SPINAL-ANESTHESIA SPEEDS ACTIVE POSTOPERATIVE REWARMING

Background: Redistribution of beady heat decreases core temperature mo re during general than regional anesthesia, However, the combination o f anesthetic-and sedative-induced inhibition may prevent effective upp er-body thermoregulatory responses even during regional anesthesia, Th e extent to which each type of anesthesia promotes hypothermia thus re mains controversial. Accordingly, the authors evaluated intraoperative core hypothermia in patients assigned to receive spinal or general an esthesia, They also tested the hypothesis that the efficacy of active postoperative warming is augmented when spinal anesthesia maintains va sodilation. Methods: Patients undergoing lower abdominal and leg surge ry mere randomly assigned to receive general anesthesia (isoflurane an d nitrous oxide; n = 20) or spinal anesthesia (bupivacaine; n = 20), F luids were warned to 37 degrees C and patients were covered with surgi cal drapes. However, no other active warming was applied during operat ion. Ambient temperatures were maintained near 20 degrees C. After ope ration, patients were warmed with a full-length, forced-air cover set to 43 degrees C. Shivering, when observed, was treated with intravenou s meperidine, Results: The mean spinal analgesia level, which was at t he sixth thoracic level during surgery, remained at the T12 dermatome after 90 min after operation. Core temperatures did not differ signifi cantly during surgery and decreased to 34.4 +/- 0.5 degrees C and 34.1 +/- 0.4 degrees C, respectively, in patients given spinal and general anesthesia, After operation, however, core temperatures increased sig nificantly faster (1.2 +/- 0.1 degrees C/h vs. 0.7 +/- 0.2 degrees C/h , mean +/- SD; P < 0.001) in patients given spinal anesthesia. Consequ ently, patients given spinal anesthesia required less time to rewarm t o 36.5 degrees C (122 +/- 28 min vs. 199 +/- 28 min; P < 0.001). Concl usions: Comparable intraoperative hypothermia during general and regio nal anesthesia presumably resulted because the combination of spinal a nesthesia and meperidine administration obliterated effective peripher al and central thermoregulatory control. Vasodilation increased the ra te of core rewarming in patients after operation with residual lower-b ody sympathetic blocks, suggesting that vasoconstriction decreased per ipheral-to-core heat transfer after general anesthesia.