Pre-emptive analgesia: how important is it in clinical reality?

Surgical trauma induces nociceptive sensitization leading to amplification and prolongation of postoperative pain. In experimental studies, preinjury (e.g. pre-emptive) neural blockade using local anaesthetics or opioids has been shown to prevent or to reduce postinjury sensitization of the central nervous system, while similar techniques applied after the injury had less or no effect. Several clinical studies have evaluated possible pre-emptive analgesic effects by administering prior to surgery a variety of analgesic drugs both systemically or epidurally. These treatment modalities were compared to the same treatment following surgery or to control groups not given such treatment. In general, the results from these studies have been disappointing, although some clinical studies have confirmed the impressive results from animal studies. The present paper discusses deficiencies in study design of clinical trials, since the question regarding the effectiveness of pre-emptive analgesic regimens lies not so much in the timing of analgesic administration (e.g. preinjury vs. postinjury treatment), but in the effective prevention of altered central sensitization. Recent evidence suggests that administration of analgesics in order to effectively pre-empt postoperative pain should start before surgery and furthermore, this treatment should be extended into the early postoperative period.