Systemic Complications of Local Anesthetics
Done By: Alaa Mourad Course title: Anesthesia Term: Fall 2015/2016 Outline:
- Introduction - Overdose reactions, Allergy, and Idiosyncrasy - Systemic Complications Cardiovascular system complications Nervous system complications complications Endocrine system complications Hematologic complications Liver complications Immunologic complications - References Introduction
•
The administration of local anesthetics is considered essential whenever potentially painful procedures are contemplated. contemplated.
•
Local anesthetics are extremely safe drugs when used as recommended. However, whenever any drug, including local anesthetics, is used, the potential for unwanted and undesirable responses exists.
•
Harmful effects of drugs range from:
-
Inconsequential to the patient and entirely reversible once the drug is withdrawn. Uncomfortable but not seriously harmful Seriously incapacitating or proven fatal to the patient.
•
Whenever any drug is administered, two types of actions may be observed: observed :
a. Desirable actions, which are sought and beneficial b. Undesirable actions, which are additional and are not sought. • Three principles are essential to be aware of: -
Principle 1: No drug ever exerts a single single action. Principle 2: No clinically useful drug is entirely devoid of toxicity. toxicity. Principle 3: The potential toxicity of a drug lies in the hands of the user.
Overdose reactions, Allergy, and Idiosyncrasy Overdose reactions
Local anesthetics are drugs that act to depress excitable membranes (e.g., the CNS and myocardium are the target organs for local anesthetics). With all local anesthetics, the dose administered varies with the anesthetic procedure, the vascularity of the tissues, the depth of anesthesia and degree of muscle relaxation required, the duration of anesthesia desired, and the physical condition of the patient. The smallest dose and concentration required to produce the desired result should be used. When administered properly and in therapeutic dosages, they cause little or no clinical evidence of CNS or CVS depression. However, signs and symptoms of selective CNS and CVS depression develop with increased blood levels in the cerebral circulation or myocardium.
Allergy
Clinical manifestations of allergy vary and include the following: - Fever - Angioedema - Urticaria - Dermatitis - Depression of blood-forming organs - Photosensitivity - Anaphylaxis Ester-type local anesthetics are much more likely to cause an allergic reaction compared to the amide-type local anesthetics because of the formation formation of PABA during the metabolic metabolic process. PABA may cause cause allergic reactions reactions that range from urticaria to anaphylaxis.
If a patient has an allergic response to either class, attempt using a product from the other class. Example: patient develops a rash with procaine switch to lidocaine. Alternatively, if a patient has a reaction to both classes, try using a preservativefree formulation such as lidocaine-MPF.
Idiosyncrasy •
A qualitatively abnormal, unexpected response to a drug, differing from its usual pharmacologic actions actions and thus thus resembling hypersensitivity. However, idiosyncrasy idiosyncrasy does not involve a proven, or o r even suspected, allergic mechanism.
•
Any adverse response that is neither overdose nor an allergic reaction.
•
It is almost impossible to predict which persons will have idiosyncratic reactions or the nature of the resulting idiosyncrasy.
•
Instances of idiosyncratic reaction have an underlying genetic mechanism. These aberrations remain undetected until the individual receives a specific drug, which then produces its nonpharmacological clinical expression.
•
Specific management of idiosyncratic reactions is difficult to discuss because of the unpredictable nature of the response. Treatment is symptomatic and includes: -
Positioning
-
Airway
-
Breathing
-
Circulation
The adverse effects of local anesthetics can be classified as: 1. Technique effects, such as needle trauma to a vessel. 2. Local effects of the drug, could be associated with its anesthetic activity or a consequence of irritation or allergy. 3. Systemic effects, most commonly observed if the agent is inadvertently injected into a blood vessel in sufficient sufficient quantities. 4. Additives effects, mostly vasoconstrictors to prolong the local effect, hyaluronidase to promote penetration, and preservatives preservatives to prevent bacterial contamination contamination
Systemic Complications Cardiovascular
Cardiovascular complications are not uncommon, however, most changes are moderate, involving: - Mild peripheral vasodilatation - Reduced cardiac output with a change in HR. Local anesthetics: - Reduce myocardial contractility and rate of conduction. - Cause direct vasoconstriction or vasodilatation of vascular smooth muscle - Cause central stimulation of the ANS. Cardiac arrest and marked myocardial depression, in which hypoxia plays a critical role, have been reported. CV collapse can be severe and refractory to treatment; most fatal cases involve bupivacaine. The CVS is more resistant to the toxic effects of LA than the nervous system. Mild circulatory depression can precede nervous system toxicity, but seizures are more likely to occur before circulatory collapse. The IV dose of lidocaine required to produce CV collapse is 7x that which causes seizures.
Nervous system
CNS effects of: - Low concentrations of local anesthetics: sedation and confusion - High concentrations of local anesthetics: seizures. The first signs of systemic toxicity: - mild sedation - diminished alertness - dizziness - tinnitus - metallic tastes - muscle twitching - perioral numbness - visual disturbances - disorientation - light-headedness Because the blood concentrations reached are sometimes higher than one would predict, toxicity can occasionally occasionally prove much more more severe than expected, expected, for example frank convulsions, sometimes progressing to respiratory arrest and loss of consciousness. LA-induced seizures have been reported more often with bupivacaine, particularly in combination with chloroprocaine
Endocrine
Local anesthetics generally have only slight endocrine and metabolic adverse effects, without clinical repercussions.
Hematologic
Methemoglobinemia has been reported with benzocaine, Cetacaine, cocaine, lidocaine, novocaine, and prilocaine. Acquired methemoglobinemia can result from exposure to chemicals that contain an aniline group, such as benzocaine and procaine, or to those that are transformed to metabolites that contain an aniline group, such as lidocaine and prilocaine. Factors that favor the onset of methemoglobinemia: - Toxic blood concentrations of LA - Aberrant hemoglobin - NADH-methem NADH-methemoglobin oglobin reductase deficiency deficiency
Liver
Reduced hepatic clearance , in addition to relative over-dosage, of LA can lead to systemic toxicity.
Immunologic
Systemic hypersensitivity reactions are not a frequent problem in local anesthesia. Systemic toxicity or allergy to additives add itives (hyaluronidase, bisulfate, parabens) has sometimes been improperly classified as hypersensitivity to LA True allergy occurrence is very low, most likely < 1% of all the adverse effects attributed to these substances. Type I hypersensitivity reactions and life-threatening anaphylaxis can rarely occur. Cross-reaction between amides also occurs, ex: articaine, bupivacaine, lidocaine, and prilocaine. Type IV delayed hypersensitivity reactions are uncommon, but allergic contact dermatitis and localized erythema and blistering have been reported. Contact hypersensitivity also occurs. Benzocaine is a potent skin sensitizer, and several cases of contact dermatitis to lidocaine have been reported. Pseudo-allergic reactions are often caused by LA when injected into the skin, w/ similar symptoms to immediate type allergy. However, true immediate hypersensitivity to LA is extremely rare.
References:
Meyler's Side Effects of Drugs Used in Anesthesia By J. K. Aronson, Pages: 79 – 84 Handbook of Local Anesthesia By Stanley F. Malamed, Chapter 18 (Systemic Complications) Figures: All images are copyrighted material and are the property of - The authors of Handbook of Local Anesthesia - Globalrph.com - Dentagama.com - Therichardcopley.wordpress.com - Dreamstime.com - Sagecreekhospital.ca - Accelrys.com - Iyad Abou Rabii, Immediate Past President at IADRPharmacology Therapeutic and Toxicology Scientific Group
