Heat exhaustion is a non–life-threatening clinical syndrome of weakness, malaise, nausea, syncope, and other nonspecific symptoms caused by heat exposure. Thermoregulation and central nervous system (CNS) function are not impaired, but patients are usually dehydrated and may have mild elevations of body temperature (< 40° C). Treatment involves rest in a cool environment and replacing fluids and electrolytes.
Rarely, severe heat exhaustion after hard work may be complicated by rhabdomyolysis, myoglobinuria, and acute kidney injury. It is distinguished from heatstroke by the absence of brain dysfunction (eg, confusion, ataxia).
(See also Overview of Heat Illness.)
Symptoms and Signs of Heat Exhaustion
Symptoms of heat exhaustion are often vague, and patients may not realize that heat is the cause. Symptoms may include malaise, weakness, dizziness, headache, nausea, and sometimes vomiting. Syncope due to standing for long periods in the heat (heat syncope) may occur. On examination, patients appear tired, are usually sweaty and tachycardic, and may have orthostatic hypotension. Mental status is intact, unlike in heatstroke. Temperature is usually normal and, when elevated, usually does not exceed 40° C.
Diagnosis of Heat Exhaustion
Clinical evaluation
Diagnosis of heat exhaustion is clinical and requires exclusion of other possible causes of a patient's symptoms (eg, hypoglycemia, acute coronary syndrome, various infections). Laboratory testing is required only if needed to rule out such disorders. Electrolyte levels should be measured to exclude severe hyponatremia in patients who have had excessive free water intake.
Treatment of Heat Exhaustion
Oral or IV fluid and electrolyte replacement
Heatstroke: Treatment) are usually not required. However, if patients with heat exhaustion have a core temperature of ≥ 40° C, measures may be taken to reduce it.
Key Points
In heat exhaustion, symptoms tend to be nonspecific, temperature is usually < 40° C, and CNS function is not impaired.
Diagnose heat exhaustion clinically, testing as indicated to exclude other clinically suspected disorders.
Have patients rest in a cool environment and try oral rehydration, transporting patients to an emergency department if these measures are unsuccessful.
