Inhaled anesthetic gases will substantially reduce the body’s ability to vasoconstrict and shiver in order to preserve and generate body heat. They will also reduce the ability of infants to undergo non-shivering thermogenesis. Prevention of hypothermia is necessary, as hypothermia leads to increased risk of infection, myocardial morbidity, and coagulopathies, to name several disadvantages.
Redistribution of heat to the peripheral tissues via vasodilation is responsible for the first 0.5-1.5o C drop in core body temperature. Prevention or mitigation of this can be accomplished by pre-warming the patient’s extremities, most importantly the lower extremities, for at least 30 minutes or more prior to the induction of general anesthesia. This will decrease the temperature gradient between the body core and the peripherals, thus decreasing the redistribution of heat.
OR room temperature plays the largest role in maintaining normothermia. To prevent heat loss to the surrounding atmosphere, insulation of the skin is necessary, as 90% metabolic heat is lost via the skin. Heat loss is proportional to the surface area exposed. Blankets, plastic sheeting, etc., are effective; however, each subsequent layer of insulation is less and less effective. The use of active warming, with circulating air warmers may be is most effective in reducing heat loss and may actually warm the patient. Finally, increasing the temperature of the OR can be somewhat effective. The OR needs to be >23degrees C in adults (73.4F), and >26degrees C in infants (78.8F) in order to prevent heat loss.
Fluid warmers are generally helpful only when large amounts of fluid is infused. While warm fluid will do very little to warm a patient, it is effective at preventing further cooling.
D I Sessler Mild perioperative hypothermia. N. Engl. J. Med.: 1997, 336(24);1730-7