Perianesthetic hypothermia is common and proven to cause numerous serious complications. The investigators propose to evaluate two clinical observations: 1) the pattern of intraoperative hypothermia differs substantially in infants, young adults, and the elderly; and, 2) patients undergoing epidural or spinal anesthesia become 1-3 degrees C hypothermic before triggering shivering. Preliminary data suggest that unexpected physiological mechanisms underlie these observations. After several hours of surgery, core temperature in young adults stops decreasing and subsequently remains constant. An increase in metabolic heat production does not contribute to this core temperature plateau and, surprisingly, decreased cutaneous heat loss also contributes little. Accordingly, the investigators propose to test the hypothesis that the core temperature plateau in young adults results from constraint of metabolic heat to the core compartment by thermoregulatory vasoconstriction. Unwarmed infants initially become hypothermic during surgery and when sufficiently hypothermic, trigger thermoregulatory vasoconstriction. However, they subsequently increase their core temperatures, sometimes returning to control values. The investigators propose to test the hypothesis that nonshivering thermogenesis contributes significantly to the increase. In contrast, the elderly continue to become hypothermic during surgery and consequently have lower postoperative core temperatures. The investigators propose to test the hypothesis that the elderly continue to become hypothermic because they do not trigger thermoregulatory vasoconstriction during anesthesia. Patients undergoing epidural or spinal anesthesia become 1-3 degrees C hypothermic before triggering shivering (above the block). Since the brain is not directly influenced by regional anesthesia, it remains unclear why protective thermoregulatory responses should be impaired during conduction anesthesia. Preliminary data indicate that a leg skin temperature near 40 degrees C is required in unanesthetized volunteers to produce cold tolerance comparable to that produced by epidural anesthesia. The investigators, therefore, propose to test the hypothesis that thermoregulatory responses to core hypothermia are impaired because regional anesthesia increases apparent lower body temperature far more than it increases actual tissue temperature. These studies will identify the age-dependent efficacy of intraoperative thermoregulatory responses. Preliminary data suggest that responses are remarkably efficient in infants and virtually ineffective in the elderly. Confirming this hypothesis would indicate that the elderly require especially aggressive temperature monitoring and thermal management during general anesthesia. The investigators also will determine the extent to which thermoregulatory control is impaired during epidural anesthesia, and evaluate its etiology. Combined, these studies will facilitate optimal thermal management of surgical patients.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Surgery, Anesthesiology and Trauma Study Section (SAT)
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University of California San Francisco
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Schmied, H; Kurz, A; Sessler, D I et al. (1996) Mild hypothermia increases blood loss and transfusion requirements during total hip arthroplasty. Lancet 347:289-92
Kurz, A; Xiong, J; Sessler, D I et al. (1995) Desflurane reduces the gain of thermoregulatory arteriovenous shunt vasoconstriction in humans. Anesthesiology 83:1212-9
Cheng, C; Matsukawa, T; Sessler, D I et al. (1995) Increasing mean skin temperature linearly reduces the core-temperature thresholds for vasoconstriction and shivering in humans. Anesthesiology 82:1160-8
Matsukawa, T; Kurz, A; Sessler, D I et al. (1995) Propofol linearly reduces the vasoconstriction and shivering thresholds. Anesthesiology 82:1169-80
Vassilieff, N; Rosencher, N; Sessler, D I et al. (1994) Nifedipine and intraoperative core body temperature in humans. Anesthesiology 80:123-8
Giesbrecht, G G; Sessler, D I; Mekjavic, I B et al. (1994) Treatment of mild immersion hypothermia by direct body-to-body contact. J Appl Physiol 76:2373-9
Urzua, J; Sessler, D I; Meneses, G et al. (1994) Thermoregulatory vasoconstriction increases the difference between femoral and radial arterial pressures. J Clin Monit 10:229-36
Emerick, T H; Ozaki, M; Sessler, D I et al. (1994) Epidural anesthesia increases apparent leg temperature and decreases the shivering threshold. Anesthesiology 81:289-98
Leslie, K; Sessler, D I; Bjorksten, A R et al. (1994) Propofol causes a dose-dependent decrease in the thermoregulatory threshold for vasoconstriction but has little effect on sweating. Anesthesiology 81:353-60
Lopez, M; Sessler, D I; Walter, K et al. (1994) Rate and gender dependence of the sweating, vasoconstriction, and shivering thresholds in humans. Anesthesiology 80:780-8

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