Acute pain: combination treatments and how we measure their efficacy.

Perioperative analgesic strategies are frequently tested using analgesic consumption as an outcome measure. This outcome measure is intuitive and superficially attractive, but has not been evaluated rigorously. Flaws in its use may be one explanation of continuing controversies surrounding the efficacy of analgesic strategies tested by this method. We contend that the analgesic consumption outcome measure is valid only when treatment groups achieve similar pain scores. A meta-analysis of perioperative gabapentin was used to test this hypothesis. Eighteen trials were identified, which were of sufficient methodological quality to include in the analysis. Trials reporting similar pain scores in treatment groups were classified as Category A and dissimilar scores as Category B. There were seven Category A trials: four reported reduced analgesic consumption with gabapentin compared with placebo, at one or more time points, and three found no difference. There were 11 Category B trials, all of which reported a decrease in analgesic consumption with gabapentin compared with placebo, at one or more time points. Analgesic consumption after gabapentin was similar for different postoperative analgesics. Sedation, dizziness, and vomiting were significant problems in pooled analysis. Analysis according to similarity of pain scores did not clarify whether perioperative gabapentin is useful in perioperative care. More rigorous examination of analgesic consumption as an outcome measure is needed, to establish whether achieving similar pain scores is as important as this paper claims and to determine those features of the analgesic delivery system, adverse effects, and other factors which may interfere with analgesic consumption as an outcome measure.