Heat stroke

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Key Recommendations

Patients with suspected heat stroke should be rapidly assessed using Advanced Trauma and Life Support protocols. Once a primary survey is complete, the patient should be removed from the heat and their temperature assessed with rectal or esophageal thermometers.[17] Central nervous system (CNS) dysfunction in the setting of an elevated core temperature should trigger a presumptive diagnosis of heat stroke, and cooling should begin immediately.

Investigation of other possible etiologies for the affected patient should also be initiated. Cardiovascular, neurologic, endocrinologic, and infectious causes of presenting signs and symptoms should all be considered. Such etiologies should be suspected in patients with hyperthermia and other nonspecific symptoms that do not resolve with passive cooling, hydration, and rest.[3] Severe exercise-associated hyponatremia (EAH) may present similarly to heat stroke in patients with exertion-related symptoms; it is usually caused by overhydration with hypotonic fluid.[18][19]

Patients at risk

Older adults are at particular risk for heat stroke, as they may be less able to recognize and respond to thermal loading.[12] In part this may be related to an increased prevalence of cognitive comorbidities (e.g., dementia, Parkinson disease), and to the fact that certain medications (e.g., diuretics, antihypertensives, anticholinergics, phenothiazines, and tricyclic antidepressants) may predispose patients to heat stroke.[1] However, other patient groups are also at greater risk for heat stroke. These include people who are unacclimatized to hot environments (as they may lack compensatory mechanisms more efficient at dissipating heat) and young, active people exercising intensely under hot, humid conditions. The use of 3,4-methylenedioxymethamfetamine (MDMA) and other recreational drugs is an important risk factor for exertional heat stroke.[20] Excess body weight may also be an independent risk factor for exertional heat stroke.[21]

Clinical symptoms and signs

CNS dysfunction in the setting of an elevated core temperature should trigger a presumptive diagnosis of heat stroke, and cooling should begin immediately. In heat stroke, core temperature is classically >104°F (>40°C). However, it should be noted that even patients with normal temperature readings can have heat stroke, either because of inaccurate measuring techniques or from effects of prior cooling. Core temperature readings may be obtained with rectal or esophageal thermometers.[17] Heat stroke may be distinguished from heat exhaustion by the presence of profound alterations in mental status, which are always present in heat stroke. A range of CNS disturbance may be present, ranging in severity from confusion to coma. Typically, patients present with confusion and agitation. Other CNS symptoms include headache, anxiety, dizziness, irritability, ataxia, and nausea/vomiting. In contrast, patients with heat exhaustion may show only milder CNS symptoms (e.g., dizziness, headache, thirst, weakness, and malaise). Furthermore, heat-exhausted patients' symptoms typically resolve within 2 hours.

Hypotension may result from cutaneous vasodilation, shock, or volume depletion. In some more serious cases it can indicate cardiovascular collapse. Tachycardia may result from hyperthermia or hypotension, and frequently accompanies both classic and exertional heat stroke. Jaundice may be present in some cases; this is caused by hepatic injury due to thermal stress, tissue hypoperfusion, and indirect effects of heat stroke. Coagulopathy as a consequence of hepatic injury or direct thermal stress may also manifest (e.g., as epistaxis or bleeding from intravenous access sites).[22] Gut hypoxia and gastrointestinal bleeding can frequently occur, resulting from hypoperfusion and endotoxin release. Although uncommon, disseminated intravascular coagulation may develop. In many patients muscle tenderness may be present, and rhabdomyolysis may develop. Acute renal failure may result from myoglobinuria due to rhabdomyolysis, or from direct tissue effects of thermal stress.

Patients with significant volume depletion may experience severe postural dizziness, postural hypotension or tachycardia; however, the diagnostic value of these clinical findings for nonhemorrhagic volume depletion is uncertain, so fluid management should also be guided by measurement of blood chemistry results whenever possible.[23][24]

Investigations

All patients with suspected heat stroke should have routine blood chemistries performed on admission to the hospital. These include CBC and differential, liver function tests, metabolic profile (including sodium), serum creatine kinase, and a coagulation profile.[25] In confirmed cases of heat stroke, these lab tests should be followed at least daily for the entire observation period, as abnormalities in organ function can be delayed in onset. The presence of hypernatremia or hyponatremia will influence fluid management.[19]

Additional testing may be warranted depending on the clinical picture. In patients with profound CNS alterations, the possibility of space-occupying lesions and infection should be excluded (e.g., with CT and where appropriate lumbar puncture). Shock often accompanies heat stroke, and as such arterial blood gases and lactic acid levels should be monitored. Because in some patients the presentation may be consistent with certain endocrine emergencies (e.g., hyperthyroidism or diabetic ketoacidosis), thyroid function tests and plasma glucose as initial diagnostic testing may be considered. Finally, pyrexia and CNS abnormalities can occur as a result of systemic infection and in certain drug overdoses. If sepsis is suspected, a chest x-ray, blood and urine cultures should be ordered. A toxicology screen may also be appropriate if drug overdose is suspected (e.g., cocaine, phencyclidines, salicylates).

Consultation and referral

Critical care or environmental specialists are often involved in the care of a patient with heat stroke. All patients with suspected heat stroke should be admitted to the hospital for a surveillance period, as multiorgan dysfunction can appear 24 to 48 hours after the event.[26] Hepatic, renal, and clotting function should be monitored and determinations followed up for 48 hours after a heat stroke event.

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