Thermoregulatory Temperature

The normal core temperature in adults ranges between 36.5°C and 37.5°C and hypothermia can be defined as core body temperature less than 36°C.(ref 1)

Inadvertent perioperative hypothermia is a common anesthesia-related complication with reported prevalence ranging from 50% to 90%.(ref 3,4 of 4) The clinical consequences of perioperative hypothermia include tripling the risk of morbid myocardial outcomes and surgical wound infections, increased blood loss and transfusion requirements, and prolonged recovery and hospitalization.(ref 5)

Physiology of thermoregulation

As humans are homeothermic mammals, core temperature is maintained within a narrow range, usually within 0.2° of 37°C regardless of the environment. This is a life saving adaptation since various physiological systems in the body require narrow temperature ranges in which they can function optimally.

Thermoregulation involves positive and negative feedback by the brain to minimize perturbations from preset normal values, or thresholds. (ref 2) In hypothermia, afferent thermal sensing arises from cold-sensitive cells located in the brain, spinal cord, deep abdominal tissue, thoracic tissue, and skin surface. The central regulation is done at hypothalamus which receives integrated input from these sensors and then initiates appropriate means in an attempt to restore normothermia. The efferent response to hypothermia is manifested via effector mechanisms that either increase metabolic heat production or restrict heat loss. These mechanisms primarily include behavioral modification, arteriovenous shunt vasoconstriction, and shivering in adults or nonshivering thermogenesis in