Simplified postoperative nausea and vomiting impact scale for audit and post-discharge review

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1 British Journal of Anaesthesia 108 (3): (2012) Advance Access publication 25 January doi: /bja/aer505 Simplified postoperative nausea and vomiting impact scale for audit and post-discharge review P. S. Myles 1,2 * and R. Wengritzky 1 1 Department of Anaesthesia and Perioperative Medicine, Alfred Hospital, Commercial Road, Melbourne, Victoria 3004, Australia 2 Academic Board of Anaesthesia and Perioperative Medicine, Monash University, Melbourne, Victoria, Australia * Corresponding author. p.myles@alfred.org.au Editor s key points In this paper, a simplified PONV impact scale, and its validation, has been described. Using the scale, one in five PONV patients could have clinically important impact. Clinically important PONV led to significant consequences and poorer recovery. Importantly, this scale can be used as a quality indicator or outcome measurement tool. Background. Postoperative nausea and vomiting (PONV) is common but many episodes may be trivial or transient. The aim of the study was to develop a simple-to-use measure of the intensity and clinical impact of PONV. Methods. We re-analysed data from a study enrolling 163 patients recovering from surgery and anaesthesia that had experienced or were at increased risk of developing PONV. A range of measures of PONV characteristics and quality of recovery were collected. We devised a simplified nausea vomiting impact scale based on patients assessment of the impact of their nausea on their postoperative recovery and the number of times they experienced vomiting. We then undertook further tests of construct and discriminant validity, and reliability and responsiveness, of the impact scale using psychometric methodology. Results. Around one in five patients with PONV had features that could classify them as having clinically important PONV. We found that patients with clinically important PONV had a much poorer quality of recovery (P,0.0005), needed more antiemetic administrations for treatment (P,0.0005), and were more likely to have consequences and complications of PONV (all P,0.01), when compared with those with lesser degrees of PONV. A change in clinically important PONV status can be reliably detected with the PONV impact scale. Conclusions. We have devised and validated a simplified PONV impact scale that can be used to identify those with clinically important PONV. The avoidance of clinically important PONV could be used as a quality indicator or outcome measure after surgery. Keywords: ambulatory surgery; anaesthesia; patient rating; patient reported outcomes; postoperative nausea; vomiting Accepted for publication: 9 December 2011 Postoperative nausea and vomiting (PONV) is a common and sometimes distressing complication after surgery. 1 3 PONV may be mild or transient, but its impact on patients can be much more severe, to include inability to mobilize after surgery, restricted oral intake, complications of protracted vomiting, and delayed recovery and discharge after surgery. 1 For ambulatory patients, this can be particularly distressing after hospital discharge when access to treatment is limited; unplanned hospital readmission may follow. 4 Ranked (ordinal) or visual analogue measurement scales used to quantify the intensity of subjective experiences such as pain, anxiety, and PONV are commonly used in anaesthesia. Scales used to measure such patient-reported outcomes can quantify the effect of interventions from a patient s perspective, and are particularly useful for interventions aiming to improve symptoms and functional status. But few scales used in anaesthesia have been validated for such a purpose, and the size of the change in score that reflects the minimal clinically important difference 5 7 is usually overlooked. 89 Both the Food and Drug Administration (FDA) and the European Medicines Agency have guidelines on the use and interpretation of subjective measurement scales, and the FDA outlines what evidence is required for claims by pharmaceutical companies in their promotional material. Evidence supporting content validity and other psychometric qualities are required by both organizations. Perhaps, the most demanding is demonstration of responsiveness the ability to detect and quantify meaningful changes in health status; in other words, the minimal clinically important difference. We have previously developed a PONV intensity scale to define clinically important PONV. 12 We first undertook a literature review, and then surveyed patients and their family members (n¼122) and clinicians (n¼58) to determine which features of PONV determine clinical significance. We found that the intensity, pattern and duration of nausea, & The Author [2012]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please journals.permissions@oup.com

2 BJA Myles and Wengritzky and repeated vomiting (three or more times), each determined clinical significance. We then included a second cohort of 163 patients with PONV and used extensive psychometric testing to demonstrate validity, reliability, and responsiveness of the scale. Subsequent clinical and research experience has highlighted some ambiguities with the PONV intensity scale, in particular the ease at which patients and non-research staff can accurately record extent and duration of nausea. In addition, the scale was proving difficult to administer to patients after discharge from hospital, limiting its usefulness in ambulatory surgery for which avoidance of PONV is particularly important. The aim of the present study was to revise the scale and validate a simplified PONV scale. Methods The study data were obtained during the conduct of our previous study, 12 for which we received Ethics Committee approval and patient-signed consent. Study subjects were recruited from the surgical patient population of a university teaching hospital. We included sequential patients undergoing a broad range of ambulatory or inpatient surgery. All patients were approached in the postoperative period after being identified as having PONV, requiring treatment for PONV, or being at high-risk of PONV Before seeking consent, we first ensured that patients were not sedated or confused, and we remained attentive to minimize any inconvenience or discomfort to the study subjects. Patients were excluded from this study if they had poor English comprehension, a psychiatric disturbance that precluded complete cooperation, a history of alcohol or drug dependence, any severe pre-existing medical condition that limited objective assessment after operation (e.g. tracheal intubation, uncontrolled pain), or the presence of any life-threatening postoperative complication. The patient PONV assessments were completed at 4 h in ambulatory surgery patients whilst they were still in hospital, or 24 h for inpatients, after surgery. Data collection included factors known to be associated with the risk of developing PONV, 1 including the Apfel risk score. 13 The frequency, intensity and duration of nausea, and the number of vomits were recorded. Other indices or consequences of what may constitute clinically important PONV were also recorded; these included immobility, the need for i.v. fluids because of an inability to tolerate oral intake, electrolyte imbalance, wound dehiscence, pneumothorax, subcutaneous 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 visual analogue scale (VAS). The limits of the nausea VAS were no nausea to nausea as bad as it possibly could be. In addition, patients were asked to rate the severity of their nausea using the following guidance: (i) mild: does not interfere with activities of daily living such as dressing, hygiene, walking, housework, gardening, and driving; (ii) moderate: sometimes interferes with activities of daily living; and (iii) severe: inability to undertake any activities of daily living, or three or more vomits. In the final 63 (of the 163) patients enrolled in the study, we added a modification to the nausea scales by directly asking patients to rate the impact of their nausea on their current functional status. The response options were: (i) not at all, (ii) sometimes, (iii) often or most of the time, and (iv) all of the time. The ratings from the first 100 patients were converted to scores of 1 3 on the modified 4-point (0 3) impact scale used on the subsequent 63 patients. The number of vomits and the above data were used along with pattern and duration to derive our previous PONV intensity scale, for which we demonstrated strong agreement. 12 The simplified PONV impact scale In the present study, we simply used the nausea ordinal response to quantify nausea intensity or impact on the patient, where (i)¼0, (ii)¼1, (iii)¼2, and (iv)¼3. In addition, we used the vomiting count to quantify vomiting intensity, scored as the number of vomits (0 2, or 3 if three or more vomits). We thus added both scores together to obtain the simplified PONV impact scale score (Fig. 1), and defined clinically important PONV as a total score of 5 or 6. We tested the construct validity of both the nausea and vomiting sub-scale scores, and their combination. We measured the quality of recovery after surgery, using the previously validated 40-item quality of recovery (QoR-40) scale The QoR-40 consists of five clinically relevant dimensions: (i) physical comfort (12 items), (ii) emotional state (9 items), (iii) physical independence (5 items), (iv) psychological support (7 items), and (v) pain (7 items). Each item is rated on a five-point Likert scale. The QoR-40 score ranges from 40 (extremely poor quality of recovery) to 200 (excellent quality of recovery). We compared the QoR-40 against the nausea impact and vomiting sub-scales, and their combination, as the principal test of construct validity (our primary outcome). In view of the fact that the QoR-40 includes three items pertaining to PONV, we repeated these analyses without the PONV items in the QoR-40 score. We correlated the nausea impact sub-scale score with the nausea VAS score, and the combined PONV impact score with the number of antiemetic drug administrations required after operation and the previous PONV intensity score, as measures of construct validity. Reliability, responsiveness, and effect size Reliability refers to the precision or reproducibility of a measurement tool. In 22 patients, we repeated the interview at a later time in the day to assess test retest reliability. Responsiveness is the ability to detect a clinically meaningful change in health. We tested responsiveness in 58 patients by repeating the interview 24 h later to assess the change in the clinical status. Any additional antiemetic medication given during the second time period was recorded as an objective indicator of a change in the health status. Patients were then asked to rate their change in the health status 424

3 Simplified PONV impact scale BJA Q1. Have you vomited or had dry-retching*? 0. No 1. Once 2. Twice 3. Three or more times 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? 0. Not at all 1. Sometimes 2. Often or most of the time 3. All of the time. To calculate the PONV Impact Scale score, add the numerical responses to questions 1 and 2. A PONV Impact Scale score of 5 defines clinically important PONV. *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. Fig 1 The PONV impact scale. on a five-point Likert scale: (i)¼excellent, (ii)¼good, (iii)¼ satisfactory, (iv)¼poor, or (v)¼very poor. The primary endpoint for comparison between the groups was the QoR-40 scores. We estimated an eight-point difference, 170 (14) vs 162 (14), with 120 subjects to achieve at least 80% power. We planned to increase the sample to allow useful group and sub-group correlational analyses. Statistical analysis Data are summarized by mean (SD), median (interquartile range [IQR]), or number (%). Missing data are not included in any analysis. Differences between proportions were analysed using the x 2 test, and risk estimates calculated using odds ratio and 95% confidence intervals (CIs). We adjusted for the use of prophylactic multimodal antiemetic therapy in our assessment of the Apfel risk score by using the Mantel Haenszel statistic. After confirming normally distributed data using the Kolmogorov Smirnov test, we used Levine s test to confirm equal variance and then Student s t-test to compare the group means. For the length of stay, these non-normal data were log-transformed to calculate geometric means before using the Levine and t-tests. Associations were measured using Spearman r or Somer s d correlation. 16 Agreement was measured using the kappa statistic for dichotomous variables. Responsiveness was measured using standardized response mean, calculated as the mean change divided by its SD, such that an effect size of.0.7 indicates a strong ability to detect a change in the clinical status. 17 All statistical analyses were performed using SPSS for Windows V17.0 (SPSS Inc., Chicago, IL, USA). A two-sided of,0.05 was considered significant; no correction was made for multiple comparisons. Results The study patient characteristics and perioperative data are presented in Table 1. The average age of participants was 50 yr, and around two-thirds were female. Most (82%) were non-smokers, and 61% had a history of PONV, motion sickness, or both. Nearly all selected patients (97%) experienced nausea in the postoperative period, and about half (45%) of these rated this as severe as defined by their inability to undertake any activities of daily living. Those with intermittent or single episode PONV had a mean duration of,1 h (40 min), and for those with constant PONV, this persisted for a mean of 6 h. Just over half (55%) of the patients vomited in the postoperative period, and most (78%) of these had only one or two vomits. There was a broad distribution of PONV impact scores (Table 2), indicating minimal floor-ceiling effect. The median and mean scores were 3.0 and 3.1, respectively. The proportion of minimum and maximum values was 3.1 and 17%, respectively. When using a cut-off value for the PONV impact score of at least 5, 21% of the cohort had clinically important PONV. Validity testing Patients with clinically important PONV had significantly higher nausea VAS scores when compared with those without clinically important PONV (Table 3). Patients with clinically important PONV also had a significantly poorer quality of recovery; the mean difference in QoR-40 scores with PONV items removed was 10 (95% CI: 4 16), P, (see also Fig. 2). Patients with clinically important PONV needed more antiemetic administrations after surgery, P¼0.001 (Table 3). 425

4 BJA Myles and Wengritzky Table 1 Patient and perioperative characteristics (n¼163). PONV, postoperative nausea and vomiting. *Risk score for nausea and vomiting (12) Characteristic n (%) Age (yr) (33) (36) (31) Body mass index (kg m 22 ) (55) (27) Female 107 (66) Non-smoker 134 (82) ASA score I 50 (31) II 66 (41) III 42 (26) IV 4 (2.5) Previous PONV 69 (42) Previous motion sickness 61 (37) Apfel score* 1 6 (3.7) 2 44 (27) 3 58 (36) 4 55 (34) Surgery type General 64 (39) Orthopaedic 41 (25) Plastic 11 (6.7) Ear, nose and throat 11 (6.7) Vascular 8 (4.9) Other 28 (17) Extent of surgery Ambulatory 11 (7) Minor 83 (51) Major 69 (42) No. of prophylactic antiemetics given 0 54 (33) 1 53 (33) 2 47 (29) 3 9 (5.5) The nausea impact sub-score had good convergent validity with the nausea VAS, r¼0.60, P, The PONV impact score was moderately strongly correlated with the previously developed PONV intensity score, 12 r¼0.67, P, Clinically important PONV as defined by each score had similarly strong agreement, k¼0.66, P, Reliability and responsiveness testing Test retest for both the nausea and vomiting sub-scales had excellent repeatability, d¼0.86 and 0.88 (both P,0.0005), respectively. The PONV impact scale subsequently had excellent repeatability, d¼0.78, P, Using a PONV impact score cut-off of 5 to determine clinically important PONV had excellent agreement on retesting, k¼0.82, P, Those with clinically important PONV had generally moderate-to-strong associations with indicators of impaired recovery after surgery (Table 4). The PONV impact scale score had excellent agreement (responsiveness) to reflect clinical improvement as rated by the patient, d¼0.78, P, A change in PONV impact scores over time was reflected in a comparable change in the number of doses of antiemetic therapy (P¼0.007), and a change in the patient self-assessment of their relief of PONV (P¼0.048). The effect size was The geometric mean hospital stay in those with clinically important PONV compared with those without important PONV was 4.4 (1.9) days vs 3.8 (2.0) days, P¼0.30. Finally, the Apfel PONV risk score was found to be a very good discriminator of nausea risk and, to a lesser extent, clinically important PONV. The rates of clinically important PONV were 2.9, 11, 54 and 31% for an Apfel score of 1 4, respectively (Table 2). Prophylactic multimodal antiemetic therapy ( 2 antiemetics) was used in 22% of patients with an Apfel score of 1 or 2, and 40% with a score of 3 or 4. The sensitivity and specificity of an Apfel score of 3 to identify clinically important PONV was 86 and 35%, respectively. However, those with an Apfel score of 3 were more likely to receive multimodal antiemetic therapy, thus reducing its incidence, and so the adjusted odds ratio for clinically important PONV was 3.4 (95% CI: ), P¼ Discussion We found that around one in five patients with PONV have clinical features consistent with distress and physical limitations affecting their recovery after surgery. The latter include inability to tolerate oral fluids and food, impaired mobilization, and an overall poorer quality of recovery all features of clinically important PONV. We used a range of psychometric techniques to evaluate our simplified PONV impact scale designed to identify clinically important PONV. The study population represented those with PONV or at high risk of PONV, recovering from many types of surgery. The validity, reliability, responsiveness, and clinical utility of the scale were found to be excellent. Because there is no gold-standard measurement of clinically important PONV, we chose to validate the PONV impact scale using a variety of methods. Face and other content validity have been previously demonstrated. 12 The evidence of construct validity was strong, with the PONV impact scale being correlated with higher Apfel scores 13 and having more severe symptoms and consequences of PONV. The size of the difference in quality of recovery, as measured by the QoR-40, between groups was large, with the 13-point difference reflecting meaningful reduction in overall quality of recovery. 14 Responsiveness to change is an important characteristic of health status measurement scales The ability 426

5 Simplified PONV impact scale BJA Table 2 Tests of construct validity using a nausea impact scale and frequency of vomiting to derive a nausea-vomiting impact scale. PONV, postoperative nausea and vomiting. QoR-40¼a 40-item quality of recovery scale (15), with a maximal score of 200. *Score¼no. of vomits (if 3 or more, score 3) + nausea impact score Total n5163 (% in each category) PONV intensity score (12), median (IQR) QoR-40 score, mean (SD) No. of antiemetic doses required after operation, median (IQR) Apfel PONV score (13), 3 or 4 (%) Nausea interferes with daily activities such as eating, drinking, and moving about 0¼not at all (3) 0 (0 0), (11), (0 0.5), ¼sometimes (23) 2¼most of the time (29) 3¼all of the time (45) 0.3 ( ) 171 (14) 2.0 ( ) (1.0 12) 165 (14) 3.0 ( ) (25 250) 153 (17) 3.0 ( ) 80 No. of vomits 0 (51) 4 (0.5 33), (18), ( ) , (17) 4 (0.5 34) 159 (12) 3.0 ( ) 68 2 (15) 1.3 (0.3 30) 163 (17) 3.0 ( ) 71 3 (17) 50 (50 300) 153 (16) 4.5 ( ) 82 Nausea-vomiting impact scale score* 0 (3.1) 0 (0 0), (11), (0 0.5), , (12) 0.4 ( ) 175 (15) 2.0 ( ) 60 2 (23) 1.3 ( ) 165 (14) 3.0 ( ) 65 3 (29) 17 (2.4 47) 157 (17) 3.0 ( ) 69 4 (11) 19 (0.9 43) 164 (16) 3.5 ( ) 72 5 (4.3) 31 (19 250) 145 (10) 3.0 ( ) (17) 50 (50 300) 153 (16) 4.5 ( ) 82 Table 3 Tests of construct validity of the nausea vomiting impact scale to classify clinically important PONV if the score is 5 or 6. PONV, postoperative nausea and vomiting. QoR-40¼a 40-item quality of recovery scale (15), with a maximal score of Clinically important PONV as defined by a nausea vomiting impact scale score 5 QoR Yes (n535) No (n5128) PONV intensity score, median [IQR] 50 [50 263] 2.2 [0.4 30], QoR-40 score, mean (SD) 151 (15) 164 (17), QoR-40 score without PONV questions, mean (SD) 141 (15) 151 (16), No. of antiemetic doses required after operation, median (IQR) 4.0 (3 6) 3.0 (2 4) to detect a clinically important change, as reflected by an effect size of 0.79, is a clear indication that a change in a person s PONV status can be meaningfully represented by the PONV impact scale. Importantly, this simplified scale can readily be used for both routine inpatient audit and postdischarge telephone or questionnaire review of ambulatory PONV impact scale Fig 2 Changes in the quality of recovery score according to the PONV impact scale. PONV, postoperative nausea and vomiting. QoR-40¼40-item quality of recovery score, ranging up to 180 (excellent recovery). surgical patients. The identification of clinically important PONV can improve the clinical interpretation of PONV studies, and encourage active efforts to reduce its occurrence. Given the weight patients and experienced clinicians 427

6 BJA Myles and Wengritzky Table 4 Tests of discriminative and predictive validity of the PONV impact scale. PONV, postoperative nausea and vomiting Consequences of PONV Clinically important PONV as defined by a nausea vomiting score 5 Odds ratio (95% CI) Yes (n535) (%) No (n5128) (%) Unable to move freely in bed ( ) Unable to drink (2.4 12), Unable to eat (2.0 10), Unable to walk ( ) 0.21 Requires IV fluids (2.0 10), Electrolyte imbalance ( ) 0.63 Other ( ) place on the more severe features of this subset of patients with PONV, 12 in contrast with milder forms of PONV, it is clinically important PONV that should be the primary focus of future PONV studies. We recommend that the PONV impact scale is measured at 6, 24 h or both after surgery for inpatients, and for ambulatory surgical patients up to 24 h posthospital discharge. The Apfel risk score performed well in our study, but it must be kept in mind that we first identified those with PONV or at high-risk of PONV and so we cannot meaningfully calculate predictive values of this score from our data. We did however confirm its utility in identifying clinically important PONV in an environment of PONV patients. The ability of the Apfel score to identify those with clinically important PONV will require a prospective study of unselected patients undergoing surgery, preferably in a setting where prophylactic antiemetic therapy is not used or can be adjusted for. There are some limitations of our study. Our study population does not represent all surgical patients, but only those with PONV or at high risk of PONV. This was a single-centre study completed in Australia. External validation in other settings, ideally recruiting unselected patients who may or may not develop PONV, is required before the PONV impact scale can widely be adopted into clinical and research practice. The attributes of severe nausea included in the guideline to patients when they rated the intensity of their nausea will obviously lead to a stronger correlation with the eventual score, meaning that the odds ratio estimates may be spuriously inflated. But there is no way of separating nausea intensity from its clinical consequences, and in any case all other tests of validity were consistently strong. Differences in hospital stay based on the presence of clinically important PONV is limited by the heterogeneous group of patients undergoing different types of surgery with different levels of postoperative pain and other factors that might affect the duration of hospital stay. In summary, we used psychometric techniques to prospectively validate and test the reliability and responsiveness of a simplified PONV impact scale in a broad surgical setting. The PONV impact scale can be used to identify clinically important PONV. Declaration of interest None declared. Funding This work was supported by an Australian National Health and Medical Research Council (NHMRC) Practitioner s Fellowship awarded to P.S.M. References 1 Gan TJ, Meyer TA, Apfel CC, et al. Society for ambulatory anesthesia guidelines for the management of postoperative nausea and vomiting. Anesth Analg 2007; 105: Myles PS, Hunt JO, Nightingale CE, et al. Development and psychometric testing of a quality of recovery score after general anesthesia and surgery in adults. Anesth Analg 1999; 88: Macario A, Weinger M, Carney S, Kim A. Which clinical anesthesia outcomes are important to avoid? The perspective of patients. Anesth Analg 1999; 89: Gupta A, Wu CL, Elkassabany N, Krug CE, Parker SD, Fleisher LA. Does the routine prophylactic use of antiemetics affect the incidence of postdischarge nausea and vomiting following ambulatory surgery?: A systematic review of randomized controlled trials. Anesthesiology 2003; 99: Revicki DA, Cella D, Hays RD, Sloan JA, Lenderking WR, Aaronson NK. Responsiveness and minimal important differences for patient reported outcomes. Health Qual Life Outcomes 2006; 4: 70 6 Lin KC, Fu T, Wu CY, Wang YH, et al. Minimal detectable change and clinically important difference of the Stroke Impact Scale in stroke patients. Neurorehabil Neural Repair 2010; 24: Cepeda M. What decline in pain intensity is meaningful to patients with acute pain? Pain 2003; 105: Myles PS, Christelis N. Measuring pain and analgesic response. Eur J Anaesthesiol 2011; 28: Moore A, McQuay H, Gavaghan D. Deriving dichotomous outcome measures from continuous data in randomised controlled trials of analgesics. Pain 1996; 66: Revicki DA, Gnanasakthy A, Weinfurt K. Documenting the rationale and psychometric characteristics of patient reported outcomes for labeling and promotional claims: the PRO Evidence Dossier. Qual Life Res 2007; 16:

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