The visual analogue pain intensity scale: what is moderate pain in millimetres?

One way to ensure adequate sensitivity for analgesic trials is to test the intervention on patients who have established pain of moderate to severe intensity. The usual criterion is at least moderate pain on a categorical pain intensity scale. When visual analogue scales (VAS) are the only pain measure in trials we need to know what point on a VAS represents moderate pain, so that these trials can be included in meta-analysis when baseline pain of at least moderate intensity is an inclusion criterion. To investigate this we used individual patient data from 1080 patients from randomised controlled trials of various analgesics. Baseline pain was measured using a 4-point categorical pain intensity scale and a pain intensity VAS under identical conditions. The distribution of the VAS scores was examined for 736 patients reporting moderate pain and for 344 reporting severe pain. The VAS scores corresponding to moderate or severe pain were also examined by gender. Baseline VAS scores recorded by patients reporting moderate pain were significantly different from those of patients reporting severe pain. Of the patients reporting moderate pain 85% scored over 30 mm on the corresponding VAS, with a mean score of 49 mm. For those reporting severe pain 85% scored over 54 mm with a mean score of 75 mm. There was no difference between the corresponding VAS scores of men and women. Our results indicate that if a patient records a baseline VAS score in excess of 30 mm they would probably have recorded at least moderate pain on a 4-point categorical scale.