158 Nausea_vomiting Scale

British Journal of Anaesth Anaesthesia esia 104 (2): 158–66 (2010)

doi:10.1093/bja/aep370 doi:10.1093 /bja/aep370 Advance Access Access publication publication December December 26, 26, 2009

CLINICAL PRA PRACTICE CTICE Development and validation of a postoperative nausea and vomiting intensity scale R. Wengritzky1, T. Mettho1, P. S. Myles1 2*, J. Burke2 and A. Kakos2 1

Academic Board of Anaesthe Anaesthesia sia and Periope Perioperativ rative e Medicine, Monash Univers University, ity, Melbourne Melbourne,, Austr Australia alia and 2 Department of Anaesthes Anaesthesia ia and Periope Perioperativ rative e Medicine, Alfred Hospital, Comme Commercial rcial Road, Melbourne, Victoria 3004, Australia *Corresponding author. E-mail: [email protected] Background. Po Post stope opera rativ tive e nau nausea sea and vo vomit miting ing (P (PONV ONV)) is com commo mon n and of con concer cern n to patients and clinicians. The effect of PONV can range from trivial and transient to major clinical importance, and it is unclear which of its characteristics lead to discomfort and distress. Methods. We first enrolled 180 participants (patients, family members, nurses, doctors) to identify the characteristics of clinically important PONV, and from these data developed a measurement scale. We then evaluated the scale in a further 163 patients report reporting ing PONV. Validity alidity,, reliability reliability,, and responsiveness of the PONV Intensity Scale were tested using psychometric techniques. Results. Most participants agreed that three or more vomits, and greater nausea severity and duration, atio n, we were re key factors factors in defin defining ing clini clinically cally important important PON PONV V. Thes These e dat dataa we were re used to deri derive ve a PONV PON V Int Intensit ensityy Scale and a scor score e to defin define e clini clinically cally important important PONV. The scale iden identifie tified d 29 patients (18%) as having clinically important PONV. Patients with clinically important PONV had a poore poo rerr qua qualit lityy of re reco cove very ry (P ,0.0 0.0005 005)) and nee needed ded tw twice ice as muc much h ant antiem iemet etic ic tr trea eatm tmen entt (P ,0.0005). The scale was strongly associated with PONV consequences and complications, with odds ratios ranging from 6.0 to 31 (all P ,0.0005). The scale had excellent reproducibility (intraclass correlation 0.99, P ,0.0005). The scale could reliably reflect a clinically important change in health status (effect size 0.82, P ,0.0005). Conclusions. The PONV Intensity Scale is a valid, reliable, and responsive measure of clinically important PONV. Br J Anaesth 2010; 104: 158–66 Keywords : anaesthesia, general; complications; vomiting, nausea

Accepted for publication: November 23, 2009

The in The inci cide denc ncee of po post stop oper erat ativ ivee na naus usea ea an and d vo vomi miti ting ng (PONV) in an untreated adult surgical population receiving gen gener eral al ana anaest esthes hesia ia is ar aroun ound d 20– 30% 30%,,1 – 1 0 but thi thiss incr in crea ease sess up to 80 80% % in pa pati tien ents ts wi with th tw two o or mo more re ri risk sk 3 factors for PONV. Although PONV is sometimes viewed as a ‘m ‘min inor or’’7 pr probl oblem, em, and pa patie tients nts ma may y be wil willin ling g to forego for ego eff effect ectiv ivee PON PONV V pr proph ophyla ylaxis xis in pre prefer ferenc encee for betterr analg bette analgesia, esia,11 th ther eree ar aree po possi ssibl blee se seri riou ouss co cons nsee1 2 12 1 3 quences. Neverthel Neve rtheless, ess, it must be ackno acknowledg wledged ed that th at som somee ep epis isod odes es of PO PONV NV ar aree mi mild ld,, tr tran ansi sient ent,, an and d inconsequential. There have been attempts to create a score that could be used to rate the severity of nausea, vomiting, and retching in pati patients ents under undergoing going chemo chemother therapy. apy.1 4 1 5 How However ever,, no

scoree or in scor inde dex x ha hass be been en va vali lida date ted d to de defin finee cl clin inic ical ally ly impo im port rtan antt PON ONV V, th thaat is is,, at wh what at po poin intt do does es PON ONV V becomee a signifi becom significant cant and impor important tant post postoper operativ ativee compl compliication, and more importantly, can this be defined from a pati pa tien ent’ t’ss pe pers rspe pect ctiv ive? e? Tec echn hniq ique uess use used d in th thee pa past st to measur mea suree PO PONV NV ha have ve inc includ luded ed abs absolu olute te cou counts nts or inc inciidence rate, Likert scales scales,, visual analogue scales (V (VAS), AS), and trea treatment tment response. response. Some studies make reference reference to ‘severe’ ‘sev ere’ PONV without any definition or justi justificat fication ion of the cut cut-of -offf val values ues tha thatt dis discri crimin minat atee sev sever eree PO PONV NV fr from om what may otherwise be a trivial event. This issue has similarities with the measurement of pain intensity, in which it is generally accepted that a clinically important reduction in pain intensity is reflected by a reduction in a 100 mm

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D o w n l o a d e d f r o m h t t p : / / b j a . o x f o r d j o u r n a l s . o r g b y o n M a r c h 1 0 , 2 0 1 0

A PONV intensity scale

VAS score of at least 15,16 and severe pain being represented by a score greater than 70.17 A clinician’s perspectives and preferences may differ from that of a patient.18 19 We aimed to use psychometric methods to develop and validate a measurement scale to define clinically important PONV which takes into account patient views and expert medical and nursing opinion in its development and evaluation. Prospective validation of the derived scale was then undertaken.

Methods This prospective observational study had two phases: (i) literature review, participant survey, and development of a PONV Intensity Scale (‘development phase’); and (ii) prospective psychometric evaluation of the scale in a second cohort of patients (‘validation phase’). Ethics committee approval and consent was obtained from all subjects. Patients were excluded from the study if they had a psychiatric disturbance that precluded complete cooperation, a history of alcohol or drug dependence, distress or any severe pre-existing medical condition that limited objective assessment after operation, or the presence of any lifethreatening postoperative complication. The participant interviews were in the most part conducted by a single fulltime investigator (T.M. for development phase, R.W. for the validation phase). However, on some occasions the participants were interviewed by an experienced anaesthesia research nurse or registrar. All the interviews were conducted according to the study protocol.

Development of the PONV Intensity Scale The developmental phase was preceded by a literature review, and then a structured questionnaire asking clinicians (anaesthetists, nurses, surgeons), patients, and their family members to identify features of PONV that would describe its intensity and clinical importance. Key features included the intensity, pattern, and duration of nausea. For vomiting, participants were asked how many times a patient would have to vomit before they would be regarded as having severe PONV. The developmental phase concluded with the composition of a PONV scale that reflected the views provided by the survey. Further details are provided in the Supplementary Appendix.

Validation of the PONV Intensity Scale The second phase of validation study evaluated the psychometric properties of the derived scale. A further 183 patients were approached in the postoperative period after being identified as having PONV, requiring treatment for PONV, or being at high risk of PONV.3 5 We chose to include a sequential cohort of adult patients from each of the following types of surgery:

(i) Ambulatory surgical patients, where hospital discharge was planned on the same day of surgery. (ii) Inpatients undergoing minor surgery, defined by a duration ,2 h and expected blood loss ,500 ml, or a planned hospital stay of ,2 days. (iii) Inpatients undergoing major surgery, defined by having at least 3 of: (i) surgery with a duration .2 h, (ii) planned hospital stay of .2 days, (iii) intracranial or body cavity (i.e. abdominal or thoracic) surgery, or (iv) expected blood loss .500 ml, or the need for postoperative i.v. patient-controlled analgesia or epidural block. We used the recommended psychometric techniques.20–26 These included tests of content, construct, discriminant, and predictive validity; inter-rater reliability; internal consistency; responsiveness and effect size. Further details are provided in the Supplementary Appendix.

Data collection In both phases of the study we recorded baseline data including patient anxiety and depression using the validated hospital anxiety and depression (HAD) Scale,27 for which scores ,7 indicate normal functioning. Nausea and vomiting were recorded as present or absent, number of vomits, and extent and duration of nausea. Pain after surgery was measured using a 100 mm VAS, and was recorded at rest and during movement (coughing, deep breathing, or walking). The quality of recovery (QoR) after surgery was measured using the QoR score or QoR-40, both validated measures of quality of recovery after surgery and anaesthesia.28 29 All measurements and ratings were completed at the time when patients rated their PONV intensity. We also recorded factors known to be associated with the risk of developing PONV, including known risk factors for PONV.3 Apfel scores were then calculated to ascertain the percentage risk for patients developing PONV, with scores of 2 or greater indicating high risk. 3 Other indices or consequences of what may constitute clinically important PONV were recorded; these included wound dehiscence, the need for i.v. fluids because of an inability to tolerate oral intake, electrolyte imbalance, pneumothorax, s.c. emphysema, and any other adverse effects identified by patients or investigators. Patients were asked to provide a global rating of their nausea intensity using a 100 mm nausea VAS. The limits of the nausea VAS were ‘no nausea’ to ‘nausea as bad as it possibly could be’. The association between the nausea VAS and the PONV Intensity Scale was used as a measure of construct validity. We also measured duration of hospital stay and expected time off work. Given that vomiting and dry-retching reflect similar physiological processes and are similarly distressing to patients, and our early experience with measuring PONV intensity identified occasional uncertainty as to how to

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rank severity of nausea, we modified the PONV Intensity Scale to clarify these issues (Fig. 1). In order to ascertain whether the revision otherwise provided comparable results with that of the first version of the scale, we measured the agreement using both versions of the scale in the final 63 patients recruited into the study. The sample size selected for this study was guided by previous studies28 29 and in part chosen for convenience, given that power calculations cannot be readily made with correlational analysis. A post hoc analysis of the derived score was planned for the development phase in order to test these assumptions, and this was used in the sample size estimation for the validation phase in order to achieve at least 80% power for a comparison of QoR-40 scores.

Statistical analysis Data are summarized as mean (SD), median [inter-quartile range (IQR)], or number (%). Differences between proportions were analysed using the x 2 test, and risk estimates were done with odds ratio (OR) or risk ratio (RR) and 95% confidence intervals (CI). For normally distributed data, Student’s t - test was used to compare means of two groups. When data were not normally distributed, Wilcoxon signed-rank test was used. In selected patients, non-normal data were log-transformed to calculate geometric means, than enabling the use of t -tests. Rating differences in the questionnaires between the groups (patients/relatives, nursing, anaesthetic and surgical staff) were investigated using non-parametric Kruskall– Wallis analysis of variance. Associations were measured using

Score

Assessment A. At 6 hours after surgery (or time of discharge if after ambulatory surgery) Q1 Have you vomited or had dry-retching*? a) No b) Once or twice c) Three or more times

0 2 50

Q2 Have you experienced a feeling of nausea (“an unsettled feeling in the stomach and slight urge to vomit”)? If yes, has your feeling of nausea interfered with activities of daily living, such as being able to get out of bed, being able to move about freely in bed, being able to walk normally or eating and drinking? a) No b) Sometimes c) Often or most of the time d) All of the time

0 1 2 25

Q3 Has your nausea been mostly: a) varying (“comes and goes ”)? b) constant (“is nearly or almost always present ”)?

1 2

Q4 What was the duration of your feeling of nausea (in hours [whole or fraction])?

__ ·__ h

For Part A, if answer to Q1 = c), score A = 50; otherwise, select the highest score of Q1 or Q2, then multiply x Q3 x Q4

PONV intensity score (0-6 h) A=

*Count distinct episodes: several vomits or retching events occurring over a short time frame, say 5 min, should be counted as one vomiting/dry-retching episode; multiple episodes require distinct time periods without vomiting/dry-retching

Scoring for Clinical Importance of PONV Total Score

Score

Clinically important PONV is defined as a total score ≥50 at any time throughout the study period. Scores at 6 and 24 (and, if considered important in the clinical context, 72) hours can be added for quantification of the entire period, or sub-scales used for each period.

Final PONV intensity score (0-72 h)

A+B+C= Fig 1 The Postoperative Nausea and Vomiting (PONV) Intensity Scale. The PONV Intensity Scale can be repeated at 24 and 72 h to measure later onset PONV.

160



Spearman rank correlation, r . Internal consistency was measured using Cronbach’s a.25 Agreement was measured using intraclass correlation (ICC) for continuous variables30 and the kappa statistic for dichotomous variables. Responsiveness was measured using standardized response means, calculated as the mean change divided by its SD.26 All statistical analyses were performed using SPSS for Windows V16.0 (SPSS Inc., Chicago, IL, USA). A P-value of ,0.05 was considered significant; no correction was made for multiple comparisons.

In the development and pilot-testing, the duration data related to clinical importance were used to develop a PONV Intensity Scale. In general, we found that moderate nausea had twice the impact of mild nausea, and severe nausea had about 24 times the impact of moderate nausea. In addition, the ratio between the duration of constant and Table 2 Patient characteristics ( n 163). No. (%) unless otherwise specified. ASA, American Society of Anesthesologists physical status; PONV, postoperative nausea and vomiting. *Risk score for nausea and vomiting (3) ¼

Characteristic

Results In the development phase, a total of 191 participants were approached for the study; 188 were eligible and 180 were enrolled (recruitment rate 96%). In the validation phase, a further 183 patients were approached; 171 were eligible and 163 were enrolled (recruitment rate 95%; Supplementary Figs 1 and 2).

Development phase Patient, surgical, and anaesthetic characteristics are presented in the Supplementary Tables 1– 4. Of the postoperative patients who experienced PONV (39%), 20 (35%) had nausea and six (11%) vomited; 10 (18%) of these patients received antiemetic treatment. In most patients there were no significant differences between the groups (patients, family members, and clinical staff) (Supplementary Tables 5–8) as to the duration of nausea regarded as clinically important (Table 1). However, the duration of moderate varying and severe nausea were different between the groups. There was general consensus among family members and staff that three or more vomits was clinically important (Supplementary Table 6). Staff were more likely to tolerate more intense nausea (in their patients) for longer than patients themselves. There was no significant correlation between the anxiety and depression score and the duration of nausea considered clinically important. Participants’ past history of PONV had little impact on their determinations of the duration of clinically important nausea (results not shown).

Table 1 Duration of nausea indicating clinical importance according to the opinions of study participants. Data are median (IQR) hours Type of nausea

Patients/Family ( n 122)

Staff ( n 58)

Total ( n 180)

P-value

60 (24–120) 108 (48–168) 24 ( 12 – 48)

60 (24–120) 84 (43–120) 24 (12 – 48)

60 (24–120) 96 (48–168) 24 (12 – 48)

0.49 0.066 0.193

48 (24–72) 1 (0.2 – 4) 2 ( 0.5 – 24)

24 (12–48) 2 (0.5 – 8) 8 (2.8 – 12)

48 (19–72) 1 (0.3 – 5) 4 (0.6 – 12)

0.026 0.030 0.005

5

Mild constant Mild varying Moderate constant Moderate varying Severe constant S evere varying

5

5

Age, mean ( SD) year Body mass index, mean ( SD) kg m 22 Female gender Ethnicity White Asian Indian/Sri Lankan Other Non-smoker ASA status I II III IV Previous PONV Previous motion sickness Apfel score* 1 2 3 4 Duration of anaesthesia, mean ( SD) h Surgery type General Orthopaedic Plastic Ear, nose, and throat Vascular Other Extent of surgery Ambulatory Minor Major Anaesthetic technique Propofol induction Total i.v. anaesthesia Neuromuscular blocker Sevoflurane Desflurane Isoflurane Nitrous oxide Spinal/epidural Anaesthetic adjuvant drugs Midazolam Fentanyl Morphine Ketamine Other opioids Intraoperative antiemetics given Dexamethasone Ondansetron Droperidol/Haloperidol Metoclopramide No. of prophylactic antiemetics given 0 1 2 3

161

50 (18) 27.5 (7.5) 107 (66) 147 (90) 8 (4.9) 5 (3.1) 3 (1.8) 134 (82) 50 (31) 66 (41) 42 (26) 4 (2.5) 69 (42) 61 (37) 6 44 58 55 2.4

(3.7) (27) (36) (34) (1.6)

64 (39) 41 (25) 11 (6.7) 11 (6.7) 8 (4.9) 28 (17) 11 (7) 83 (51) 69 (42) 163 (100) 18 (11) 128 (79) 107 (66) 35 (22) 3 (1.8) 4 (2.5) 13 (8) 67 (41) 113 (69) 117 (72) 3 (1.8) 29 (18) 104 (64) 49 (30) 15 (9.2) 6 (3.7) 54 53 47 9

(33) (33) (29) (5.5)


Wengritzky et al.

varying nausea was about 2:1. We thus created a scoring system that reflected the relationship between nausea intensity, pattern, and duration according to the relative durations reported by the participants. Although there were some differences between clinical staff and patients, particularly with the duration of severe nausea, we chose to place more emphasis on patient ratings. We thus developed a score to measure PONV intensity, where a score !50 defined clinically important PONV: PONV Intensity Scale severity of nausea (1 mild, 2 moderate, 3 severe)Âpattern of nausea (1 varying, 2 constant)Âduration of nausea (in hours). The PONV intensity score was first pilot-tested on postoperative patients in the development phase of the study, with results available in the Supplementary material. This was then adapted to create an Intensity Scale (Fig. 1) that underwent extensive prospective validation. ¼

¼

¼

¼

¼

¼

defined by a score of !50. The median (IQR) PONV Intensity Scale for all participants was 8.0 (0.9–40). The mean nausea VAS scale was 52 (SD 30). Patients with clinically important PONV had significantly higher nausea VAS scales when compared with those without clinically important PONV (Table 4). Patients with clinically important PONV scores also had a significantly poorer quality of recovery (Supplementary Fig. 3). In addition, to ensure that a spurious correlation did not exist between the QoR-40 scales and patients with clinically important PONV, three items related to nausea and vomiting were removed from the QoR-40 scale and the significant difference remained marked: mean difference 15 (95% CI 9–21), P,0.0005. Patients with clinically important PONV needed twice as many doses of antiemetic (Table 4), and had greatly increased risk of typical complications and other consequences of PONV (Fig. 2). Women were more likely than men to have higher PONV intensity scores [17 (1.5–48) vs 1.8 (0.2–19), P 0.001], and to be classified as clinically important PONV [OR 3.0 (95% CI 1.1–8.2), P 0.032]. An increase in preoperative Apfel scores was associated with an increase in the proportion of patients with clinically important PONV: 1 0%, 2 14%, 3 31%, 4 55%; P 0.004. The median (IQR) hospital stay for patients with clinically important PONV was 4 (3–5) days and for those without clinically important PONV 3 (2–6) days, P 0.50; the estimated time off work was 42 (28–105) days and 30 (14– 60) days, respectively, P 0.15. ¼

Validation phase

Patient, surgical, and anaesthetic data for the validation cohort (Table 2) showed that this cohort represented a fairly high-risk group for developing PONV, with nearly 96% of patients being classified with an Apfel Scale of 2 or greater. Around 40% had a past history of PONV, motion sickness, or both. Despite being a high-risk population for developing PONV, 33% of patients did not receive antiemetic prophylaxis and a further 33% received only one antiemetic. Nearly all (97%) patients experienced nausea in the postoperative period, and about half (45%) of them were in the severe category (Table 3), and just more than half Nausea VAS (55%) of the patients vomited in the postoperative period. During the conduct of the study we found that the nausea VAS was quick to administer and easily understood by Validity testing investigators and patients. Its common use in previous While 45% of participants were categorized as having studies and our ease of use raised the possibility of this ‘severe’ characteristics of PONV, less than half of them being a useful measure of nausea intensity, despite not (18% of the cohort) had clinically important PONV as having been previously validated. We thus evaluated its ability to discriminate clinically important PONV from unimportant PONV using two cut-off values: ¼

¼

¼

¼

¼

¼

¼

¼

Table 3 Characteristics of patients with postoperative nausea and vomiting. No. (%) unless otherwise specified Nausea experienced Nausea pattern Varying Constant Nausea severity rating Mild Moderate Severe Duration of nausea, median (IQR) Total duration of varying, min Constant, h Number of vomits 0 1–2 3–4 5–10 .10 Dry-retching

158 (97)

(1) Nausea VAS score !50. A cut-off value of 50 or more, being the mid-point and close to the calculated

107 (66) 51 (30)

Table 4 Tests of construct validity of the PONV Intensity Scale to classify clinically important PONV using a scale score !50 Clinically important PONV

37 (23) 47 (29) 74 (45)

Yes ( n 29)

40 (15–80) 6.5 (0.5– 22) 73 (45) 54 (33) 21 (13) 12 (7.4) 3 (1.8) 68 (42)

5

Nausea VAS scale, mean ( SD) QoR-40 score, mean (SD) No. antiemetic doses required, median (IQR)

162

Mean difference (95% CI)

P-value

No ( n 134) 5

81 (23)

46 (28)

35 (24 – 46)

,0.0005

146 (15)

164 (16)

18 ( 12 – 25)

,0.0005

6.0 (5 – 9)

3.0 (2 – 4)

3.0

,0.0005



mean VAS score, was first arbitrarily used as an alternative criterion of clinically important PONV; this resulted in 116 patients (71%) being classified as having clinically important PONV (Table 5). Although statistically significant, we found that the discriminatory ability was less than when using the PONV Intensity Scale. The agreement between both scales to identify clinically important PONV was poor (k 0.29; P,0.0005). (2) Nausea VAS score !75. A cut-off value of 75 [being close to the 75th centile (VAS 76)] resulted in 47 patients (29%) being classified as having clinically important PONV. When using a nausea VAS of 75 or more (VAS75), results were statistically significant, and the discriminatory ability was comparable with the PONV Intensity Scale (Table 5). The agreement between both scales to identify clinically important PONV was moderately strong (k 0.49; P,0.0005). However, if vomiting on three or more occasions is included in this definition, the agreement remains moderate (k 0.39). ¼

The PONV Intensity Scale had a stronger correlation (r 0.58, P,0.0005) with the total number of antiemetic doses needed when compared with the nausea VAS75 (r 0.50, P,0.0005). There was no difference in agreement between the two measures with the total number of vomits (r 0.30 vs r 0.29; both P,0.0005); however, there was a large difference between the associations between the PONV Intensity Scale (r 0.83, P,0.0005) and VAS75

Table 5 Tests of construct validity of the nausea VAS to classify clinically important PONV using a score !50 or !75. PONV, postoperative nausea and vomiting; QoR-40, a 40-item quality of recovery scale (9), with a maximal score of 200; VAS, a 100 mm visual analogue scale Using VAS scale

P-value

No ( n 47)

154 (15)

170 (15)

16 (11 – 21)

,0.0005

143 (14)

157 (15)

14 (10 – 19)

,0.0005

5

Revision of the PONV Intensity Scale A total of 63 patients were tested with the original and revised versions of the PONV Intensity Scale. The revised PONV Intensity Scale identified 27% of this cohort as having clinically important PONV. There was a strong correlation between both versions of the scale (r 0.83; P,0.0005). Agreement between the versions to determine clinical significance (scores !50) were strong (k 0.69; P,0.0005). Consistent with results obtained with the original version of the PONV Intensity Scale, agreement between clinically important scales and VAS75 was moderate (k 0.46; P,0.0005). Correlation between the revised Intensity Scale and the VAS75 was also moderate (r 0.58; P,0.0005).

Reliability testing Test–retest and inter-rater reliability were completed in 22 patients using a single method. The reliability coefficient was excellent for the PONV Intensity Scale [ICC 0.99 (95% CI 0.99–1.0), P,0.0005], and strong for the nausea VAS75 [ICC 0.91 (95% CI 0.78–0.96), P,0.0005]. We also used the revised PONV Intensity Scale in 16 patients, for which correlation was also excellent [ICC 0.97 (95% CI 0.91– 0.99), P,0.0005]. The six items used to determine severity of nausea for the PONV Intensity Scale had very good internal consistency (Cronbach’s a 0.78). The inter-item correlations are shown in Supplementary Table 9. Most items had moderate to strong correlation, with no evidence of redundancy.

Responsiveness testing and effect size The correlations between the change in PONV Intensity Scales [original version (n 36) and revised version (n 22)] with the reduction in number of antiemetics needed at the second interview were moderately strong (r 0.74, P,0.0005; and r 0.53, P 0.011, respectively). For those patients who had changed from having clinically important PONV scores to unimportant PONV scores, there was a significant reduction in the number of medications required since the first interview when using both versions of the PONV Intensity Scale (P 0.007 and P 0.036, respectively). Of the eight patients who changed from having clinically important to unimportant PONV using the original version of the scale, seven (88%) rated themselves as having good relief on responsiveness questioning. ¼

4.0 (3 – 6)

2.0 (1 – 3)

2.0

,0.0005

¼

¼

Using VAS scale !75 Yes (n 47) Yes (n 47) 150 (15) 166 (16)

17 (10 – 21)

,0.0005

140 (15)

13 (8 – 18)

,0.0005

¼

QoR-40 score, mean ( SD) QoR-40 score without PONV questions, mean (SD) No. antiemetic doses required, mean (IQR)

Mean difference (95% CI)

Yes ( n 116) 5

QoR-40 score, mean ( SD) QoR-40 score without PONV questions, mean (SD) No. antiemetic doses required, median (IQR)

50

(r 0.58, P,0.0005) with duration of nausea experienced. Further analyses were completed using consequences of PONV (Table 6), which demonstrate that although both the Scales and VAS75 were able to identify consequences of PONV, the scale was a more sensitive measure. If vomiting on three or more occasions is included in this definition the agreement is less (results not shown).

¼

153 (15)

¼

5.0 (3 – 7)

3.0 (1 – 4)

2.0

,0.0005

163

¼


Wengritzky et al.

Table 6 Tests of predictive validity for the PONV Intensity Scale (v1) and nausea VAS; all P,0.0005. OR, odds ratio; PONV, postoperative nausea and vomiting; VAS, a 100 mm visual analogue scale Consequences of PONV

Clinically important PONV Yes ( n 29)

No ( n 134)

59% 72% 90% 97% 66% 31% 45%

19% 24% 37% 48% 13% 1.5% 5%

5

Unable to move freely in bed Unable to drink Unable to eat Unable to walk Requires i.v. fluids Electrolyte imbalance Others

OR (95% CI)

5

6.2 (2.6–15) 8.4 (3.4–21) 14.6 (4.2–51) 30.6 (4.0–232) 13.1 (5.2–33) 29.7 (6.0–148) 14.7 (5.1–42)

Unable to drink Unable to eat Unable to walk Requires i.v. fluids Electrolyte imbalance Other Cx 1

0 1

Odds ratio

0 0 1

0 0 0 1

Fig 2 The risk (expressed as odds ratio) of having an adverse consequence of emesis in patients classified as having clinically important PONV using the PONV Intensity Scale.

Similarly for the revised scale, five of six (83%) patients rated themselves as having good PONV relief. Good PONV relief was defined as a health status change that was either ‘satisfactory’, ‘good’, or ‘excellent’. The differences in PONV Intensity Scale between the two interview times were then analysed. Log transformations of the scales were done owing to positively skewed data, and we compared geometric means. A significant difference was found in the DPONV Intensity Scales between patients who had a change from clinically important PONV to unimportant PONV (n 8) and those who had no clinical change (n 28). The geometric mean scores were 301 (3.7) and 4.6 (14), respectively (P,0.0005). Similar results were obtained when using the revised version of the scale (n 6 vs n 16), geometric means of 155 (3.1) and 3.6 (14) ( P 0.001). The effect size for the change in PONV scales at the second interview when compared with the first, comparing patients who had a change from clinically important to unimportant PONV and those who had no clinical change was calculated using the difference in geometric means divided by their pooled standard deviation. The effect size was 0.82, illustrating excellent discriminatory ability. 29 ¼

¼

¼

¼

¼

Discussion This study sought to develop a measurement tool for PONV intensity in order to identify clinically important PONV. The development phase found minimal differences

75

OR (95% CI)

Yes ( n 47)

No ( n 116)

51% 62% 75% 89% 49% 19% 30%

16% 21% 35% 43% 11% 1.7% 5%

5

Unable to move freely in bed

1 . 0

VAS scale

5

5.7 (2.7– 12) 6.1 (2.9– 13) 5.3 (2.5– 11) 11.0 (4.1– 30) 7.6 (3.4– 17) 13.5 (2.8– 65) 7.8 (2.8– 22)

between staff and patient opinion for the indices used to measure clinical importance. Patients are likely to prioritize their comfort and quality of recovery after surgery over other complications.31 32 However, clinical staff are more likely to be mindful of other serious complications of PONV and so perhaps are less likely to place importance on severe nausea itself. This study used a range of psychometric techniques to identify clinically important PONV. Content validity was achieved through literature review and consultation with experienced clinicians. The evidence of construct validity was strong, with the PONV Intensity Scale correlating with higher Apfel scores3 and having more severe and clinically important PONV. Inter-dimension correlations with factors known to be associated with PONV morbidity were consistently positive. Patients with clinically important PONV required more antiemetic therapy, had higher rates of complications associated with severe PONV, and took longer to recover from their surgery. Clinically important PONV, as determined by the PONV Intensity Scale, was associated with a poor quality of recovery. 23 33 The 18-point difference in the QoR-40 in those with and without clinically important PONV reflects a major difference in the quality of recovery, being comparable with the change in a patient’s health status that occurs from immediately after cardiac surgery to full recovery at about 3 months.33 Reliability and responsiveness were also confirmed. The reliability coefficients of the PONV Intensity Scale exceeded the established recommendations,20 indicating that the scale can provide reliable assessment for both group and individual measurements, comparisons, or both. The strength of the PONV Intensity Scale to yield consistent responses when different raters are used effectively demonstrates the ease of use and clinical utility of the scale. To overcome difficulties in measuring responsiveness, we approached it in a number of ways, each adding strength to the ability of the scale to detect an important clinical change. We found that a reduction in the PONV Intensity Scale was accompanied by a significant reduction in antiemetic dosage and patient self-ratings of improvement. The effect size was large (0.82), illustrating that a clinically important change can readily be determined by the scale.

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During the validation phase of the study we revised the PONV Intensity Scale to simplify the process by which a final score is obtained and to eliminate the need to make clinical decisions regarding severity. Furthermore, it was broken down into three time frames, 0–6 h, 6–24 h, and 24–72 h, to allow for specific PONV research in the future; each time frame can be used separately or combined to calculate a final scale. We then further evaluated the revised version and found it to be essentially interchangeable with the original PONV Intensity Scale. We believe that the revised scale was simpler to use, being less susceptible to misinterpretation or uncertainty. The PONV Intensity Scale can be readily modified into a questionnaire format for patients to complete at home, or by telephone interview. In both phases of the study we found that about 18% of those with PONV could be classified as having clinically important PONV. That is, many episodes of PONV are unimportant (to patients and clinicians). We do not want to diminish the potential significance of PONV in perioperative practice, in fact we would emphasize that clinically important PONV deserves the same attention as other serious postoperative complications, and it is this that requires more stringent management than currently implemented. There have been previous attempts to create a scale that could be used to rate the severity of emesis in patients undergoing chemotherapy,14 15 34–37 but none were developed for use in the postoperative setting. None of these measurement tools sought patient opinions as to what constitutes clinically important nausea and vomiting. It was expected that patients with clinically important PONV would have higher VAS scores. We found that the nausea VAS75, in particular, had good results on validity testing, but these were not as strong as for the PONV Intensity Scale. We therefore propose the VAS75 as a screening tool in the clinical setting for rapid assessment or audit tool, and the PONV Intensity Scale is recommended for detailed research. In our study, 70% of patients had three or more risk factors but only 35% received double- or triple-antiemetic prophylaxis. There are several reasons as to why this occurred. Anecdotally, there is a lack of preoperative identification of risk factors. Under-treatment also may be because of belief by the anaesthetist that PONV is not so important. It is hoped that a clearer understanding of what is clinically important PONV, and its risk prediction, will go a long way to redress any under-treatment issues in the future. In summary, we used psychometric techniques to prospectively validate and test the reliability and responsiveness of the PONV Intensity Scale in a broad surgical setting. The PONV Intensity Scale can be used to identify clinically important PONV.

Supplementary material Supplementary material is available at British Journal of Anaesthesia online.

Acknowledgements The authors gratefully acknowledge the assistance of Ms Sophie Wallace, MPH, Research Manager in the Department of Anaesthesia and Perioperative Medicine, Alfred Hospital, Melbourne, Australia; and the cooperation of their anaesthetic, surgical, and nursing colleagues in the conduct of this study.

Funding The Alfred Hospital Research Trust, Melbourne, Victoria, Australia. Dr Myles is the recipient of an Australian National Health and Medical Research Council (NHMRC) Practitioner’s Fellowship, Canberra, Australian Capitol Territory, Australia; and is supported by the NHMRC Clinical Research Excellence in Therapeutics (ID 219284), Monash University, Melbourne, Victoria, Australia.

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