[Review: effect of preventive analgesia on postoperative pain]

Preventive analgesia (administration of a technique or analgesic drug with the aim of reducing postoperative pain, hyperalgesia and allodynia) has shown to be effective in experimental studies. However, the results in patients have been controversial. A review has been made of the clinical trials published during the last 5 years to test the efficacy of preventive analgesia on postoperative pain. A search was made of the published literature in Medline, with the terms "pre-emptive analgesia", "preventive analgesia" and "postoperative pain", selecting prospective, controlled, randomised and double blind studies that compared analgesic regimens before and after the incision or the same or very similar postoperative conditions. A total of 27 studies were found during the period 2005-2010 that complied with the inclusion criteria. Analgesia measurement variables were analysed, such as postoperative pain, time passed until the first rescue, and total analgesic requirements. Preventive analgesia was effective in 15 of the 27 studies, with pre-incisional epidural drug administration being the most effective (local anaesthetics with or without opioids, clonidine). The possible effectiveness of preventive analgesia in humans is still controversial, partly due to the wide heterogeneity in the inclusion criteria, types of patients, or the analgesia measurement parameters analysed by the studies. More studies are required with common criteria and objectives.