Postsurgical pain outcome assessment

Reliable and valid measures of pain are essential for conducting clinical trials of pain treatments. Perhaps the most important aspect of a pain measure's validity is its sensitivity, or ability to detect changes in pain over time and due to treatment. Several factors may affect a measure's sensitivity, including the complexity of the rating task for the measure, the number of pain intensity levels assessed by the measure, the dimension of pain assessed (e.g. pain intensity vs. pain relief), and the number of individual ratings (e.g. single rating vs. composite score) used to create the measure. The purpose of this study was to compare the relative sensitivity of three measures of outcome and a composite made up of all three measures for detecting analgesic effects in two samples of persons participating in a randomized controlled trial. One hundred and twenty-three patients who had undergone knee surgery and 124 women who had undergone a laparotomy were given one of three medications in the day after their surgery: morphine, ketorolac, or placebo. Two measures of pain intensity (a visual analog scale (VAS) and a 4-point verbal rating scale (VRS)) were administered at baseline, and these measures plus a 5-point VRS of pain relief were administered at 16 additional time points up to 24 h following surgery. As predicted, we found variability in the sensitivity of the outcome measures used in these studies, with the 4-point VRS showing less sensitivity than the VAS or relief ratings. However, contrary to our prediction, a composite measure of outcome made up of all three measures was not consistently superior to the individual measures for detecting treatment effects. Finally, we found that pain relief ratings were related to, but also distinct from, change in pain intensity as measured by changes in pain intensity ratings from baseline to each postmedication assessment point. These findings have important implications for the assessment of pain in clinical trials. (C) 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.