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COLD & HEAT

The human body maintains a steady temperature through the balance of internal heat production and environmental heat loss. Heat exchange between the body and environment occurs via four common processes: radiation, evaporation, conduction, and convection. In extreme temperatures, the body’s thermoregulation may fail. This results in the core body temperature moving toward the temperature of the external environment. Cold and heat exposure may cause a wide spectrum of conditions; the severity varies considerably among individuals. Many of these conditions are preventable with appropriate education and planning. Preventive measures must be implemented on an individual and population level.

The likelihood and severity of extreme temperature-related conditions depend on physiologic and environmental factors. Physiologic risk factors include extremes of age; cognitive impairment; poor physical conditioning, sedentary lifestyle or immobility; poor acclimatization; concurrent injury; prior temperature-related injury; and numerous underlying medical conditions, especially those affecting cognition and thermoregulation. Pharmacologic risk factors include medications, holistic or alternative treatments, illicit drugs, tobacco, and alcohol. There is a subset of medications associated with a particularly high likelihood of worsening temperature-related conditions, such as those that impact sweating and the central nervous system (ie, anticholinergics, stimulants, and sedatives) and those that affect cutaneous blood flow such as peripheral vasoconstrictors or vasodilators. Environmental risk factors include changing weather conditions (eg, humidity, wind, rain, snow), inadequate clothing or housing (homelessness, or housing with inadequate temperature control), and occupational or recreational exposure.

DISORDERS DUE TO HEAT

ESSENTIALS OF DIAGNOSIS

  • Spectrum of preventable heat-related illnesses: heat cramps, heat exhaustion, heat syncope, and heat stroke.

  • Heat stroke: hyperthermia with cerebral dysfunction in a patient with heat exposure.

  • Best outcome: early recognition, initiation of rapid cooling, and avoidance of shivering during cooling.

  • Best choice of cooling method: whichever can be instituted the fastest with the least compromise to the patient. Delays in cooling result in higher morbidity and mortality in heat stroke victims.

General Considerations

Heat-related illnesses are among the most commonly seen environmental emergencies seen in emergency departments. In the United States from 2006 to 2010, there were at least 3332 deaths attributed to heat stroke. The amount of heat retained in the body is determined by internal metabolic function and environmental conditions, including temperature and humidity. Hyperthermia results from the body’s inability to maintain normal internal temperature through heat loss. Hyperthermia results from either compromised heat dissipation mechanisms or abnormally high heat production. Heat loss occurs primarily through sweating and peripheral vasodilation. The direct transfer of heat from the skin to the surrounding air, by convection or conduction, occurs with diminishing efficiency as ambient temperature rises, especially above 37.2°C, the point at which heat transfer reverses direction. At normal temperatures, evaporation accounts for approximately 20% of the body’s heat loss, but at high temperatures it becomes the major mechanism for dissipation of heat. With vigorous exertion, sweat loss can be as much as 2.5 ...

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