Annals of the New York Academy of Sciences
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Ann. N. Y. Acad. Sci. · Mar 1997
Isoflurane produces marked and nonlinear decreases in the vasoconstriction and shivering thresholds.
In summary, we present a new model for evaluating thermoregulatory effects of drug administration, pregnancy, illness, etc. Specifically, we experimentally manipulated both skin and core temperatures, and subsequently compensated for the changes in skin temperature using the relationships between skin and core contributions to thermoregulatory control. We thus were able to report our results for warm- and cold-responses in terms of calculated core-temperature thresholds at a single designated skin temperature. ⋯ In contrast, volatile anesthetics produce a nonlinear reduction in the major cold-response thresholds, reducing the vasoconstriction and shivering thresholds disproportionately at higher anesthetic concentrations. Midazolam not only produces a different magnitude of thermoregulatory impairment, but also a novel pattern of threshold changes. Anesthetic-induced thermoregulatory impairment thus depends both on anesthetic type and dose.
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Ann. N. Y. Acad. Sci. · Mar 1997
Thermoregulatory vasoconstriction does not impede core warming during cutaneous heating.
Recent studies evaluating perioperative cutaneous-to-core heat transfer indicate that: Thermoregulatory vasoconstriction prevents further core cooling in anesthetized subjects during mild cooling. Thermoregulatory vasoconstriction only slightly decreases core cooling rates in anesthetized subjects during vigorous cooling. Thermoregulatory vasoconstriction does not impair vigorous core rewarming during anesthesia. ⋯ Under conditions of mild thermal stress, thermoregulatory vasoconstriction is thus able to protect core temperature by reducing cutaneous heat transfer and functionally isolating the peripheral and core thermal compartment. Consequently, anesthetic-induced alterations in vasomotor tone is one of the major factors influencing core temperature in patients who are not actively cooled or warmed. In contrast, thermoregulatory tone is insufficient to prevent core temperature perturbations in patients undergoing vigorous cutaneous cooling or warming.