Original Contributions
Prospective validation of clinically important changes in pain severity measured on a visual analog scale*,**,*

https://doi.org/10.1067/mem.2001.118863Get rights and content

Abstract

Background: In a landmark hypothesis-generating study, Todd et al found that a difference of approximately 13 mm (95% confidence interval [CI] 10 to 17 mm) on a visual analog scale (VAS) represented the minimum change in acute pain that was clinically significant in a cohort of trauma patients. Study Objective: We test the hypothesis that the minimum clinically significant change in pain as measured by the VAS in an independent, more heterogeneous validation cohort is approximately 13 mm. Methods: This was a prospective, observational cohort study of adults presenting to 2 urban emergency departments with pain. At 30-minute intervals during a 2-hour period, patients marked a VAS and were asked if their pain was “much less,” “a little less,” “about the same,” “a little more,” or “much more.” All data were obtained without reference to prior VAS scores. The minimum clinically significant change in pain was defined a priori as the difference in millimeters between the current and immediately preceding VAS scores when “a little more” or “a little less pain” was reported. Results: Ninety-six patients enrolled in the study, providing 332 paired pain measurements. There were 141 paired measurements designated by patients as “a little less” or “a little more” pain. The mean clinically significant difference between consecutive ratings of pain in the combined “little less” or “little more” groups was 13 mm (95% CI 10 to 16 mm). The difference between this finding and that of Todd et al was 0 mm (95% CI –4 to 4 mm). Conclusion: These data are virtually identical to previous findings indicating that a difference of 13 mm on a VAS represents, on average, the minimum change in acute pain that is clinically significant. [Gallagher EJ, Liebman M, Bijur PE. Prospective validation of clinically important changes in pain severity measured on a visual analog scale. Ann Emerg Med. December 2001;38:633-638.]

Introduction

Pain is the most frequent reason for emergency department visits in the United States.1 Accurate assessment of pain intensity, which is a necessary prerequisite to rational choice of analgesics, represents a clinically challenging proposition. This challenge is related to the complex nature of pain, which requires cortical interpretation of sensory stimuli within the context of personal and cultural norms for expression of discomfort.2

One of the most frequently used pain rating scales is the visual analog scale (VAS).3 The VAS is a unidimensional scale, with several appealing characteristics. It is easy to use, requires no verbal or reading skills, and is sufficiently versatile to be employed in a variety of settings.4, 5, 6

In an important, hypothesis-generating study, Todd et al7 concluded that a 13-mm difference (95% confidence interval [CI] 10 to 17 mm) on the VAS represented the smallest measurable change in acute pain severity that was clinically important. In this study, the minimum clinically significant difference was defined as the mean difference between VAS scores taken 20 minutes apart among patients experiencing “a little more pain” or “a little less pain.” Despite the relatively small sample size (N=48) consisting exclusively of trauma patients, the findings of this study have become the criterion standard for defining the smallest analgesic effect worth obtaining in the management of acute pain in the ED.

The present study was designed to test the hypothesis that the minimum clinically significant difference in acute pain intensity, as measured by the VAS, is approximately 13 mm in an independent validation cohort of ED patients with heterogeneous causes of pain.

Section snippets

Materials and methods

A prospective, observational cohort study was performed in 2 urban EDs. All English- and Spanish-speaking patients 18 years of age or older presenting to either ED with acute pain as a component of their chief complaint were eligible for inclusion. Acute pain was operationally defined as pain of recent onset (within 24 hours) or exacerbation (also within 24 hours) of preexisting pain of sufficient severity to cause the patient to seek emergency care. Patients with altered mental status or

Results

Of 166 patients in acute pain approached by research assistants, 28 refused to participate, and 42 were unable to do so because of altered mental status, poor vision, lack of comprehension of instructions, or inability to provide informed consent. The remaining 96 patients were entered into the study, generating 332 paired pain measurements for analysis. Seventy-two individuals completed the maximum number of 5 VAS measurements. Mean age of the cohort was 37 years (range 19 to 71 years), of

Discussion

The VAS entered the realm of pain research in the 1980s, demonstrating a greater sensitivity to increments or decrements in pain than other instruments.9, 10 In contrast with verbal rating scales, which require a patient to choose a categorical pain descriptor (eg, mild, moderate, severe), the VAS provides a smooth continuum of choices. If a patient's pain decreases slightly over time, a verbal scale may lack the sensitivity to detect it because a qualitative shift in degree of pain would be

Acknowledgements

Author contributions: EJG and ML designed the study. ML supervised the conduct of the trial and data collection. PEB managed the data, provided statistical consultation, and performed the data analysis. EJG, ML, and PEB drafted the initial manuscript and each contributed substantially to its revisions. EJG takes responsibility for the paper as a whole.

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Address for correspondence: E. John Gallagher, MD, Department of Emergency Medicine, Albert Einstein College of Medicine, Montefiore Medical Center, 111 East 210th Street, Bronx, NY 10467; 718-920-7459, fax 718-798-0730; E-mail [email protected].

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