Perioperative Prewarming: Heat Transfer and Physiology

Abstract

To appreciate the strategy of prewarming, perioperative personnel should have a basic understanding of the physics of heat transfer and the thermoregulatory pathophysiology of anesthesia. The dominant cause of postinduction hypothermia is anesthesia‐related redistribution of heat within the body; the role of cutaneous heat loss is minimal. Physiologic thermoregulatory system changes that occur in response to anesthesia make it almost impossible to reverse intraoperative hypothermia. However, prewarming is an effective strategy to prevent postinduction hypothermia from redistribution because it creates a temporary excess of heat in the body’s peripheral thermal compartment. Perioperative nurses should implement active and passive prewarming strategies in accordance with the warming devices at their facility and available time. This article focuses on two major topics necessary to understand prewarming: the effect of anesthesia on postinduction thermoregulation and thermodynamic conditions that successful treatment strategies must exploit to produce desired outcomes.

Effects of peripheral active warming and passive insulation on core body temperature during feline ovariohysterectomy: a multi-arm randomized clinical trial

“… 6 , 7 Phase 1 is a rapid decrease in core temperature occurring within the first hour following induction and resulting from the decreased sympathetic tone and opening of arteriovenous shunts, which redistributes blood from the core to the periphery. 6 , 9 , 10 Minimal heat loss is thought to occur through mechanical means (conduction, convection, etc) during this phase, but a decrease in metabolic heat production of around 22% is reported in humans. 9 Phase 2 begins after the first hour and consists of a linear, progressive decline in core body temperature as heat losses outweigh metabolic heat production.…”