Lopez M, Ozaki M, Sessler D I, Valdes M
Department of Anesthesia, University of California, San Francisco 94143-0648.
Anesthesiology. 1993 Jun;78(6):1046-54. doi: 10.1097/00000542-199306000-00006.
During combined epidural/isoflurane anesthesia, the core temperature triggering finger-tip vasoconstriction is approximately 1 degree C less than that triggering redilation. This hysteresis suggests that thermoregulatory responses are not dependent entirely on current thermal status (state-dependence), but may be influenced also by the system's recent thermal history (direction-dependence). Once triggered, the gain and maximum response intensity of many thermoregulatory responses is nearly normal during isoflurane anesthesia. However, it remains unknown whether preserved gain and maximum response intensities are a characteristic paradigm describing thermoregulatory responses to general anesthetics. Also unknown is whether the sweating and pre-capillary vasodilation thresholds are comparably impaired by different volatile anesthetics. Accordingly, the authors tested the hypotheses that, during one minimum alveolar concentration of enflurane anesthesia: (1) there is a direction-dependent hysteresis for sweating; (2) the sweating and active vasodilation thresholds increase approximately 1.2 degrees C, as they do during one minimum alveolar concentration of isoflurane; and (3) the gain and maximum intensity of sweating are well preserved.
Six female volunteers each were studied on 2 days, once during epidural anesthesia alone and once with combined enflurane (1.7%)/epidural anesthesia. On each study day, core hyperthermia was induced by cutaneous warming restricted to the legs. Warming continued until chest sweating reached maximal values; the volunteers then were cooled gradually until sweating stopped. The core temperature at which the sweating rate departed from baseline values was considered the activation threshold. Gain was expressed as the slope of the sweating rate versus core temperature curve within the range 25-75% of the maximum sweating rate. Hysteresis was evaluated by subtracting the tympanic membrane temperature at which the sweating rate suddenly increased during warming (approximately 25% above baseline values) from that at which sweating precipitously decreased during cooling (approximately 75% of maximum values).
The sweating threshold was 1.4 +/- 0.7 degrees C higher during combined enflurane/epidural anesthesia than during epidural anesthesia alone. Maximum intensity was approximately 700 g.m-2.h-1, and the gain approximately 1,300 g.m-2.h-1.degrees C-1 during each treatment. No hysteresis was detected on either study day.
One minimum alveolar concentration of enflurane increased the sweating threshold only slightly more than previously reported for isoflurane. As in previous studies of sweating and vasoconstriction during isoflurane anesthesia, gain and maximum response intensity were well preserved during enflurane anesthesia. An increase in the interthreshold range (temperatures not triggering thermoregulatory responses), with little change in gain and maximum response intensities, appears to be the typical effect of volatile anesthetics. Sweating during enflurane anesthesia appears to be state-dependent and little influenced by the direction of core temperature perturbations.
在硬膜外/异氟烷联合麻醉期间，触发指尖血管收缩的核心温度比触发血管再扩张的核心温度约低1摄氏度。这种滞后现象表明，体温调节反应并非完全取决于当前的热状态（状态依赖性），还可能受到系统近期热历史的影响（方向依赖性）。一旦触发，许多体温调节反应在异氟烷麻醉期间的增益和最大反应强度接近正常。然而，尚不清楚保留的增益和最大反应强度是否是描述对全身麻醉药体温调节反应的特征模式。同样未知的是，不同挥发性麻醉药对出汗和毛细血管前血管舒张阈值的损害是否相当。因此，作者检验了以下假设：在一个最低肺泡浓度的安氟醚麻醉期间：（1）出汗存在方向依赖性滞后现象；（2）出汗和主动血管舒张阈值升高约1.2摄氏度，与一个最低肺泡浓度的异氟烷麻醉期间相同；（3）出汗的增益和最大强度得到良好保留。
6名女性志愿者在2天内接受研究，一天仅接受硬膜外麻醉，另一天接受安氟醚（1.7%）/硬膜外联合麻醉。在每个研究日，通过仅对腿部进行皮肤加温诱导核心体温过高。加温持续至胸部出汗达到最大值；然后逐渐冷却志愿者直至出汗停止。出汗率偏离基线值时的核心温度被视为激活阈值。增益表示为出汗率与核心温度曲线在最大出汗率的25%至75%范围内的斜率。通过将加温期间出汗率突然增加时（比基线值高约25%）的鼓膜温度减去冷却期间出汗急剧减少时（最大值的约75%）的鼓膜温度来评估滞后现象。
安氟醚/硬膜外联合麻醉期间的出汗阈值比仅硬膜外麻醉期间高1.4±0.7摄氏度。在每种治疗期间，最大强度约为700 g·m⁻²·h⁻¹，增益约为1300 g·m⁻²·h⁻¹·℃⁻¹。在任何一个研究日均未检测到滞后现象。
一个最低肺泡浓度的安氟醚使出汗阈值升高的幅度仅略高于先前报道的异氟烷。与先前关于异氟烷麻醉期间出汗和血管收缩的研究一样，安氟醚麻醉期间增益和最大反应强度得到良好保留。阈间范围（不触发体温调节反应的温度）增加，而增益和最大反应强度变化不大，似乎是挥发性麻醉药的典型效应。安氟醚麻醉期间的出汗似乎取决于状态，受核心温度变化方向的影响很小。
