Heatstroke is hyperthermia accompanied by a systemic inflammatory response causing multiple organ dysfunction that may result in death. Symptoms include temperature > 40° C and altered mental status; sweating may be absent or present. Diagnosis is clinical. Treatment includes rapid external cooling, IV fluid resuscitation, and support as needed for organ dysfunction.
Heatstroke occurs when compensatory mechanisms for dissipating heat fail and core temperature increases substantially. Inflammatory cytokines are activated, and multiple organ dysfunction may develop. Organ dysfunction may occur in the central nervous system (CNS), skeletal muscle (rhabdomyolysis), liver, kidneys, lungs (acute respiratory distress syndrome), and heart. Hyperkalemia and hypoglycemia may occur. The coagulation cascade is activated, sometimes causing disseminated intravascular coagulation.
Heatstroke is sometimes divided into 2 variants, although the usefulness of this classification is controversial (see table 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 older, sedentary people with no air-conditioning and often with limited access to fluids. It can occur rapidly in children left in a hot car, particularly with closed windows.
Exertional heatstroke occurs more abruptly and affects healthy active people (eg, athletes, military recruits, factory workers). It is a common cause of death in young athletes. Intense exertion in a hot environment causes a sudden massive heat load that the body cannot modulate. Rhabdomyolysis is common; acute kidney injury and coagulopathy are somewhat more likely and severe. Heat exhaustion can transition to heatstroke as heat illness progresses and is characterized by impairment of mental status and neurologic function.
Some Differences Between Classic and Exertional Heatstroke
Characteristic | Classic Heatstroke | Exertional Heatstroke |
|---|---|---|
Onset | 2–3 days | Hours |
Patients usually affected | Older, 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 | Usually hot and dry but sometimes moist with sweat | Often moist with sweat |
(See also Overview of Heat Illness.)
Symptoms and Signs of Heatstroke
Central nervous system (CNS) dysfunction, ranging from confusion or bizarre behavior to delirium, seizures, and coma, is the hallmark of heatstroke. Ataxia may be an early manifestation. Tachycardia, even when the patient is supine, and tachypnea are common. Sweating may be present or absent. Temperature is > 40° C.
Diagnosis of Heatstroke
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
Status epilepticus (interictal)
Stroke
Thyroid storm
Treatment of Heatstroke
Aggressive cooling
Aggressive supportive care
Classic and exertional heatstroke are treated similarly. The importance of rapid recognition and effective, aggressive cooling cannot be overemphasized.
Cooling techniques
The main cooling techniques are
Cold water immersion
Evaporative cooling
Cold water immersion
Evaporative cooling is also very effective and works best if the patient has adequate peripheral circulation (requiring adequate cardiac output). Evaporative cooling can be accomplished quickly by spraying tepid water over the patient and using a large industrial fan (often used by the janitorial department). The use of warm or tepid water maximizes the skin-to-air vapor pressure gradient and minimizes vasoconstriction and shivering. With this technique, most patients who have heatstroke can be cooled in < 60 minutes. In addition, ice or chemical cold packs can be applied to the neck, axillae, and groin or to hairless skin surfaces (ie, palms of hands, soles of feet, cheeks) that contain densely packed subcutaneous vessels to augment cooling, but are not adequate as the sole cooling method.
Cooling measures should be stopped once temperature reaches approximately 39° C to avoid overcooling and causing iatrogenic hypothermia.
Other measures
Necessary resuscitation should proceed while cooling is done. Neuromuscular blockade with endotracheal intubation and mechanical ventilation may be needed to control shivering and prevent aspiration in obtunded patients. Supplemental oxygen is given because heatstroke increases metabolic demand. IV hydration with 0.9% saline solution should be started with 1 to 2 L of cooled 0.9% saline to help decrease core temperature. Fluid deficits range from minimal (eg, 1 to 2 L) to severe dehydration. IV fluids should be given as boluses, assessing responses and the need for additional boluses by monitoring blood pressure, urine output, and central venous pressures.
Patients should be admitted to an intensive care unit and observed for multiple organ dysfunction, disseminated intravascular coagulation, and rhabdomyolysis. Hemodialysis may be required. Antipyretics have no value and can contribute to liver or kidney damage.
Prognosis for Heatstroke
Mortality and morbidity are significant in heatstroke patients but vary markedly with age, underlying disorders, maximum temperature and, most importantly, duration of hyperthermia and promptness of cooling.
Key Points
Heatstroke differs from heat exhaustion by the presence of CNS dysfunction and temperature > 40° C.
If the diagnosis of heatstroke is not obvious in febrile, obtunded patients, consider a wide variety of other disorders, such as infection, intoxication, thyroid storm, stroke, seizures (interictal), neuroleptic malignant syndrome, and serotonin syndrome.
Rapid recognition of heatstroke and effective, aggressive cooling are extremely important.
Use cool water immersion or evaporative cooling to rapidly cool the patient.
Patients will require intensive care monitoring with aggressive supportive care.
