Thermoregulation: physiological and clinical considerations during sedation and general anesthesia

Abstract

Mild hypothermia is common during deep sedation or general anesthesia and is frequently associated with patient discomfort and shivering. Greater declines in temperature can produce an even greater number of significant detrimental effects. This article reviews principles of thermoregulation and influences of anesthetic agents. An understanding of these will provide a foundation for strategies to reduce heat loss and better manage patient discomfort when it occurs.

Figure 1

Hypothalamic thermoregulation. Temperature inputs to the hypothalamus are integrated and compared with threshold temperatures that trigger appropriate thermoregulatory responses. Normally these responses are initiated at as little as 0.1°C above and below normal body temperature of 37°C (98.6°F). Therefore the difference between temperatures that initiate sweating versus those initiating vasoconstriction is only 0.2°C. This is defined as the interthreshold range and represents the narrow range at which the body does not initiate thermoregulatory efforts. Most general anesthetics depress hypothalamic responses, widening this interthreshold range to as much as 4°C. Therefore patients are less able to adjust to temperature changes that occur during treatment.