Thermoregulatory vasoconstriction does not impede core warming during cutaneous heating

Area of Science:

• Anesthesiology
• Physiology
• Thermoregulation

Background:

• Forced-air warming effectively increases core temperature intraoperatively.
• Postoperative warming efficacy is reportedly lower due to uniform vasoconstriction in hypothermic patients.
• Vasoconstriction reduces heat transfer by limiting cutaneous heat loss and peripheral-to-core heat flow.

Purpose of the Study:

• To test the hypothesis that thermoregulatory vasoconstriction decreases cutaneous heat transfer and restricts peripheral-to-core heat flow.
• To evaluate the impact of vasoconstriction on the efficacy of forced-air warming in anesthetized subjects.

Main Methods:

• Eight healthy male volunteers undergoing anesthesia were studied.
• Passive cooling to 33°C was followed by forced-air warming for 2 hours.
• Vasoconstriction was induced by reducing isoflurane, while vasodilation was maintained with sufficient isoflurane.
• Peripheral and core heat content changes were measured using thermocouples and core temperature.

Main Results:

• Cutaneous heat transfer was similar during vasoconstriction and vasodilation.
• Forced-air warming increased peripheral and core heat content comparably in both conditions.
• Core temperature increased at similar rates during vasoconstriction (1.2°C/h) and vasodilation (1.3°C/h).

Conclusions:

• The hypothesis that thermoregulatory vasoconstriction impairs forced-air warming was not confirmed.
• Anesthetic-induced vasodilation, rather than thermoregulatory vasoconstriction, may explain differences in warming efficacy.
• Further research into nonthermoregulatory anesthetic effects on warming is warranted.