Kurz A, Plattner O, Sessler D I, Huemer G, Redl G, Lackner F
Department of Anesthesia and Intensive Care, University of Vienna, Austria.
Anesthesiology. 1993 Sep;79(3):465-9. doi: 10.1097/00000542-199309000-00008.
Thermoregulatory vasoconstriction minimizes further core hypothermia during anesthesia. Elderly patients become more hypothermic during surgery than do younger patients, and take longer to rewarm postoperatively. These data indicate that perianesthetic thermoregulatory responses may be especially impaired in the elderly. Accordingly, the authors tested the hypothesis that the thermoregulatory threshold for vasoconstriction during nitrous oxide/isoflurane anesthesia is reduced more in elderly than in young patients.
The authors studied 12 young patients aged 30-50 yr and 12 elderly patients aged 60-80 yr. All were undergoing major orthopedic or open abdominal surgery. Anesthesia was induced with thiopental and fentanyl, and maintained only with nitrous oxide (70%) and isoflurane (0.6-0.8%). Core temperature was measured in the distal esophagus. Fingertip vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients. A gradient of 4 degrees C identified significant vasoconstriction, and the core temperature triggering vasoconstriction identified the thermoregulatory threshold.
The vasoconstriction threshold was significantly less in the elderly patients (33.9 +/- 0.6 degree C) than in the younger ones (35.1 +/- 0.3 degrees C) (P < 0.01). The gender distribution, weight, and height of the elderly and young patients did not differ significantly. The end-tidal isoflurane concentration at the time of vasoconstriction did not differ significantly in the two groups.
These data indicate that thermoregulatory responses in the elderly are initiated at temperatures approximately 1.2 degrees C less than that in younger patients. Thus, it is likely that elderly surgical patients become more hypothermic than do younger patients, at least in part, because they fail to trigger protective thermoregulatory responses.
体温调节性血管收缩可在麻醉期间使核心体温进一步降低的情况最小化。老年患者在手术期间比年轻患者体温更低，且术后复温所需时间更长。这些数据表明围麻醉期体温调节反应在老年人中可能尤其受损。因此，作者检验了以下假设：在氧化亚氮/异氟烷麻醉期间，老年人血管收缩的体温调节阈值比年轻患者降低得更多。
作者研究了12名年龄在30至50岁的年轻患者和12名年龄在60至80岁的老年患者。所有患者均接受大型骨科手术或开腹手术。用硫喷妥钠和芬太尼诱导麻醉，仅用氧化亚氮（70%）和异氟烷（0.6 - 0.8%）维持麻醉。在食管远端测量核心体温。使用前臂与指尖的皮肤温度梯度评估指尖血管收缩情况。4℃的梯度表明存在显著的血管收缩，触发血管收缩的核心体温确定了体温调节阈值。
老年患者的血管收缩阈值（33.9±0.6℃）显著低于年轻患者（35.1±0.3℃）（P<0.01）。老年患者和年轻患者的性别分布、体重和身高无显著差异。两组血管收缩时的呼气末异氟烷浓度无显著差异。
这些数据表明，老年人的体温调节反应在比年轻患者低约1.2℃的体温时启动。因此，老年手术患者可能比年轻患者体温更低，至少部分原因是他们未能触发保护性体温调节反应。
