central sensitisation. These phenomena, although evoked within a matter of minutes, can outlast the surgical tissue injury for several hours or days and drive acute postoperative pain until the surgical wound has healed. 4 Pre-emptive analgesia is a treatment that prevents establishment of the altered sensory processing that amplifi es postoperative pain. The treatment should cover the entire duration of high-intensity noxious stimulation that can lead to establishment of central and peripheral sensitisation caused by incisional and associated infl ammatory injuries. Of these two injuries, the associated infl ammatory reactions are probably of greater clinical signifi cance. 5 Two approaches have been used to reveal pre-emptive analgesia. One is to demonstrate a reduction in pain intensity and/or analgesic use beyond the period during which an effective concentration of a drug is maintained in the vicinity of its site of action. This approach is based on a study design comparing preoperative treatment and non-treatment groups. The other approach is to prove that a treatment applied before surgery is more effective than the same treatment provided at the end of surgery. The latter has become the most common study design for preemptive analgesia. 6