Reliability of the visual analog scale for measurement of acute pain

Objective: Reliable and valid measures of pain are needed to advance resear ch initiatives on appropriate and effective use of analgesia in the emergen cy department (ED). The reliability of visual analog scale (VAS) scores has not been demonstrated in the acute setting where pain fluctuation might be greater than for chronic pain. The objective of the study was to assess th e reliability of the VAS for measurement of acute pain. Methods: This was a prospective convenience sample of adults with acute pain presenting to two EDs. Intraclass correlation coefficients (ICCs) with 95% confidence interv als (95% CIs) and a Bland-Altman analysis were used to assess reliability o f paired VAS measurements obtained 1 minute apart every 30 minutes over two hours. Results: The summary ICC for all paired VAS scores was 0.97 [95% Cl = 0.96 to 0.98]. The Bland-Altman analysis showed that 50% of the paired m easurements were within 2 mm of one another, 90% were within 9 mm, and 95% were within 16 mm. The paired measurements were more reproducible at the ex tremes of pain intensity than at moderate levels of pain. Conclusions: Reli ability of the VAS for acute pain measurement as assessed by the ICC appear s to be high. Ninety percent of the pain ratings were reproducible within 9 mm. These data suggest that the VAS is sufficiently reliable to be used to assess acute pain.