EFFECT OF PREEMPTIVE NERVE BLOCK ON INFLAMMATION AND HYPERALGESIA AFTER HUMAN THERMAL-INJURY

Background: Postoperative pain relief may be improved by reducing sens itization of nociceptive pathways caused by surgical trauma. Such a re duction may depend on the timing and efficacy of analgesia and the dur ation of the nociceptive block versus the duration of the nociceptive input. We examined whether a prolonged nerve block administered before a superficial burn injury could reduce local inflammation and late hy peralgesia after recovery from the block, Methods: The effects of a pr eemptive saphenous nerve block on primary and secondary hyperalgesia, skin erythema, and blister formation, were compared to the opposite un blocked leg for 12 h after bilateral thermal injuries (15 X 25 mm, 49 degrees C for 5 min) in 20 healthy volunteers, Recovery from the block was identified by return of sensation to cold. Results: Six subjects were excluded because of insufficient initial block (2 subjects) or be cause the block lasted beyond the study period (4 subjects). The remai ning 14 subjects experienced significantly reduced primary (P = 0.005) and secondary hyperalgesia (P = 0.01) in the blocked leg after return of cold sensation compared to the unblocked leg, Erythema intensity a nd blister formation were not significantly affected by the blockade ( P = 0.94 and P = 0.07, respectively). Conclusions: These data suggest that a prolonged, preemptive nerve block reduced late hyperalgesia aft er thermal injury, whereas the erythema and blister formation were not significantly affected.