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Emergency And Acute Medicine: Hyperthermia
Basics
Description Hyperthermia represents a spectrum of heat-related illness caused by progressively overwhelming heat stress, ranging from dehydration and electrolyte abnormalities to thermoregulatory failure and multisystem organ dysfunction. Normal body temperature is maintained by balancing heat production and dissipation. At temperatures above 42°C (108°F), oxidative phosphorylation becomes uncoupled and critical enzymes fail. Heat stroke is defined by a core temperature >105°F (40.5°C) with failure of thermoregulation, severe CNS dysfunction, and multisystem organ failure. Classic heat stroke is nonexertional, typically affecting the elderly, very young, or debilitated patients who cannot escape a hot environment; it develops over days to weeks and is associated with severe dehydration and hot, often dry skin. Exertional heat stroke occurs in younger, healthy individuals under intense physical exertion, develops over hours, and may occur despite ongoing sweating. Heat exhaustion involves moderate temperature elevation, usually <104°F (40°C), preserved thermoregulation and CNS function, and fluid or salt depletion; without treatment it may progress to heat stroke.
Etiology Predisposing factors impair heat dissipation or increase heat production. Medical conditions include extremes of age, dehydration, cardiovascular disease, obesity, diabetes, hyperthyroidism, pheochromocytoma, febrile illness, and skin disorders limiting sweating. Pharmacologic contributors include sympathomimetics, cocaine, PCP, LSD, MAO inhibitors, antipsychotics, anxiolytics, anticholinergics, antihistamines, beta-blockers, diuretics, laxatives, and drug or alcohol withdrawal. Environmental risks include high heat and humidity, prolonged exertion, immobility, lack of air conditioning, poor acclimatization, and occlusive clothing.
Pediatric considerations Children are at increased risk due to higher body surface area–to–mass ratio and reduced sweating capacity.
Diagnosis
Signs and symptoms Heat stroke presents with the classic triad of hyperthermia, CNS dysfunction, and hot skin. Core temperature exceeds 105°F (40.5°C). Neurologic findings include delirium, coma, seizures, ataxia, and confusion. Cardiovascular findings include tachycardia, hypotension, wide pulse pressure, and conduction abnormalities. Pulmonary findings include tachypnea, respiratory alkalosis, hypoxemia, and noncardiogenic pulmonary edema. GI symptoms include nausea, vomiting, and diarrhea. Renal failure, rhabdomyolysis, hepatic failure with extreme transaminase elevation, and coagulopathy including DIC may occur and indicate poor prognosis. Heat exhaustion causes headache, fatigue, malaise, impaired judgment, nausea, vomiting, tachycardia, dehydration, tachypnea, and profuse sweating without severe CNS dysfunction. Heat cramps cause painful muscle cramps after heavy sweating and hypotonic fluid replacement, leading to hyponatremia. Heat edema presents as dependent lower-extremity swelling in nonacclimatized individuals. Heat syncope presents as transient loss of consciousness during heat exposure, especially in the elderly. Prickly heat causes a pruritic maculopapular or vesicular rash due to sweat duct obstruction.
Essential workup Measure accurate core temperature using a rectal or esophageal probe. Establish history of heat exposure. Heat exhaustion is a diagnosis of exclusion. Heat stroke requires both core temperature >40.5°C and severe CNS dysfunction.
Diagnosis tests and interpretation
Laboratory Obtain CBC (leukocytosis, hemoconcentration), electrolytes, BUN, creatinine, glucose, urinalysis (myoglobin), creatine kinase for rhabdomyolysis, ABG (acidosis and elevated lactate common in exertional heat stroke), blood and urine cultures if sepsis is considered, toxicology screen, PT/PTT and DIC panel, liver function tests, and troponin (elevation suggests poor prognosis).
Imaging ECG in elderly or cardiac risk patients. Chest radiograph for ARDS or aspiration. Head CT for altered mental status. Lumbar puncture may be required to exclude CNS infection.
Differential diagnosis Sepsis, thyroid storm, pheochromocytoma, stimulant or anticholinergic toxicity, meningitis or encephalitis, cerebral malaria, delirium tremens, neuroleptic malignant syndrome, malignant hyperthermia, and serotonin syndrome.
Treatment
Prehospital Remove patient from heat source, disrobe, and initiate cooling with wet sheets.
Initial stabilization/therapy Ensure airway, breathing, and circulation. Begin continuous core temperature monitoring. Initiate rapid cooling if temperature >104°F (40°C). Give IV 0.9% normal saline bolus if hypotensive. For altered mental status, administer glucose, thiamine, and naloxone as indicated.
Emergency department management Cooling is the priority. Use evaporative cooling with misted warm water and high airflow; combine with ice packs to groin and axilla. Cold-water immersion is effective but often impractical. Advanced techniques such as cold peritoneal lavage, extracorporeal circulation, or cold dialysis may be considered for refractory cases. Stop cooling at 102°F (39°C) to prevent hypothermia. Antipyretics are ineffective and alcohol sponge baths should be avoided. Supportive care includes aggressive isotonic fluid resuscitation while avoiding fluid overload. Insert Foley catheter to monitor urine output; target >2 mL/kg/hr if rhabdomyolysis is present. Treat seizures, agitation, and shivering with benzodiazepines. Avoid vasopressors and antiarrhythmics until adequate cooling, as many arrhythmias resolve with temperature normalization. Treat associated heat syndromes with appropriate hydration, electrolyte replacement, elevation or compression, and topical therapy as indicated.
Medication Benzodiazepines such as diazepam or lorazepam for seizures or agitation; naloxone when opioid toxicity is suspected.
Follow-up and disposition
Admission criteria All patients with heat stroke require ICU admission. Heat exhaustion requires admission if severe electrolyte abnormalities, renal failure, rhabdomyolysis, or advanced age are present.
Discharge criteria Patients without heat stroke or severe heat exhaustion who normalize clinically after treatment may be discharged with counseling.
Key points Heat stroke cannot be diagnosed without both core temperature >40.5°C and severe CNS dysfunction. Rapid cooling and supportive care are the cornerstones of management. Continuous core temperature monitoring is standard of care, and evaporative cooling is the preferred first-line method.
Basics
Description Hyperthermia represents a spectrum of heat-related illness caused by progressively overwhelming heat stress, ranging from dehydration and electrolyte abnormalities to thermoregulatory failure and multisystem organ dysfunction. Normal body temperature is maintained by balancing heat production and dissipation. At temperatures above 42°C (108°F), oxidative phosphorylation becomes uncoupled and critical enzymes fail. Heat stroke is defined by a core temperature >105°F (40.5°C) with failure of thermoregulation, severe CNS dysfunction, and multisystem organ failure. Classic heat stroke is nonexertional, typically affecting the elderly, very young, or debilitated patients who cannot escape a hot environment; it develops over days to weeks and is associated with severe dehydration and hot, often dry skin. Exertional heat stroke occurs in younger, healthy individuals under intense physical exertion, develops over hours, and may occur despite ongoing sweating. Heat exhaustion involves moderate temperature elevation, usually <104°F (40°C), preserved thermoregulation and CNS function, and fluid or salt depletion; without treatment it may progress to heat stroke.
Etiology Predisposing factors impair heat dissipation or increase heat production. Medical conditions include extremes of age, dehydration, cardiovascular disease, obesity, diabetes, hyperthyroidism, pheochromocytoma, febrile illness, and skin disorders limiting sweating. Pharmacologic contributors include sympathomimetics, cocaine, PCP, LSD, MAO inhibitors, antipsychotics, anxiolytics, anticholinergics, antihistamines, beta-blockers, diuretics, laxatives, and drug or alcohol withdrawal. Environmental risks include high heat and humidity, prolonged exertion, immobility, lack of air conditioning, poor acclimatization, and occlusive clothing.
Pediatric considerations Children are at increased risk due to higher body surface area–to–mass ratio and reduced sweating capacity.
Diagnosis
Signs and symptoms Heat stroke presents with the classic triad of hyperthermia, CNS dysfunction, and hot skin. Core temperature exceeds 105°F (40.5°C). Neurologic findings include delirium, coma, seizures, ataxia, and confusion. Cardiovascular findings include tachycardia, hypotension, wide pulse pressure, and conduction abnormalities. Pulmonary findings include tachypnea, respiratory alkalosis, hypoxemia, and noncardiogenic pulmonary edema. GI symptoms include nausea, vomiting, and diarrhea. Renal failure, rhabdomyolysis, hepatic failure with extreme transaminase elevation, and coagulopathy including DIC may occur and indicate poor prognosis. Heat exhaustion causes headache, fatigue, malaise, impaired judgment, nausea, vomiting, tachycardia, dehydration, tachypnea, and profuse sweating without severe CNS dysfunction. Heat cramps cause painful muscle cramps after heavy sweating and hypotonic fluid replacement, leading to hyponatremia. Heat edema presents as dependent lower-extremity swelling in nonacclimatized individuals. Heat syncope presents as transient loss of consciousness during heat exposure, especially in the elderly. Prickly heat causes a pruritic maculopapular or vesicular rash due to sweat duct obstruction.
Essential workup Measure accurate core temperature using a rectal or esophageal probe. Establish history of heat exposure. Heat exhaustion is a diagnosis of exclusion. Heat stroke requires both core temperature >40.5°C and severe CNS dysfunction.
Diagnosis tests and interpretation
Laboratory Obtain CBC (leukocytosis, hemoconcentration), electrolytes, BUN, creatinine, glucose, urinalysis (myoglobin), creatine kinase for rhabdomyolysis, ABG (acidosis and elevated lactate common in exertional heat stroke), blood and urine cultures if sepsis is considered, toxicology screen, PT/PTT and DIC panel, liver function tests, and troponin (elevation suggests poor prognosis).
Imaging ECG in elderly or cardiac risk patients. Chest radiograph for ARDS or aspiration. Head CT for altered mental status. Lumbar puncture may be required to exclude CNS infection.
Differential diagnosis Sepsis, thyroid storm, pheochromocytoma, stimulant or anticholinergic toxicity, meningitis or encephalitis, cerebral malaria, delirium tremens, neuroleptic malignant syndrome, malignant hyperthermia, and serotonin syndrome.
Treatment
Prehospital Remove patient from heat source, disrobe, and initiate cooling with wet sheets.
Initial stabilization/therapy Ensure airway, breathing, and circulation. Begin continuous core temperature monitoring. Initiate rapid cooling if temperature >104°F (40°C). Give IV 0.9% normal saline bolus if hypotensive. For altered mental status, administer glucose, thiamine, and naloxone as indicated.
Emergency department management Cooling is the priority. Use evaporative cooling with misted warm water and high airflow; combine with ice packs to groin and axilla. Cold-water immersion is effective but often impractical. Advanced techniques such as cold peritoneal lavage, extracorporeal circulation, or cold dialysis may be considered for refractory cases. Stop cooling at 102°F (39°C) to prevent hypothermia. Antipyretics are ineffective and alcohol sponge baths should be avoided. Supportive care includes aggressive isotonic fluid resuscitation while avoiding fluid overload. Insert Foley catheter to monitor urine output; target >2 mL/kg/hr if rhabdomyolysis is present. Treat seizures, agitation, and shivering with benzodiazepines. Avoid vasopressors and antiarrhythmics until adequate cooling, as many arrhythmias resolve with temperature normalization. Treat associated heat syndromes with appropriate hydration, electrolyte replacement, elevation or compression, and topical therapy as indicated.
Medication Benzodiazepines such as diazepam or lorazepam for seizures or agitation; naloxone when opioid toxicity is suspected.
Follow-up and disposition
Admission criteria All patients with heat stroke require ICU admission. Heat exhaustion requires admission if severe electrolyte abnormalities, renal failure, rhabdomyolysis, or advanced age are present.
Discharge criteria Patients without heat stroke or severe heat exhaustion who normalize clinically after treatment may be discharged with counseling.
Key points Heat stroke cannot be diagnosed without both core temperature >40.5°C and severe CNS dysfunction. Rapid cooling and supportive care are the cornerstones of management. Continuous core temperature monitoring is standard of care, and evaporative cooling is the preferred first-line method.
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