Pre-emptive analgesia: evidence, current status and future directions
Although some studies of pre-emptive analgesia have reported small reductions in post-operative pain or analgesic consumption in favour of pre-incisional vs. post-incisional or post-operative treatment, most have not demonstrated any benefit at all. This paper reviews recent evidence supporting the effectiveness of pre-emptive analgesia and discusses factors that may be responsible for the lack of consistent results. These factors include problems with the accepted definition of pre-emptive analgesia, the potential pre-emptive analgesic effects of other agents (e.g. opioids, nitrous oxide, pentobarbitone) used routinely as part of the general anaesthetic, the role of post-operative inflammation in initiating and enhancing a state of central sensitization, and the lack of a true placebo control condition. Given the constraints of clinical research and current standards of practice, it is unlikely that studies of pre-emptive analgesia using conventional analgesics or local anaesthetics will yield large reductions in post-operative pain or analgesic consumption. Extending the pre-emptive treatment well into the post-operative period using balanced, multimodal analgesia, may prolong the initial advantage conferred by the pre-operative blockade and possibly interfere with the development of long-lasting pain.