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.