Leslie K, Sessler D I
Department of Anaesthesia, Royal Melbourne Hospital, Parkville, Victoria, Australia.
Anesthesiology. 1996 Jun;84(6):1327-31. doi: 10.1097/00000542-199606000-00008.
Hypothermia is nearly as common, and may be as severe, during spinal and epidural anesthesia as during general anesthesia. The authors have proposed that thermoregulatory failure results when regional anesthesia increases apparent leg skin temperature to a level far exceeding actual leg skin temperature. Extensive dermatomal blocks will alter thermal input to the hypothalamus from a greater skin-surface area more than less extensive ones and thus might be expected to impair central thermoregulatory control more. Accordingly, they tested the hypothesis that reduction in the shivering threshold is directly related to the number of dermatomes blocked during spinal anesthesia.
Eleven men, aged 62 +/- 6 yr (mean +/- SD), undergoing urologic surgery were studied. Ice-cold lactated Ringer's solution was administered intravenously before spinal blockade and the shivering threshold (triggering core temperature) was established. Spinal anesthesia then was induced using a randomly assigned dose of 0.5% bupivacaine (2-4 ml). Again, sufficient cold lactated Ringer's solution was given to induce shivering. Tympanic membrane, ambient and skin temperatures were measured, and extent of block was defined by loss of temperature discrimination. Presence of shivering was evaluated by a blinded observer. Mean upper-body skin and ambient temperatures, cooling rates and intravenous fluid volumes at the two thresholds were compared using paired, two-tailed t tests (P < 0.05). Linear regression defined the relationship between reduction in shivering threshold and the number of dermatomes blocked.
There were no significant differences between mean upper-body skin and ambient temperatures, cooling rates or intravenous fluid volumes at the control and spinal shivering thresholds. Spinal anesthesia reduced the shivering threshold in direct relation to the number of dermatomes blocked: delta threshold = 0.74 - 0.06 (dermatomes blocked); r2 = 0.58, P < 0.006.
Extensive spinal blockade impairs central thermoregulatory control more than less extensive blockade. Clinicians can thus anticipate more core hypothermia during extensive than during restricted spinal blockade.
在脊髓麻醉和硬膜外麻醉期间，体温过低几乎与全身麻醉时一样常见，且可能同样严重。作者提出，当区域麻醉使腿部皮肤表面温度明显升高到远超实际腿部皮肤温度的水平时，就会导致体温调节功能衰竭。广泛的皮节阻滞比范围较小的阻滞会改变更多皮肤表面积传入下丘脑的热输入，因此可能会更严重地损害中枢体温调节控制。据此，他们检验了以下假设：脊髓麻醉期间寒战阈值的降低与被阻滞的皮节数量直接相关。
对11名年龄为62±6岁（均值±标准差）、接受泌尿外科手术的男性进行研究。在脊髓阻滞前静脉输注冰冷的乳酸林格液，并确定寒战阈值（触发核心温度）。然后使用随机分配剂量的0.5%布比卡因（2 - 4毫升）诱导脊髓麻醉。再次给予足够的冷乳酸林格液以诱发寒战。测量鼓膜温度、环境温度和皮肤温度，并通过温度辨别丧失来确定阻滞范围。由一名不知情的观察者评估是否存在寒战。使用配对双尾t检验比较两个阈值下平均上身皮肤温度、环境温度、降温速率和静脉输液量（P < 0.05）。线性回归确定寒战阈值降低与被阻滞皮节数量之间的关系。
对照和脊髓麻醉后的寒战阈值下，平均上身皮肤温度、环境温度、降温速率或静脉输液量之间无显著差异。脊髓麻醉使寒战阈值降低与被阻滞的皮节数量直接相关：阈值变化量 = 0.74 - 0.06（被阻滞的皮节数量）；r² = 0.58，P < 0.006。
广泛的脊髓阻滞比范围较小的阻滞更严重地损害中枢体温调节控制。因此，临床医生可以预期，与有限的脊髓阻滞相比，广泛的脊髓阻滞期间会出现更多的核心体温过低情况。
