Leg heat content continues to decrease during the core temperature plateau in humans anesthetized with isoflurane

Area of Science:

• Anesthesiology
• Physiology
• Thermoregulation

Background:

• Thermoregulatory responses during anesthesia are known but their clinical significance is unclear.
• Nonshivering thermogenesis does not increase heat production in anesthetized adults.
• Vasoconstriction reduces heat loss but may not achieve thermal steady state.

Purpose of the Study:

• To test if thermoregulatory vasoconstriction prevents further core hypothermia.
• To determine if the stable core temperature represents a thermal steady state or continued body heat loss.

Main Methods:

• Six healthy volunteers were anesthetized and paralyzed.
• Core hypothermia was induced via fan cooling for 3 hours post-vasoconstriction.
• Leg heat content was calculated using thermocouples and skin temperature.

Main Results:

• Core temperature decreased by 1.0°C in the hour before vasoconstriction, and only 0.4°C in the subsequent 3 hours.
• Leg heat content decreased by 49 kcal in the 3 hours after vasoconstriction.
• A significant reduction in the rate of core cooling was observed post-vasoconstriction.

Conclusions:

• Thermoregulatory vasoconstriction clinically reduces the rate of core cooling during anesthesia.
• A plateau in core temperature is achieved partly by heat sequestration to the core.
• Body heat content continues to decrease despite a stable core temperature.