Clinical Observations of Tachyphylaxis During Long-Term Epidural Analgesia

Abstract

Tachyphylaxis has been defined by Bromage [1] as a decrease in segmental spread, duration, and intensity of epidural blockade caused by repeated injections of local anesthetics into the epidural space. He observed that the effect of each subsequent dose of local anesthetic was reduced if 10–60 min were allowed to elapse between complete regression of the block and reinjection of the local anesthetic [1]. It was possible to delay the development of tolerance, however, if the local anesthetic was reinjected before the block had regressed by two segments. Because of the difficulty of incorporating the control of epidural blocks into the daily routine of the ward, we began using a continuous infusion technique for the relief of postoperative pain in 1972 [2, 3]. However, it soon became apparent that patients would occasionally complain of pain. There is, however, still some controversy as to whether the pain seen during continuous infusion of local anesthetics is caused by a developing tolerance to the local anesthetic. Therefore, an attempt was made to evaluate the dose-effect relationship in 80 consecutive patients who had undergone implantation of an aortofemoral bypass and who were to be kept pain free by continuous thoracic epidural analgesia.