Vassilieff N, Rosencher N, Sessler D I, Conseiller C
Department of Anesthesiology and Intensive Care, Cochin Port-Royal University Hospital, Paris, France.
Anesthesiology. 1995 Dec;83(6):1162-6. doi: 10.1097/00000542-199512000-00005.
Both accidental and perioperative hypothermia are common in the elderly. The elderly are at risk because their responses to hypothermia may be delayed or less efficient than in those of younger subjects. For example, the vasoconstriction threshold during isoflurane anesthesia is approximately 1 degree C less in elderly than younger patients. However, the extent to which other cold defenses are impaired in the elderly remains unclear, especially in those older than 80 yr. Operations suitable for spinal anesthesia provided an opportunity to quantify shivering thresholds in patients of varying ages. Accordingly, the hypothesis that the shivering threshold is reduced as a function of age during spinal anesthesia was tested.
Twenty-eight ASA Physical Status 1-3 patients undergoing lower extremity orthopedic procedures were studied. Spinal anesthesia was induced without preanesthetic medication, using bupivacaine sufficient to produce a dermatomal level near T9. Electrocardiogram signals were recorded at 10-min intervals. Subsequently, an observer masked to patient age and core temperature identified the onset of sustained electromyographic artifact consistent with shivering. The tympanic membrane temperature triggering shivering identified the threshold.
Three patients did not shiver at minimum core temperatures exceeding 36.2 degrees C. Fifteen patients aged < 80 yr (58 +/- 10 yr) shivered at 36.1 +/- 0.6 degrees C; in contrast, ten patients aged > or = 80 yr (89 +/- 7 yr) shivered at a significantly lower mean temperature, 35.2 +/- 0.7 degrees C (P = 0.002). The shivering thresholds in seven of the ten patients older than 80 yr was less than 35.5 degrees C, whereas the threshold equaled or exceeded this value in all younger patients (P = 0.0002).
Age-dependent inhibition of autonomic thermoregulatory control in the elderly might be expected to result in hypothermia. That it usually does not suggests that behavioral regulation (e.g., increasing ambient temperature, dressing warmly) compensates for impaired autonomic control. Elderly patients undergoing spinal anesthesia, however, may be especially at risk of hypothermia because low core temperatures may not trigger protective autonomic responses. Furthermore, hypothermia in the elderly given regional anesthesia may not be perceived by the patient (who typically feels less cold after induction of the block), or by the anesthesiologist (who does not observe shivering). Consequently, temperature monitoring and management usually is indicated in these patients.
意外低体温和围手术期低体温在老年人中都很常见。老年人面临风险，因为他们对低体温的反应可能比年轻人延迟或效率更低。例如，异氟烷麻醉期间老年人的血管收缩阈值比年轻患者低约1摄氏度。然而，老年人其他体温调节防御功能受损的程度尚不清楚，尤其是80岁以上的老年人。适合脊髓麻醉的手术为量化不同年龄段患者的寒战阈值提供了机会。因此，对脊髓麻醉期间寒战阈值随年龄降低这一假设进行了测试。
研究了28例接受下肢骨科手术的美国麻醉医师协会（ASA）身体状况1 - 3级患者。在未使用麻醉前用药的情况下诱导脊髓麻醉，使用足以产生接近T9皮节水平的布比卡因。每隔10分钟记录心电图信号。随后，一名对患者年龄和核心体温不知情的观察者确定与寒战一致的持续性肌电图伪迹的开始。引发寒战的鼓膜温度确定阈值。
3例患者在核心体温超过36.2摄氏度时未出现寒战。15例年龄<80岁（58±10岁）的患者在36.1±0.6摄氏度时出现寒战；相比之下，10例年龄≥80岁（89±7岁）的患者在显著更低的平均体温35.2±0.7摄氏度时出现寒战（P = 0.002）。10例80岁以上患者中有7例的寒战阈值低于35.5摄氏度，而所有年轻患者的阈值等于或超过该值（P = 0.0002）。
老年人自主体温调节控制的年龄依赖性抑制可能会导致体温过低。但通常并非如此，这表明行为调节（例如，提高环境温度、穿暖和的衣服）可补偿受损的自主控制。然而，接受脊髓麻醉的老年患者可能特别容易发生体温过低，因为低核心体温可能不会触发保护性自主反应。此外，接受区域麻醉的老年人的体温过低可能患者（通常在阻滞诱导后感觉不太冷）或麻醉医生（未观察到寒战）都未察觉到。因此，通常应对这些患者进行体温监测和管理。
