Objective: The aim of this study was to define the degree of change on a visual analogue scale that corresponded to a clinically meaningful reduction in the level of pain reported by patients experiencing acute pain.
Method: Secondary analysis of data was performed from prospective, descriptive studies of 152 adults and 73 children presenting to emergency departments with acute pain. At presentation and at 20 min intervals to a maximum of three measurements, patients marked the level of their pain on a 100 mm, non-hatched visual analogue scale. At each follow up, they also gave a verbal rating of their pain as 'a lot better', 'a little better', 'much the same', 'a little worse' or 'much worse'. Data from the groups reporting that pain was 'a lot better' and 'about the same' were analysed for mean and median absolute change in visual analogue scale and compared.
Results: Of 559 pain comparisons, 60 were rated as 'a lot better' and 257 as 'about the same'. The mean absolute change in visual analogue scale for the group reporting that pain was 'a lot better' was 24 mm (median = 19 mm, 95% confidence interval = 17-31 mm). For the group reporting that pain was 'about the same', the mean visual analogue scale change was 0 mm (median = 0 mm, 95% confidence interval = -1 to 1 mm).
Conclusion: When evaluating treatments for acute pain, a difference in visual analogue scale pain score of less than about 20 mm is unlikely to be clinically meaningful. Studies should be designed and reported relative to this benchmark rather than the minimum clinically significant difference in visual analogue scale pain score.