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AMBULATORY ANESTHESIA

Reliability and Validity of the Perioperative Opioid-Related Symptom Distress Scale

Department of Anesthesia and Critical Care, University of Chicago Hospital, Chicago, Illinois

Address correspondence and reprint requests to Jeffrey L. Apfelbaum, MD, Department of Anesthesia and Critical Care, University of Chicago Hospital, 5841 S. Maryland Ave., Chicago, IL 60637. Address e-mail to jeffa{at}dacc.uchicago.edu

	Abstract

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A reduction in opioid use may reduce the incidence and severity of opioid-related side effects. However, no published studies have demonstrated this relationship. In a prospective, placebo-controlled, randomized trial of analgesia for laparoscopic cholecystectomy, we validated an opioid-related symptom distress scale (SDS) questionnaire and clinically meaningful events (CMEs). A total of 193 patients completed the SDS questionnaire every 24 h after discharge for 7 days. This analysis was based on data from Day 1 only. The SDS assessed 12 common opioid-related symptoms, including nausea, vomiting, and difficulty passing urine, by 3 ordinal measures: frequency, severity, and bothersomeness. Patients with responses of "frequently" to "almost constantly," "moderate" to "very severe," or "quite a bit" to "very much bothered" were considered to have a CME. A detailed postoperative recovery survey of patient functional status and experience of adverse effects was used to validate the SDS. Validation measures in the recovery survey were categorized as nonspecific (e.g., level of normal activities) and specific (e.g., number of times vomited in 24 h, minutes of nausea in 24 h, and ability to void normally). SDS scores and CMEs for nausea, vomiting, and difficulty passing urine were strongly associated with three related validation measures from the recovery survey: minutes of nausea within 24 h, number of times vomited within 24 h, and ability to void normally, respectively (P < 0.0001). There was also a strong association between SDS scores and CMEs for nausea, vomiting, and voiding and general recovery validation measures, although the association was significantly weaker than that for symptom-specific validation measures. CMEs for nausea, vomiting, and voiding showed a high specificity and lower sensitivity with directly assessed responses. The SDS questionnaire and CMEs are valid tools for assessing postoperative opioid-related symptoms after laparoscopic cholecystectomy. Symptoms defined as CMEs through the SDS may be more sensitive than those identified by direct assessment.

IMPLICATIONS: The symptom distress scale (SDS) was designed to evaluate the level of distress associated with the adverse effects of commonly used opiates. This study reports on the reliability and validity of the SDS in a group of patients undergoing laparoscopic cholecystectomy. The validity of the SDS was demonstrated by using specific symptoms directly assessed in the clinical trial and patient responses to questions regarding general satisfaction and daily activities.

	Introduction

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It is a commonly held perception that reducing the opioid dose for postsurgical patients reduces opioid-related adverse effects. However, there are few well designed studies to demonstrate this relationship, and some of them suggest that opioid-related adverse effects are not dose dependent (1–3).

Symptom distress is defined as the degree of discomfort reported by patients from symptoms experienced. It is often measured by symptom occurrence (frequency), characteristics (severity), and distress (bothersomeness) (4–6). A symptom distress scale (SDS), created for a clinical trial to measure opioid-related adverse effects directly, assessed the effect of reducing opioid doses on postoperative pain treatment (7,8). The validity of the opioid-related SDS as a tool to monitor the effect of opioid-related adverse effects after surgery has not been reported.

The opioid-related SDS was adapted from the Memorial Symptom Assessment Scale (MSAS), a validated instrument for the evaluation of symptom frequency, severity, and distress (4). The MSAS and other SDSs have been validated to assess symptoms in cancer patients (4,9), but not in patients in a postoperative setting. The rates of opioid-related adverse effects collected through spontaneous reports in clinical trials may be less than rates obtained through direct assessment (2,3,7,8). Therefore, the benefit of new pain-management drugs with opioid-sparing effects may be underestimated. The use of an SDS scale is one way to assess symptoms beyond adverse events reported spontaneously. This scale may be useful when adverse events differ in type and magnitude or when treatments vary.

Valdecoxib, a highly specific inhibitor of the cyclooxygenase-2 enzyme, and its parenteral prodrug parecoxib sodium are effective opioid-sparing analgesics for postoperative pain (10–13). Because of their cyclooxygenase-1-sparing nature, they also have no clinically significant effects on platelet aggregation or bleeding time compared with conventional nonspecific nonsteroidal antiinflammatory drugs (14,15). We used the opioid-related SDS to assess the analgesic efficacy of parecoxib and valdecoxib for treating postoperative pain after laparoscopic cholecystectomy (LC) (16). To establish the validity of the SDS, we tested the correlation of SDS scores and clinically meaningful events (CMEs) with external variables.

	Methods

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This analysis was based on data from a previous study that included patients aged 18–75 yr who required elective ambulatory LC (16). Patients were excluded if they had clinically diagnosed acute pancreatitis, were scheduled to undergo any other surgical procedure expected to produce more trauma than LC alone, had acute preoperative pain other than biliary colic, required chronic pain treatment, or had current or recent cancer. Written informed consent was obtained from all patients, and the study protocol was approved by the institutional review boards of the 24 study sites.

The study design and dosing regimen are reported elsewhere. Briefly, patients received IV parecoxib 40 mg or placebo 30–45 min before surgery and oral valdecoxib 40 mg or placebo each day after surgery up to Day 4 and as needed on Days 5–7. Additionally, all patients received standard-of-care IV fentanyl on demand for treatment of pain in the early postoperative period and were allowed to take supplementary hydrocodone 5 mg/acetaminophen 500 mg (Vicodin®; one or two tablets orally every 4–6 h as needed, with a maximum number of six tablets for Day 0 and eight tablets for Days 1–7) (16).

Opioid-related symptoms were assessed daily with an opioid-related SDS adapted from the MSAS (4). A Health Outcomes Recovery Questionnaire (HORQ) was also administered and included questions regarding patient satisfaction, daily activities, and opioid-related symptoms. The HORQ was used to validate the opioid-related SDS in this analysis. The SDS and HORQ were administered by telephone on Days 1–2 and collected via patient diary on Days 3–7.

Because opioid use is usually greatest in the first 24 h after surgery, the patient is at most risk for opioid-related adverse effects during this period. Therefore, we focused on Day 1 responses only.

Previous analyses using this opioid-related SDS demonstrated a linear dose-response relationship between the morphine-equivalent dose and the incidence of CMEs, irrespective of treatment regimen (i.e., whether patients received placebo or parecoxib/valdecoxib plus standard-of-care opioids). Therefore, we thought that differences in treatment effects should not affect the correlation between SDS-measured symptoms and external validation measures, and analyses in this study were conducted among all eligible patients.

Twelve opioid-related symptoms were assessed by the SDS: nausea, vomiting, constipation, difficulty passing urine, difficulty concentrating, drowsiness or difficulty staying awake, feeling lightheaded or dizzy, feeling confused, feelings of general fatigue or weakness, itchiness, dry mouth, and headache. SDS scores for each symptom were assessed according to frequency, severity, and bothersomeness and were recorded by using categorical scales (Appendix 1) according to methods developed by Portenoy et al. (4). The average SDS score for each symptom was calculated by taking the mean of patient-reported scores for each of the three symptom distress dimensions (Appendix 1). The overall composite SDS score was the mean of each of the 12 individual symptom SDS scores. By taking the mean score of all 12 symptoms in each dimension, dimension-specific composite SDS scores for frequency, severity, and bothersomeness were created.

Definitions of CMEs are reported in Appendix 1 (4). The total number of CMEs on Day 1 was also calculated, ranging from 0 to 12, by summing all CMEs for each patient. Total CMEs were categorized as zero, one, two, or three or more CMEs. If more than one dimension had a response that fit the CME category, a CME for that symptom was recorded.

The HORQ administered on Day 1 included questions regarding daily activities and opioid-related symptoms. Validation measures are summarized in Appendix 1. Questions related to general activities (activity level and hours of assistance required) were used to validate each of the 12 opioid-related SDS scores, the CMEs, and the summary measures. Questions related to specific symptoms (e.g., nausea, vomiting, and difficulty passing urine) were used to validate corresponding SDS scores and CMEs for individual symptoms and summary measures. Some response levels for a given measure were combined during analysis because of small patient counts.

Spontaneous adverse events for the 12 opioid-related symptoms, as reported to study investigators on Day 1, were also summarized and used to validate corresponding CMEs as derived from SDS scores.

Demographic and patient characteristics were described by using means for continuous variables and proportions for categorical variables. Cronbach’s coefficient was used to assess the internal consistency of frequency, severity, bothersomeness, and overall mean scores for each symptom and for summary SDS scores.

Content validity asks whether all relevant concepts are represented by the measure. On the basis of the literature, relevant concepts necessary to assess opioid-related symptoms were represented (i.e., high frequency of symptoms of opioid use) (17). Histograms were created for mean frequency, severity, and bothersomeness SDS scores and overall mean SDS score from two groups: patients with one CME or more or patients without CMEs. The Wilcoxon test and N-way analysis of variance, with adjustment for potential confounders, were used to compare SDS scores between patients with and without CMEs.

Construct validity asks whether the measures that the SDS evaluates correlate with measures of other variables in the hypothesized way. To assess construct validity, an exploratory principal components analysis with orthogonal varimax rotation was initially performed with mean SDS scores for all 12 symptoms.

Day 1 SDS scores were assessed by comparing symptom scores with validation measures. General validation measures were compared with each of the 12 opioid-related SDS scores and with summary dimension-specific measures. Symptom-specific validation measures were compared with SDS scores for nausea, vomiting, and difficulty passing urine and with summary dimension-specific measures.

Pairwise correlation between mean SDS scores and continuous measures (hours of assistance, percentage of normal activities performed, minutes nauseated, and times vomited) was assessed by Spearman correlation and linear regression, after adjusting for confounders. Association of mean SDS scores with validation measures was tested by N-way analysis of variance before and after adjusting for potential confounders.

CMEs for each symptom were compared with dichotomous validation measures by Fisher’s exact test and with ordinal validation measures by the Cochran-Armitage trend test. Association of the number of patients with zero, one, two, or three or more CMEs with validation measures was assessed by using the Cochran-Armitage trend test for dichotomous variables or the Jonckheere-Terpstra test for ordinal variables (18).

Known group validity assesses whether scores for patients reporting nausea, vomiting, and so on as adverse events are different from scores for patients who did not report such adverse events. Directly assessed clinical measures were available to evaluate the known group validity. The expectation was that patients who reported nausea, vomiting, and/or difficulty passing urine would report a higher degree of bothersomeness, frequency, and severity for these symptoms on the SDS.

Responsiveness calculates the sensitivity and specificity of SDS scores for nausea, vomiting, and difficulty passing urine with the respective validation measures. For the nausea or vomiting validation measure, both "yes, but no medication" and "yes, and taking medication" categories were combined to calculate sensitivity and specificity. The validity of these CMEs was also assessed with the statistic (19).

Reported spontaneous adverse events for the 12 symptoms were also compared with CMEs to assess responsiveness. Both specificity and sensitivity of the CME to detect a spontaneously reported adverse event were measured, as was the statistic.

All analyses were performed with SAS (Version 8.2; SAS Institute Inc., Cary, NC). All P values are two tailed (8).

	Results

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The efficacy data for this study, SDS scores, and opioid-related CME outcomes are reported elsewhere (7,8,16). Of the 193 patients included in this analysis, 104 received parecoxib/valdecoxib plus opioids, and 89 received the placebo plus opioids. Patients who received IV parecoxib and oral valdecoxib 40 mg each day required significantly less fentanyl (21% less) and less oral opioid rescue medication and reported less pain intensity than those who received placebo (P < 0.05). Additionally, IV parecoxib and follow-up oral valdecoxib resulted in a significant reduction of opioid-related adverse effects, as measured by SDS scores and CMEs (7). Regardless of the treatment arm, once the daily morphine equivalent dose reached a threshold, every 3- to 4-mg increase was associated with one additional clinically meaningful opioid-related symptom (8).

Table 1 shows the distribution of demographic characteristics and clinical features for all study patients. Table 2 shows mean individual SDS scores by level of symptom frequency, severity, and distress and by CMEs. Internal consistency among the three dimensions, for all symptoms and for composite measures, was confirmed by the Cronbach coefficient (range, 0.92–0.98). Patients with responses of "frequently to constantly," "moderate to very severe," and "quite a bit" to "very much" bothered for each symptom had significantly higher individual SDS scores than those without such responses for all symptoms except for confusion (P < 0.0001). No frequent, severe, or bothersome events were recorded for confusion. Patients with a specific CME had significantly higher SDS scores than those without, except for confusion (Table 2). The SDS scores of patients with a CME were 10 times more than those of patients without a CME.

Composite frequency, severity, and bothersomeness SDS scores, as well as overall SDS scores, were significantly associated with the following: percentage of normal activities performed (0%–100%), hours of assistance needed at home (0–24 h), minutes of nausea, and number of times vomited within the last 24 h (P < 0.001). However, correlation of each symptom SDS score with the external measures varied; e.g., both nausea and vomiting were slightly correlated with the percentage of normal activities performed (r = 0.185 and r = 0.158, respectively) but were not significantly correlated with hours of assistance needed at home. Conversely, because minutes of nausea and number of times vomited were specifically related to SDS scores for nausea and vomiting, correlations among these variables were much stronger (minutes of nausea with SDS nausea, r = 0.922; minutes of nausea with SDS vomiting, r = 0.517; times vomited and SDS nausea, r = 0.481; times vomited and SDS vomiting, r = 0.899). As shown above, correlation coefficients between two nausea measures (r = 0.922) and between two vomiting measures (r = 0.899) were much stronger than those comparing nausea and vomiting simultaneously (r = 0.517 and r = 0.481).

Patients able to perform normal or light activity outside the home had significantly lower frequency, severity, and bothersomeness, as well as overall SDS scores, than those with lower levels of activity (P 0.01) (Table 3). Nausea, difficulty concentrating, drowsiness, and fatigue had a major effect on the level of patients’ daily activities. Patients with less-than-normal levels of daily activity also had significantly larger proportions of CMEs for nausea, vomiting, drowsiness, dizziness, and fatigue, as well as total CMEs (P < 0.05).

Minutes of nausea within the last 24 h was strongly associated with the nausea SDS score (Table 5). A trend of an increasing number of minutes of nausea with the SDS nausea score was clear (P < 0.0001). Although the vomiting SDS score and other composite scores were also associated with the minutes of nausea in the last 24 h, the trend of association was not as clear as that for the nausea SDS score. Analysis based on CMEs for nausea and vomiting also showed clear trends of association (P < 0.0001).

The number of times vomited within the last 24 h was also associated with nausea and vomiting SDS scores and CMEs (Table 6). Specificity, sensitivity, and statistics were 0.94, 0.82, and 0.55 (95% CI, 0.33–0.76) for nausea; 0.99, 0.64, and 0.72 (95% CI, 0.49–0.95) for vomiting; and 0.94, 0.82, and 0.55 (95% CI, 0.33–0.76) for nausea and vomiting (P < 0.0001).

The SDS score for difficulty passing urine was strongly associated with the external measure used to assess patient voiding. For patients who voided normally, the mean SDS score was 0; it increased to 2.085 for those not able to void normally (P < 0.0001) (Table 6). Although composite dimension SDS scores and the overall SDS score were also significantly associated with voiding conditions, the association was not as strong as for difficulty passing urine (mean SDS scores: 0.3–0.4 vs 0.7–0.9). Difficulty-passing-urine CMEs were consistent with patient-reported voiding, and there were no patients with a difficulty-passing-urine CME among the normally voiding patients. Of abnormally voiding patients, 67% had a CME for difficulty passing urine. The specificity, sensitivity, and statistics for difficulty-passing-urine CMEs against patient-reported voiding were 1.00, 0.67, and 0.78 (95% CI, 0.62–0.95) (P < 0.0001).

When patients who reported adverse events spontaneously were compared with patients who had corresponding CMEs, a larger percentage of patients experiencing CMEs did not report adverse events spontaneously (Table 7). Overall, the specificity of spontaneously reported adverse events to assess CMEs ranged from 0.96 and 0.99, and the sensitivity ranged from 0.08 to 0.40. The coefficients ranged from 0.06 to 0.44 across the 12 opioid-related symptoms, indicating marginal reproducibility between spontaneously reported adverse events and CMEs (Table 7).

	Discussion

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SDS scores and the percentage of patients with a CME were strongly correlated with external, directly assessed, symptom-specific measures (such as nausea, vomiting, and voiding) and general recovery measures (such as levels of daily activity and hours of assistance needed at home). The association between symptom-specific SDS scores or CMEs and symptom-specific clinical measures—such as minutes of nausea, number of times vomited in 24 hours, and ability to void normally—was much stronger than the trends in association between SDS scores and recovery measures. Patients with multiple CMEs were more likely to report lower levels of satisfaction, lower levels of daily activity, and the need for more hours of assistance at home than those with no CMEs.

Thus, we were able to prove consistency of nausea, vomiting, and voiding with symptom-specific directly assessed clinical measures. Both SDS scores and CMEs are powerful new tools for monitoring opioid-related adverse events, such as nausea, vomiting, and difficulty passing urine, in a postoperative setting. This new scale may provide an alternative method to other means of recording and reporting opioid side effects, such as spontaneous reports, that will be of value in comparative studies of opioid dose reduction. Because specific external variables were lacking for drowsiness, dizziness, fatigue, difficulty concentrating, itchiness, dry mouth, and headache, similar analyses were not possible for these symptoms. These symptoms may be effects of general anesthesia rather than being opioid specific. Nonetheless, individual and composite SDS scores and CMEs for drowsiness, dizziness, and fatigue were significantly associated with patients’ levels of daily activity and hours of assistance needed at home. These symptoms have a negative effect on patients’ daily activity levels and, therefore, potentially on patients’ return to normal function after surgery.

The high specificity and low sensitivity of spontaneously reported adverse events for CMEs suggest that spontaneous reports do not capture all of the events that the CME does. Many patients who indicated an event in the SDS did not also spontaneously report an adverse event. Moreover, the high specificity and sensitivity of CMEs for nausea, vomiting, and voiding compared with direct assessments suggest that symptoms recorded by CMEs can also be measured by direct assessment but that CMEs may be interpreted as the more clinically meaningful.

CMEs may be more easily interpreted in clinical practice than numeric SDS scores because symptoms are interpreted and perceived differently by patients. In a recent study, patients reacted differently to the adverse effects of opioids with analgesia in the postoperative period when patient-controlled analgesia was used to deliver opioids (20). Patients had different relative preferences for different types of opioid-related side effects and were willing to different degrees to trade off pain relief for fewer adverse effects. Therefore, it is important to assess CMEs as interpreted by patients when the incidence of adverse events is assessed. High statistics between CMEs of specific symptoms and clinically specific symptoms suggest that CMEs could be used to collect opioid-related adverse effects when postoperative pain is managed. However, neither SDS scores nor CMEs alone were sufficient to accumulate data about all complications. It may be necessary to use both in clinical practice to gain a full picture of patient pain and adverse effect management.

These analyses were based on data from outpatients who had undergone ambulatory laparoscopic procedures for cholecystectomy. Because the severity of postoperative pain and opioid doses to manage pain may vary for surgical procedures, our results may not be generalizable to patients who have had other surgical procedures after which fewer or more opioids have been administered. Additional studies should be conducted to establish the validity of using the opioid-related SDS questionnaire after a broader spectrum of surgical procedures. Our analyses are based on data from a well controlled clinical trial. In clinical trials, inclusion and exclusion criteria for patients, procedures, and postoperative management may differ significantly from clinical practice. Therefore, caution should be exercised in the application of our findings to clinical practice. The validation measures reported were based only on scores obtained from postoperative Day 1, when most opioid-related adverse effects occur. Further analyses may be necessary to assess the validity of opioid-related SDS scores and CMEs over a longer postoperative recovery period.

In conclusion, SDS scores and CMEs obtained from the SDS questionnaire are valid tools for monitoring opioid-related adverse effects in surgical patients who have received opioids to manage postoperative pain.

	Acknowledgments

 
Supported by Global Health Outcomes, Pfizer Global Pharmaceuticals (Skokie, IL), and Pharmacia Corp. (Peapack, NJ).

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Apfelbaum, J. L. Articles by Chen, C. Search for Related Content PubMed PubMed Citation Articles by Apfelbaum, J. L. Articles by Chen, C. Related Collections Ambulatory Pain Pharmacology