Clinical Significance of Reported Changes in Pain Severity,☆☆,

Presented at the Society for Academic Emergency Medicine Annual Meeting, Washington DC, May 1995.
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Abstract

Study objective: To determine the amount of change in pain severity, as measured by a visual analog scale, that constitutes a minimum clinically significant difference. Methods: Patients 18 years of age or older who presented with acute pain resulting from trauma were enrolled in this prospective, descriptive study. The setting was an urban county hospital emergency department with a Level I trauma center. In the course of a brief interview, patients were asked to indicate their current pain severity with a single mark through a standard 100-mm visual analog scale. At intervals of 20 minutes for the next 2 hours, patients were asked to repeat this measurement and, in addition, to contrast their present pain severity with that at the time of the previous measurement. They were to indicate whether they had "much less," "a little less," "about the same," "a little more," or "much more" pain. All contrasts were made without reference to prior visual analog scale measurements. A maximum of six measurements of pain change were recorded per patient. Measurements ended when the patient left the ED or when the patient reported a pain score of zero. The minimum clinically significant change in visual analog scale pain score was defined as the mean difference between current and preceding visual analog scale scores when the subject noted a little less or a little more pain. Results: Forty-eight subjects were enrolled, and 248 pain contrasts were recorded. Of these contrasts, 41 were rated as a little less and 39 as a little more pain. The mean difference between current and preceding visual analog scale scores in these 80 contrasts was 13 mm (95% confidence interval, 10 to 17 mm). Conclusion: The minimum clinically significant change in patient pain severity measured with a 100-mm visual analog scale was 13 mm. Studies of pain experience that report less than a 13-mm change in pain severity, although statistically significant, may have no clinical importance. [Todd KH, Funk KG, Funk JP, Bonacci R: Clinical significance of reported changes in pain severity. Ann Emerg Med April 1996;27:485-489.]

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INTRODUCTION

Investigators involved in pain research commonly use visual analog scales to measure pain severity and pain relief.1 Among other advantages, visual analog scales offer ease of use in a variety of settings and can be administered with a minimum of training. Visual analog scales are sensitive to treatment effects, and their data can often be analyzed with parametric statistical techniques.2 The latter characteristics are particularly important to investigators seeking a powerful assessment tool

MATERIALS AND METHODS

A prospective, descriptive study of the acute pain experience was conducted in an urban county hospital ED with a Level I trauma center. The study protocol was approved by the Emory University Human Investigations Committee.

The study was conducted on eight nonconsecutive days in December 1994 and January 1995 when research assistants were available. Between the hours of 10 AM and 6 PM, ED patients 18 years of age or older who had trauma with complaints of pain were enrolled in the study.

RESULTS

Forty-eight patients were enrolled; they produced a total of 248 pain contrasts, for a mean of 5.2 pain contrasts per subject. Thirty-two patients completed the maximum number of six contrasts. Characteristics of the study group and their injuries are detailed in Table 1. Initial pain severity scores varied over the entire 100-mm range, with a slight skew toward more severe scores, as shown in Figure 1. Mean and median initial pain scores were 56 mm and 60 mm, respectively.

. Initial pain severity

DISCUSSION

Others have attempted to determine the minimum clinically important difference for a variety of assessment instruments, including quality of life measures for chronic heart and lung disease, rheumatoid arthritis, and other arthritic conditions.4, 5, 6 The basic approach in these studies has involved referencing differences in instrument scores to categorical ratings of changes in health status. For example, patients may be asked to rate themselves using an instrument and then to compare their

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From the Division of Emergency Medicine, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia.

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Address for reprints: Knox H Todd, MD, MPH, Center for Injury Control, Rollins School of Public Health of Emory University, 1518 Clifton Road Northeast, Room 254, Atlanta, Georgia 30322, 404-727-1265, Fax 404-727-8744

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