analgesia, Reduce the dose of barbiturates to 50% , Protects the myocardium and brain from ischemic changes, Act as antidysrhythmic agents and Provide good muscle relaxation. o
LONG ACTING BARBITURATES
Pentobarbital sodium is the long acting barbiturate used in anaesthesia and is marketed in vials containing 50 mg/ml and 65 mg/ml. Use of pentobarbital is restricted to small animal and swine anaeshesia. The standard solution is diluted and given intravenously. Dose - Dogs & cats 20 - 30 mg/kg without premedication 10 - 20 mg/kg with premedication. For continuous infusion an initial loading dose of 2 - 5 mg/kg is given followed by 1 - 2 mg/kg/hr. A special preparation containing 240 mg/ml of pentobarbital is available and is used for euthanasia of animals. For euthanasia it is administered at the rate of 48 mg/kg (1 ml/5kg). This solution is often used to castrate large boars. The solution is administered deep into both the testicles at a dose not exceeding 24 mg/kg. Castration is performed immediately after reaching light stage of anaesthesia by ligation of the cord and emasculation. The testicles must be disposed carefully otherwise dogs may get access and die due to poisoning.
DISSOCIATIVE ANAESTHETICS
Ketamine hydrochloride and tilatamine are the commonly used dissociative anesthetics in veterinary field. Phencyclidine is another cyclohexamine product withdrawn from use because of drug abuse. The dissociative anaesthesia is characterized by o Profound amnesia, superficial analgesia and catalepsy o Involuntary spontaneous movements o Persistence of reflexes like swallowing, pharyngeal palpebral and corneal o Large dose may induce convulsions o Lack of muscle relaxation KETAMINE
Ketamine is a popular anaestheic used in veterinary and human anaesthesia due to its wide margin of safety and compatibility with other agents. It was first synthezied in 1963 and introduced in human anaesthesia in 1965 and in veterinary anaesthesia in 1970. Ketamine alters the central nervous system activity to sensory impulses without blocking it at spinal cord or brain stem levels. It allows the impulses to reach the cortical receiving areas but not perceived because of the depression and dissociation of limbic system and other cortical association areas. It can cause seizures even in patients not known to be epileptic and may occur even after 24 hours administrations. The depression effects of ketamine are determined in the central nucleus of thalamus, neocorticothalamic axis and nociceptive cells in the medial medullary reticular formation. Cardiovascular effects - Ketamine increases heart rate, cardiac out put, peripheral vascular resistance, systemic and pulmonary blood pressure, cardiac contractility and myocardial oxygen consumption. The cardiovascular stimulation is attributed to o Stimulation of sympathetic discharge o Vagolytic activity and o Negative inotropic effects on heart. Respiratory effects - The effect of ketamine on respiratory functions are increase in respiratory rate with or without decrease in tidal volume. Also the partial arterial carbon dioxide level (PaO2) will increase with reduction in partial arterial oxygen level (PaCo2). Muscle relaxation will be poor hence must be used with other drugs which produce muscle relaxation. It induces copious salivation and lacrimation. Salivation can be controlled by the prior administration of anticholinergics.
Ketamine is metabolized in the liver and certain amount is excreted as unchanged through urine. Decreases total RBC counts due to the sequestration of RBCs in the spleen Classical stress leukogram; leukocytosis with lymphopenia and neutrophilia can be observed following ketamine administration. Induces hyperglycaemia Contraindicated in patients with increased intracranial pressure or in patients who are undergoing brain or spinal cord surgery as it increases the cerebrospinal fluid flow and pressure. Not recommended for intraocular surgery as it increases the blood pressure and intraocular pressure. Ketamine maintains the uterine blood flow hence can be a useful alternative for thiopentone in cardio vascular surgery. The aims of combining ketamine with other agents are to achieve o Muscle relaxation o Eliminate side effects like salivation and recovery delirium. o Improve visceral analgesia and o Prolong the period of anaesthesia DOSE RATE OF KETAMINE
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In cats the dose of ketamine is 10 - 30 mg/kg I.M. If it is combined with narcotics, tranquilizers or sedatives the dose can be reduced to 5 - 15 mg/kg I.M. and 2- 5 mg/kg I.V. The standard protocols are Xylazine 1.0 mg/kg I.M. and Ketamine 20 --- 25 mg/kg I.M. Acepromazine 0.1 mg/kg I.M. and Ketamine 20 --- 25 mg/kg I.M. Midazolam 0.2 mg/kg I.M. and Ketamine 10 mg/kg I.M Midazolam 0.2 mg/kg I.V and Ketamine 5 mg/kg I.V Meditomidine 80 µg/kg I.M. and Ketamine 2.5 – 7.5 mg/kg I.M. Meditomidine 40 µg/kg I.V and Ketamine 1.25 mg/kg I.V Butorphenol 0.4 mg/kg I.M, Meditomidine 40 µg/kg I.M. and Ketamine 5 mg/kg I.M. Butorphenol 0.1 mg/kg I.V. Meditomidine 40 µg/kg I.M. and Ketamine 1.25 mg/kg I.V
Dogs o o o o
Xylazine 1 - 2 mg/kg I.M (lower dose in larger dogs) and Ketamine 10 mg/kg IM/IV Diazepam 0.2 - 5 mg/kg I.V and Ketamine 5 mg/kg I.V Meditomidine 40 µg/kg I.M. and Ketamine 5- 7.5 mg/kg I.M. Butorphenol 0.1 mg/kg I.M, Meditomidine 25 µg/kg I.M. and Ketamine 5 mg/kg I.M. 15 minutes later.
Horses o Xylazine 1.1 mg/kg I.V and 4 to 5 minutes after Ketamine 2.2 mg/kg I.V. To prolong the anaesthesia half of the initial dose of both the drugs must be repeated at every 10 to 20 minutes. Diazepam at the rate of 0.22 mg/kg I.V can be combined to reduce muscle fasciculation. Often glyceryl quaiacolate is combined with xylazine and ketamine at the rate of 50 mg/kg I.V and even administered as mixture to maintain anaesthesia and this mixture gives good muscle relaxation. Detomidine 20 µg/kg I.V and Ketamine 2.2 mg/kg I.V Promazine 1.0 mg/kg and Ketamine 1.5 – 2.0 mg/kg I.V Acepromazine 0.05 – 09.10 mg/kg and Ketamine 2.2 mg/kg I.V Cattle o Xylazine 0.1 mg/kg and Ketamine 2 - 5 mg/kg I.V o Detomidine 20 µg/kg and Ketamine 2 - 5 mg/kg I.V Sheep and Goats o Xylazine 0.04 - 0.06 mg/kg and Ketamine 2.2 - 4.4 mg/hg I.V o Detomidine 40 µg/kg and Ketamine 2.2 - 4.4 mg/kg I.V Pigs o Xylazine 2 mg/kg, Oxymorphone 0.075 mg/kg and Ketamine 2 mg/kg I.V o Acepromazine 0.4 mg/kg and after 30 minutes Ketamine 15 mg/kg I.M. o Acepromazine 0.44mg/kg, Xylazine 2.2mg/kg and Ketamine 1230 mg/kg I.M o (Further maintenance is done with a mixture containing 0.5 to 1 ml of xylazine (100mg/ml) and 1 ml of ketamine (100mg/ml). TILATAMINE
Tilatamine is closely related to ketamine and is two to three times potent than ketamine. It induces muscle rigidity and tonic-clonic convulsions if administered alone hence it is marketed in combination with a benzodiazepine Zolazepam. (Telozol in USA and Zoletil in Australia) It contains 250 mgs of tilatamine and 250 mgs of zolazepam. This combination provides muscle relaxation and a dissociative state of anaesthesia in dogs, cats and wild animals. Its use in horses may result in potential severe reactions. Premedication with xylazine minimizes the adverse reactions in horses. Animals anaesthetized with telozol – zolazepam will respond to palpebral, laryngeal, pharyngeal, pedal and pinnal reflexes. Salivation is more marked and can be controlled by the use of anticholinergic premedication. Anticolinergic premedicationis very important while using this combination Dossage o Cat @ 7 - 15 mg/kg I.M; 5 - 10 mg/kg I.V o Dog @ 10 - 15mg/kg I.M; 5 - 7 mg/kg I.V o Horses o Xylazine 0.5 - 1.0 mg/kg
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Tilatamine zolazepam 0.5 - 1.0 mg/.kg I.V
STEROID ANAESTHETIC
Combination of alphaxalone and alphadolone is marketed as Saffan (in veterinary) and Althesin (in human). Alphaxalone is insoluble in water and can be dissolved in Cremophor EL (polyoxyethylated caster oil). Alphadolone is another steroid which has hypnotic property and increase the solubility of alphaxalone in cremophor. Each milliliter of Saffan contains 9 mgs of alphaxalone and 3 mgs of alphadolone. This preparation is viscid and the pH is around 7. Saffan froths in syringes due to the presence of cremophor EL and is miscible with water. Low solubility of these steroids in water made them less popular. Saffan is used in cats. In dogs it induces histamine release and causes severe hypotension hence not recommended in dogs. It selectively decreases cerebral oxygen consumption to a greater extend by reducing the blood flow. Indicated in cats with head injuries. Retching, vomiting and twitching of facial muscles may occur during induction. In cats it does not induce significant change in cardiac index and systemic vascular resistance. It induces respiratory depression. It poduces good muscle relaxation. It can be used in cats for caesarian section because the neonates are less depressed at the dose of 4.0 mg/kg. Some trials have been conducted on dogs for caesarian section. All the dogs were given prior anti histaminic medication and premedicated with phenothiazines. It may cause oedema of ear pinnae and paws in cats due to histamine release. It has got week antioestrogenic effect It may induce laryngeal oedema In horses it produce excitement for upto 30 minutes during induction and recovery is associated with marked tactile and hyperaesthesia, twitching and violent kicking. It is not recommended in horses. Dose o Cats 4 - 6 mg/kg I.M/I.V o Pigs 4 - 6 mg/kg I.V o Pig neonates 2 - 3 mg/kg I.V o Sheep 1.65 - 3 mg/kg I.V
IMIDAZOLE DERIVATIVES Metomidate
Metomidate is a non-barbiturate crystalline power belonging to imidazole group. In room temperaturethedissolved solution is stable only 24 hours. Metomidate has hypnotic and central muscle relaxant property, but does not have analgesic property hence oftencombined with fentanyl or azaperone premedication. It is mainly used in pigs and birds. In horses it was used with azaperone (0.2 – 0.8 mg/kg) at the rate of 3.5 mg/kg I.V. Recovery was violent. It is not recommended in horses. Dose Birds 3 - 20 mg/kg I.M
Etomidate
Etomidate is a white crystalline power available as 20 mg dissolved in 10 ml of a mixture containing 35% propylene glycol and 65% water (v/v). Intravenous injection is associatred with high incidence of spontaneous movements, involuntary muscle tremors and hypertonus. Premedication with fentanyl or diazepam reduces the side effects. It induces less cardiovascular depression and does not release histamine. Hence it is used in dogs for caesarian section at the dose of 1.5 - 3.0 mg/kg I.V along with diazepam (0.2 mg/kg I.V total dose not exceeding 5 mg). Etomidate is recommended in high risk allergic patients who had exhibited or are expected to exhibit severe anaphylactic responses. Etomidate like thiobarbiturates decrease the circulating cortisol concentration in hyperadrenocortism, hence can be used as safe induction agent in these patients. ALKYLPHENOLS
Propofol is a lipophilic alkylphenol (2-6 diisoprophylphenol) becoming popular in human and veterinary anaesthesia. It is an oil at room temperature and can not be injected hence was formulated with Cremaphor EL (polyoxyethylated casteroil) as vehicle.Cremaphor EL as
with other agents induced histamine release in human and animals. Now the vehicle is changed and reformulated with a parental nutritional agent called as Intralipid which contains soybean oil, glycerol and purified egg phosphatide. The new formulation is milky in colour. The vehicle added favors bacterial growth hence the open ampule after 6 to 12 hours must be discarded. Propofol induce rapid loss of unconsciousness in 20 to 40 seconds after I.V. administration due to its lipophilic nature. It crosses the blood-brain barrier in one arm-brain circulation and further redistributed from plasma, brain and well-perfused tissues to less perfused tissues as thiopentone. Recovery periods are shorter without any undesirable side effects in propofol anaesthesia half of the calculated dose in infused as a bolus and the remaining half is administered in a slow phase. Propofol can be administered in continuous infusion to maintain anaesthesia. It is conjugated in the liver and metabolized as glucuronide and sulphate and excreted in urine. Cardiovascular effects - Propofol induce 20 to 40% reduction in arterial blood pressure due to reduction in cardiac output and systemic vascular resistance. Its use is cautioned in dogs with serious volume depletion. Respiratory effects - Propofol induce apnea and greater respiratory depression. Propofol does not affect hepatic and renal functions It can be used for long term sedation and anaesthesia in intensive care patients, as it does not alter adrenocortical function. It reduces the intraocular pressure hence can be used in patients undergoing intraocular procedures Propofol is a good induction agent for caesarian section in dogs and cats. It reported that the puppies were bright and the mother was alert enough to care the puppies immediately following recovery. It is a safe anaesthetic in branchycephalic breeds of dogs. Dose o Dogs 3 - 4 mg/kg I.V. in premedicated, 5 - 6.5 mg/kg I.V. in Unpremedicated (continuous infusion 0.4 – 0.6 mg/kg/minute) o Cats 8 mg/kg I.V. inunpremedicated (continuous infusion 0.51 mg/kg/minute) o Horses 2.0 mg/kg with xylazine 0.5 mg/kg I.V.(continuous infusion 0.2 mg/kg/minute) o Sheep and goats = 3 - 4 mg/kg I.V o Rabbit = 7.5 - 15 mg/kg I.V o Mouse = 26 mg/kg I.V o Birds = 1-15 mg/kg I.V o Reptiles = 10 mg/kg
PURE AGONISTS - MORPHINE
Morphine is derived from the dried milky exudates of the unripe seed capsules of the opium poppy (Papaver somniferum). The exudates contains 3-25% of morphine, 5% noscapine and 0.8% papaverine. The laboratory synthesis of morphine is different hence still it is derived from opium poppy. The laboratory synthetic agents are codeine, heroin (dimorphine = diacetylmorphine) and oxymorphine. Morphine acts and produces o Analgesia o Drowsiness o Produce nausea and vomiting by stimulating chemoceptor trigger zone for vomiting. It induces dopaminergic excitement in cats, horses, pigs, dogs and cattle. o Induce respiratory depression o Depress cough o The effects on myocardium are not significant; but produce increase in vagal tone and slowing of heart. o Morphine is used as a postoperative analgesic for pain relief in veterinary practice. o Morphine decreases motility of stomach with increase of antral portion. Initial use may cause defecation and chronic use will result in constipation. o It is absorbed from the gut and oral mucosa. o It is used in the treatment of congestive heart failure to relieve pain and decrease after load. o Preservative free morphine can be administered epidurally to relieve pain. Dose o Horses Morphine gives good results in horses if administered after xylazine sedation. Xylazine 1.0 mg/kg I.V and morphine 0.6 mg/kg I.V o Dogs 0.2 – 0.5 mg/kg (total dose not exceeding 10 mg) I.M/I.V o Cats 0.05 – 0.1 mg/kg S.C/I.M. must be administered with caution because it may induce CNS stimulation. Hence must be used with suitable tranquilizer. o Morphine is administered after administration of Acepromazine. Acepromazine 0.1 mg/kg I.M. and Morphine 0.6 mg/kg I.M. PATHADINE, MEPERIDINE AND OXYMORPHONE
Pathadine o Pathadine is a vagolytic and negative inotropic drug at clinical doses. o It reduces salivation and respiratory secretion without inducing vomiting and defecation.
Pathadine induces histamine release if administered through intravenous route. o Dose Dogs = 2 - 6.5 mg/kg S.C/I.M Catls = 2 - 4.4 mg/kg S.C/I.M Meperidine o It is a synthetic product, less potent (one tenth of morphine) and used in dogs and cats. o Intravenous administration causes release of histamine hence most often used along with acepromazine. (Phenothiazines are potent antihistaminics) o Dose: Dogs and Cats 2-5 mg/kg I.M Oxymorphone o Oxymorphone is a synthetic derivative having 10 times greater potency than morphine. o It is widely used in dogs and cats for its analgesic property. Analgesia lasts for 4 hours. o It does not cause histamine release as meperidine. o It is used popularly in small animal anaesthesia due to its analgesic and lack of release of histamine. o The only limitation with drug is stimulation of vagus leading to bradyarrhythmias and it can be reduced or prevented with the use of antichlinergic agents in the protocol. o It is also administered epiduraly to control pain in the hindquarters (0.025 - 0.05 mg/kg). o Dose Dogs 0.05 - 0.2 mg/kg I.V/I.M/S.C (total dose not exceeding 4.5 mg) Cats 0.05 - 0.4 mg/kg I.V/I.M/S.C Horses 0.02 - 0.03 mg/kg I.V/I.M. o
FENTANYL CITRATE AND ETORPHINE Fentanyl citrate
Fentanyl is a synthetic opioid product related to phenylpiperidines. Its analgesic property is 80 times greater than morphine. Cardiac out put, heart rate, respiratory rate and arterial oxygen tension (PaO2) are reduced following administration of fentanyl. Fentanyl citrate is available alone, or in combination with droperidol (Innovar vet contains 0.4 mg of fentanyl and 20 mg of droperidol per milliliter) or fluanisone. (Hypnorm contains 0.315 mg of fentanyl and 10 mg of fluanisone per milliliter) Fentanyl combinations provides good intra operative analgesia. In dogs and primates it produces sedation and myosis whereas in horses it produces excitement and mydriasis. It is not recommended in cats.
Dose - Dogs 0.01 - 0.02 mg/kg I.M/I.V. (see butyrophenones for other doses). The other synthetic pure agonists are afentanil, sufentanil, lofentanil and carfentanil.
Etorphine
Etorphine is a potent synthetic morphine derivative. Its general properties are similar to morphine. The dose of etorphine is 0.5 mg/500 g B.W Etorphine is an extremely long acting agent whose effects are maintained by enterohepatic recycling. The action of this drug can only be terminated by the administration of the specific antagonist Diprenorphine. In clinical dose etorphine along may produce initial excitement hence it is marketed in combination with phenothiazine derivatives. Separate combinations are available for large and small animals. Each pack of the marketed drug will be having two components. 1-Immobilon and 2-Revivon.
Preparation
Immobilon L A contains Etorphine 2.45 mg/ml and acepromazine 10 mg/ml Immobilon S A contains Etorphine 0.074 mg/ml and Methotrimeprazine 18 mg/ml Revivon L A contains Diprenorphine 3.0 mg/ml Revivon S A contains Diprenorphine 0.272 mg/ml This mixture is popularly used to capture elephants and giraffes Not recommended for domesticated and wild felines Etorphine is extremely potent in human and any accidental injection may cause death if not treated with naloxone or diprenorphine.
PENTAZOCAINE, BUTORPHENOL TARTRATE AND BUPRENORPHINE
Pentazocaine o It is used as an analgesic. o In human it causes dysphoria and hallucination and pentazocaine is developed to prevent drug abuse. o In clinical doses it produces pulmonary vascular resistance. o In horses it is used in the treatment of colic and administered at the rate of 0.33 mg/kg I.V. o Dose -3 mg/kg for 1 to 3 hours of analgesia. o Penlog -Duration of analgesia 3-4 hour .Onset 1 min – one hour Butorphenol tartrate o Butorphenol is used in horses, cats and dogs. o It produces sedation, analgesia and increase in pulmonary vascular resistance. o Dose
Horse = 0.1 mg/kg I.V Dogs = 0.2 – 0.8 mg/kg I.M/S.C Cats = 0.2 – 0.4 mg/kg I.V/I.M/S.C Onset 1 mint – 15 mint I.V. rapid Buprenorphine o Respiratory depression is more and often treated with intermittent positive pressure ventilation. o Dose Horses = 6 - 10 µg/kg Dogs = 0.01 - 0.02 mg/kg S.C/I.M/I.V Cats = 0.005 - 0.02 mg/kg S.C/I.M.
CENTRALLY ACTING MUSCLE RELAXANTS (guaifenisin)
Glyceryl quaiacolate ether (Guaifenisin) is the centrally acting muscle relaxant and it acts on the internuncial neurons of the spinal cord. It affects the polysynaptic reflexes more than monosynaptic reflexes hence it has got little action on the diaphragm. It does not influence the respiratory canters in brain. Diaphragmatic muscle is composed of mainly striated titanic fibers and not striated tonic fibers; hence GGE does not affect the diaphragm. It also induces sedation and hypnosis due to its action on the reticular formation of the brain stem. It has got bactericidal action. In practice, it is administered as 5% (50 mg/ml) solution in 5% dextrose. Concentration greater than 10% is irritant to body tissues and can induce haemolysis. GGE dissolves readily in 5% dextrose if warmed slightly. GGE is used in combination with other agents in 5% dextrose solution as induction and maintenance agent. These mixtures are administered after routine premedication. The maximum dose of GGE is 90 to 100 mg/kg and if this dose is exceeded it will cause spasm, hypertonicity of muscles and cardiac arrest. GGE does not cross the placental barrier due to its high molecular weight.
Horses
GGE 50 mg/ml (5% solution) in 5% dextrose mixed with xylazine 0.5 mg/ml and ketamine 1.0 mg/ml is the routinely used mixture in horses. Induction is achieved at the dose rate of 1.1 ml/kg and further maintenance is done with this mixture at the rate of 2.75 ml/kg/hour. Alternatively induction can be done using xylazine (1.1 mg/kg I.V) and ketamine (2.2 mg/kgIV) andfurther maintenance can be done with this mixture. GGE can be combined with thiopentone or thiamylal (1-3 grams) and administered in horses (See barbiturates)
Cattle
GGE 50 mg/ml (5% solution) in 5% dextrose mixed with xylazine 0.05 mg/ml and ketamine 1.0 mg/ml is the mixture used in cattle. 1.0 ml/kg I.V is administered for induction and further maintenance can be done with this mixture. PURE ANTAGONISTS
Naloxone hydrochloride, nalorphine hydrochloride and diprenoorphine are the opioid pure antagonists used for the reversal of the effects of pure agonists and partial agonists. In horses naloxone is used in the control of crib biting. Dose—Naloxone-- Dogs and cats = 0.04 - 0.1 mg/kg I.V/I.M/S.C Horses -- 0.005 = 0.2 mg/kg I.V Diprenorphine- Dogs & Cats = 0.0272 mg/kg I.V
Horse = 0.02 - 0.03 mg/kg I.V CHLORAL HYDRATE
Chloral hydrate is used as a reliable sedative hypnotic in cattle and horses. It is less expensive and still perfectly acceptable sedative agent. It has deeply penetrating aromatic odour and is bitter in taste. The central nervous system depression is due to its metabolic product namely 2,2,2 trichloro ethanol, hence the sedative effect is prolonged even after cessation of administration. It does not have analgesic property. Trichloro ethanol conjucates with glucuronic acid to urochloralic acid and excreted. Chloral hydrate depresses the motor and sensory responses at sedative dose and produces cerebral and medullary center depression at anaesthetic dose resulting in muscle relaxation and depression of cardiac and respiratory system. In cattle it can be drenched preferably through stomach tube, at the dose of 30 to 120 grams dissolved as 1 in 20 solution in water.
Bullls that are uncontrollable and free in the yard can be controlled by water deprivation for brief period and allowing them to drink chloral hydrate dissolved water (90 to 120 grams in 12 litres of water). Chloral hydrate is administered as 10% solution intravenously in cattle at the dose of 80 to 90 mg/kg. Chloral hydrate is combined with magnesium sulphate at 2:1 or 3:1 ratio (weight) and administered in cattle. It is combined with magnesium sulphate and pentobarbital and administered to horses (Equithesin mixture). Intravenous dose of chloral hydrate in horses o Chloral hydrate alone 5 to 10 mg/kg for mild sedation and hypnosis, 20 to 40 mg/kg for moderate sedation and hypnosis, 50 to 75 mg/kg for profound sedation and hypnosis and 150 to 250 mg/kg for anaesthesia. o Chloral hydrate 100 mg/kg and thiopentone 1.5 to 2 mg/kg o Chloral hydrate 100 mg/kg and ketamine 1.5 to 2 mg/kg o Promazine 0.6 to 0.8 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiopentone 5 to 7 mg/kg o Acepromazine 0.04 to 0.08 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiamylal 2 to 4 mg/kg. o Xylazine 0.4 to 0.6 mg/kg, 7% chloral hydrate 20 to 40 mg/kg and thiamylal 1 to 2 mg/kg. Disadvantages of chloral hydrate o Prolonged hangover with ataxia and stupor o Perivascular administration causes pain, swelling and necrosis o Induces abortion in mares
MODULE-12: GENERAL ANAESTHESIA - INHALANT ANAESTHETIC AGENTS AND MAINTENANCE Learning objectives This module deals with
Inhalant Anaesthetic Agents and Its Maintenance INTRODUCTION
The inhalant anaesthetics are chloroform, ether, trilene, cyclopropane, enflurane, desflurane, halothane, isoflurane and sevaflurane. Their uptake and distribution determine the anaesthetic action of these inhalant agents. The uptake and distribution depends on Solubility coefficient - At any given temperature the mass of a gas dissolved in a solution (i.e. its concentration in the solution) varies directly with its tension
and is governed by the solubility of the gas in the particular solvent. For example the blood gas partition coefficient of nitrous oxide is 0.47. This means that there will be 47 parts of nitrous oxide inblood for every 100 parts of nitrous oxide per unit volume (litre) of alveolar air. The solubility of most of the inhalant agents in brain and other tissues except fat are almost common as that of blood. That means the tissue – blood partition coefficient will be almost the same. Whereas halothane is almost 60 times more soluble in fat than other tissues; hence the blood partial coefficient will be lesser than the fat. Brain – lipid (fat) coefficient will be almost equal (2.6) because of the lipid nature of brain. Blood flow - The inhaled anaesthetic gas is diluted in the residual air when it enters pulmonary ventilation and then distributed to alveolar membrane. From alveolar membrane two types of diffusion take place. The major diffusion process takes place into the pulmonary blood (pulmonary circulation) and it reaches equilibrium with alveolar tension immediately. The second process occurs across the capillary membrane of the lung into the interstitial fluid, then to the cells through the cell membrane and finally into the venous blood leaving the lung (bronchial circulation). In thismanner the arterial and venous tension of the anaesthetic slowly increases towards the ventual equilibrium with the inspired air. Solubility of inhalant anaesthetic is defined as a concentration distribution ratio between alveolar concentration and the tissue concentration. The solubility of inhalant anaesthetics influences the induction and recovery time. Methoxyflurane is highly soluble than isoflurane in the body tissues hence the induction and recovery will be slow. Mininimum alveolar concentration (MAC) - MAC is the concentration of the inhalant anaesthetic in the alveoli to produce lack of response in 50% of the subjects to a standard stimulus. This term is used to mention the potency of the anaesthetic. The MAC of each inhalant anaesthetic varies in each species. The other factors are o Physical and chemical properties of the agent o Absorption o Pulmoanry blood flow o Cardia output perfusion o Lipid content of tissues o Final elimiantion NITROUS OXIDE
Nitrous oxide is the oldest anaesthetic gas available as liquid at room temperature in cylinders (See anaesthetic equipment). Its MAC is more than 100% in animals (Dogs 188%, Cats 255%). It has got good analgesic property and combining narcotics, which interact selectively with opiate receptor endorphin system, potentiates the analgesia.
Nitrous oxide is used as the principle anaesthetic at a level of 80% in combination with 20% oxygen for dental extraction in human. In veterinary anaesthesia, it is combined with other injectable and inhalant agents. It is used as fresh gas source or carrier gas. It helps in additional uptake of the inhalant agent and potentiate the desirable effects at a minimal concentration of the inhalant agent (Second gas effect). It is eliminated rapidly from the body because of low partition coefficient and relatively insoluble nature. Nitrous oxide moves rapidly through tissues faster than carbon dioxide and diffuses into the closed cavities filled with gas such as pneumothorax and distended intestinal loops due to obstruction or strangulation and induces detrimental effects by inducing further distension. It is not used in ruminants, as it will diffuse into the rumen and results in distension and increase in transdiaphragmatic pressure. In horses prolonged administration induce distension of bowels and increase in transdiaphragmatic pressure. It induces tachypnoea at higher concentration due to direct central stimulation. During recovery it may induce diffusion hypoxia following prolonged administration. The outward movement of nitrous oxide from the alveoli reduce the alveolar partial pressure of oxygen. The expired air may contain more than 10% of nitrous oxde. In older animals and animals maintained for a longer duration with nitrous oxide must be supplemented with oxygen. Prolonged exposure to nitrous oxide causes bone marrow depression due to depletion of Vit.B12. Hence it can cause occupational hazards to humans. The theatre environment must have less than 25 ppm of nitrous oxide. Nitrous oxide is administered at 66 to 70% of the total inspired air. Oxygen is given at 30% concentration. DIETHYL ETHER
It is a colourless, highly volatile and inflammable liquid with a boiling point 35oC. One pound of ether mixed in air can given 277 cubic feet of flammable mixture. The ignition temperature is 304 C. The MAC is 1.92%. It gives an irritating vapour and may cause salivation if not premedicated with anticholinergics. In low concentration the vagal activity is decreased and at higher concentration it induce arrhythmia. Catecholamine level increases following ether administration. The use of ether is decreased due to its explosive and inflammable nature. Health hazards are more in human exposed to ether for a prolonged period. METHOXYFLURANE
Methoxyflurane is a halogen-substituted ethyl ether (O2,2-dichloro-1,1 difluoro ethyl methyl ether). Its boiling point is 104oC and is non-flammable and nonexplosive. Its molecular weight is 165.9 and the specific gravity is 1.41 at 25oC. It has fruity odour and an antioxidant butylated hydroxyflurane is added for stability. This antioxidant may accumulate in the vaporizer wick hence methoxyflurane vaporizer must be often cleaned and rinsed with diethyl ether. The MAC is 0.23. It reacts with metal, rubber and soda lime, and decomposes if exposed to ultraviolet light. Methoxyflurane induce dose dependent central nervous system depression. Though it can be used to mask induction, its better to induce with injectable anaesthetics. It does not alter the cardiac function much except slight hypotension, which is associated with reduction in cardiac contractility, and cardiac out put. Concurrent use of epinephrine and adrenaline are contraindicated as methoxyflurane sensitizes the myocardium to the actions of catecholamines. Compared to halothane the sensitization and cardiac arrhythmia are less. Methoxyflurane reduce the minute volume and induces respiratory acidosis. It is highly soluble in fat hence recovery will be prolonged in obese patients. Biotransformation of methoxyflurane results in fluoride ions, which are potent toxic agents to kidneys and is further aggravated by the concurrent use of tetracycline. Methoxyflurane is contraindicated in patients with renal disease. In veterinary practice its use is restricted to small animals. It can be used in most of the breathing circuits with oxygen and nitrous oxide. HALOTHANE
Halothane is colourless volatile liquid with aboiling point of 50.2oC and the vapour pressure is 244.1 mmHg at 20oC. It is non-flammable and nonexplosive. Halothane is a potent anaesthetic with a molecular weight of 197.4 and specific gravity 1.86 at 25oC. Halothane reacts with metal and soda lime and decomposes if exposed to ultra violet light. It is marketed in amphor coloured bottles with thymol. The MAC varies in various species. o Dogs 0.87%, o Cats 0.75%, o Horses 0.9% o Pigs 1.25% The MAC is reduced when combined with agents like morphine (reduced 84%), alfentanil (48%), xylazine and nitrous oxide.
Halothane reduces cerebrospinal fluid production and pressure hence can be used in patients undergoing brain and spinal cord surgeries and in patients with increased intracranial pressure. It suppress adrenal cortical hormone release by 50% due to its action and inhibition on the carrier - mediated transport system of choline. Halothane depress cardiac out put,mean arterial pressure and coronary blood flow. Halothane decreases arrhythmogenic thresholds and sensitizes the myocardium for the actions of catecholamines. Exogenous administration of epinephrine or adrenaline induces cardiac arrhythmia and ventricular stand still. It induces AV shunts (arterio-venous shunts) and is further aggrevated by hypoxia. (21 to 22%) thus resulting in ventilation perfusion mismatch. Oxygen exchange is further reduced in patients with pulmonary diseases. The minute volume decreases during halothane anaesthesia due to the decreased contractility of inspiratory muscles. Halothane induces hepatic hypoxia. In ponics following halothane anaesthesia 138% increase in plasma bilirubin excretion, 16% reduction in plasma bilirubin and 46% reduction in biliary bile acid concentration was noticed. Centrilobular necrosis is the toxic manifestation induced by halothane in liver. The incidencesof hepatic necrosis are higher in goats following halothane anaesthesia. Halothane undergoes biotransformation in the liver. The metabolic products or the intermediary products induce allergic and toxic responses similar to autoimmune diseases. The metabolic intermediary products bind with the bivalent genes responsible for self-protein synthesis in the liver. Following binding the genes will alter the coding and non-self protein will be synthesized which may result in allergy, anaphylaxis or autoimmune like diseases. Experimental studies revealed that halothane has got teratogenic and mutogenic properties. In human the rate of successful deliveries following embryo transfer or gamete intra fallopian transfer were less as compared with isoflurane. Initial conception rate was high followed by higher incidence of aborption. Halothane suppress the number and activity of natural killer cells (NK cells) and produce immune suppression, thus favouring higher incidences of post anaesthetic infection. This property is taken as an advantage in patients undergoing tissue transplantation. It’s better to revaccinate horses with tetanus toxoid following halothane exposure. ISOFLURANE
Isoflurane is the new inhalant anaesthetic widely used in human anaesthesia. It is relatively insoluble hence induction and recovery are quick. It is non-inflammable and does not react with metal, rubber or soda lime. It does not decomposed if exposed to ultra violet light. Its vapour pressure is almost equal to halothane hence halothane vaporizers can be used after cleaning thymol. It has got pungent odour.
It provides cardiac stability. Reduction in blood pressure is noticed during isoflurane anaesthesia due to the reduction in peripheral vascular resistance, not due to myocardial depression as in halothane. It increase the myocardial perfusion by reducing the coronary vascular resistance. It has little or no action on sensitizing the myocardium for the actions of catecholamines. Hence it is recommended in patients with cardiac diseases. It does not interfere with of central autoregulation of blood pressure, hence indicated in patients with head injures. It has better muscle relaxation property than halothane and does not promote convulsions. It induces more respiratory depression than halothane and results in hypoventilation. Only 2% are metabolized in the liver due to its relative insolubility, hence recommended in patients with liver diseases. SEOFLURANE
It is the newest inhalant anaesthetic used in humans. Still trials are conducted in veterinary anaesthesia. PROPERTIES OF INHALANT ANAESTHETICS Property
Halothane
Isoflurane
Sevoflurane
Formula
CBrCIH-CF3 CF3-CHCl-OCF2H
CFH2-O(CF3)2
Type
Halogenated Ether
Ether
Molecular weight
197.4
184.5
187.0
Sp.gr.
1.86
1.50
Preservative
Thymal
Not required
Not required
Soda lime
Yes
No
Yes
U.V. Light
Yes
No
Metal
Yes
No
Boiling point C@ 760 mm Hg
50.2
48.5
-Vaplour pressure (mm hg)
243, 32%
239, 31%
Reaction
No
MAC OF COMMONLY USED INHALANTS Agent
Dogs
Cats
Horses
Halothane
0.86
0.98
0.88
Enflurane
2.2
2.37
2.12
Isoflurane
1.28
1.63
1.31
Methoxyflurane
0.23
0.23
-
Nitrous oxide
188.0
255.0
-
MODULE-13: MONITORING ANAESTHESIA Learning objectives This module deals with
Pre operative patient monitoring History Physical and Clinical Examination Functions of CNS, Cardio vascular, Pulmonary during anaesthesia monitoring INTRODUCTION
Pre, intra and post operative monitoring are most important for the final out come of anaesthesia and surgery. The monitoring procedures are aimed to assess the functions of cardiovalscular, pulmonary and CNS and body temperature, fluid and electrolyte balances. Intraoperative monitoring must be carefully done because during this stage the anaesthetic drug will act on various compensatory mechanisms and surgery will be having its effects on physiology and anatomy of the patient (See Table 1 and Table - 2 for parameters). TABLE 1
Normal physiological, cardiovascular, respiratory and hematobiochemical parameters of domestic animals (Dog, cat, horse and cattle)
Parameters
Dogs
Cats
Horses
Cattle
Rect. Temp 0C
37.5 - 39.2
37.8 - 39.2
37 - 38
38 - 39
Heart rate/min
70 - 110
115 - 200
35 - 60
70 - 120
Cardiac output ml/kg
100 - 200
120
30 - 45
80 - 240
Blood vol.ml/kg
75 - 90
47 - 66
65 - 70
60 - 100
Systolic
120 - 140
120 - 140
90 - 130
120 - 150
Diastolic
80 - 100
80 - 100
65 - 85
75 - 100
Mean
100 - 110
100 - 110
85 - 120
90 - 120
Resp. rate/min
10 - 30
24 - 42
8 - 20
15 - 35
Minute volume ml/dkg/min
170 - 350
200 - 350
PaO2 mm Hg
>100
>100
85 - 90
80 - 110
PaCO2 mm Hg
28 - 49
35 - 49
38 - 40
30 - 50
pH
7.27 - 7.46
7.25 - 7.43
7.40 - 7.45
7.34 - 7.45
HCO3 mmol/lit
20 - 25
17 - 22
24 - 32
20 - 28
Hb g/dl
14 - 17.5
8 - 15
11 - 19
8 - 16
10
7
Blood pressure mm of Hg
Tidal volume ml/kg
RBC x 10 cu.mm
150 - 600
WBC x 10 cu.mm
9 - 13
10 - 15
5.5 - 12.5
7 - 10
N%
65 - 70
55 - 60
50 - 60
25 - 30
L%
20 - 25
30 - 35
30 - 40
60 - 65
E%
2-5
2-5
2-5
2-5
M%
5
5
5-6
5
B%
<1
<1
<1
<1
PCV %
40 - 55
25 - 45
32 - 52
24 - 46
ESR mm/hr
1-5
7 - 27
2 - 12
2-4
T.S. Protein g/dl
6 - 7.8
6 - 7.5
6 - 8.5
6.7 - 7.5
Albumin g/L
26 - 37
30 - 35.5
Globulin g/L
26.4 - 40.4
30 - 34.8
400
300 - 700
Fibrinogen mg/ml
200 - 400
50 - 30
Blood glucose mg/ml
65 - 118
70 - 110
75 - 115
45 - 75
BUN mg/ml
10 - 28
20 - 30
10 - 25
25 - 30
Creatinine mg/ml
0.44 - 1.32
0.7 - 1.59
1.0 - 2.4
0.84 - 1.77
Total cholesterol mmol/l
3.5 - 6.99
2.46 - 3.37
1.94 - 3.89
2.07 - 3.11
ALT (GPT) IU/L
21 - 102
6 - 83
3 - 23
14 - 30
AST (GOT) IU/L
23 - 66
26 - 43
226 - 366
78 - 132
Lactate dehydrogenase IU/L
45 - 233
63 - 273
100 - 412
692 - 445
Creatinine kinase IU/L
14 - 460
100 - 850
97 - 188
150 - 450
Sorbitol dehydrogenase IU/L
4 - 20
6 - 30
Sodium mEq/L
130 - 143
Chloride mEq/L
98 - 109
Potassium mmol/L
4.37 - 5.35
4 - 4.5
2.2 - 4.1
Calcium mg/L
3.9 - 5.8
10.3 - 13.3
Icterus index,unit
2-5
2-5
5 - 20
5 - 15
Bile acids umol/L
0-5
0-5
5 - 28
20 - 80
Bilirubin mmol/L (total)
1.71 - 8.55
2.57 - 8.55
7.1 - 34.2
0.17 - 8.55
Cortisol nmol/L
27 - 188
9 - 71
36 - 81
17 +/-2
TABLE 2
Normal physiological, cardiovascular, respiratory and haematobiochemical parameters of domestic animals (Sheep, goat and pig) Parameters
sheep
goat
pig
Rec. temperature
37 - 40
38 - 40
38 - 40
Heart rate/min
70 - 130
70 - 130
60 - 200
Cardiac output ml/kg
110 - 160
60 - 230
66 - 184
Blood vol. ml/kg
55 - 70
55 - 90
50 - 100
Systolic
80 - 120
80 - 120
80 - 120
Diastolic
60 - 80
60 - 80
60 - 80
Mean
80 - 110
90 - 120
75 - 100
Blood pressure mm Hg
Resp.rate/min
15 - 40
15 - 25
10 - 45
Tidal vol.ml/kg
7-8
7-8
11
Minute vol.ml/kg/min
100 - 133
PaO2 mm Hg
75 - 100
85 - 95
75 - 80
PaCO2 mm Hg
30 - 40
33 - 38
30 - 40
Ph
7.43 - 7.53
7.42 - 7.48
7.38 - 7.50
Bicarboante mmol/L
21 - 28
24 - 27
Hb g/dl
8 - 16
8 - 14
RBC x / cumm
11
WBC x /cu.mm
7 - 10
8 - 12
15 - 122
N%
25 - 30
35 - 40
30 - 35
L%
60 - 65
50 - 55
55 - 60
M%
5
5
5-6
E%
2-5
2-5
2-5
B%
<1
<1
<1
PCV %
30 - 46
20 - 38
32 - 50
T.S. Protein g/dl
6-8
6.5 - 7.5
6.7 - 7.5
Albumin g/L
24 - 30
27 - 39
79 - 89
Globulin g/L
35 - 57
27 - 49
52 - 64
Fibrinogen mg/ml
100 - 500
100 - 400
100 - 500
Blood glucose mg/dl
50 - 80
50 - 75
85 - 150
BUN mg/dl
8 - 20
10 - 20
10 - 30
Creatinine mg/ml
1.6 - 1.68
0.884 - 1.59
1.41 - 1.50
T.cholesterol mg/dl
1.35 - 1.97
2.07 - 3.37
0.93 - 1.40
ALT (GPT) IU/L
24 - 83
31 - 58
AST (GOT) IU/L
167 - 513
32 - 84
300 - 400
10 - 16 7
Lactate dehydrogenase IU/L
238 - 440
123 - 392
380 - 634
Potassium mmol/L
3.9 - 5.4
3.5 - 6.7
4.4 - 6.7
Icterus index (unit)
2-5
2-5
2-5
Total Bilirubin mmol/I
1.71 - 8.55
0 - .71
0 - 1.71
Cortisol nmol/L
62+/-10
65+/-8
82+/-3
PRE OPERATIVE PATIENT MONITORING-
Preoperative assessment of the patient is done for the safe administration and maintenance of anaesthesia. It will help in tailoring a suitable anaesthetic regimen suitable for the patient. The importance of preoperative assessment o To prepare the patient for safe administration of anaesthesia o To assess the cardiovascular, pulmonary, hepatic, renal functions and haemato biochemical and electrolyte balances (eg. In diabetic patients half of the insulin dose is administered after stabilization). HISTORY
Identification
Identification includes the details of species, breed, sex, age and other identification marks.
Main complaint
The main complaint is detected to find out whether the disease condition will interfere with the normal anaesthetic practice and to tailor suitable anaesthetic regimen.
History of the present illness
Details of the duration of illness, clinical signs and severity of illness are collected.
Previous medical history
This includes the collection of detils regarding the previous illness, medication, vaccination, deworming, anaesthetics administered, poisoning, application of cetoparasiticide etc., (e.g thiopentone is used as induction agent in patients with the history of epilepsy, horse that suffered from myocarditis will be an anaesthetic risk patient. PHYSICAL AND CLINICAL EXAMINATION
Physically examination includes general body condition, palpatin, percussion, auscultation, measurement of heart, pulse and respiratory rates, examination of lymph nodes, rectal temperature, appearance of the mucous membrane, reflex status, integument, location of the lesion and weight of the animal.
Weight calculation o Horse = (Heart girth cm- 63.7)/0.38 = body weight in Kg.
Systemic examination
Systemic examination includes the assessment of cardiovascular, pulmonary, hepatic, renal gastrointestinal, central nervous system, endocrine and musculoskeletal functions.
Presurgical laboratory examination
It includes the determination of a complete blood count and total plasma protein.
Further tests-- Includes ECG, X-rays and other special examinations. INDIRECT MONITORING
Indirect monitoring of CNS function is assessed by the reflex status. The reflex status is modified by the stages of anaesthesia, drugs used and cerebral blood flow. The following reflexes are assessed o Pedal reflex o Palpebral reflex o Corneal reflex o Lacrimation o Yawning o Swallowing reflex o Laryngeal reflex o Anal reflex o Pupillary reflex o Eyeball position o Hearing sense PEDAL REFLEX
This reflex is elicited by applying firm pressure on the interdigital skin in dogs and cats, squeezing the claws to gather in cattle and swains and firm pressure on the pastern on horses. This relfex is abolished in stage III anaesthesia. Pedal reflex is reliable in barbiturate anaesthesia to assess the depth of anaesthesia, where as with halogenated inhalants it disappears even in the light plane of anaesthesia. PALPEBRAL REFLEX
Tapping the skin at the medial canthus or running the finger along the eyelashes stimulates this reflex. It is abolished in the light plane of anaesthesia in dogs where as in horses sluggish response can be noticed even at surgical plane of anaesthesia when inhalants are used. Palpebral reflex is not abolished during ketamine anaesthesia CORNEAL REFLEX
This reflex is stimulated by gentle palpation of the cornes on the lateral aspect. The response is observed by the closure of eyelids. In horses absence of corneal reflex indicates deep plane of anaesthesia, in dogs its not reliable and in cattleit may be abolished by repeated stimulation. Corneal reflex is not abolished during ketamine anaesthesia.
LACRIMATION AND YAWNING Lacrimation
In horses and cattle lacrimation is reduced during deep plane of anaesthesia, leading to drying of cornea. It may result in keratitis and ulceration. Sterile mineral oil or plain eye ointment must be instilled to prevent corneal ulcer.
Yawning
Dogs under light plane of anaesthesia yawn when the mouth is opened. SWALLOWING AND LARYNGEAL REFLEX
Swallowing reflex
This reflex disappears at the light plane of anaesthesia with exception of young foals. This reflex is protected in ketamine anaesthesia.
Laryngeal reflex
This reflex is abolished in the light plane anaesthesia except with ketamine induction. In cats local anaesthetic is sprayed on the larynx to prevent laryngeal spasm before intubation. ANAL REFLEX
This reflex is abolished in the middle of III stage of anaesthesia in dogs and cats. In horses it is abolished soon after induction with ketamine. This reflex is elicited by sudden gentle manipulation of the anus and the response will be sphincter contraction. PUPILLARY REFLEX
In general the pupil in unpremedicated animals will dialate during early excitement phase and then constricts progressively upto surgical anaesthesia. Again the pulil will dialate as the animal enters into the IV stage of anaesthesia (progressive medullary paralysis) followed by respiratory and cardiac arrest. Premedicants alter the papillary reflex. E.g. Atropine induces pupillary dialatation and narcotics induce constriction in dogs.
EYEBALL POSITION
The position of eyeball depends on the species and the anaesthetic used. In small animals the eyeball rotates medially and ventrally in the early stages and then centrally placed at plane I surgical anaesthesia when inhalants like halothane or isoflurance is used. In horses under halothane anaesthesia nystagmus is common during light plane of anaesthesia and it is centrally placed at the surgical plane of anaesthesia. In ruminants the eyeball rotates ventrally in light plane of anaesthesia, then gradually rotates dorsally and finally fix to the central position. OTHER REFLEXES
Muscle relaxation
It will be modified with the use of anaesthetics and muscle relaxants. In small animals the jaw tone is used as the criteria of muscle relaxation and anaesthetic dept.
Hearing sense
It is the last sense to disappear during induction and the first sense to reappear during recovery. ELECTROENCEPHALOGRAPH
The normal EEG pattern is low voltage high frequency activity in the activated state of brain. During cerebral hypoxia, hypoglycemia, hypothermia, hyponatremia and at excessive depth of anaesthesia it becomes high voltage and low frequency. Then it become isoelectric (burst suppression) as the condition worsened and finally becomes complete inactive. Intracranial pressure also provides valuable information regarding the cardiovascular and pulmonary system and underlying disease. Cardiovascular Functions-
HEART RATE
Heart rate can be monitored by using stethoscope, electronic stethoscope, oesophageal stethoscope, electronic heart rate meters, elecrocardiography and Doppler blood flow detector. Heart rates below 50 to 60 bpm in dogs and cats, 25 bpm in horses and ruminants is considered to be low heart rate. Heart rate above 250bpm in dogs, 300 bpm in cats, 75 bpm in horses and ruminants are considered as high heart rate. The alteration in heart rate must be simultaneously compared with cardiac output and blood pressure. BRADYCARDIA
Bradycardia may arise due to o Excessive depth of anaesthesia o Excessive vagal tone (often increased by intubation vasovagal reflex and traction of abdominal organs) o Terminal hypoxia o Endogenous and exogenous toxaemias o Conduction disturbances in myocardium o Hyperkalaemia o Hypothyroidism
Treatment o o o o o o
Administration of atropine or glycopyrrolate. Dopamine 2.5 to 20ug/kg/min (40 to 200 mg in 250 to 500 ml of 5% dextrose or saline )I.V. Dobutamine 2.5 to 20 ug/kg/min (20 to 200 mg in 250 to 500 ml of 5% dextrose or saline)I.V. Mephenteramine 0.1 to 0.75 mg/kg I.V. duration 15 to 30 minutes Ephedrine 0.05 to 0.5 mg/kg I.V. duration 15 to 30 minutes. Isoproterenol 5 to 10 ug/kg/min (0.4 ti 1.0 mg in 250 to 500 ml of 5% dextrose or saline )I.V. TACHYCARDIA
Tachycardia m ay arise due to o Light level of anaesthesia o Hypovolaemia o Hypoxia o Hypercarbia o Hyperthyroidism Normally pulse rate may either be equal or slightly deficit of heart rate because all the contraction may not produce palpable effective wave and waves may overlap. The abnormal conditions which causes deficit of pulse rates are o Premature contraction, o Variable diastolic ventricular filling o Electromechanical dissociation of heart.
HEART RHYTHM
Supraventricular and ventricular ectopic pacemaker activities are common during general anaesthesia. The other arrhythmia are sinus bradycardia, tachycardia and atrioventricular conduction block and all these conditions may response to the treatment suggested for bradycadia. Other forms of arrhythmia o Premature atrial contraction o Premature ventricular contraction o Pacemaker actrivity o Bundle branch blocks Premature ventricular contraction may progressively lead to ventricular tachycardia and fibrillation. The atrial and ventricular premature contraction may be caused by o Too light level of anaesthesia (due to the release of catecholamines) or due to deep plane or anaesthesia (due to hypoxia and hypercapnia) o Hypoxia and hypercapnia o Hypovolaemia and hypotension o Exogenous catecholamine therapy o Digitalis toxicity potentiated by hypokalemia o Hypokalemia potentiated by respiratory or metablic alkalosis or insulin therapy o Hypercalcemia potentiated by respiratory acidosis o Anaesthetics sensitizing the myocardium for the actions of catecholamine activity (halothane and xylazine) o Endocarditis and myocarditis o Endocardial stimulation by the catheters or epicardial stimulation by the tubes or surgery
High preload or afterload o Severe hypothermia o End stages of visceral organs function o Increased intracranial pressure and intracranial diseases If the premature ventricular contraction is persistent with heart rate exceeding 180 to 200 the following treatments must immediately be adopted. o Check the oxygen supply and maximize the inspired oxygen level. (10 ml/kg/min in circle system and 200 ml/kg/min in nonbreathing system) o Institute intermittent positive pressure ventilation o Start fluid aministration o Discontinue the agents which results or lower the threshold for the onset of arrhythmia. o Administer anyone of the following. Lignocaine 1 to 5 mg/kg I.V. Procainamide 1 to 5 mg/kg I.V Propranolon 0.05 to 0.3 mg/kg I.V Verapamil 0.05 to 0.15 mg/kg I.V The other ECTG abnormalities are o Change in the rhythm o Change in the configuration of PQRST o Absence of P wave or shortened P – R interval (Right ventricular hypertrophy, Bundle branch block and ventricular premature contraction all will show bizarre – locking ORS o Abnormal T wave (tent shaped) due to hyperkalemia and hypoxia o Depressedor elevatedor slurred S – T segment due to myocardial hypoxia. o
ECG lead placement in anaesthetized animal (LEAD II) Small animals RA LL LA
Right arm or any where on the body rostral to the heart Left hind leg or any where on the body caudal to the heart Left arm or any where on the body (ground) Large animals
RA Right arm or low on the chest towards the sternum (negative pole) LL Left hind leg or on the chest above the spine of scapula (Positive pole) LA Left arm or on the neck (ground) VENTRICULAR PERFORMANCE
Ventricular performance is the contractile force of the heart, and can be assessed by the loudness on auscultation using ordinary stethoscope or oesophageal stethoscope or heart sound amplifier. Diminished heart sound is due to hyproventilation, myocardial weakness, hypoxia, anaesthetics, severe metabolic disturbances, endo and exogenous foxins, execessive or insufficient end-diastolic filling volume. Ventricular performance can be improved by o Dopamine 2.5 to 20 ug/kg/min (40 to 200 mg in 250 to 500 ml of 5% dexotrose or saline) o Dobutamine 2.5 to 20 ug/kg/min (40 to 250 to 500 ml of 5% dextrose or saline) o Mephenteramine 0.1 to 0.75 mg/kg/I.V o Calcium chloride 10% 0.1 mg/kg. I.V. o Digitalis o Amrinone (new inotropic agent ) 0.75 to 3 mg/kg I.V (peak effect in 10 minutes and the duration is 30 to 120 minutes) CARDIAC OUTPUT
Cardiac output can be measured by dye dilution technique or thermodilution technique. Indocyanian green a dye is injected into the right atrium at a known concentration. The change in the concentration at the down stream (pulmonary artery or aorta) is measured and the cardiac output is calculated. In thermodilution technique iced saline or saline in room temperature is administered in the right atrium and change in the temperature is assesses at downstream using thermodilution catheter located in the pulmonary artery. The thermodilution catheter is inserted into the right atrium through jugular vein using fluoroscopy or blindly (flow directional balloon catheters are used for blind methods). The causes for reduced cardiac output o Insufficient venous return o Ventricular restrictive diseases (hypertrophy, pericardial tamponade or pericardial fibrosis) o Decreased contractility o Excessive bradycardiaand arrhythmis o Regurgitation and retrograde flow o Stnosis o Positive inotropic drugs are administered to correct the cardiac output. PERIPHERAL PERFUSION
It is assessed by the colour of the mucous membrane and the capillary refill time. The normal capillary refill time is less than 2 seconds.
Pale mucous membrane and prolonged refill time are due to reduction in perfusion. The other methods to assess the peripheral perfusion is by the use of ultrasonic Doppler, electromagnetic flow probes, radionuclide imagery, nuclear magnetic resonance and position emission tomography. The reasons for reduced peripheral perfusion o Stress induced increase in sympathetic tone o Hypovolemia o Low cardiac output o Fear and pain o Exogenous alpha – Receptor agonist catecholamine therapy. BLOOD PRESSURE
Blood pressure is one of the important parameter to be monitored during anaesthesia because adequate blood pressure is needed to perfuse the brain and heart. A minimum 50 to 60 mm of Hg mean arterial blood pressure (MAP) is to be maintained for coronary and cerebral perfusion. Arterial blood pressure can be measured by o Direct and Indirect techniques in animals. Indirect technique o In indirect technique a cuff is placed snugly around the limb or tail and inflacted until the blood flow is occluded. o The extraluminal pressure just to occlude the blow is considered as the pressure, which is above the systolic pressure. As the cuff pressure is reduced the flow will restore. o The flow can be assessed by direct palpation of the artery (only for systolic pressure) or by auscultation for Korotkoff sounds. o The first sound represents systolic pressure and the muffing or disappearance of the sound represents the diastolic pressure. o Pediatric cuffs are well suited for veterinary use. o Cuff Placement Dogs above the elbow Horses Coceygeal artery Sheep and goats above the elbow or around the tibia Direct technique o direct method of blood pressure measurement is done by catheterization of a suitable artery and connecting it to an aneroid manometer to assess the mean arterial pressure. o A transducer is placed in machines to record both diastolic and systolic pressure. o Catheterization of artery Dogs femoral artery, dorso metatarsal artery,l lingual artery Horses Facial artery, metatarsal artery, common digital artery Cattle Middle coccygeal artery, median auricular artery
o
o o o
Sheep & goat Auricular artery Cat Superficial musculocutaneous branch of femoral artery. The normal systolic, diastolic and mean arterial pressure is 100 to 160, 60 to 100 and 80 to 120 mm of Hg respectively. Systolic pressure below 80 and mean arterial pressure below 60 mm of Hg are considered as hypotension and will result in poor cerebral and coronary perfusion. The mean arterial pressure can be calculated from systolic and diastolic pressure using the formula: MAP in mm of Hg + Diastolic + ((Systolic – diastolic)/3) The mean blood pressure is not the half of the total of systolic and diastolic pressure. The MAP is always close to the diastolic pressure. The difference between the systolic and diastolic pressure is called as pulse pressure. TREATMENT OF HYPOTENSION
Discontinue the anaesthetics and adjuncts, which induces hypotension and use the agents like diazepam and ketamine. Lactated Ringer’s 10 to 40 ml/kg is administered over a period of 10 to 30 minutes. Multielectrolyte sodium containing crystalloid replacement solutions can be administered routinely at the rate of 10 ml/kg/hr plus 2 to 3 times the volume of estimated blood loss. During major procedures like thoracotomy, fracture repair and laparotomy it can be increasedupto 20 ml/kg. During anemia and hypoproteinemia crystalloid solutions are not administered. If the PCV is less than 20% blood is indicated and if the total serum protein is less than 3 to 3.5 g/dl further volume replacementis done only by plasma or dextran. Sympathomimetic drugs are used in extreme hypotension with caution and continuous monitoring as they may induce cardiac arrhythmia. (See Anaesthetic emergenices) CENTRAL VENOUS PRESSURE
Central venous pressure (CVP) is the luminal pressure of the intra thoracic anterior vena cava or right atrium. The central venous catheters are positioned through percutaneous catheterization of jugular vein. The zero level of the manometer is maintained at the heart level. The nomal CVP is 0 to 10 cm of H2O in small animals, t to 15 cm of H2O in awake horses, 25 to 35 cm of H2O in anaesthetized recumbent horses and 5 to 10 cm ofH2O in cattle, sheep and goats. Increase in CVP could be noticed in reduced cardiac output vascconstriction and hypervolemia.
CVP decreases during vasodilatation, hypovolemia and obstruction to venous return. Fluid therapy is indicated when increase in CVP is noticed with heart failure. PULMONARY ARTERY PRESSURE AND WEDGE PRESSURE
Pulmonary artery and wedge pressures indicate the functional capacity of the left side of the heart. A flow directional balloon catheter is inserted into the jugular vein to pass the right atrium, right ventricle to reach the pulmonary artery bifurcation. Pulmonary wedge pressure is recorded when the balloon is in inflated condition and pulmonary artery pressure isrecorded when the balloon is in deflated condition. Normal pulmonary artery systolic and diastolic pressures are 20 to 40 mm Hg and 5 to 10 mm Hg respectively. The pulmonary wedge pressure is 3 to 8 mm Hg. Pulmonary artery diastolic pressure will almost be equal to wedge pressure. Increase in pulmonary artery and wedge pressure is observed during positive pressure ventilation, mitral insufficiency and excess pulmonary venous pressure. During spontaneous ventilation the pulmonary artery and wedge pressure will decrease. Pulmonary Functions-----RESPIRATORY RATE
Carbon dioxide is the primary chemical stimulant of respiratory centers to maintain normal respiratory pattern. Hypocapnia in anaesthetized patients may resulting apnea. In anaesthetized patients each respiration must be long and large to satisfy the ventilatory requirement and oxygen demand. BRADYPNEA
The reasons for bradypnea are Cerebral oedema, neoplasia or haematoma. Anaesthetic depression and hypoxia Medullary dysfunction The altered breathing patterns are o Apnea due to medullary dysfunction o Diaphargmatic breathing: during respiration the diaphragmatic component precedes and thoracic component. o Cheyne – Stokes breathing: It is characterized by cyclic hyperventilation and hypoventilation due to the delay in medullary response to changing carbon dioxide tension. o Biot’s breathing: characterized by cyclic hypoventilation and apnea and this pattern is also a sign of serous medullary disturbance.
Apneustic breathing: This pattern is associatedwithbrain stem disease and is commonly seen in ketamine anaesthesia. o Agnoal gasps: Characterized by periodic retraction of the hyoid apparatus and gasping through the mouth may or may not associate with diaphragmatic contraction. During surgical procedures apnea may develop due to o Spinal cord oedema secondary to CSF tapping o Injection of contrast agents for myelography o Due to neuromuscular blocking agents o Deep anaesthesia. o
TACHYPNEA
Elevated respiratory rate (tachypnea) may be associated with normoventilation or hypoventilation. Reasons for tachypnea o Hypercapnia o Hypoxia o Hypotension o Hyperthermia o Too light level of anaesthesia inducestachypnea and hyperventilation o Too deep anaesthesia induces tachypnea and hypoventilation o Airway obstruction resultsiln tachypnea and hypoventilation o Pneumothorax, hydrothorax, chylothorax, haemothorax and diaphragmatic hernia o Space occupying abdominal lesions such as gastric/intestinal tympany, ascitis, neoplastic mass, gravid uterus and pyometra o Atelectasis and airway collapse o Anesthetic drugs like ketamine, diazepam and certain narcotics.
Treatment o o o o
Proper intubation Articifial ventilation oncein 30 seconds in case of apnea Institution of intermittent positive pressure ventilation Sighing of the patient once every minute (squeezing the rebreathing bag) NATURE OF VENTILATORY EFFORT
The normal respiratory effort is smooth, easy, regular and comprised of thoracic and diaphragmatic movements. The abnormal ventilatory efforts are o Exaggerated breathing effort- indicative of respiratory stimulation. o Stertorous- indicative of upper airway obstruction o Wheezing- indicative of lower airway narrowing o Crepitation- indicative of fluid bubbling sound
o o
Intercostal retraction during inspiration- indicative of upper airway obstruction Predominance of diaphragmatic component during inspiration-indicative of deep anaesthesia. COLOR OF MUCOUS MEMBRANE
Cyanosis indicates severe hypoxemia. If cyanosisis noticed during anaesthesia immediately the oxygen supply must be checked for the correct delivery. The oxygen is supplied at the rate of 10 ml/kg/min in circle system and 20 ml/kg/min in nonrebreathing system. The other reasons for cyanosis are shock, hypothermia, cardiac arrest and intrathoracic lesions. Drugs like acetaminophen induces cyanosis in cats and benzocaine induces cyanosis in dogs and cats. VENTILOMETRY
Measurement of ventilation volume is ventilometry. Visual observation suggests the volume roughly. Ventilometers are fitted on the expiratory side of the breathing circuit will indicate the tidal and minute volume. The normal ventilation is 150 to 250 ml/kg/min. Minute volume below 100 ml.kg/min is considered as hypoventilation and above 300 ml/kg/min as hyperventilation. BLOOD GAS
Arterial blood is collected in 2 ml heparinized syringe with 22 to 25 gauge needle and the needle is corked or the needle guard is replaced immediately. The syringe is kept in ice and sends for analysis using blood gas analyzer.
Partial pressure of carbon dioxide (PaCO2)
The normal PaCO2 is 35 to 45 mm Hg. PaCO2 less than 35 mm Hg indicates hyperventilation. PaCO2 above 45 mm Hg indicates hypoventilation. PaCO. PaCO2 above 60 mm Hg indicates severe respiratory acidosis PaCO2 less than 20mm Hg indicates severe respiratory alkalosis and decreased cerebral blood flow PvCO2 (venous) will be 2 to 5 mm Hg greater than PaCO2. PaCO2 indicates the ventilatory status of the patient PaCO2 level can be used to calculate the alveolar partial pressure of oxygen (PAO2) using the formula o PAO2 = FiO2 x ( P B – P H20 ) – PaCO2 / R
FI02 – Fractional concentration of inspired oxygen (normal air contains 21% oxygen hence it is 0.21. PB – Barometric pressure (normally 760 mm Hg at sea level) given in the blood gas report. PH20 – Water vapour pressure (47 mm Hg when the air is fully saturated at 37oC) given in the blood gas report. R - Respiratory quotient, it is a constant, which is equal to 0.8 (ratio of carbon dioxide production to oxygen consumption)
Partial pressure of oxygen (PaO2)
The normal PaO2 is 90 to 100 mm Hg. Pa02 less than 60 mm Hg indicates hypoxia and hypoventilation Animals breathing enriched oxygen mixture will be having higher Pa02 Pa02 indicates the oxygenating capability of the lung METABOLIC ACIDOSIS
The pH will indicate the metabolic acidosis and is attributed to the lactic acidosis secondary to inadequate tissue perfusion due to vasoconstriction, hypotension, hyperthermia or infusion of acidotic fluids. Bicarbonate is administered only for the patients having bicarbonate deficit, not for all acidotic conditions. The amount of bicarbonate in mEq to be administered is calculated as base or bicarbonate deficit x 0.3 x body weight in kg (approximately 1 to 5 mEg/kg). The commercially available bicarbonate powder is equal to 12 mEq per grams. Bicarbonate solution must be administered slowly because rapid administration may cause alkalemia, hypokalemia, decreased ionized calcium, hypotension, nausea, vomiting, collapse and even cardiac arrest. TEMPERATURE
Recording body temperature is important in anaesthetized patients as it indicates the systemic function. The temperature can be recorded at deep rectum, cervical oesphagus, pharynx and under the tongue. During anaesthesia drop in temperature could be noticed due to the reduction in metabolic rate. Premedicants like acepromazine deplete the catecholamine in the thermoregulatory center and render the animal to pick up the environmental temperlature.(See hypothermia and hyperthermia in Anaesthetic complication) URINE OUTPUT
It is an indirect assessment of visceral perfusion. Urinary catheters are placed aseptically and the urine is collected.
The normal expected urine output in anaesthetized animals is 1 to 2 ml/kg/hr. If the urine output is reduced lactated Ringer’s is administered at the rate of 20 to 40 ml/kg rapidly to induce diuresis. The other agents administered to induce diuresis are o Furosemide 5 mg/kg diuresis occurs in 5 to 10 minutes o Glucose, Mannitol (0.5 g/kg over 20 to 30 minutes) as infusion o Dopamine 1 to 5 µg/kg/min.
MODULE-14Anaesthetic Emmergencies & its management REASONS FOR ANAESTHETIC EMERGENCIES
Human error o Not familiar with the equipment and anaesthetic drug and its action, miscalculation of dose, incorrect route of administration and wrong medications. Equipment problems o Failure to deliver oxygen, empty cylinders, misconnected gas lines and kinked or plugged endotracheal tubes. Ventilatory problems o Hypoventilation due to anaesthetic over dose, hyperventilation due to inadequate anaesthesia and ventilatory depression. Circulatory problems o Hypotension, bradycardia, tachycardia and shock.
BRADYCARDIA
Bradycardia may arise due to o Excessive depth of anaesthesia o Excessive vagal tone (often increased by intubation vasovagal reflex and traction of abdominal organs) o Terminal hypoxia o Endogenous and exogenous toxaemias o Conduction disturbances in myocardium o Hyperkalaemia o Hypothyroidism
Treatment o o o o o o
Administration of atropine or glycopyrrolate. Dopamine 2.5 to 20ug/kg/min (40 to 200 mg in 250 to 500 ml of 5% dextrose or saline )I.V. Dobutamine 2.5 to 20 ug/kg/min (20 to 200 mg in 250 to 500 ml of 5% dextrose or saline)I.V. Mephenteramine 0.1 to 0.75 mg/kg I.V. duration 15 to 30 minutes Ephedrine 0.05 to 0.5 mg/kg I.V. duration 15 to 30 minutes. Isoproterenol 5 to 10 ug/kg/min (0.4 ti 1.0 mg in 250 to 500 ml of 5% dextrose or saline )I.V.
Reasons for intraoperative bradycardia
Due to increase in vagal tone o Difficulty in intubation o Deep abdominal surgery o Intraocular surgery o Neck and thoracic surgery o Effect of anaesthetics o Premedication with atropine or glycopyrrolate will control this o condition. Non vagal bradycardia o Excessive depth of anaesthesia o Hypoxia o Hypothermia o Hyperkalemia TACHYCARDIA
Tachycardia may arise due to o Light level of anaesthesia o Hypovolaemia o Hypoxia o Hypercapnia o Hyperthyroidism
Normally pulse rate may either be equal or slightly deficit of heart rate because all the contraction may not produce palpable effective wave and waves may overlap. The abnormal conditions which causes deficit of pulse rates are o Premature contraction, o Variable diastolic ventricular filling o Electromechanical dissociation of heart. Heart rate above 180 per minute in dogs and above 200 per minute in cats are considered as tachycardia. SHOCK
Shock is defined as inadequate blood flow to the vital organs or the inability of the body cells to metabolize nutrients normally. The tissue perfusion depends on the cardiac function, circulatory volume and integrity of vascular function. Shock can be classified as o Hypovolemic shock o Cardiogenic shock o Vasculogenic shock o Hyperdynamic shock o Hypodynamic shock
HYPOVOLEMIC SHOCK Causes
Due to inadequate volume of fluids or blood due to the loss of whole blood, plasma or loss of water and electrolytes Loss of blood in accident Loss of polasma protein into inflamed body cavities Loss of fluid and electrolytes in diarrhea
Symptoms
Depressed, dull and lack luster/lusterless eyes Pale or white or blue mucous membrane Reduced capillary refill time Cold extremities Tachycardia Fast and weak pulse Elevated respiratory rate
Reduced body temperature
CARDIOGENIC SHOCK Causes
Occurs when the heart fails to pump adequate blood to maintain perfusion. Failure could be due to reduced venous filling and reduced cardiac output. This condition is common in small animals. Cardiac tamponade Rupture of chordae tendinae Toxic myocardial depression Cardiac arrhythmia Severe prolonged systemic vascular resistance
Symptoms
Depressed, dull and lack luster/lusterless eyes Pale or white or blue mucous membrane Reduced capillary refill time Cold extremities Tachycardia Fast and weak pulse Elevated respiratory rate Reduced body temperature Distended pulsating peripheral veins Hepatomagaly Peripheral oedema Cardiac dysrhythmia Heart murmurs
VASCULOGENIC SHOCK Causes
The vessels supplying the blood to the tissues are affected and the perfusion is reduced Arteriolar constriction Prolonged sympathetic stimulation Vasomotor paralysis due to head injuries Endotoxic and septic shock can also be categorized under vasculogenic shock as the toxins produce vasodilation due to the release of histamine, bradykinin and prostoglandins.
HYPERDYNAMIC SHOCK Causes
An early stage of septic shock is an example of hyperdynamic shock.
Signs Stage I
Increase in cardiac output Decrease in arteriovenous oxygen difference Decrease in systemic vascular resistance Blood pressure may be normal or reduced Oxygen utilization at cellular level is reduced
Stage 2
Cardiac output may be normal Hypotension Respiratory acidosis with metabolic alkalosis Elevated heart rate
Stage 3
Reduction in cardiac out put Elevated heart rate Increased difference in arteriovenous oxygen level Increase in systemic vascular resistance Hypotension Brick red mucous membrane due to peripheral vasodilation Pyrexia due to toxins and damaged leukocytes
HYPODYNAMIC SHOCK
It occurs at the terminal stage of sepsis or during the absorption of toxins. This can be otherwise called as fourth stage of septic shock. Hypodynamic shock is common in large animal practice. E.g. terminal stage of horses with colic and cow with coliform mastitis.
Signs
Myocardial depression Maldistribution of blood volume High peripheral resistance Endothelial damage Infarcts in vital organs Acute respiratory failure and hypoxaemia
SIGNS OF CPR
No ausculatatable heart sound No palpable pulse Cyanotic mucous membrane Dilated pupil No ventilatory attempts or agonal gasps Unconsciousness It is really a true emergency condition, which is to be treated immediately within a period of 2 to 3 minutes. The basic life support in cardio pulmonary resuscitation(CPR) is the optimal management of airway(A), Breathing(B) and circulation(C). Otherwise called as ABC of CPR.
AIRWAY
The head must be immediately extended If not intubated, intubate the animal immediately. Examine for the possible obstruction of the airway with food materials or kinked endotracheal tube In emergency perform tracheostomy to maintain airway patent In case of bronchospasm treat the animal with aminophylline 5 mg/kg I.V. TREATMENT OF CPR
Airway
The head must be immediately extended If not intubated intubate the animal immediately. Examine for the possible obstruction of the airway with food materials or kinked endotracheal tube In emergency perform tracheostomy to maintain airway patent In case of bronchospasm treat the animal with aminophylline 5 mg/kg I.V.
Breathing
Institute artificial respiration using rebreathing bag or mechanical ventilators at the rate of 12 to 20 breaths per minute. Supply 100% oxygen Or use Ambu type resuscitation bag (using room air 21% oxygen) or mouth to endotracheal or mouth to muzzle procedures to maintain breathing Analeptic agents like doxapram can be administered at the rate of 1 mg/kg I.V. The other agents are specific alpha 2 antagonist (yohimbine) and opioid pure antagonists (naloxone) (See premedication).
Circulation
External cardiac massage by chest compression at the rate of 90 to 120 per minute. In dogs the chest compression can be attempted by placing the hands on either side of the chest. In cats the forefinger and the thumb is used. Open cardiac massage is done at the rare of 60 to 100 per minute. If surgery is performed in the thorax its easy to provide open chest massage. During abdominal procedures if emergency occurs the thoracic cavity can be entered through the diaphragm. Defibrillation - The defibrillation is done using external or internal paddles of cardiac defibrillators. The power setting depends on the weight of the animals. In small animals the heart is defibrillated at the rate of 1 to 10 J/kg using external paddles and 0.1 to 1 J/kg using internal paddles. DRUGS USED IN CPR
Calcium solutions
Administered as inotropic agent or in hypocalemic agent. (halothane decreases calcium availability in heart muscles. It strengthens the myocardial contraction. Dose Calcium chloride 10% solution at the rate of 0.1 mg/kg I.V, Calcium gluconate 10% solution at the rate of 0.5 mg/kg I.V.
Dobutamine
It is a sympathomimetic amine, whichstimulates beta 1 and beta 2 adrenergic receptors and to a lesser extend alpha 1 receptor. It decreases peripheral vascular resistance and increases cardiac output, blood pressure and tissue perfusion. Rapid intravenous administration may cause cardiac dysrhythmias. Dose 0.25 to 20 µg/kg/min in small animals and 0.5 to 2.0 µg/kg/min in large animals (40 to 200 mg in 250 to 500 ml of 5% dextrose or saline).
Ephedrine
It stimulates beta 1, beta 2 and alpha 1 receptors. The cardiac output and blood pressure are increased. It is indicated in mild to moderate hypotension. Dose 0.05 to 0.5 mg/kg I.V in small animals and 0.022 to 0.66 mg/kg I.V in large animals as a bolus.
Isoproternol
It is a sympathomimetic amine, which stimulates beta 1, beta 2 and adrenergic receptors located in the heart, bronchialsmooth muscles, skeletal muscle vasculature and alimentary tract. It decreases peripheral vascular resistance, diastolic blood pressure and mean arterial pressure and increases cardiac output and systolic blood pressure.
Epinephrine
It is a sympathomimetic amine that stimulates alpha 1, 2 and beta 2 adrenergic receptors. It dilates the vasculature of muscles and constricts cutaneous, mucosal and renal vasculature. The systolic, MAP andpulmonary blood pressures are increased following administration. It can cause dysrhythmia if administered during halothane anaesthesia. It is administered at a dose of 5 ml of a 1 in 1000 solution for a 454 kg horse. In extreme condition it is administered through intracardiac route.
Doxapram (Dopram)
It is a nonspecific analeptic agent used to act on the peripheral chemoreceptors. Dose. 0.55 mg/kg I.V. to reverse the effect of xylazine it is administered at the rate of 1.0 mg/kg I.V.
Sodium bicarbonate
It is a buffer aids in reversing metabolic acidonin. Dose mEq of HCO3 = 0.3 x base deficit (mEq/L) x Body weight.
Coricosteroids
These group of agents increases the glucose production, induce hypdokalemia by sodium retention. They have inotropic effect on the heart and maintain vasomotor response and suppress the adrenal gland. Indicated in shock and malignant hyperthermia.
Lignocaine
Indicated in premature ventricular contraction. Only the epinephrine free preparation is used. Dose 0.5 to 2 mg/kg in large animals and 1 to 5 mg/kg in small animals followed by 40 to 60 µg/kg/min I.V. It is contraindicated in slow ventricular rate combined with sinus arrest, sinoatrial block or atrioventricular block.
Module -15
= Neuroleptanalgesia
PHENOTHIAZINE DERIVATIVES Phenothiazine derivatives
Phenothiazine derivatives are basically three ring structures in which two benzene rings are linked by a sulphur and nitrogen atom. The steriochemical model of phenothiazine derivatives is similar to epinephrine, norepinephrine and dopamine. They act on the central nervous system by depressing the brain stem and connections of the cerebral cortex. These agents increase the dopamine and norepinephrine turn over in the brain and block the peripheral actions of catecholamines at alpha 1 receptors.
These agents are weak anticholinergics and have extrapyramidal stimulating properties. Acepromazine maleate, triflupromazine hydrochloride, chlorpromazine, promazine, promethazine and methotrimeprazine are the commonly used phenothiazines. Among these agents acepromazine, triflupromazine and chlorpromazine are used in veterinary anaesthesia.
Clinical properties and uses
Produce sedation, general calming and reduction in motor activity Antagonize dopamine excitatory chemoceptors and suppress vomiting. At high doses and some times in clinical doses induce extrapyramidal signs such as rigidity, tremors and catalepsy. Hence contraindicated in patients; o With the previous history of epilepsy, o Undergoing myelographic procedures o With the history of recent intake of organophophorus drugs or toxicity Pulmonary functions are maintained following the administration of phenothiazines except slight depression in respiratory rate Induce urine production due to the suppression of antidiuretic hormone Animals undergoing intradermal allergic tests should not be administered with phenothiazines as they are potent antihistaninics Depletes catecholamines of the thermoregulatory center and render the animal’s body temperature susceptible to the changes in the environmental temperature. Tranquilization with phenothiazines is contraindicated in animals undergoing epidural, spinal or segmental anaesthesia. Following induction of regional anaesthesia there will be vasodilation in the anaesthestised part of the body and this effect is compensated by the vasoconstriction in the unanaesthetized parts of the body to maintain cardiac out put. This response is abolished by the generalized vasodilationinduced by phenothiazines. Clinical doses of phenothiazine derivatives
CLINICAL DOSES OF PHENOTHIAZINE DERIVATIVES Drug Acepromazine
Dose
Dogs = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.05 mg/kg I.M. Cats = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.1 mg/kg I.M. Horses = 0.02 – 0.05 mg/kg I.V, 0.04 – 0.09 mg/kg I.M.
Chlorpromazine
Promazine
Dogs = 0.55 – 4.4 mg/kg I.V, 1.1 – 6.6 mg/kg I.M. Cats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M Horses = 1.1 – 2.2 mg/kg I.M. Cattle = 0.2 – 1.1 mg/kg I.V, 0.2 – 2.2 mg/kg I.M. Sheep = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M. Goats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M. Pigs = 1.0 – 2.0 mg/kg I.M.
Horses = 0.44 – 1.1 mg/kg I.V/I.M. Cattle = 0.44 – 1.1 mg/kg I.V/I.M. Goats = 0.44 – 1.1 mg/kg I.V/I.M. Sheep = 0.44 – 1.1 mg/kg I.V/I.M. Pigs = 0.44 – 1.1 mg/kg I.V, 0.44 – 4.0 mg/kg I.M.
Dogs = 1.00 mg/kg
Triflupromazine
Cattle = 0.02 – 0.05 mg/kg i.V, 0.04 – 0.09 mg/kg I.M. Pigs = 0.1 mg/kg I.M.
Module- 16-Acupuncture, Electro-anaesthesia, Hypothermic anaesthesia
ACUPUNCTURE -
INTRODUCTION
Acupuncture (AP) can be used to obtain pain relief in clinical disorders or as an alternative or complementary method of inducing pain control during surgical procedures. AP analgesia (AA) is a misnomer. It should really be called AP hypoalgesia. It is a pain inhibition phenomenon caused by stimulation of peripheral nerves via certain AP points. The degree of pain inhibition may be complete or partial. In vet surgery, the AA technique, if applied carefully, often is sufficient to allow surgery without the use of other anaesthetics. Consciousness is retained throughout the operation but many animals become slightly drowsy (as if slightly sedated) during and for a short time after AA stimulation. All other sensations (touch, traction, pressure, tickle etc) and reflexes (to sight or sound stimuli, fear, traction etc) are intact. AA can be induced by simple AP (manual twirling of the needles) but it is more common to use electrical stimulation (ES) via the needles. In this case the technique is called Electro-APanalgesia (EAA). In emergencies a slight degree of hypo-algesia can be obtained in humans and animals by heavy digital pressure over the correct AP/nerve points. This method may have application in time of war or national disasters, when anaesthetists and anaesthetics may not be available. AA also can be induced by other stimuli, such as injection or electro-static fields applied to the points. Since the late 1980s, research on uses of low-power (cold) Laser as an AA stimulus is ongoing, with some positive results. However, it is too early to attempt to assess that method. Stimuli via the AA points are carried in the peripheral sensory nerves to the spinal cord. They reach the midbrain via the ascending spino-thalamic tracts. In the midbrain the ascending signals cause release of endorphin, serotonin and other neurotransmitters which activate a "descending inhibition mechanism" and prevent the "pain signals" from the surgical area from reaching the cerebral cortex. Thus, AA can be said to "close" various "pain gates" in the nervous system. These gates are thought to be located in the spinal cord, thalamus and possibly other areas. The result is that the human (and, presumably, the animal) patient can feel the knife, the touch and traction etc but does not "feel pain". Stimulation-Produced-Analgesia (SPA): Since the 1970s, western researchers, working independently of the Chinese, found that various types of stimuli applied indirectly or directly to the nervous system can reduce or abolish clinical and operative pain. Transcutaneous Electro-Stimulation Analgesia (TESA) has been used in childbirth in the human female and is somewhat comparable to EAA. Dorsal Column Stimulation (DCS) of the spinal cord has been used in intractable pain in humans. ES via electrodes implanted in specific sites in human or animal brain can induce a high degree of analgesia, usually involving the entire body. Direct ES of human thalamic or spinal areas can abolish clinical pain. Vaginal stimulation (electrical or mechanical) can cause potent whole-body analgesia in rats. TYPES OF OPERATIONS UNDER AA
Since the mid 1970s, major surgery has been done in animals under AA as the sole analgesic agent in many countries in the West. These include France, Germany, Austria, Belgium, USA, Canada and Australia. Workers in Eastern countries such as China, Japan, Taiwan etc have used the method for many years. The animal species involved include horses, mules, donkeys, cattle, sheep, goats, pigs, monkeys, dogs, cats, rats, cavies, guinea pigs and mice. Types of surgery successfully done in animals include: o caesarean section, ovario-hysterectomy; o gastric and intestinal surgery; o nephrectomy; o removal of mammary and skin tumours; o surgery of the eye, ear, anal and vaginal region, limbs and teats; o surgery on the lip, oesophagus, trachea, frontal sinuses; o rumen; o navel hernia repair; o surgery on the bladder and urethra; o orthopaedic surgery (bones, joints); o removal of parotid and submaxillary glands; o castration, orchidopexy, inguinal hernia. The late Dr. Westermayer's method for reposition of the prolapsed uterus has been mentioned already, as has AP therapy for the relief of dystocia.
EQUIPMENT AND METHODS OF RESTRAINT FOR AA Equipment
Most AA is done using electrostimulation (ES) through needles in the correct points (Electro-AP analgesia = EAA). The choice of points will be discussed later. Many different types of electrostimulator are on the market. Some are made in China, others in Japan, USA, Canada, Europe and Australia etc. The equipment should be strong, portable and battery-operated. It should have outputs for at least 8 electrodes. There is little standardization of equipment. Newer models for human use would be adequate for EAA in animals. It is safer to use models which deliver a bipolar waveform, (+) and (-), at each electrode. This prevents the development of serious electrolytic lesions which could arise if a monopolar waveform was used for long periods, as in prolonged surgery. The Model 71-3 General Purpose Electro-AP Apparatus is suitable for AA as well as AP therapy. I had 8 teeth extracted and 8 teeth filled under EAA with the Model 71-3. I used mainly ChiaChe (ST06) plus Earlobe "Dental Analgesia Point" on the affected side. Needles were inserted 12-20 mm in the points. Voltage was increased slowly to maximum tolerance (anaesthesia mode, densedisperse waveform). Occasionally adjustable waveform at 5-10 Hz was used.
After 30 minutes of induction, the output was usually at a setting of 4-5 on a 10 point scale. When heavy needle-probing of the gum caused no pain, dentistry could begin. Dental fillings under EAA were uneventful except in deep root fillings. If "nerve pain" arose, turning up the voltage usually controlled it. Extraction was painless or caused minimal pain in 5/8 cases but 3/8 extractions caused moderate to severe pain but were completed without the use of drug analgesia. An impacted wisdom-tooth required 10 minutes of very strong rocking to remove it from its socket. There was rather severe pressure-pain with that attempt but I was able to tolerate it without asking for another anaesthetic. My dentist told me that most patients could not have had the tooth removed unless they had general anaesthesia. In human patients, Caesarean section has been done in Japan using electrostatic or electromagnetic fields around the hands and feet. The apparatus used does not appear to have been tested in Europe or America. Childbirth has been helped in 60-80% of women treated by transcutaneous ES analgesia (TESA) of the thoraco-lumbo-sacral region. The apparatus used was the Travisens, available from Dan Sjo Elektronik AB, Box 144-17224, Sundbyberg, Sweden. TESA does not appear to have been tested in animals.
Restraint for AA in animals
Surgery under AA requires adequate restraint because consciousness and all sensations and reflexes (except those of pain) are retained. In large animals, operations under AA may be performed with the animal in the standing position or in dorsal, lateral or ventral recumbency, depending on the type of operation and whether or not the animal is quiet. Horses and nervous cattle should be knocked by ropes or a short-acting knock-down anaesthetic. Nervous animals may be given a tranquilliser i/v. Recumbent animals should be roped securely and an attendant should ensure that the head is kept down. A blindfold over the animal's eyes helps to avoid fright by visual stimuli. Unnecessary noise, movement and fuss should be kept to a minimum. The standing position may be used for surgery in quiet cattle. An attendant may hold the nose and the animal should be restrained in a suitable cattle crate, or ropes may be used through rings in the wall to keep the animal in one position. Kicking may be prevented by the usual methods as applied in operations under local anaesthesia. Small animals are normally operated on in lateral, dorsal or ventral recumbency. If a special operation-harness is not available they are restrained by tying bandages from the hocks and elbows to suitable anchor-points on the operating table. Dogs are excellent subjects for AA but it is advisable to tie a tape bandage around the jaws to prevent biting. It helps if the owner or an attendant talks to the dog and comforts the animal from time to time during surgery. Cats are difficult animals to handle and some vets who have tried AA in cats have ceased to use the technique in this species.
AA TECHNIQUES IN LARGE AND SMALL ANIMALS
Electro-AP analgesia (EAA) is the most common method used. When the animal is properly restrained, AP needles are placed to the correct depth in the AA points related to the operation site. The stimulator is checked to ensure that the power switch is off. The output leads are then connected to the needles. Do not connect the leads from one output across the thoracic or posterior cervical region. This is especially advisable if the instrument uses (+) and (-) electrodes. In this case the correct connection would be as in the diagram on the next page. An output circuit placed across the thorax may interfere with cardiac function and may, on rare occasions, cause cardiac arrest. Tape or suture the needles firmly in position. Otherwise, they are liable to become dislodged by muscle twitches induced by the stimulation, or by struggling in nervous animals. When the needles are in position, the output controls are checked to ensure they are set at zero. Attach the leads and turn on the power switch. Turn up the output controls slowly until the needles begin to twitch in time with the frequency of the stimulator. Increase the output voltage from each control to the maximum tolerance of the patient. At that point, the animal indicates a degree of discomfort or pain (restlessness, defensive reaction, struggling, vocalisation etc). Reduce the output to a "strong but acceptable level" (that which can be tolerated without obvious discomfort). Excessive stimulation reduces the EAA effect and to weak a stimulus may induce little or no analgesia. Note: A needle can not twitch unless it is embedded in reactive muscle. As long as one of a pair is twitching, the paired needle is also receiving a similar stimulus. Needles may not twitch in points such as GV26. If output voltage is too high at such points, the animal will indicate discomfort. In that case, reduce the output to the tolerance of the patient. Every 5 minutes or so, after switch-on, the operation site is tested for analgesia using rat-tooth forceps, towel clip, clamp or pin prick. Initially, full sensitivity to pain is present, as indicated by local muscle twitch or guarding, vocalisation or defence reactions/struggling. After 5-10 minutes, the response to pain stimulus decreases. After 20-40 minutes, in successful cases, the animal makes no response to strong pain stimuli in and around the operation site. The operation may then commence. Pain stimuli may exceed the hypoalgesia (thereby inducing pain response by the animal) at certain stages of the operation, especially during incision and suturing of the skin, serosa (peritoneum, pleura etc) and incision of periosteum and nerves. During these stages of the operation the frequency or output voltage should be increased. This is normally sufficient to counteract the pain. Occasionally (in those animals which respond poorly to AA) it may be necessary to use small volumes of local anaesthetic injection or spray at these stages. In the first few minutes after stimulation begins it is usual for the animal to show a mild stress reaction (dilated pupils, increased blood pressure, faster
respiration and heart rate). These quickly return to normal or near normal levels, and should remain at this level during the operation. Studies of EEG patterns in animals under AA indicate that brain waves are in the alpha range (8-13 cycle per second) i.e., similar to those of drowsiness or light sleep. However, the animals are still conscious and can eat or drink and (in dogs) wag the tail if petted by someone they know. Because sight and hearing are unaffected (pupil reflex is also intact), unnecessary noise should be avoided and a blindfold may be desirable. Pupillary dilation and salivation occurs in some animals. If salivation is excessive or retching/vomiting occurs, this usually indicates that excessive traction on mesentery/internal organs is the cause. This may be partly counteracted by increase in frequency or output of the AA stimuli. ELECTRO NARCOSIS
Since the end of the last century many investigations with electroanaesthesia have been performed in animals and man. The interest in this method of anaesthesia has emerged because anaesthesia is achieved immediately after the onset of the current and the recovery is very rapid after cutting off of the current. Recently a battery operated appuratus became available (Feenix Stockstill) for application of electroanaesthesia and electroimmobilisation under field conditions, and an experiment was conducted with 10 calves, 10 sheep, and 9 pigs, which were equipped with EEG and ECG electrodes. to check the analgesic and other practical effects of the apparatus. The duration of current administration was 20 minutes. Three animals of each species were used as control animals. In all animals, during administration of the current, the breathing movements appeared to be somewhat impaired. The body temperature, the plasma cortisol level, and the pulse rate were raised durring the current administration. Moreover, the pulse rate was irregular. The corneal reflex remained positive in all animals, and the reaction to painful stimuli was positive in 15 out of 29 experimental animals. The body temperature, pulse rate, and plasma cortisol level remained constant in the control animals. Before and after administration of the current the electroencephalogram recordings were similar, except in one calf and one sheep, both of which showed patterns suggesting a decreased consciousness. The electrocardiogram recordings showed pronounced changes in cardiac activity. In one pig the heart activity stopped some minutes after the onset of the current. Changes in the electroencephalogram and electrocardiogram were not observed in the control animals during their treatment. The results suggest that the apparatus did not cause electroanaesthesia or electrosleep but had mainly an electroimmobilising effect on the experimental animals. Because of the dubious effects on the animals' welfare, the use of such an apparatus cannot be recommended. HYPOTHERMIA
Hypothermia may develop in animals anesthetized in a cool environment. A decrease in temperature of 1-3ºC below normal has been demonstrated to provide substantial protection against cerebral ischemia and hypoxaemia in anaesthetized dogs. Life threatening cardiovascular depression may develop when the temperature decreases below 32.8ºC. Rectal or esophageal temperature should be monitored at regular intervals during inhalation anesthesia , during protracted total intravenous anesthesia and during recovery from anesthesia. Basically ,the causes consists of a reduction in heat production by the animal , usually coupled with an increased heat loss. It is very difficult to influence production of heat but care should be taken not to wet the animal excessively to reduce evaporative heat losses, placing the animal on a warm surface and covering with blankets , drapes , wrapping of extremities with towel and blanket and plastic insulation or hot air circulating devices. Respiratory heat losses are increased when animal breathes cold dry gas from non-rebreathing system, such losses are reduced by the use of rebreathing circuits,and also maintaining low flow rate and attachment of humidifier to endotracheal tube. Fluids to be administered i.v. should be warm.
The adverse effects of perianaesthetic hypothermia are 1. 2. 3. 4. 5. 6. 7.
Impaired cardiovascular function. Hypoventilation Decreased metabolism and detoxification of anesthetic drugs Weakness during recovery Decreased resistance to infection Increased incidence of surgical wound infection Increased postoperative protein catabolism
MODULE-17:
MUSCLE RELAXANTS
Learning objectives This module deals with
Physiology of neuromuscular transmission Reversal of Neuromuscular Blockade Ventilation
INTRODUCTION
Anaesthesia is comprised of narcosis, analgesia and muscle relaxation. Muscle relaxation is best achieved by the administration of neuromuscular blocking agents. Use of neuromuscular blocking agents To provide the muscle relaxant component of anaesthesia To minimize the dose of general anaesthetics To provide easy access to the deep structures in the abdomen To aid in intubation without laryngeal spasm To prevent fighting the ventilator during controlled ventilation To help removal of foreign bodies from the proximal portion of oesophagus as it is composed of striated muscles. To aid in reducing the luxated joints To ensure immobility of the patient during delicate surgery To stabilize the eyeball in central position during ophthalmic surgery
PHYSIOLOGY OF NEUROMUSCULAR TRANSMISSION
The large myelinated nerve from the ventral horn of the spinal cord carries impulses to the muscles. It carries stimuli to several muscle fibres that must be activated for contraction. As the nerve approaches the muscle cell its branches lose their myelin sheaths and the terminal ends lie in grooves on the surface of the muscle fibre and are covered by Schwann cell. The area where the nerve ending lies close to the proximity of the muscle fibre is called neuromuscular junction. The muscle fibre membrane forms the groove and the grooves are deeply corrugatede and called as secondary clefts. The small gap between the nerve fibre terminal and the muscle membrane is 60 nm wide and is called as junctional cleft. The areas of secondary cleft are rich in mitochondira. The action potential traveling along the motor fibre produces depolarization of the nerve terminal and triggers the release of acetylcholine, which crosses the junctional cleft to stimulate nicotinic-cholinoceptors of the post synaptic muscle membrane. Acetylcholine is synthesized from choline and acetate in the presence of an enzyme acetyltransferase. The acetylcholine molecules are present as uniform sized vesicles near the presynaptic membrane and these areas are called as active zones. When acetylcholine is released it travels a minimum distance across the junctional cleft to reach the receptors. Interaction between the receptor and acetylcholine triggers an end plate potential, which is converted into muscle action potential leading tocontraction. After activating the receptor the
acetylcholine is rapidly hydrolysed to choline and acetate. The drugs used for neuromuscular blockade are classified into o depolarizing muscle relaxants o nondepolarizing muscle relaxants. DEPOLARIZING MUSCLE RELAXANTS
Depolarizing drugs produce intial muscle fasciculations and their action is rapid. Depolarized muscles are unresponsive to other stimuli such as electrical stimulation. Their action is not reversed by anticholinesterases. In partial paralysis neuromuscular monitoring slow depression of muscle twitch, no fade and no post titanic facilitation are noticed. The only drug used in this group is suxamethonium chloride (Succinyl choline). It is hydrolysed by cholinesterase and pseudocholineesterase into choline and succinic acid. Cholinesterase is synthesized in the liver. Hence liver damage, cachexia and malnutrition may prolong the action of suxamethonium. Organophosphorous compounds (use as ectoparasiti-cides) decrease the action of pseudocholinesterase, hence not recommended in patients recently exposed to such agents. Isoflurane, respiratory alkalosis, hypothermia and magnesium ions potentiate the effect of suxamethonium. Its effects are antagonized by halothane, acidosis and nondepolarizing drugs. Its administration is associated with the release of potassium into the blood from the muscles, which may result in cardiac irregularities. However prolonged administration results in decrease in serum potassium level. In dogs 0.3 mg/kg intravenously produces muscle relaxation and it extends upto 25 to 30 minutes. Repeat dose may result in dual block (nondepolarizing) which can be reversed with anticholinesterase drugs.
NONDEPOALRIZING MUSCLE RELAXANTS
These drugs do not produce muscle fasciculations and are slow in action. Their effects can be reversed using anticholinesterase. The relaxed muscles will response to other stimuli such as electrical stimuli. During partial paralysis monitoring it shows fade andpost titanic facilitation followed by exhaustion and depression of muscle twitch. Acidosis, magnesium slats and volatile anaesthetics potentiate the action of these agents. Nondepolarizing drugs are either quaternary ammonium or steroid compounds. The following are nondepolarising muscle relaxing agents o Tubocurarine chloride o Gallamine triethiodide o Pancuronium bromide o Vecuronium bromide o Atracurium besylate
TUBOCURARINE CHLORIDE
Tubocurarine is derived from Chondrodendron tomentosum tree. Not recommended in dogs due to its profound cardiac defects/effects. GALLAMINE TRIETHIODIDE
It has atropine like action on the heart. It also blocks the muscarinic effects of acetylcholine and acts directly on the B receptors resulting in tachycardia and rise in blood pressure which may lead to greater blood loss during surgery. This drug is excreted through kidney hence not indicated in patients with renal diseases. Dose - 1 mg/kg I.V, Duration: around 29 minutes.
PANCURONIUM BROMIDE
It is an amino-steroid having no steroidal effects. Only 30% is metabolises and the rest is excreted unchanged through bile (10%) and the reaming through the kidney. It is contraindicated in patients having renal and hepatic diseases. It has minimal effects on cardiovascular system and some times produces rise in heart rate. Dose 0.06 mg/kg I.V, Duration around 31 minutes. VECURONIUM BROMIDE
It is a steroidal agent supplied in lyophilized form and soluble in water (stable for 24 hour only). Its duration of action is less than pancuronium. The drug is primarily excreted through bile in an unchanged form hence can not be used in patients with hepatic diseases and recommended in patients with renal disorders. It has got minimal cardiovascular effects and does not release histamine. Dose 0.1 mg/kg I.V., Duration 18 to 25 minutes. ATRACURIUM BESYLATE
It is a novel muscle relaxant, which does not depend on body system tometabolize. It is broken down by a self-destruction process known as Hofmann elimination. It is a safer drug for cardiac and renal patients. It is administered with caution inpatients with the history of anaphylaxis as it may release histamine.
Dose: 0.5 mg/kg I.V, duration around 40 minutes further maintenance can be done with incrementaldose (0.2 mg/kg) or by continuous infusion (0.5 mg/kg/hr). CISATRACURIUM BESYLATE
This drug is 5 times potent than atracurium, has no cardiovascular effects, does not release histamine, and is eliminated by Hofmann effects. No clinical literature is available on its use in veterinary anaesthesia. The other nondepolarizing drugs are mivacurium, rocuronium and doxacurium.
REVERSAL OF NEUROMUSCULAR BLOCKADE
Reversal of nondepolarizing drugs is achieved by establishing high concentration of acetylcholine at the binding site. It is achieved by the administration of certain drugs, which will inhibit cholinesterase, and the drugs are pyridostigmine, edrophonium and neostigmine. In clinical condition reversal is attempted when at least two twitches are present. Atropine (0.04 mg/kg) or glycopyrrolate (0.01 mg/kg) administered intravenously atleast one minute prior to the administration of reversal agent to block the muscarinic effects of acetylcholine. Neostigmine 0.1 mg/kg I.V or Edrophoniumj 1.0 mg/kg I.V. Intermittent positive pressure is discontinued only after achieving train of four responses (all must be of equal force). The action of neuromuscular blocking agents are potentiated and prolonged by aminoglycoside antibiotics e.g. streptomycin, gentamicin, and tobramycin by decreasing the release of acetylcholine. Calcium can be given prophylactically in these patients. The other antibiotics include polypeptide antibiotics like tetracycline, lincomycin and metronidazole. VENTILATION
There following are the different types of ventilation o Spontaneous ventilation o Assisted ventilation o Controlled ventilation o Intermittent positive pressure ventilation
TYPES OF VENTILATION Spontaneous ventilation
It refers to breathing without any assistance from mechanical ventilator or the anaesthetist squeezing the rebreathing bag. Spontaneous ventilation can be abolished by hyperventilation.
Assisted ventilation
The patient initiates the respiration but the tidal volume is increased or assistedby the ventilator or by squeezing the rebreathing bag.
Controlled ventilation
The total breathing function of the patient is done entirely by a mechanical ventilator or by the squeezing of rebreathing bag.
Intermittent positive pressure ventilation
This is a technique used in controlled ventilation or assisted ventilation to force air into the lung during inspiration and lower it to atmospheric pressure or slightly below during expiration.
USES
To provide ventilation during neuromuscular blockade and respiratory muscle paralysis due to toxins. To maintain near normal acid base status and oxygenation during long surgical procedures. To reduce ventilation-perfusion mismatch during prolonged periods of anaesthesia. To provide controlled respiration during thoracotomy. Intermittent positive pressure ventilation is essential to maintain pulmonary function in dogs, cats and in horses during open thorax as their mediastinum is incomplete. (fenestrated mediastinum). In cattle, sheep and goats the mediastinumis complete (unfenestrated mediastinum) hence thoracotomy can be performed in one side with out the need of ventilator. But still use of intermittent positive pressure in these animals also helps in maintaining cardiopulmonary parameters. Used in patients whose respiratory centre is depressed by drugs, increased intracranial pressure, cerebral ischemia, and cardiac or respiratory arrest.
Used in thoracic diseases, which affect the negative pressure of the thorax. (-5 cm of H2O during expiration and -12 cm of H2O during inspiration) eg. Diaphragmatic hernia, pleural effusion, pneumothorax. Used in patients having inadequate respiratory exchange due to obstruction or pulmonary oedema. Guidelines o Volume, pressure, rate and inspiratory: expiratory ratio must be properly set in the ventilators. Volume o Small animals 10 to 20 ml/kg o Large animals 10 to 15 ml/kg (maximum limit is for open thorax) Pressure o 15 to 30 cm of H20 Rate per minute o Dogs 8--- 14 o Cats 10---14 o Horses 6 --- 10 o Cow 6 --- 10 o Sheep & goats 8 --- 12 o Pigs 8 --- 12 Inspiratory: Expiratory ratio o It should be 1:2 or 1:3 to minimize the interference with venous return the inspiratory time is kept shorter than expiratory time.
MODULE-18: GENERAL PRINCIPLES OF CHEMICAL RESTRAINT OF WILD AND ZOO ANIMALS Learning objectives This module deals with
Chemical Immobilization of Wild Animals CHEMICAL IMMOBILIZATION OF WILD ANIMALS
Wild animals are chemically restrained for the following reasons o Animal translocation and transportation o To study the ecology and population estimate o For veterinary studies o To relieve wild animals in distress
Control of animals causing distress to the public Various devices used for injecting the drug from a distance are drug darts, projectile syringes (short range, long range, and extra long range), blow gun rifle, blow pipe, and stick syringe. o
Primates
Ketamine – 5-20 mg /kg intramuscular Xylazine 2 mg/kg intramuscular
Chimpanzee
Ketamine 10-15 mg/kg body weight Xylazine 2 mg/kg
Kangaroo
Xylazine 8 mg/kg body weight and Ketamine 3 mg/kg combination Thiopentone less than 20 mg/kg body weight
Antelope
Xylazine 0.23 mg /kg and Ketamine 11.54 mg/kg body weight combination
Deer
Xylazine 0.89-8.0 mg/kg body weight Ketamine 10-20 mg/kg body weight
Camels
Xylazine 0.27-0.51 mg/kg intramuscular
Bears
Xylazine 2-4 mg/kg and Ketamine 4.5-9mg/kg (Combination)
Bison
Chloral hydrate 250mg/kg body weight
Elephant
Asian elephant 100-175 mg Xylazine (total dose)
Etorphine-Acepromazine combination (2.4 mg/ml-Etorphine and 10mg/ml of Acepromazine per ml) Dose 1 ml/4 feet of shoulder height
Reptiles
Ketamine 20 mg/kg intramuscular Xylazine 1 mg/kg
Snakes
Ketamine 50-130 mg/kg intramuscular Tiletamine 10-20 mg/kg intramuscular
MODULE-19: ANAESTHESIA OF LABORATORY ANIMALS Learning objectives This module deals with
Injectable Anesthesia Inhalant Anesthesia Gas Delivery Systems Anesthetic Machine Preparation, Monitoring and Maintenance of normal physiology
INJECTABLE ANESTHESIA
Anesthetic induction using injectable anesthetics is fairly simple. It involves admininsistration of the drug and monitoring the depth of anesthesia. Supportive care may be needed. Maintenance of injectable anesthesia can be through repeated bolus doses of the drug or through a constant infusion. Infusion rates are calculated based on the clearance time of the drug. Bolus dosing is simpler. Typically, 1/2 of the original dose is given for repeat doses. Injectable anesthetics can be administered by various routes depending upon the specific compound. The most frequently used routes of administration in laboratory animals are intraperitoneal, intramuscular and intravenous. Less frequently used routes, among others, are intrathoracic, oral and rectal. Techniques are described below. Contact RAR at 624-9100 for training materials on handling animals and administering injections.
Intravenous(IV)
Method - An appropriate vein must be selected. For large animals, the saphenous, cephalic or jugular veins are best. For rodents, the tail veins are best. For rabbits and swine, ear veins may be used. The vein is held off proximal to the venipuncture site. The vessel may be stroked with a finger to stimulate blood flow into it. The needle is inserted at a 30-45° angle to the vessel. Then the needle is lowered to align with the longitudinal axis of the vessel and advanced slightly. Draw back. If blood appears in the hub of the needle, the drug may be injected. If not, try redirecting the needle (before you pull it out of the skin) and repeat. You may need to try several times while learning. Using a new, sharp needle for each stick, even if it is the same animal, will improve your chances for success. Once the needle is withdrawn, it is necessary to put pressure on the vessel to prevent bleeding. Advantages - rapid delivery of drug, ability to titrate dose, irritating substances may be given IV Disadvantages - small veins are hard to access (i.e. small animals), restraint is critical, developing skill in venipuncture takes experience
Intramuscular(IM)
Method - Insert the needle into a large muscle mass. Draw back slightly. If blood is aspirated, you are in a blood vessel. Redirect the needle. When the needle is placed correctly, inject the drug. The best muscle masses to use are for small animals, the caudal thigh muscles. For larger animals, the lateral dorsal spinal muscles or the cranial or caudal thigh muscles may be used. When administering into thigh muscles, inject from the lateral aspect, or if from the caudal aspect, direct the needle slightly lateral. This will help avoid injecting into the sciatic nerve. Advantages - Fairly rapid absorption, technique is simple
Disadvantages - IM injections are painful, small volumes are necessary, the animal may try to bite or escape
Intraperitoneal (IP)
Method - The animal is usually restrained in dorsal recumbency. The drug may be injected anywhere in the caudal 2/3 of the abdomen. However, it is best to try to avoid the left side in rodents and rabbits because of the presence of the cecum. After the needle is inserted, draw back. If anything is aspirated, you have likely hit the viscera. Withdraw and get a new needle before trying again. If the needle is placed correctly the drug may be injected. Advantages - relatively large volumes may be injected (0.5 ml in mice, 2 ml in rats, etc.) Disadvantages - technique is more difficult than IM injections, drug may be administered into the viscera resulting in no effect or in a complication.
Subcutaneous (SQ)
Method - Pinch an area of loose skin. Inject into the center of the "tent" created by pinching. Advantages - Technique is the simplest of any, large volumes may be given (basically as much as the tent of skin will hold that doesn't cause discomfort to the animal) Disadvantages - Irritating substances cannot be given this way, absorption is slow
INHALANT ANESTHESIA
Induction of inhalation anesthesia can be difficult. Anesthetic gases are irritating to eyes and nasal passages. Animals may resist as they begin to lose consciousness or they may stop breathing temporarily. For this reason induction using a mask or nose cone held over the animal's nose can only be performed on smaller or non-fractious animals. In smaller animals gas can be delivered into an induction chamber large enough to contain the entire animal. Induction via a nose cone or chamber requires delivery of the anesthetic gas at 2-3x MAC. Frequently an injectable anesthetic is used to induce anesthesia and the inhalation agent is used for maintenance. Maintenance of inhalation anesthesia is normally accomplished by delivering approximately 1.2 MAC to an animal via a mask or nose cone,
or directly into the lungs via an endotracheal tube. Intubation is recommended whevever possible, particularly when a procedure will be prolonged. Endotracheal access is essential to provide ventilation support.
GAS DELIVERY SYSTEMS
The most complicated aspect of using inhalant anesthesia is the delivery system. A delivery system must provide the anesthetic gas to the animal at a known and constant rate. It must also ensure that animals receive adequate oxygen. There are several types of delivery systems typically used in laboratory animals.
ANESTHETIC MACHINE
The best method of delivering an inhalant anesthetic is with an anesthetic machine. These machines precisely mix the gas with air or oxygen and can be easily adjusted. Machines can vary in construction and design. Anesthetic machines typically require more training to learn to operate. Anesthetic concentration is accomplished by sets of mixing valves or a precision vaporizer. Vaporizers are easier to use but are very expensive. Vaporizers are calibrated for the specific anesthetic gas to be used. Anesthesia circuits can be re-breathing or non-rebreathing. o Re-breathing circuits include typical circle systems used in large animals. The gas/oxygen mixture is delivered to the animal via a one-way valve. When the animal breathes out the gas passes out another valve attached to a y-piece. This is passed over a carbon dioxide absorbent and then back into the system. Additional gas and oxygen are continuously delivered to replace that lost. o Re-breathing circuits conserve anesthetic gas and the animal's body heat. The CO2 absorbent must be replaced regularly. o Non-rebreathing circuits are primarily used for smaller animals that cannot cycle the valves in a re-breathing system. With newer machines non-rebreathing circuits are normally only necessary for rodents and birds. In older machines with metal valves a nonrebreathing circuit may be necessary for rabbits and cats as well. A Bain system is the most common non-rebreathing circuit available.
The non-rebreathing circuit is attached to the same anesthetic supply as used for a re-breathing system. However, the exhaust line is connected directly to the waste gas scavenging system. o Non-rebreathing circuits depend on gas and oxygen being delivered at a higher pressure than is present in the exhaust line. This tends to increase anesthetic usage and can increase body heat loss in the patient. Anesthesia machines must have a waste gas scavenging system. Normally the exhaust line on a non-rebreating system or the pop-off valve on a re-breathing system is connected to a vacuum line or to the building exhaust. Other scavenging systems can be used, contact RAR at 624-9100 or Environmental Health & Safety at 626-5804 for further information on anesthetic delivery systems. o
Apparatus for rodent anesthesia
Left: a non-re-breathing nose cone that can be used with a large animal anesthetic machine; Middle: a typical drop system closed anesthetic chamber; Right: a gas scavenging system that can be used with a drop system.
PREPARATION, MONITORING AND MAINTENANCE OF NORMAL PHYSIOLOGY
A variety of things must be done to prepare for anesthesia. Once animals are under anesthesia they must be monitored closely while they are anesthetized to ensure that they do not become too deep and die, and to ensure that they do not become too light and experience pain from the surgical procedure. Normal physiologic functions such as body temperature, respiration and cardiovascular function must also be monitored and supported while the animal is anesthetized. For all major surgical procedures on non-rodent mammals, an intraoperative anesthesia record must be kept and included with the
surgeon's reports as part of the animal's record. The anesthetist must be prepared to handle emergencies if they occur. PREPARATION
Withhold food and water from large animals for 12 h prior to anesthesia and from small animals for 2 h to prevent regurgitation and aspiration. It is not necessary to withhold food and water from rodents prior to anesthesia. Prolonged food or water deprivation are distressful to animals and are rarely necessary. Please consult RAR's policy for fasting requests. Have all drugs and equipment ready before the animal is anesthetized. You may not have time to look for things once the animal is under. Have an assistant: Anesthesia takes time to perform and monitor. A person should be available to assist so the surgeon does not have to break sterility to monitor the animal or administer medications. Premedication with atropine or glycopyrrolate (anticholinergics) may reduce the respiratory tract secretions in some animals Protect the eyes from drying out using an ophthalmic ointment and protect them from being contaminated with surgical scrub solutions. Also protect pressure points, such as bony protrusions, from pressure necrosis or peripheral nerve damage by providing padding between the animal and the table.
RESPIRATION
Most anesthetics cause direct depression of the respiratory center in the brain and reduce ventilation. This is complicated by other factors that may interfere with respiration. When an animal is in lateral recumbency the lung that is down is being compressed by the rest of the body. Likewise, animals in dorsal recumbency may experience compression of the diaphragm by abdominal viscera. The airway may be compromised by regurgitated food or pharyngeal and tracheal secretions that normally would be removed by reflex swallowing or coughing. These reflexes are lost during anesthesia. There are several ways to monitor and support the ventilation of an anesthetized animal. Intubate the trachea whenever possible, even if injectable anesthetics are being used. Intubation can be achieved on animals as small as a rat. This will prevent aspiration pneumonia and allow you to assist respiration if the animal stops breathing. Contact RAR at 624-9100 for training materials. Assist respiration during the procedure. This can be done with a mechanical ventilator. However, mechanical ventilation is rarely needed
(unless a thoracotomy or diaphragmectomy is being performed) and can be detrimental to the animal if over-done. Attaching an AMBU bag to the endotracheal tube or using an anesthetic machine's rebreathing bag will allow you to administer a deep breath every 2-5 min during the procedure. This will inflate all areas of the lungs and improve gas exchange. If the animal is not intubated, ventilation can be performed using a nose cone or face mask. Monitor respiratory function throughout the procedure and recovery. o Monitor respiratory rate and depth (compare to normal for your species. You can expect them to be slightly decreased). Observe chest movement, or use a stethoscope or esophageal stethoscope. o Monitor the color of the mucous membranes (gums, conjunctiva, vulvar mucosa). A bluish color means the animal is not getting enough oxygen- ventilate! o Red-tinged foam present in the airway along with dyspnea (difficulty breathing) may indicate pulmonary edema. This can result from overventilation or overhydration. A diuretic like furosemide can be administered, but prognosis is poor. o Sophisticated respiratory monitoring can be achieved by measuring blood gasses, or expired oxygen and carbon dioxide concentration or by use of a pulse oximeter.
FLUID THERAPY
Many anesthetics have direct effects on the heart or vasculature, decreasing cardiac output and blood pressure. This is further complicated by increased fluid requirements during anesthesia and surgery that may result in hypovolemia. Fluid requirements are increased because: breathing dry, cold oxygen (if inhalant anesthesia is used) increases respiratory fluid loss; the animal has not received its normal fluid intake since it was fasted; fluid may be lost through hemorrhage or exposure of moist viscera to room air; many anesthetics are metabolized in the kidney (creating a slight diuresis minimizes renal toxicity). To minimize the effects of surgery and anesthesia on hydration: o Place an intravenous catheter whenever possible to provide access for fluids and medications o Supplement fluids, intravenously if possible; otherwise intraperitoneally or subcutaneously Fluid should be supplemented at the rate of 5-10 ml/kg/hour during anesthesia Monitor hydration status- Overhydration results in frequent urination and pulmonary edema, underhydration results in sticky mucous
membranes, loss of skin elasticity, the eyes sinking into the orbit, decrease in blood pressure and increase in heart rate To replace blood loss with saline or lactated ringers, administer 3X the volume of blood lost by slow IV drip. Monitor the hematocrit. If it drops below 20%, whole blood replacement may be necessary. Monitor cardiovascular function by monitoring one or more of the following: o Mucous membrane color and capillary refill time (the time it takes for the mucous membranes to regain their normal color after pressure is applied) o Heart rate and rhythm - stethescope or esophageal stethoscope o Pulse rate and pressure - using your fingers o Blood pressure - arterial catheter or Doppler cuff required o ECG - If the animal has pale mucous membranes, the capillary refill time is greater than 2 seconds, or if the other cardiovascular parameters are out of normal range (determine normal for the species you are using!) you may have a cardiovascular emergency. Increasing the rate of intravenous fluid administration will improve cardiac output temporarily. However the depth of anesthesia will need to be reduced and if there is a primary cardiac problem it will require specific treatment. Consult with an RAR veterinarian for more information on anesthetic emergencies.
THERMOREGULATION
Animals frequently become hypothermic during anesthesia because of inhalation of cold gases, exposure of body cavities to the room air, and loss of normal thermoregulatory mechanisms and behaviors. Hypothermia depresses all physiologic functions, including respiration and cardiac function, slows the metabolism of anesthetics and results in prolonged recoveries. All of these can contribute to anesthetic death. Hyperthermia is less common, but may occur because of excessive application of heat, hot surgery lights or malignant hyperthermia in genetically pre-disposed animals. To thermoregulate your patient:
o
o o o
o
Monitor the body temperature frequently using a thermometer during the procedure and during anesthetic recovery. While animal normals vary from species- to-species, in general, when body temperature drops below 99° F, an animal is considered hypothermic. Below 95-96° F an animal cannot regain normal body temperature without supplementation. Prevent heat loss by insulating cold surfaces with a blanket Prevent heat loss during gas anesthesia by utilizing low flow techniques that conserve heat Supplement heat with a thermal blanket (keep blanket temperature below 40 C to prevent burns!) or with pre-warmed fluids Treat hyperthermia by administering intravenous fluids or applying water to foot pads or exposed skin. Only use an ice bath as a last resort, as it may cause cardiovascular shock.
MONITORING ANESTHESIA Monitoring anesthesia
The depth of anesthesia must be monitored carefully. Animals that are too light will experience pain and may move during the procedure. Animals that are too deep run the risk of experiencing cardiopulmonary arrest. If an animal is too light the anesthesia should be supplemented, if too deep, animals on gas anesthesia can be turned down. Animals given injectable anesthetics can not be lightened directly. Instead respiratory and cardiovascular support must be administered until the anesthetic is metabolized and the animal begins to lighten on its own. To monitor the depth of anesthesia, perform the following:
o
o
Reflexes - these reflexes disappear as the animal becomes deeper in the following order: Palpebral reflex - touching the eyelids causes blinking. The animal is light if it is blinking. Toe pinch reflex - pinching the toe or foot web will cause a pain response. If the animal withdraws the toe it is not deep enough. If it doesn't, it is not sensing pain. Corneal reflex- touching the cornea of the eye with a tuft of cotton results in a blink. Once the animal has lost its corneal reflex, it is too deep. Muscle tone increases as the depth of anesthesia decreases, unless the animal is receiving a cataleptic drug like ketamine in the absence of a sedative. Test muscle tone by pulling on the lower jaw or a limb. Rigid tone indicates inadequate depth of anesthesia.
Monitor cardiopulmonary function and body temperature
As an animal becomes too deeply anesthetized, respiration and cardiac output decrease, resulting in poor blood oxygenation and tissue perfusion and decreased blood pressure and temperature. Likewise, elevations in heart rate and blood pressure may be indications that an animal may be feeling pain and is anesthetized too lightly. Monitor as previously described.
Anesthetic Emergency Drugs Doxopram (Dopram)
Dose (mg/kg) 1-5 IV (10x in farm animals)
Indications
Respiratory stimulant, for complete respiratory arrest only, use with CPR
Furosemide (Lasix) 2- IV, IM
For pulmonary edema. Administer as needed
Naloxone (Narcan) 0.04 IV
For reversal of narcotic sedation or respiratory depression
Yohimbine
0.1-0.15 IV
Reversal of xylazine or detomidine sedation
Atropine
0.02-0.04 IV
For bradycardia
Epinephrine
0.1 ml/kg IV,
For cardiac arrest only. Administer IV,
(1:1000)
IT, IC, IM
intratracheal or intracardiac and perform cardiac massage
Lidocaine
2, IV (0.5 mg/kg in cats)
For diagnosed ventricular tachycardia only. Administer to effect and monitor
Recovery
Monotoring and support must continue until the animal is completely recovered from anesthesia. Complete recovery means the animal is able to hold itself in a normal upright position, has returned to normal body temperature and all physiological indices are within normal limits. Anesthetic recovery can be rapid for gas agents and short anesthetic episodes. Recovery time can be prolonged if animals were under for a long time or if injectable agents were used.
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PART – III DIAGNOSTIC IMAGING SECTION MODULE-20:
PRODUCTION AND PROPERTIES OF X – RAYS Learning objectives This module deals with
Types of X-ray apparatus Parts of X-ray machine Production of X-rays Properties of X-rays BASIC INTERACTION OF X-RAY WITH MATTER
For an x-ray examination, the part to be examined is kept between the x-ray source and an x-ray film. Thus the x-ray beam emitted by the machine traverse through the part to be examined to reach the film, carrying useful information that is recorded as a image on the film. While passing through the patient. Some x-rays are differentially transmitted through the patient carrying information.Some photons are absorbed and least to exist. Some are deviated from their course as scatter radiation which decreases the quality of a radiograph by causing fog on the film.X ray photon can interact with matter in five ways of which the Photoelectric effect and Compton effect are important in diagnostic radiology. o Coherent scattering o Photoelectric effect o Compton effect o Pair production o Photo disfiguration
Photoelectric effect
The effect is mostly produced when x-ray photos interact with inner shell electrons of a atom (KLM). It occurs more with low energy incident photons and high atomic numbers element, provided that the photons have sufficient energy to over come electron building energy with atom.
Compton effect
As an incident photon encountered a free electron of the outer shall of the atom, the photon travel in a new direction as scatter radiation.Compton effect produce almost all the surface radiation encountered is diagnostic radiology.It is the major radiation hazzard y fluorspar examinations. Photon defected at a narrow angle is electron to reach the film being exposed to cause fog.When an incident photon with energy slightly greater than the binding energy of a k shell electron encounter the scatter, the k shell electron is
affected from its shell. The photon disappears as most of its energy is utilized to over come the binding energy of k shell electron. The free electron flies off as photoelectron. Another electron from an adjacent or outer shell of another atom immediately fills in to the void created by an ejected electron. As this electron drops in to the created void, it gives off energy is the form of characteristicradiation.
Uses in diagnostic radiology
Contrast of the image is enhanced. No scatter radiation – Excellent quality of radiology Increases radiation ion of patient. TYPES OF X-RAY APPARATUS
Portable apparatus
Portable x-ray machines are widely used in veterinary practise. The advantages are o They are less than other types of machines. o They need little maintanence. o They can be operated from any 15 A electrical point . o They can be easily transported. o They are light and easily manoeuvered . The disadvantages is their low milliamperage necessitates longer exposure time and it predisposes to movement blur. Maximum output is 70 - 90 Kv and 15-30 mA. Uses o Suitable for x-raying of limbs below stifle and elbow of large animals and abdomen and skeletal system of small animals.
Mobile x-ray apparatus
In machines of this type the transformer are larger to permit higher output and hence cannot be transported easily. They are mounted on wheels , and are cumbersome to use for restive animals. The output varies from 40-60 mA and 90Kv. (the maximum of 125 kv and 300mA) Uses o Can be used for large animal for radiographing head , neck, and limbs and this machine is quite useful for small animal practices
Fixed x-ray apparatus
This machine requires transformer which have to be built in the room and special electric connection (3 phase). The output ranges from 300 - 1000mA
and 120-200kv. This type of mahcines are suitable only for big institutions because of high expenses involved. Suitable for both large animal and small animal radiography. Properties of x-ray beam
X-rays are invisible to eye & travel at high speed & at straight lines They can penetrate objects depending on atomic no, density, thickness of the material Photographic effect - on photographic emulsions x-rays ionises silver halides on the photo film Fluoroscent effect - certain chemicals such as zinc sulphide, calcium tungstate etc fluoresce when exposed to x-rays & emit green or blue light. This effect is utilised to intensify the x-ray effect by using intensifying screen in the x-ray cassetes. Biological effect - x-rays ionises the atoms & bring about disturbances in the cells by chemical activity which may cause either destruction or activation or mutation.
Collimation of X-ray beam
The x-rays because of diverting property is capable of extending to a considerable width. So the X-ray machine incorporate some mean to collimate or restrict the beam. The purpose is three fold & they are o To prevent unnecessary radiations of the patients or persons restraining the animals o To reduce the scattered radiations. o To minimize genetrical distortion. This is done by using cones or light beam diaphragm in a semi-darkened room. PARTS OF X-RAY MACHINE
It consists of four main parts o X-ray tube, o Transformers, o Tube stand and o Control panel.
X-ray tube
An X-ray tube consists of a large thermionic diode glass tube which has been evacuated to produce a high vaccum and in to which are sealed two electrodes, the cathode (-) and the anode (+).
Stationary or rotating is placed 1 - 3 cm apart. The glass tube is made of borosilicate to with stand high temperature generated inside. The passage of a high kilo voltage electric current across the electrodes results in the production of X-rays. The glass tube isfitted in to an oil filled casing and the whole assembly is housed in a metal encased with lead covering with a small opening for the useful X-rays to exit after filtration. The vacuum in the tube creates a free flow for the electron beam and also prevents oxidation of cathode filament. This also increases tube life. The oil in the tube helps to dissipate heat apart from acting as a electrical insulator. Cathode o The negative electrode consists of tungsten filament and a focussing cup and it serves as the source of electrons. Tungsten is preferred because of its high melting point ( 3370 c) and high atomic number.The tube current is measured in milliampereage and decides the number of electrons flowing per second from the filament to the target. o Modern machines have two filaments made of tungsten -rhenium alloy to increase the thermionic emission efficiency and hence the tube life. Focussing cup is a concave cup made of nickel or molybdenum and its function is to restrict the electron cloud to a small beam. o Immediately prior to making an x ray exposure the filament is heated to create an electron cloud by a low voltage current (average about 10 volts and amperege about 3-5.)The tube current decides the quantity or intensity of the x rays produced and also can be altered in the control panel. Anode o Anode is the target made up of thin sheet of tungsten embedded in a copper block serves to obstruct the electrons to make them give up their energy. As 99 % of it is converted in to heat, the heat produced at the target is rapidly transferred to the copper block and hence to the oil. The anode angle differs according to individual tube design and may vary between 10 deg and 20 deg and the size of the focal spot may vary from 0.3mm to 2 mm. o It is important that the x ray beam should arise from the smallest practical portion of the anode. This area is often termed as target or focal spot. o Larger x ray tubes possess rotating anode to with stand the heat generated due to large exposure. o There are two types of anode - stationary and rotating. o The stationary one is used in dental x ray machines.
Transformers
This consists of an auto transformer, a step down or filament transformer and a high tension transformer. A auto transformer corrects the fluctuations in input voltage, step down transformer permits the suitably reduced current to the cathode, and the high tension transformer produces a high voltage current for the production of x rays.
Tube stand
This is to support the x ray tube during the exposure.
Control panel
This contains the meters switches, on and off voltameter, kilovoltage selector, milli amperage selector the timer, and exposure button. PRODUCTION OF X-RAYS
X rays are produced by energy conversion when a fast moving streams of electrons is suddenly decelerated in the target anode of the x-ray tube,or by bombarding a tungsten target with an electron beam it gives up some of electron of its energy . Most of the energy (over 99A) will be transformed into heat; the reminder of the energy will be converted into x-rays. As x-ray beam passes thriough the patient differential absorption takes place depending on the tissue density and shadowgraph is obtained.
Electron orbits and energy level
Electrons are negatively charged particles revolving round the nucleus.Since an atom is electrically neutral in its normal state, it must contain an equal number of protons and electrons. The atom resembles a tiny planetary system with the nucleus as the sun and the electrons as the orbiting planets. X rays are generated by two different processes when high speed electrons lose energy in the target of the x ray tube due to radiative interaction.
Characteristic radiation or Line radiation
When the projectile electron interacts with the electron in the K shell of the traget atom rather than the electron in the outer shell it results in the ejection of electron in the K shell if the energy of the projectile electron exceeds the binding energy of the ejected electron. This results in transient electron vacancy in the K shell into which an electron from the outer shell or from another atom falls and this process continues till the atom becomes stable. This
shifting of electrons results in emission of X-ray photon which possoses an energy equal to the difference between the binding energies of the electrons involved. Hence the X-ray photon energy is characterisitic of the shells involved in an element and so called as characteristic radiation. Bremstrahlung radiation or Breaking radiation
When the projectile electron approaches the nucleus of the atom avoiding the orbital electrons, it slows down, due to the opposite charges, and gets difflected from its original course. During this the incident electron loses its kinetic energy, due to its slow down, and this loss of kinetic energy is emitted as X-ray photon. The X-ray produced by this type is called bremstrahlung or breaking radiation. The incident electron may also collide with the nucleus at times, converting all its kinetic energy to a single X-ray photon. TYPES OF X-RAY APPARATUS
X-rays remain the main domain in diagnosis although various other imaging specialities were later explored and being practiced. The main reason behind this is the cost of the equipment involved in the latest imaging techiniques. This makes use of X-rays for its wide application amd so also its potential harmful effects. Hence physics of X-ray production and priciples involved must be explained. Matter in the universe is a substance made up of mass and occupies space. Einstein law of conversion of energy states matter and energy can neither created nor destroyed as its mass, energy or charge remain unchanged Like matter, energy may exist is many forms eg: Kinetic energy, electric energy, potential energy, chemical energy, nuclear energy, heat energy, electro magnetic energy etc. energy of one form can easily be converted into another form. For example X-rays are produced in X-ray machine from electrical energy.
MODULE-21: FACTORS INFLUENCING PRODUCTION OF X- RAYS Learning objectives This module deals with
Factors affecting radiographic quality FACTORS AFFECTING RADIOGRAPHIC QUALITY
An good diagnostic radiograph is one is which there excellent details, correct density and the proper scale of contrast. The proper use of various radiographic exposure factors KVP, mA Time and FFD are employed.
Detail
Detail is the degree of definitions of an object on a radiograph. Good detail is the true reproductions of an object. The factors affecting the detail are: o Shorter Focal Spot film distance. (FFD) o Closeness of the object to the film. o Use of intensifying screen. o Movement of either the patient, cassette on movement of the machine. o Screens, film contrast. o Over exposure or under exposure. o Focal spot size. o Any condition fogging the film will bring out loss of detail.
Density
Radiographic density is determined by the amount of light absorbed by an exposed x-ray film and is a measure of the degree of blackness of the film. Radiographic density is affected by te subject density which the weight per unit volume of different body constituents. The density of the radiograph varies directly with milliamperage, provided all other factors remains constant. Higher milliamperage produces more x-rays and thus more density and lower milliamperage results is less density. Radiographic density varies directly with exposure time.Radiographic contrast is the difference in density between the image of parts or structures on the radiograph.
Contrast
Contrast is the difference between blacks, grays and whites. There can be long scale contrast and short scale contrast. Radiographic contrast varies inversely with the kilovoltage. The lower the kv produces a radiograph with a “short scale of contrast”. Secondary radiation and scattered radiations causes lack of contrast. Improper development of film and use of warm developer cause lack of contrast.To get good radiograph in veterinary patients the following technique should be followed o Fastest exposure time possible (To prevent movement blur) o Higher kvp.
o o
Constant distance Constant milliamperage
Viewing of the radiograph
Radiograph should be viewed on a good, evenly lit viewing box, in a semi darkened room. Over exposed film should be viewed against bright light. Though provisional diagnosis can be given on a wet film, it is advisable to wait till the film is dry, before giving final diagnosis. When viewing radiographs of the dorsoventral or ventrodorsal or skull, the left side of the film should be facing the viewers right side and when viewing the lateral views it would be better that the anterior aspect should be directed towards the left side of the viewers. Always follow the same conventions. To give radiological interpretation the viewer must have a comprehensive data of clinical and physical examinations and also have a knowledge of the range of radiological animal anatomy and for this a library of normal films taken in the standard position is an asset.
MODULE-22: PRINCIPLES OF VIEWING AND INTERPRETING X - RAY FILMS Learning objectives
------- This module deals with,
Handling of X-rays Viewing of X-rays Interpretation of X-rays HANDLING, VIEWING AND INTERPRETATION OF X-RAYS
Handling
Cassettes with exposed film should be opened in a dark room and the film is removed by holding the corners. The film is loaded in a suitable size cassette and stored in lead lined boxes.
The loaded cassettes and the exposed film cassettes are kept with radiopaque surface upwards. Unexposed film boxes are always kept in lead lined boxes.
Viewing
Radiography should be viewed on a good evenly lit viewing box in a semi darkened room. Dorsoventral chest, ventrodorsal abdomen or skulls are viewed with a right side of the film facing the viewer’s left side. Lateral view radiographs are viewed by placing it facing left. Radiographs of extremities are viewed with lateral aspect on left side of the viewer.
Interpretation
The three important factors to be considered before interpreting a radiograph are o Case history, o Physical examination and o Correct radiographic technique.
Radiographic diagnosis
Radiographic diagnosis consists of two parts namely location of the lesion and classification of the lesion. Location of the lesion requires knowledge of normal radiographic anatomy, basic radiographic signs in terms of changes such as size, architecture, contour, density, position and function. A systematic and methodical examination of each radiograph will prevent overlooking unexpected lesion.
Classification of Lesion---The lesions in the radiograph are classified as developmental, metabolic, traumatic, infectious, neoplastic, and degenerative. Module 23 - RADIOLOGICAL PATHOLOGY OF THORAX Cardiomegaly
Outline of the heart becomes more rounded. Occupies a much larger area of the thorax. Trachea and major blood vessels are seen displaced. Posterior border of heart becomes straighter.
Cardiac silhouette in contact with sternum and diaphragm.
Bronchitis
Slight increase in the radio-density of the bronchial tree
Pneumonia
Areas of increased density of lung substance. Areas of consolidation can be visualized
Pneumothorax
Collapse of the lungs. Presence of air in the pleural cavity Floating heart shadow
Fluid in the pleural cavity
Fluid shadow will be masking the structures in the thorax. Fluid level appears as area of increased density. Typical leafy appearance
Diaphragmatic Hernia
Disappearance of the normal diaphragm line. Displacement of lungs and visualization of part of GI tract in thoracic cavity.
Tuberculosis
Areas of opacity in lung parenchyma Recognition of cavitations and calcified nodules in the lung parenchyma or pleura.
Module-24 = RADIOLOGICAL PATHOLOGY OF ABDOMEN Gastric torsion
Greatly distended gas filled organ occupying the major portion of the anterior abdomen. Compartmentalization of stomach.
Oesophageal achalasia
Distended organ occupying the upper half of the chest in the lateral view Dorsoventral view-distended organ projecting beyond the shadow of the spine
Oesophageal foreign body
Thickening of the oesophageal wall Increased density from that of the surrounding tissues.
Pyloric Obstruction
Enlargement of the stomach Accumulation of fluids/material (accumulation of barium) in pyloric area.
Intussusceptions
Sausage shaped mass with increased density Thin layer of gas outlining the layers of intussusceptions Barium enema- ‘coiled watch spring’ pattern.
Hydronephrosis
Large mass with a smooth outline in the anterior abdomen filled with fluids, with appearance of homogenous density
Kidney calculi
Small irregular dense areas roughly central to the kidney outline
Cystic calculi
Radiopaque cystic calculi easily visualized slightly radiopaque calculi can be demonstrated by using penumo cystography.
Prostate enlargement
Relatively dense mass just anterior and ventral to the pelvic brim in the position normally occupied by the bladder, which is displaced anteriorly.
Metritis and pyometra
Slight thickening and enlargement of uterus- may be uniformly tubular or sacculated. Displacement of the colon.
Module-25 = RADIOLOGICAL PATHOLGY OF Limb (BONES AND JOINTS ) Radiographic signs of bone diseases
Altered contour of the bone Altered size of the bone Decreased one density Change in trabecular pattern
Radiographic signs of joint diseases
Widening or narrowing of the joint space Cystic changes Swollen joint capsule-soft tissue swelling
Osteoporosis
Diminished density of the bone.
Small animals
Hip dysplasia o Bony exostosis, new bone formation involving acetabulum- thickened disorganized appearance of the femoral neck-remodeling and flattening of the femoral head. Hip dislocation o Abnormal width of intra articular space. Long bone fractures o Disruption of the continuity of a bone
Module-26 = CONTRAST RADIOGRAPHY - CLASSIFICATIONS
Radiography is founded upon the principle that an object when exposed to an incident x-ray beam will absorb a part of the x-ray beam and a part willpenetrate the object and interact with the film. Radiodense objects absorb larger percentage of the x-rays than radiolucent objects resulting in less film exposure and the recording of white object image. In other words, the absorption of x-ray by the tissues of the body, and thus their radidensity, depends upon the atomic weight of the principal substances of which the tissues are composed. That means absorption capacity of an organ or object is directly proportional to the number of orbital electrons in the atom of the molecule of the absorbing material (atomic number). Comparison of equal volumes of different tissues/with their densities.
Density
Barium - 56 Bone - 14 (Average) Muscle, Organ, fluid Soft tissue 7.4 (Average) Fat - 6.3 Gas (Air) - 1 to 2 The differences in density (radiographic contrast) between bones, muscles, fat and gas form the basis of plain film radiography. Ex: Kidney is seen clearly in a plain radiography if there is perirenal fat around the organ. Bone is clearer because of surrounding soft tissues. But the kidney pelvic is not visible or the mucous pattern of bladder or stomach are not seen normally due to lack of contrast. Artificial methods of delineating such organs are required and so a suitable contrast medium is employed. The contrast medium may have either high atomic weight and provide positive contrast or a low atomic weight and provide negative contrast. Examples of positive contrast media re Barium sulphate, organic iodine compounds. Examples of negative contrast media area co2, o2 and N20 or atmospheric air.
Positive contrast agents
Positive contrast agents can be precisely classified and may be divided into five main groups. Agents used for the demonstration of Alimentary tract.
The substance used for this purpose should be insoluble and non absorbable and inert. The substance used routinely for this purpose is barium sulphate.
Water soluble agents
These form the largest single group of contrast agents. The ideal criteria for the contrast media included in this group are that they should be (1) opaque to xrays and they all contain iodine (2) pharmacologically inert (3) very water soluble so that they can be injected at high concentrations (4) chemically stable so that the iodine is not released in the body (5) rapidly excreted by the kidneys; (6) of low viscosity for injecting quickly through a small catheter and (7) of low toxicity and irritancy so that large quantities can be employed. The conventional water soluble contrast media are ionic and are therefore hypertonic and their osmolality ranges from 4 to 7 of that of blood. The newer low osmolar non-ionic contrast agents have ratio 3 contrast as compared to the conventional high osmolar ionic contrast agents which have only ratio 16. Contrast property. Ex: Conray, Urografin (Ionic agent); Iohexol, Iopamidol metrizamide (non-ionic) Agents excreated selectively through biliary system to study the gall bladder, after absorption from alimentary system or intravascular injection. Ex: Biligrafin and Ipodate calcium powder (solu-Biloptin) (Scheringe).
Viscous and oily agents
These agents are developed to overcome immediate climination which occure with the water soluble preparation. Viscous solution are used to demonstrate bronchial tree and the uterus. Oily solutions are used in those situation in which it is essential to avoid even the slightest local irritation once introduced they are slowly climinated.
Radiographic quality
Gaseous agents: Are those most frequently employed. They are cheap easy to administer and are comparatively safer.
INTRAVASCULAR CONTRAST AGENTS AND CONTRAST RADIOGRAPY CONVENTIONAL IONIC MEDIA Generic name Proprietary name Meglumine iothalamate Conray-280 Sodium iothalamate Conray-420 Meglumine diatrizoate Urografin-150 Sodium diatrizoate Urografin-370 NEW LOW OSMOLAR NON-IONIC MEDIA Metrizamide Amipaque
Iopamidol Iohexol
Niopam Omnipaque
MODULE- 27 :-CONTRAST RADIOGRAPHY OF THORAX & ABDOMEN => THORACIC CAVITY Angiography
The radiographic demonstration of the vascular system by the injection of a water soluble organic iodide compound into a suitable vessel. Specialized techniques o Arteriography-Arteries o Venography-Veins o Aortography-aorta o Portal venography–Portal vein o Angiocardiography-Heart and vessels o
Cerebral angiography–Cerebral vessels.
o
Technique-
Contrast agents are injected rapidly by means of a syringe of an appropriate volume connected to a hypodermic needle or cannula or catheter which is inserted into a suitable blood vessel. Radiographs are taken immediately on completion of the injection. ALIMENTARY TRACT
Indications
To reveal obstruction of the alimentary tract. Ex: Tumour or stenosis. To find out distorsion of the wall of alimentary tract such as enlargement. Ex: Dilatation of stomach or oesophagus. To find out displacement of the alimentary tract. Ex: Hernia. To reveallesions in the wall of the alimentary tract. Ex: Neoplasms – Ulcer.
Procedure
Oesophaqus o No preparation is required. Take plain radiography and administer Barium sulphate paste about 50 to 100 Gms. Orally (Braium Swallow) and taken with lateral and ventrodorsal projections immediately after administration. o Normal oesophequs should not retain bacium. Only a thin streak of barium indicating the position of the oesophegus and outlining the
mucous surface is seen as normal oesophagus is a collapsed tubular structure. Stomach o 50 to 100% suspension of about 15 to 100 ml. Is given orally observed under fluoroscopy or x-rays are taken at regular intervals 10 minutes, 30 mts, 1 hr. and 4 hrs. etc. at different angles like left lateral, right lateral, ventro dorsal and oblique if necessary to demonstratethe different areas of stomach and mucosal surface. o The stomach should be empty by starving overnight or by administering laxative or enema if necessary. o Normal stomach start emptying the barium within minutes after the administration. Space occupying lesions or obstructive lesions can be easily demonstrated. Small Intestine o To promote easy passage of the contrast agent 25% suspension is preferred. Repeated x-rays at interals could demonstrate lesions inside or outside the intestine easily. Intestinal motility can be assessed. Large Intestine o To demonstrate large intestine barium is best given by enema. Double contrast gastrography or colonography can be obtained by combining air (negative contrast agent) The functional and anatomical abnormalities could be better assessed by means of flucroscopy apparatus, if available.
MODULE- 28 :- CONTRAST RADIOGRAPHY OF SPINAL CORD & URINARY SYSTEM = MYELOGRAPHY
Indication
To outline the neural canal To demonstrate disc lesions and other space occupying lesions. Contrast agents used o Oily fluid containing 40% iodine (Ex. Myodil). o Water soluble: Metrizamide soluble. Iohexol, Iopamidol solution.
Technique
Cysterna puncture Lumbar puncture Under general anaesthesia the contrast agent is injected into the sub-arachnoid space. In the first method cisterna magna is punctured and in the second
method sub-arachnoid puncture is made using a spinal needle between 4th and 5th Lumbar vertebral space in lateral recumbent position.If myodil is used the quantity is 0.5 to 2 ml. Per animal. The animal may be positioned in an inclined plane for easy flow caudally. Pictures are taken at 5 mts. And 10 mts. Interval under lateral and ventrodorsal projection. If Metrizamide or any other water soluble agent is used, 0.3 ml. To 0.5 ml/kg.body wt. Is injected into the subarachnoid space and x-rays are taken immediately. The advantage of the new water soluble non-ionic solution is that it gives better visualization of the spinal canal and the agent gets eliminated within few hours. In the case of oily agents the contrast material will tend to globulate and remain in the canal for longer period causing at times undesirable side effects. UROGRAPHY: (PYELOGRAPHY AND CYSTOGRAPHY)
Intravenous urography (Intravenous pyelography, IVP)
Pyelography is used to demonstrate kidney shadow when it cannot be demonstrated in a straight radiography. To show the presence or absence of lesions in the renal pelvis. To get a rough indications about renal function. Contrast agents used o Ionic contrast agents such as sodium Iothalamate (conray-420); Meglumine Iothelamate (conray-280); Sodium and Meglumine diatrizoate (Uregrafin 60% or 76%); Sodium diatrizoed (Hypoque). Non-ionic contrast agents such as Iohexol (Omnipaque-300); Iopamidol (Niopem) Metrizamide have also been used. Dosage: To give better demonstration upto 600 mg to 1200 mg/kg. Body weight may be administered I/V usually 1 to 2 ml/kg. Body weight. Preparation: With hold food for 24 hrs. and water for 12 hrs. Empty the bowels with enemata. Anaesthesis as optional Technique o Inject the dyeasa single bolus I/V by taking about 1 minute. Straight firms may be taken before injection and subsequent to injection at 1 mt. 5 mts., 10 mts. And 20 mts. With ventrodorsal and lateral projections. Use of a compression bandge over the abdomen will enhance the clarity of renal pelvis and ureter. o This technique is popularly known as intravenous pyelography or excretory urography. Another method to carry out this procedure is to mix the contrast agent about 1200 mg/kg. With 150 to 250 ml. Of normal saline and given by drip taking about 20 to 40 mt. Time to give more accurate evidence of kidney function and is a safer method.
Cystography
Indications
1. To recogrise radiolucent small calculi 2. To demonstrate space occupying lesions in the bladder. 3. To demonstrate abnormal prostate gland. Preparation: The G.I. tract should be empty. Iodine compund 10 to 20% about 40 to 100 ml. Are employed after catheterizing the bladder. Procedure: After evacuating the bladder, inject the contrast agent either iodine solution or air (100 to 300 ml). Radiography is taken (lateral & ventrodorsal projections). For double contrast small quantity of iodine solution followed by air may be used for better visualization of the interior of bladder.
Module- 29 =RADIATION HAZARDS AND ADOPTION OF SAFETY INCREASERS Dangers of radiations
Ionising radiation used in diagnostic radiography is potentially harmful and if proper protective measure are taken the risk is small compared with the benefit to the patient. Certain tissues especially those which contains many multiplying cells, such as blood forming organs (bone marrow, lymphoid tissue, spleen), the gonads, embryos and cetain tumours are radiosensitive. X-rays have long term effect of producing Cancer, long after irradiation injury has healed.
MODULE-30: ULTRASONOGRAPHY - PRINCIPLES AND ITS APPLICATION IN VETERINARY PRACTICE Learning objectives This module deals with
Principles of ultrasonography Properties of ultrasound waves Different modes of echo display PRINCIPLES OF ULTRA SONOGRAPHY
Introduction Medical sonography is the only diagnostic imaging modality that does not use electromagnetic radiation. Modern ultrasound instruments are highly sophisticated pieces of equipment. A basic understanding of the physics of ultrasound, its interactions with tissue and the functions of the controls are important while using the machines. In 1957 – Ian Donald invented – scanner or diagnostic ultrasound. What is ultrasound?
Sound waves of frequencies greater than audible to the human ear i.e greater than 20- 20,000 Hz. is called Ultrasound waves. Diagnostic ultrasound uses frequencies between 1 to 10 MHz A sound wave travels in a pulse or a wave and when it is reflected back it becomes an Echo and this pulse-echo principle, is used for ultrasound imaging. A transducer is a device that converts one form of energy to another. The piezoelectrical crystal in an ultrasound transducer generates a pulse. When this crystal is stimulated electrically it changes its shape and produces sound waves of a particular frequency. Mechanical transducers are devices where the movement of crystals suspended in a coupling medium generates ultrasound.where as
electronic transducers also called array transducers do not have intrernal coupling medium and are fired electronically.
How is ultrasound generated?
When a high voltage electrical current is applied crystals in the transducer are vibrated and this is called piezo electric effect. A sound wave travels in a pulse and when it is reflected back it becomes an Echo. It is this pulse-echo principle, which is used for ultrasound imaging. A pulse is generated by one or more piezoelectrical crystal in an ultrasound transducer. When this crystal is stimulated electrically it changes its shape and produces sound waves of a particular frequency. As the transducer is placed in close contact with the body surface through a coupling medium it undergoes continuous modification, which occurs through three processes those are absorption, reflection and scattering. By means of the echo principle, an image can be produced on the display of the scanner which relates to the acaustic independence of tissues encountered by the ultrasound beam and the depth / distance of tissue interfaces.
PROPERTIES OF ULTRASOUND WAVES
Frequency, wavelength and velocity are parameters used to describe the sound waves. Diagnostic ultrasound frequency ranges between 2 mega Hertz and 13 mega Hertz. Wave length is the distance travelled by the sound in one cycle and is expressed in millimeters and is important for image resolution. Velocity is the rate at which sound travels through an acoustic medium. As a rule it is greatest in solids, lower in liquids and lowest in gases.Medically sound waves travel fastest in bone and slowest in gas filled structures. This causes a problem for diagnostic ultrasound machines, because they use the average velocity of sound in soft tissue 1540m/s.
Interaction of ultrasound with matter
Absorption: It occurs when the tissues absorb heat energy in the sound beam. Absorption process forms the basis of therapeutic ultrasound. Reflection: The reflection gives rise to an echo and forms the basis for ultrasound scanning. Interfaces between tissues of different acoustic impedence give rise to different echoes. These echoes are converted by piezoelectric effect into electrical signals and displayed onto a oscilloscope screen. Scattering: It occurs when the beam encounters an interface that is irregular and smaller than the sound beam. The portion of the beam than interacts with this interface is scattered in all directions. Since the scattering interfaces are small, only a small portion of the beam is involved. Once the echoes are converted into electrical signals, these are processed and transformed into a visual display of the measure of the amplitude of the echo. This is known as echo quantification.
Generation of images on the display
Two basic shapes of ultrasound images are encountered: images made in sector fashion are pie shaped and linear fashion are rectangular Images are usually generated from the systemic scanner converter or frame store which processes the reflected ultrasound in to a form required for screen presentation. Information is displayed regarding distance and amplitude. Each echo position is represented as a dot on the screen. Thus a two dimensional image is generated. The brightness of each dot is related to the amplitude of the reflection and is referred as a grey scale display. Resolution is the ability of the ultrasound machines to distinguish echoes on the basis of time, space and strength. o Axial resolution: Ability to differentiate two objects lying closely together in the direction of the beam. o Lateral resolution: Ability to different the two objects lying side by side. The ultrasound beam is refracted when it enters a tissue of different acoustical density. The image of refraction depends on the relative velocity of sound in the two tissues. Depth of sound wave penetration varies inversely with frequency. DIFFERENT MODES OF ECHO DISPLAY
Different modes of echo display
Different modes of echo display are Brightness mode, B – mode B scan or grey scale used commonly for abdominal scanning and cardiac imaging. Static B mode: Transducer is moved in the scanning plane by hand.
Real time B mode: Sound beam automatically and rapidly moves in the scan plane. In this method the image is continuously updated to allow movement. Motion mode: M–mode mainly used for echocardiography. A MODE or amplitude mode is simplest form of display. It displays two parameters of the echoes in the form of spikes, ie., distance from the transducer and the amplitude. The horizontal line shows the distance and the amplitude is depicted on the vertical line. It is used for ocular biometry.
Different types of basic probes
Linear curvilinear and sector probes Transducers are classified based on the location of crystals on the scan head. When elements are located at the end of the probe they are called end fire transducers and they are used in abdominal and cardiac scanning. Side fire trasducers are used for intracavity scanning like large animal reproductive scanning.
Doppler ultrasonography
The pitch of a siren in a train changes with the proximity of the train movement, due to difference in the sound wave frequency, called Doppler shift, the principle used in imaging the direction and velocity of blood flow. It was first proposed by Johann Christian Andreas Doppler in 1842. Four Doppler modes are used in medical ultra sonography. They are Continous wave Doppler, pulsed wave Doppler colour Doppler and power Doppler.
MODULE-31:- RADIATION THERAPY - PRINCIPLES, ISOTOPES AND THEIR USES IN DIAGNOSIS AND THERAPY Learning objectives This module deals with
Radiation therapy and its methods Complications 0f radiation therapy RADIATION THERAPY - INTRODUCTION
Radiation therapy for the treatment of neoplasm of domestic animals has been used since the discovery of X-ray. Dr. R. Eberlin was the first to report on the use of radiotherapy in veterinary practice.
Radiotherapy is usually indicated for localised solid neoplasm’s that cannot be excised completely. It is not indicated if neoplasm has the potential of high incidence of metastasis. The other indication are : 1. When surgery is expected to or has already failed. 2. When the regional or distant metastasis not occurred. 3. When radical surgery is unable to remove whole of the neoplasm. 4. When bulk of the neoplasm needs reduction in size so that it can subsequently be removed surgically. Radiotherapy is not done by a single dose, rather multiple treatments are given over a period of time, termed fractioned therapy. In animals, it is usually in 10-12 fractions of a radiation dose of 4-5 Gy each time, usually three times per week.
METHODS OF RADIOTHERAPY Teletherapy
The radiation source is kept at a distance from the lesion. It is of four types o Superficial X-ray therapy: Given through X-ray machine with energy range of 60-100 keV. o Deep X-ray therapy: Given through X-ray machine with energy range of 100- 200 keV. o Super voltage therapy: Provided through (i) X-ray machine having linear accelerator or betatron or cyclotron, (ii) isotropic Xray machine with cobalt or cesium. It is used in deep and substantial lesions o Particulate beam therapy: Electron, neutron or proton beam can also be used as a mode of teletherapy.
Brachytherapy
It is the therapeutic use of radioisotope either within the interstitium or on the surface of a neoplasm. The isotopes used are 198 Au , 60 Co, 125 K. Specific methods of brachytherapy are o Interstitial brachytherapy: Sources of radiation are within the interstitium of the neoplasm. o Pliesotherapy: It is surface brachytherapy for superficial lesions. o Systemic brachytherapy: 132 I and 32 P can be used systemically. It is used in extensive lesions and specific malignant conditions.
COMPLICATIONS OF RADIOTHERAPY
Complications of radiotherapy are o Immediate (minute to days): epilation, erythema , hematological depression and GI disturbances and chromosomal aberration. o Latent (months to years): leukemia , life span shortening , cancer, lethal gene expression etc.
MODULE-32: SCAN AND MRI - PRINCIPLES AND THEIR APPLICATION Learning objectives This module deals with
Digital Radiography (DR) Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Nuclear Medicine DIGITAL RADIOGRAPHY (DR)
Basic principles
DR involves translating x-ray energy into an electric signal that is in turn converted to digital data (numbers). The process may be direct, indirect, or hybrid. In direct DR, the x-ray energy is converted directly into an electrical signal. In indirect DR, the x-ray energy is first converted to light by using a phosphorescent plate; the light is then converted to an electrical pulse. The data are recorded on a plate, which is connected to a computer, and the x-ray image is available for viewing almost immediately after exposure. It can then be stored or printed out. Hybrid radiographic processes record the output of the phosphorescent plate with a system
similar to that found in a digital camera. CR and DR systems have a number of advantages compared with film screen systems. The linear response of digital systems to the x-ray exposure means that these systems are relatively forgiving of errors in radiographic technique. However, the quality of DR images depends on software processing to produce a degree of contrast that is familiar to the reader. DR and CR images are stored on a computer hard drive and should be saved as DICOM (Digital Imaging and Communication in Medicine) files. Some form of backup device is recommended, ideally at another location. The images may be quite large files, but they can be easily transmitted to a remote location for review by a radiologist or other specialist. These images may be manipulated in multiple ways, including adjusting brightness and contrast, applying sharpening filters, inverting the image, and magnifying part or all of the image.
COMPUTED TOMOGRAPHY (CT) Basic principles
CT is an imaging method that uses the principles of tomography. Tomography is the demonstration of a slice through the body displayed without interference from structures lying above or below the level under examination. CT uses x-rays generated by a high-output x-ray tube. The tube is mounted on a gantry opposite a series of detectors. The tube and the detectors rotate in unison around the subject under examination. A fanshaped beam of x-rays passes through the body at a predetermined level. The pattern of x-rays that reaches the detectors is recorded—a projection. The entire gantry assembly is then rotated slightly, and the procedure is repeated, generating a new projection. A series of such projections is obtained, completely encompassing the body under examination. A computer uses complex mathematical formulas to create an image from the series of projections. This image represents a slice of the body at the level under examination. The advantage of CT is its ability to distinguish different types of soft tissue, such as brain white and gray matter or liver and gallbladder. CT
achieves this degree of contrast by being able to measure very fine differences in the ability of tissues to stop x-rays passing through them. CT images are digital, and a computer is used for viewing. The gray scale can be adjusted to highlight specific features such as bone or soft tissue (windowing). In CT imaging, tissues and structures are described in terms of attenuation, which is a measure of the capacity of a tissue to stop x-rays. Attenuation is equivalent to radiopacity in radiography. The appearance of a tissue is defined in relation to some reference tissue or its expected normal appearance. Thus isoattenuating means having the same attenuation and would be displayed as the same shade of gray. If the tissue attenuates or stops the x-rays less than the reference tissue or less than expected, it is described as hypoattenuating and is portrayed as a darker shade of gray. The term hyperattenuating is used to describe tissues with more attenuation than expected. These terms are relative rather than absolute, and the reference tissue or structure is usually stated. Superimposed structures are eliminated. Iodinated contrast agents such as those used for myelography or excretory urography may be used by intravenous injection. Lesions with abnormal circulation may show marked contrast enhancement after such injections. In viewing CT images, brightness and contrast are adjusted to highlight specific structures. CT can resolve far greater contrast than can be displayed on a monitor or appreciated by the human eye. Therefore the gray scale of the image is adjusted to assign useful grays to tissues with varying levels of attenuation, referred to as the window. A lung window will show detail within the lungs, but almost all other structures appear white with little detail. A bone window will display detail of skeletal structures such as cortex and trabeculae, whereas soft tissues appear gray with little detail and lungs appear quite black. A soft tissue window shows good contrast and detail within soft tissue structures such as the liver. Hepatic veins can be distinguished from the gallbladder and other soft tissues, whereas bone appears white and lungs dark. CT may be used to image almost any body part. Among the more common applications are diseases of the nasal cavity, sinuses, and ears. It may also be used to evaluate the spine, brain, joints, lungs, mediastinum, pleural cavity, and abdominal masses MAGNETIC RESONANCE IMAGING (MRI)
Basic principles
Unlike CT, no ionizing radiation is used in magnetic resonance imaging (MRI). MRI uses hydrogen atoms to generate an image. Hydrogen is universally distributed in the body, principally in water molecules.
Hydrogen atoms are essentially spinning protons and have an electrical charge. Each atom acts as a tiny bar magnet. Under normal circumstances, these tiny magnets are arranged randomly. MRI uses relatively strong magnetic fields, ranging from 0.05 to 3.0 tesla in clinical use. In a strong magnetic field, a small majority of the protons will be forced to point in the direction of the field while spinning at a specific rate. A radio signal pulse at the same frequency as the spin of the protons will knock them out of their equilibrium state. As the protons return to their original state, they release energy in the form of a radio signal, effectively an echo of the original pulse used to disturb the protons. This signal is collected by a scanner, processed, and displayed. Smaller gradient magnetic fields are used to localize signals from specific blocks of tissue. Whereas CT offers good soft tissue detail, the contrast seen with MRI is superb. Different sequences of radiopulses can be used to emphasize different tissue characteristics. Manipulation of the parameters such as the timing and duration of the radiopulse and the interval before an echo is recorded is used to highlight tissue features. MRI has superb contrast resolution in soft tissues and is very sensitive to changes such as edema and hemorrhage. Signal intensity is used to describe the appearance of tissues in MRI, just as attenuation is in CT imaging. It is a relative measure of the radio signal generated by tissues in response to the stimulating radio energy pulse. If something is termed isointense, it has the same appearance as some reference tissue—for example, a mass might be isointense to the gray matter of the brain. Hypointense means less signal and appears darker, whereas hyperintense means more signal and a brighter appearance. As in CT, these terms are relative and must be defined in relation to the expected normal appearance, reference tissue, or appearance before the use of contrast. Bones, ligaments, and tendons appear quite dark on all image sequences because they have very little water content and therefore very little hydrogen to generate a signal. Nonetheless, MRI can provide useful data about these structures. Like CT, MRI uses contrast agents that enhance lesion visibility. However, in the case of MRI, the agents are based on gadolinium, which alters the local magnetic field and changes signal intensity. Lesions that accumulate gadolinium appear bright (hyperintense) with some sequences. MRI is capable of distinguishing or resolving objects of approximately 1 mm in size, which is termed spatial resolution. This is similar to CT but compares poorly to radiographic systems, which can resolve objects of 0.1 mm in size. MRI has excellent contrast, showing different soft tissues as distinct shades of gray, which creates the impression of much finer detail.
Unlike CT, which is limited to images in the plane of the gantry, images can be obtained in any plane, so slices can be varied infinitely to highlight lesions. MRI applications include imaging disease of the central nervous system, nasal cavity and sinuses, joints, and the abdomen. NUCLEAR MEDICINE (SCINTIGRAPHY)
Basic principles
Scintigraphy is a branch of nuclear medicine. It is an imaging technique in which radionuclides (radioactive elements emitting gamma rays) are administered to a subject. The radionuclides are attached to chemicals to form radiopharmaceuticals that accumulate in the tissue of interest. Mostradiopharmaceuticals are analogues of physiologic substances or biologic organic molecules. Their presence, and their concentration, can be detected by gamma-ray detection equipment—usually a gamma ray camera. The gamma rays are converted by the camera into signals from which a computer produces a digital format that is used to construct an image of the area under examination. Nuclear medicine images are described in terms of uptake of the radiopharmaceutical. The degree of uptake is subjectively assessed in some techniques, while in others quantitative analysis is performed. In this way normal and abnormal tissues can be identified by the selective accumulation of the radioactive substances within them.
MODULE - 33 :ECOCARDIOGRAPHY - PRINCIPLES AND ITS APPLICATION Learning objectives This module deals with
Doppler Ultrasound Types of Doppler Ultrasound Applications of Doppler Ultrasound DOPPLER ULTRASOUND
A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. It helps to evaluate blood flow through major arteries and veins, such as those of the legs and neck. It can show blocked or reduced blood flow through narrowing in the major arteries of the neck that could cause a stroke. It also can reveal blood clots in leg veins (deep vein thrombosis, or DVT) that could break loose and block blood flow to the lungs (pulmonary embolism). During pregnancy, Doppler ultrasound may be used to look at blood flow in an unborn baby (fetus) to check the health of the fetus. During Doppler ultrasound, a handheld instrument (transducer) is passed lightly over the skin above a blood vessel. The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). If there is no blood flow, the pitch does not change. Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. These graphs or pictures can be saved for future review or evaluation. See a picture of a Doppler ultrasound. TYPES OF DOPPLER ULTRASOUND
The basic types of Doppler ultrasound are
"Bedside" or continuous wave Doppler: This type uses the change in pitch of the sound waves to provide information about blood flow through a blood vessel. The veterinarian listens to the sounds produced by the transducer to evaluate the blood flow through an area that may be blocked or narrowed. This type of ultrasound can be done at the bedside in the hospital with a portable machine to provide a fast estimate of the extent of blood vessel damage or disease. Duplex Doppler: Duplex Doppler ultrasound uses standard ultrasound methods to produce a picture of a blood vessel and the surrounding organs. Also, a computer converts the Doppler sounds into a graph that gives information about the speed and direction of blood flow through the blood vessel being evaluated. Color Doppler: Color Doppler uses standard ultrasound methods to produce a picture of a blood vessel. Also, a computer converts the Doppler sounds into colors that are overlaid on the image of the blood vessel and that represent the speed and direction of blood flow through the vessel. Power Doppler is a special type of color Doppler. Power Doppler can get some images that are hard or impossible to get using standard color Doppler. Power Doppler is most commonly used to evaluate blood flow through vessels within solid organs.
APPLICATIONS OF DOPPLER ULTRASOUND
Non-invasive Generally painless Does not use radiation Can show if you have any blocked arteries in neck, arms, abdomen, coronary arteries and limbs Can show if you have any blood clots in the veins in limbs Can show the amount and speed of blood flow in your veins and arteries Can be used instead of some more invasive procedures further reading.
MODULE-34: PRINCIPLES AND APPLICATIONS OF SCINTIGRAPHY, GAMMA CAMERA, XERORADIOGRAPHY AND DOPPLER Learning objectives-This module deals with- Nuclear Scintigraphy NUCLEAR SCINTIGRAPHY
Scintigraphy ("scint," Latin scintilla, spark) is a form of diagnostic test used in nuclear medicine, wherein radioisotopes (here called radiopharmaceuticals ) are taken internally, and the emitted radiation is captured by external detectors (gamma cameras) to form twodimensional images.
The principle is based on the use of pharmaceutical labelled with radioisotope which after entry into the blood stream get localised in particular tissue or organ. Thus the localisation of radioisotope can be detected by using camera due to emission of gamma rays. Most widely used radioisotope is Technetium-99m. This isotope has the advantage of a short half life of 6hrs and thus animal can be discharged next day after the scan . in addition, radiation exposure is minimum. The distribution of the labelled isotope can be detected by a gamma camera or a hand held detector. In both the case sodium iodide crystalis used which absorbs gamma rays emitted by the radioisotope from the patient and converts it to light flashes. The light is converted to an electrical impulse. This impulse is shown on a oscilloscope or converted to an image. Image can be produced in colours or in a grey colour. A scan appears as a image formed of dots. The interpretation is based on the appearance of increased (hot spots) or decreased (cold spots) radioactivity region. Active process produces hot spots where as cold spots observed in case of abscess. It is mainly used to detect functional disorders of kidney, liver , GI tract, lungs thyroid glands etc. Using this technique it is easier to detect localised increase or decrease in bone turn over as a result of trauma or disease. Any inflammatory or pathological process that causes increased bone activity can be diagnosed by scintigraphy. Usefull in diagnosing occult lameness. It has also been used to study renal, cardiac, lung functions , images of vertebral column and detecting the neoplasms. Problems associated with scintigraphy are 1. Cost of the gamma camera 2. Precise and strict safety precautions required. 3. Non specificity to the aetiology and difficulty encountered some times in interpreting the scan especially skeletal system. ------------------------------------#@#------------------------------------------------------------THE END
