Pediatrics
Determining the minimum clinically significant difference in visual analog pain score for children*

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Abstract

Study Objective: We sought to determine the minimum clinically significant difference in visual analog scale (VAS) pain score for children. Methods: We performed a prospective, single-group, repeated-measures study of children between 8 and 15 years presenting to an urban pediatric emergency department with acute pain. On presentation to the ED, patients marked the level of their pain on a 100-mm nonhatched VAS scale. At 20-minute intervals thereafter, they were asked to give a verbal categoric rating of their pain as “heaps better,” “a bit better,” “much the same,” “a bit worse,” or “heaps worse” and to mark the level of pain on a VAS scale of the same type as used previously. A maximum of 3 comparisons was recorded for each child. The minimum clinically significant difference in VAS pain score was defined as the mean difference between current and preceding scores when the subject reported “a bit worse” or “a bit better” pain. Results: Seventy-three children were enrolled in the study, yielding 103 evaluable comparisons in which pain was rated as “a bit better” or “a bit worse.” The minimum clinically significant difference in VAS score was 10 mm (95% confidence interval 7 to 12 mm). Conclusion: This study found the minimum clinically significant difference in VAS pain score for children aged 8 to 15 years (on a 100-mm VAS scale) to be 10 mm (95% confidence interval 7 to 12 mm). In studies of populations, differences of less than this amount, even if statistically significant, are unlikely to be of clinical significance. [Powell CV, Kelly A-M, Williams A. Determining the minimum clinically significant difference in visual analog pain score for children. Ann Emerg Med. January 2001;37:28-31.]

Introduction

“Health care is both a technical and an ethical enterprise. The ethical obligation to manage pain and relieve the patient’s suffering is at the core of a health care professional’s commitment.”1

Managing pain is one of the key goals of health care workers. However, to assess the quality of pain-management efforts and to evaluate new pain-management techniques, pain must be measured, the results must be analyzed, and differences must be assessed for significance.

In pain research, the method commonly used for the quantification of pain severity and relief is the visual analog scale (VAS).2 The VAS is easy to use, the results are reproducible, and it can be applied in a variety of practice settings.2 It is sensitive to treatment effects, and the data derived can usually be analyzed by using parametric statistical techniques.3, 4 It has been validated for use with adults and children as young as 5 years5, 6; however, research suggests that children younger than 8 years may be unable to meaningfully separate pain intensity from affective distress.7

Despite the strengths of VAS as a measurement and research tool, relying on statistically significant differences may overestimate the clinical importance of small differences in scores. Although statistical significance is an essential requirement for judging one treatment to be superior to another, it is not necessarily the same as clinical significance. For pain research, one of the challenges is to determine the minimum clinically significant difference (MCSD) in pain experience.

Previous research in adults has found the MCSD in VAS pain scores to be of the order of 10 mm.8, 9 Additionally, it has been shown that the MCSD in the VAS score did not differ in adults with age, sex, or cause of pain.9

Pain experience is a complex interplay of physiologic, psychologic, cultural, and situational factors.10 Children differ from adults in many of these ways,7, 10 and thus it is possible that the MCSD in the VAS pain score for children is quite different from that for adults. To date, no studies investigating the MCSD in the VAS pain score in children have been published.

The aim of this study was to determine the MCSD in VAS pain score for children.

Section snippets

Materials and methods

This prospective, single-group, repeated-measures study of children between 8 and 15 years was conducted in the emergency department of Sunshine Hospital, a 200-bed community teaching hospital with a pediatric ED. The project was approved by the Research and Ethics Committee of the North Western Healthcare Network.

This observational study was conducted on a convenience sample of children between 8 and 15 years (inclusive) presenting to the ED with acute pain of either traumatic or nontraumatic

Results

A total of 73 children completed the study, with a mean age of 12 years (median, 12 years). Causes of pain were limb trauma (n=36), abdominal pain (n=22), head/face trauma (n=6), medical (n=3), back trauma (n=2), abdominal trauma (n=2), and headache (n=2). No patients with sickle cell disease were enrolled.

Sixty-three children completed 3 comparisons, 8 completed 2 comparisons, and 2 completed only 1 comparison. The average number of comparisons per subject was 2.8. Initial VAS scores covered

Discussion

To improve the quality of pain management and to evaluate new pain management techniques, pain must be measured, the results must be analyzed, and changes must be assessed for clinical significance. The determination of clinical significance poses the biggest challenge.

The method commonly used for measuring pain is the VAS. Despite its power as a measurement and research tool, it can be tempting to overestimate the clinical importance of small differences in scores because they reach

Acknowledgements

We acknowledge the assistance of the nursing staff of the Department of Emergency Medicine, Sunshine Hospital, for their efforts in data collection, and Professor Michael Campbell of the Sheffield Centre for Health and Related Research, University of Sheffield, and Associate Professor Stephen Farish, University of Melbourne, for statistical advice.

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*

Address for reprints: Anne-Maree Kelly, MD, Department of Emergency Medicine, Western Hospital, Private Bag, Footscray, Vic 3011, Australia; +61 3 9319 6315, fax +61 3 9318-4790; E-mail, Anne-Maree [email protected].

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