Neuronal plasticity and pre-emptive analgesia: implications for the management of postoperative pain

Prevention of injury-induced functional alterations in the central nervous system by pre-emptive analgesia or other techniques is a fascinating working hypothesis based on substantial scientific evidence. Although experimental data may provide a rationale for this concept, translation into clinical practice has led to some debate, especially about interpretation of results from studies in postoperative patients (Katz et al. 1992a, 1993; Dahl et al 1992a, 1993b; Dahl & Kehlet 1993a). This may partly be due to a difference in experimental versus clinical benefits from pre-emptive analgesia and furthermore, clinicians may ask if preoperative administration of morphine or other opioids is really a "novel approach" (Katz 1993) to the management of postoperative pain. Thus, administration of opioids for premedication, and during induction and maintenance of general anaesthesia has been common clinical practice for decades. In spite of this practice, patients have suffered from unacceptable postoperative pain. Several critical elements must be addressed before the concept can be applied into clinical practice. Thus, the idea originates from experimental studies, often with anaesthetized or decerebrated animals, and with nociceptive stimuli which did not involve severe ongoing tissue damage. The various types of noxious stimuli (C-fiber stimulation, heat-, chemical-, inflammatory- and neuronal lesions) may differ from the surgical injury, and the time-scale of the experiments, and the profiles of analgesic effects and efficacy may differ from the clinical situation. In a study of patients undergoing gynaecological laparotomy, increased sensitivity to noxious electrical stimulation of the sural nerve was observed postoperatively, with a corresponding trend in the nociceptive flexion reflex.(ABSTRACT TRUNCATED AT 250 WORDS)