Answer
Effective thermoregulation, controlled by the hypothalamus, is critical for proper function of the human body, with normal temperature exhibiting diurnal variation between 36-37.5°C. Heat is both produced endogenously and acquired from the environment. Metabolic reactions in human bodies are exothermic, contributing 50-60 kcal/h/m2 of body surface area, or 100 kcal/h for a 70-kg person. During strenuous exercise, heat production increases 10- to 20-fold. [3] Environmental heat transfer involves the following 4 mechanisms [3] :
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Conduction: Direct physical contact transfers heat from a warmer object to a cooler object. Water is about 25 times more conductive (more effective at conducting heat) than air.
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Convection: Heat is transferred through air and water vapor molecules surrounding the body. Convective heat transfer depends on wind velocity and explains the effect of wearing loose-fitting clothing in warm climates to keep cool.
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Radiation: Heat is transferred by electromagnetic waves. Radiation is the major source of heat gain in hot ambient climates; up to 300 kcal/h can be gained on a hot summer day.
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Phase change: The conversion of a solid to a liquid (melting) or a liquid to a gas (evaporation) results in heat transfer. Evaporation of 1 L of sweat from the body results in a loss of 580 kcal of heat.
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Sample display of equipment useful for various cooling techniques. Clockwise from top: ice pack and water, air-cooling blanket, Foley catheter, and intravenous fluids.
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Sample display of equipment useful for cooling via gastric lavage. Clockwise from top: ice water, nasogastric tube, endotracheal tube, and lavage bag.
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Sample display of equipment useful for cooling via peritoneal lavage. Clockwise from top: iced water, peritoneal catheter, and saline fluid.
