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The thermoregulatory threshold in humans during halothane anesthesia.
D I Sessler1, C I Olofsson, E H Rubinstein
1Department of Anesthesia, University of California, San Francisco 94143-0648.
Anesthesiology
|June 1, 1988
Summary
General anesthesia with halothane suppresses thermoregulation. Active vasoconstriction occurs only when core body temperature drops significantly, indicating a delayed thermoregulatory response in patients under anesthesia.
Area of Science:
- Anesthesiology
- Physiology
- Thermoregulation
Background:
- Anesthetics are generally assumed to suppress thermoregulatory mechanisms.
- The precise extent of active thermoregulation during general anesthesia remains unclear.
- Available thermoregulatory responses in anesthetized, hypothermic patients include vasoconstriction and non-shivering thermogenesis.
Purpose of the Study:
- To investigate the effects of halothane anesthesia on thermoregulatory responses.
- To determine the threshold for vasoconstriction during general anesthesia.
- To assess the utility of skin-surface temperature gradients as an index of thermoregulation.
Main Methods:
- Measured skin-surface temperature gradients (forearm minus fingertip temperature) as an index of cutaneous vasoconstriction.
- Studied unpremedicated patients undergoing elective donor nephrectomy, anesthetized with 1% halothane and paralyzed with vecuronium.
- Patients were randomly assigned to maximal warming or standard temperature management protocols.
Main Results:
- Normothermic patients did not exhibit significant vasoconstriction.
- Hypothermic patients showed significant vasoconstriction at esophageal temperatures between 34.0-34.8°C (average 34.4°C).
- Increased skin-temperature gradients correlated with decreased perfusion in hypothermic patients.
Conclusions:
- Active thermoregulation occurs during halothane anesthesia but is initiated at a significantly lower core temperature (approx. 2.5°C below normal).
- Skin-surface temperature gradients provide a simple, non-invasive method for quantifying the thermoregulatory threshold during anesthesia.