Heatstroke

Heatstroke is a life-threatening condition in which body temperature rises above 40°C (104°F) due to an imbalance between heat generation and heat dissipation. Heatstroke can be nonexertional (due to prolonged exposure to high temperatures) or exertional (due to excessive physical exertion). The body's temperature setpoint, regulated by the hypothalamus, remains normal during heatstroke, unlike in fever, where it is physiologically raised. Children and elderly individuals are at greatest risk due to difficulties staying hydrated as well as impaired/underdeveloped heat sensation and thermoregulation. In addition to hot and humid weather, certain substances (e.g., vasoconstrictors, cocaine) and medical conditions (e.g., seizure, thyroid storm) can also cause heatstroke. Affected individuals may present with headache, nausea, hot skin without sweating, tender muscles, and neurological symptoms (e.g., confusion, tremors, or seizures). Laboratory findings include elevated muscle enzymes (e.g., creatine kinase) and lactic acidosis due to rhabdomyolysis. A rapid reduction of the core body temperature with fanning and ice water is essential to prevent life-threatening complications such as renal and hepatic failure with bleeding, and coma. Differential diagnoses include fever, heat exhaustion (hyperthermia < 40°C/104°F with normal CNS function), neuroleptic malignant syndrome, and malignant hyperthermia. Heatstroke prevention involves staying hydrated, avoiding strenuous exercise in hot environments, wearing temperature-appropriate clothing, and avoiding substances that interfere with heat dissipation.

• Hyperthermia: an elevation of normal body temperature due to failed thermoregulation.
• Heatstroke: a life-threatening condition that presents with hyperthermia > 40°C (104°F) and central nervous system dysfunction (e.g., altered mental status).

Ice water immersion is associated with an increased mortality in elderly patients!

• The normal physiologic response to increased body temperature is hypothalamus-mediated peripheral vasodilation (to expose blood to the cooler air) and sweating (to dissipate heat into the environment).
• In heatstroke, the hypothalamic thermoregulatory response is inadequate to maintain a normal temperature.
• Causes include:
  • Increased heat production (e.g., strenuous exercise, sepsis, status epilepticus, cocaine and amphetamines, thyroid storm)
  • Decreased heat dissipation (e.g., high ambient temperature or humidity, vasoconstrictor drugs, skin diseases, burns, reduced CNS response due to alcohol and sedatives)
  • Reduced behavioral responsiveness (e.g., infants, the elderly, and chronically ill individuals who are unable to control their environment and water intake)
• High body temperature → protein denaturation, phospholipid and lipoprotein damage, and membrane lipid liquefaction → cell damage and loss of function (including myocardiocytes and neurons) → cardiovascular collapse → multiorgan failure and possibly death

• Hot, potentially dry skin ^[2][3][4]
• Body temperature > 40°C (104°F)
• Headache
• Fatigue
• Nausea, vomiting
• Tachypnea
• Tachycardia with normal blood pressure
• Musculoskeletal features: tender, rigid, limp, or cramping muscles
• Central nervous system
  • Delirium, hallucinations
  • Loss of consciousness
  • Convulsions
  • Tremors
• Acute respiratory distress syndrome

Heatstroke is mainly a clinical diagnosis.

• Laboratory studies
  • ↑ WBC
  • Lactic acidosis, hypoglycemia
  • ↑ Creatine kinase as a sign of rhabdomyolysis (a frequently encountered complication)
  • ↑ Liver enzymes (in case of hepatic injury)
  • ↑ Urea and creatinine as a sign of acute renal injury (∼ 30% of cases) ^[5]
  • Coagulation studies to assess for disseminated intravascular coagulation (see “Disseminated intravascular coagulation”)
• ECG: sinus tachycardia, nonspecific and ischemic ST-T wave abnormalities (stress-induced cardiomyopathy) ^[6]
• CT to rule out other causes of CNS impairment

Heatstroke vs. fever

Heat exhaustion

• Definition: a heat-related injury characterized by hyperthermia ≤ 40°C (104°F) and an inability to maintain cardiac output with normal central nervous system function.
• Clinical features
  • Nausea, vomiting
  • Diaphoresis
  • Dehydration
  • Tachycardia
  • Headache, dizziness, mild confusion (resolves quickly with treatment)
  • Normal mental status
• Diagnostics: clinical diagnosis
• Treatment
  • Discontinue strenuous exercise immediately, move to cool environment, and remove excess clothing
  • Oral rehydration (preferably with chilled, salt-containing fluids, flavored sports drinks, or water)
  • If symptoms persist or altered mental status develops: management as of heat stroke
    • Measure electrolytes and treat potential imbalances
    • See diagnosis and treatment of heatstroke for details

Other

• Neuroleptic malignant syndrome (NMS)
• Malignant hyperthermia

The differential diagnoses listed here are not exhaustive.

• Rapid reduction of the core body temperature to 39°C (102.2°F)
  • Immersion in ice water (most effective cooling modality) ^[7]
  • Cooling by spraying water
  • Fanning
  • Cold IV crystalloids
• Rehydration
• Electrolyte imbalance treatment

Antipyretics (e.g., acetaminophen and other NSAIDs), which interrupt the change in the hypothalamic setpoint caused by pyrogens in fever, are not effective in heatstroke and may even be harmful due to the risk of bleeding.

• Limit strenuous physical activity, alcohol intake, and use of medications and drugs that interfere with heat dissipation in hot environments.
• Ensure adequate hydration and sufficient breaks for cooling off.