A qualitative and quantitative systematic review of preemptive analgesia for postoperative pain relief: the role of timing of analgesia.

THE concept of preemptive analgesia to reduce the magnitude and duration of postoperative pain was paved in 1983 by Woolf, who showed evidence for a central component of postinjury pain hypersensitivity in experimental studies. Subsequently, an overwhelming amount of experimental data demonstrated that various antinociceptive techniques applied before injury were more effective in reducing the postinjury central sensitization phenomena as compared with administration after injury. Finally, these promising experimental findings were taken into clinical testing of the hypothesis. Although early reviews of clinical findings were mostly negative, there is still a widespread belief of the efficacy of preemptive analgesia among clinicians. The definition of preemptive analgesia has varied, thereby causing confusion and misunderstanding of the concept. Because the original observations in experimental studies suggested that timing of analgesic treatment was important to obtain efficient reduction of postinjury pain hypersensitivity phenomena, we performed an updated review of studies to compare the role of timing of analgesia i.e., preoperative versus intraoperative or postoperative initiation of analgesia. In this review we are not considering studies designed to compare preemptive analgesia versus no treatment. We have only included double-blind, randomized, controlled trials of identical or very similar analgesic regimens, where the only difference between study groups was timing of analgesia.