Propofol linearly reduces the vasoconstriction and shivering thresholds

Area of Science:

• Physiology
• Anesthesiology
• Thermoregulation

Background:

• Thermoregulatory control involves both skin and core temperatures.
• Maintaining constant skin temperature is crucial but challenging for evaluating warm and cold thresholds.
• Established cutaneous contributions to sweating (10%) and vasoconstriction/shivering (20%) allow for temperature compensation.

Purpose of the Study:

• To develop and validate a novel, minimally invasive method for determining thermoregulatory thresholds during propofol anesthesia.
• To quantify the effects of varying propofol concentrations on sweating, vasoconstriction, and shivering thresholds.
• To analyze propofol's impact on core-temperature thresholds by mathematically compensating for skin temperature variations.

Main Methods:

• Five volunteers underwent four experimental days with varying propofol concentrations (0, 2, 4, 8 µg/ml).
• Skin and core temperatures were manipulated to induce sweating, vasoconstriction, and shivering.
• Mathematical compensation for skin temperature changes was applied using known cutaneous contributions to thermoregulation.

Main Results:

• Propofol significantly decreased core temperatures for vasoconstriction and shivering.
• The concentration-response slopes for vasoconstriction and shivering were similar to previous findings.
• Increasing propofol concentration only slightly increased the sweating threshold.

Conclusions:

• The new method is nearly noninvasive and requires minimal core-temperature manipulation.
• Propofol markedly reduces vasoconstriction and shivering thresholds but only slightly alters the sweating threshold.
• The range between vasoconstriction and shivering thresholds changes minimally during propofol anesthesia.