Hyperthermia

Etiology: Exogenous heat exposure (e.g., heat stroke) and endogenous heat production (e.g., drug-induced hyperthermia, malignant hyperthermia) are two mechanisms by which hyperthermia can result in dangerously high internal temperatures.
- Heat stroke: thermoregulatory failure in association with a warm environment; can be categorized as exertional (e.g., due to exercise in high heat or humidity) or classic (typically occurring in pts with chronic diseases that predispose to heat-related illnesses)
Clinical features: high core temperature in association with an appropriate history (heat exposure, certain drug treatments) and dry skin, hallucinations, delirium, pupil dilation, muscle rigidity, and/or elevated levels of CPK
Diagnosis: It can be difficult to distinguish fever from hyperthermia. The clinical history is often most useful (e.g., a history of heat exposure or of treatment with drugs that interfere with thermoregulation).
- Hyperthermic pts have hot, dry skin; antipyretic agents do not lower the body temperature.
- Febrile pts can have cold skin (as a result of vasoconstriction) or hot, moist skin; antipyretics usually result in some lowering of the body temperature.

Treatment: Hyperthermia

Before cooling is initiated, endotracheal intubation, CVP determination, and continuous core-temperature monitoring should be considered.
Evaporative cooling (spraying cool water on exposed skin while fans direct continuous airflow over the moistened skin) is the most practical and effective technique for reducing body temperature. Invasive methods (e.g., IV infusion of cold fluids, cold thoracic and peritoneal lavage, cardiopulmonary bypass) are effective but rarely necessary.
Given the risk of dehydration, IV fluids are necessary or at least appropriate. The CVP, particularly in classic heat stroke, may be deceptively high; rarely, measurement of wedge pressures via a pulmonary artery catheter may be necessary to guide resuscitation.

For a more detailed discussion, see Dinarello CA, Porat R: Fever and Hyperthermia, Chap. 23, p. 123; Kaye ET, Kaye KM: Fever and Rash, Chap. 24, p. 127; Kaye KM, Kaye ET: Atlas of Rashes Associated with Fever, Chap. 25e; Bleeker-Rovers CP, van der Meer JWM: Fever of Unknown Origin, Chap. 26, p. 135; and Danzl DF: Heat-Related Illnesses, Chap. 479e, in HPIM-19.

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