Original Contributions
Reliability and validity of a visual analog scale for acute abdominal pain in the ED*,**

Presented at the Annual Meeting of the Society for Academic Emergency Medicine, Atlanta, GA, May 2001.
https://doi.org/10.1053/ajem.2002.33778Get rights and content

Abstract

The objective of the study was to assess the validity and reliability of the visual analog scale (VAS) in the measurement of acute abdominal pain, and to identify the minimum clinically significant difference in VAS scores among patients with acute abdominal pain. The study was undertaken in preparation for a randomized clinical trial of opioid use in acute abdominal pain. A prospective, observational cohort study of a convenience sample of patients presenting to 2 urban EDs with the chief complaint of acute abdominal pain was conducted. At time 0 and 1 minute later each subject indicated pain severity on a 100mm VAS. This was repeated every 30 minutes for 2 hours. Patients were also asked to contrast their current pain severity with their pain in the preceding 30 minutes using one of 5 graded verbal descriptors: “much less pain,” “little less pain,” “the same pain,” “little more pain,” and “much more pain.” Validity was assessed by performing an analysis of variance for linear trend on the association between the 5 categorical pain descriptors and change in VAS scores. Reliability was assessed using the intra-class correlation coefficient (ICC) between VAS scores taken 1 minute apart, supplemented by a Bland-Altman analysis. The minimum clinically significant difference in pain was defined as the mean difference between sequential VAS scores obtained 30 minutes apart when the patient noted a “little less” or “little more” pain. Differences in VAS scores increased linearly as pain descriptors escalated from “much less” to “much more” pain (P <.001). Reliability was high, ICC = 0.99 [95%CI 0.989 to 0.992] for 0 and 1 minute VAS scores. The minimum clinically significant difference in acute abdominal pain was 16 mm (95% CI 13, 18 mm). VAS measures of acute abdominal pain are valid and reliable. The 95% CI surrounding the minimum clinically significant difference of approximately 16mm overlaps with the 95% CI of minimum clinically significant difference of approximately 13mm reported previously in traumatic and other types of acute pain. We conclude that the VAS is a methodologically sound instrument for quantitative assessment of acute abdominal pain and for detecting clinically important changes in such pain. (Am J Emerg Med 2002;20:287-290. Copyright 2002, Elsevier Science (USA). All rights reserved.)

Section snippets

Study design

A prospective observational cohort design was used to assess the validity and reliability of VAS pain measurements. The study was approved by the Institutional Review Boards of the 2 hospitals from whose EDs all acute abdominal pain patients were obtained. All patients gave written informed consent in English or Spanish.

Study setting and population

The study took place in 2 large academic EDs serving an inner-city population. All English and Spanish speaking patients 18 years of age or older who presented to the ED with

Results

A total of 101 patients were enrolled in the study, 61% were women and the mean age was 40 years (range 15 to 88). There were 469 paired measures on the VAS made one minute apart, and 371 measures of change in pain over 30 minute time periods.

Discussion

There have been no previously published studies of the reliability and validity of VAS measures of acute abdominal pain. One previous study of reliability of a VAS for pain in an ED sample with heterogeneous causes of pain found a similar level of reliability, with an ICC of 0.98, and an interval ranging from −16 to +16 mm that included 95% of the differences taken 1 minute apart.15 A study of postoperative pain that looked at reproducibility of VAS pain assessments over a 3-minute interval

Limitations

The findings of this study come from a sample of patients who presented to 2 inner-city EDs in a single county. Although the results may not be generalizable to patients in other settings, the striking similarity of the findings in this study of acute abdominal pain, a study of traumatic pain,8 and two studies enrolling all ED patients with pain,9, 10 suggests that the ability of patients to rate their own pain on a VAS is relatively independent of study population demographics.

The actual

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0735-6757/02/2004-0005$35.00/0

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