How is heat stroke defined?

Updated: Aug 02, 2019
  • Author: Robert S Helman, MD; Chief Editor: Joe Alcock, MD, MS  more...
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Heat stroke is defined as hyperthermia exceeding 40°C (104°F) associated with an altered sensorium. [1, 2] However, when a patient is allowed to cool down prior to measurement of the temperature (as may occur during transportation in a cool ambulance or evaluation in an emergency department), the measured temperature may be lower than 41°C, making the temperature criterion relative. Anhidrosis, or lack of sweating, has been cited as a feature of heat stroke, but some patients with heat stroke present with profuse sweating. Because of variable presentations, a high index of suspicion is needed to avoid delays in diagnosis and treatment.

Clinically, two forms of heat stroke are differentiated: classic, or nonexertional, heat stroke (NEHS) and exertional heat stroke (EHS). NEHS, which occurs during environmental heat waves, is more common in the very young and the elderly and should be suspected in children, elderly persons, and chronically ill individuals who present with an altered sensorium. NEHS occurs because of failure of the body's heat dissipating mechanisms.

On the other hand, EHS affects young, healthy individuals who engage in strenuous physical activity, and EHS should be suspected in all such individuals who exhibit bizarre, irrational behavior or experience syncope. EHS results from increased heat production, which overwhelms the body's ability to dissipate heat.

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