Heatstroke is hyperthermia accompanied by a systemic inflammatory response causing multiple organ dysfunction and often death. Symptoms include temperature > 40° C and altered mental status; sweating is often absent. Diagnosis is clinical. Treatment is rapid external cooling, IV fluid resuscitation, and support as needed for organ dysfunction.

Heatstroke occurs when thermoregulatory mechanisms do not function and core temperature increases substantially. Inflammatory cytokines are activated, and multiple organ dysfunction may develop. Endotoxin from GI flora may also play a role. Organ dysfunction may occur in the CNS, skeletal muscle (rhabdomyolysis), liver, kidneys, lungs (acute respiratory distress syndrome), and heart. The coagulation cascade is activated, sometimes causing disseminated intravascular coagulation. Hyperkalemia and hypoglycemia may occur.

There are 2 variants (see Table 2: Heat Illness: Some Differences Between Classic and Exertional Heatstroke):

• Classic
• Exertional

Classic heatstroke takes 2 to 3 days of exposure to develop. It occurs during summer heat waves, typically in elderly, sedentary people with no air-conditioning and often with limited access to fluids.

Exertional heatstroke occurs abruptly in healthy active people (eg, athletes, military recruits, factory workers). Intense exertion in a hot environment causes a sudden massive heat load that the body cannot modulate. Rhabdomyolysis is common; renal failure and coagulopathy are somewhat more likely and severe.

Table 2
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Some Differences Between Classic and Exertional Heatstroke Characteristic Classic Heatstroke Exertional Heatstroke Onset 2–3 days Hours Patients usually affected Elderly, sedentary people Healthy active people (eg, athletes, military recruits, factory workers) Risk factors No air-conditioning during summer heat waves Intense exertion, particularly without acclimatization Skin Hot and dry Often moist with sweat

A syndrome similar to heatstroke may occur after using certain drugs (eg, cocaine, phencyclidineSome Trade Names
No US trade name

[PCP], amphetamines, monoamine oxide inhibitors). Usually, an overdose is required, but exertion and environmental conditions can be additive.

Malignant hyperthermia (see Heat Illness: Malignant Hyperthermia) can result from exposure to some anesthetics in genetically predisposed patients. Neuroleptic malignant syndrome (see Heat Illness: Neuroleptic Malignant Syndrome) can develop in patients taking antipsychotics. These disorders are life threatening; malignant hyperthermia has a high mortality rate.

Symptoms and Signs

Global CNS dysfunction, ranging from confusion to delirium, seizures, and coma, is the hallmark. Tachycardia, even when the patient is supine, and tachypnea are common. In classic heatstroke, the skin is hot and dry. In exertional heatstroke, sweating is relatively common. In both, temperature is > 40° C and may be > 46° C.

Diagnosis

• Clinical evaluation, including core temperature measurement
• Laboratory testing for organ dysfunction

Diagnosis is usually clear from a history of exertion and environmental heat. Heatstroke is differentiated from heat exhaustion by presence of the following:

• CNS dysfunction
• Temperature > 40° C

When the diagnosis of heatstroke is not obvious, other disorders that can cause CNS dysfunction and hyperthermia should be considered. These disorders include the following:

• Acute infection (eg, sepsis, malaria, meningitis, toxic shock syndrome)
• Drugs
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Status epilepticus (interictal)
• Stroke
• Thyroid storm

Laboratory testing includes CBC, PT, PTT, electrolytes, BUN, creatinine, Ca, CK, and hepatic profile to evaluate organ function. A urethral catheter is placed to obtain urine, which is checked for occult blood by dipstick, and to monitor output. Tests to detect myoglobin are unnecessary. If a urine sample contains no RBCs but has a positive reaction for blood and if serum CK is elevated, myoglobinuria is likely. A urine drug screen may be helpful. Continual monitoring of core temperature, usually by rectal or esophageal probe, is desired.

Prognosis

Mortality rate is significant but varies markedly with age, underlying disorders, maximum temperature, and, most importantly, duration of hyperthermia and promptness of cooling. About 20% of survivors have residual brain damage, regardless of intervention. In some patients, renal insufficiency persists. Temperature may be labile for weeks.

Treatment

• Aggressive cooling
• IV cooled normal saline

The importance of rapid recognition and effective, aggressive cooling cannot be overemphasized. Cooling methods that do not cause shivering or cutaneous vasoconstriction are preferred, although ice-soaked towels and ice water immersion are effective.

Cooling techniques: Evaporative cooling is comfortable and convenient and considered the most rapid method by some experts. During the process, patients are continually wetted with water, and the skin is fanned and vigorously massaged to promote blood flow. A spray hose and larger fans are best and may be used for large groups of people in the field. Comfortable, tepid (eg, 30° C) water is adequate because evaporation causes cooling; cold or ice water is not needed. Cool water immersion in a pond or stream can also be used in the field.

Ice packs applied to the axillae and groin can be used but not as the sole cooling method. In life-threatening cases, packing a patient in ice, with close monitoring, has been advocated to rapidly reduce core temperature.

Other measures: The patient is admitted to an ICU, and IV hydration with 0.9% saline solution is begun as in heat exhaustion (see Heat Illness: Treatment). Theoretically, 1 to 2 L of IV 0.9% saline cooled to 4° C, as used in protocols to induce hypothermia after cardiac arrest, may also help cooling. Organ dysfunction and rhabdomyolysis are treated (see elsewhere in The Manual). An injectable benzodiazepine (eg, lorazepamSome Trade Names
ATIVAN
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, diazepamSome Trade Names
VALIUM
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) may be used aggressively to prevent agitation and seizures (which increase heat production); seizures may occur during cooling. Because vomiting and aspiration of gastric contents are possible, measures to protect the airway may be required. Severely agitated patients may require paralysis and mechanical ventilation.

Platelets and fresh frozen plasma may be required for severe disseminated intravascular coagulation. IV NaHCO₃ to alkalinize the urine may help prevent nephrotoxicity if myoglobinuria is present. IV Ca salts may be necessary to treat hyperkalemic cardiotoxicity. Vasoconstrictors used to treat hypotension may reduce cutaneous blood flow and decrease heat loss. Hemodialysis may be required. Antipyretics (eg, acetaminophenSome Trade Names
GENAPAP
TYLENOL
VALORIN
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) are of no value. DantroleneSome Trade Names
DANTRIUM
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is used to treat anesthetic-induced malignant hyperthermia but has no proven benefit for other causes of severe hyperthermia.

Last full review/revision February 2010 by James P. Knochel, MD

Content last modified February 2012