Skip to Main Content

++

KEY POINTS

++

KEY POINTS

  1. Adults thermoregulate with their environment by cutaneous vasomotor adjustments, sweating, shivering, and, when not under anesthesia, environmental behavioral adaptation (dressing appropriately, modifying environmental temperature).

  2. Neonates do not shiver but can generate heat via nonshivering thermogenesis.

  3. Heat loss occurs via sweating and cutaneous vasodilation. Heat conservation results from cutaneous vasoconstriction and behavioral adaptation.

  4. Although not precisely defined, core temperature reflects mean temperature of the well-perfused organs (eg, brain, heart, kidney, lungs).

  5. Hypothermia that develops during general anesthesia typically follows a predictable pattern: (1) an initial rapid decrease in core temperature ranging between 0.5°C and 1.5°C during the first hour after induction principally the result of internal redistribution of heat; (2) a more gradual linear decline in core temperature, usually lasting 2-3 hours that results from cutaneous heat loss exceeding metabolic heat production (typically 0.5-1°C/hour); and (3) a plateau phase when core temperature stabilizes after 3-4 hours, representing the thermoregulatory balance of continual heat production and loss.

  6. Following redistribution-mediated decreases in temperature, body heat loss occurs via radiation (60% of heat loss) and convection (30%), with <10% occurring via evaporation, and a negligible amount via conduction.

  7. Postanesthesia shivering is most likely mediated via normal thermoregulatory response to hypothermia.

  8. Hypothermia during regional anesthesia is caused by depression of both regional thermal afferent input and efferent responses, such as vasoconstriction and shivering, loss of heat to the operating room environment, and redistribution of heat within the body.

  9. Hypothermia during anesthesia may be ameliorated by patient prewarming.

  10. The control of ambient temperature, skin insulation, warm IV solutions, heating and humidifying inspired gases, the application of a forced-air convective heating system, and the use of new generation circulating-water convective heating systems.

  11. Although there is an abundance of experimental evidence for the neuroprotective effects of hypothermia, aside from the clinical application for cardiac surgery under deep hypothermic circulatory arrest, there are few, if any, other settings where its efficacy is well founded. Any protection afforded to it may be the result of its ability to prevent postcerebral injury hypothermia.

++

INTRODUCTION

++

Hypothermia is a common perioperative occurrence resulting in a number of clinical consequences that range in significance from mild to serious (Table 83-1).1 As normal body temperature is 37°C, and taking into account a 1°C diurnal variation with an additional variation of 0.5°C in females depending on the menstrual cycle, perioperative hypothermia can be defined as a core temperature of <36°C.2 As with other mammals, humans require a nearly constant internal body temperature to maintain optimal homeostatic function. Significant deviation in this internal temperature can result in alterations in numerous metabolic and physiologic functions that, if not reversed, may contribute to significant morbidity and eventually, mortality. The human body has evolved a sophisticated thermoregulatory control system by which to maintain core temperature (usually to within 0.2°C of its ideal target temperature). Anesthetics profoundly affect these control mechanisms, and when coupled by adverse environmental conditions (such as a cool operating room) and other heat-losing perioperative events, the ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.