Prospective validation of clinically important changes in pain severity measured on a visual analog scale

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.