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Last updated: March 22, 2021

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Heatstroke is a life-threatening condition in which the body temperature exceeds 40°C (104°F) because of an imbalance in heat generation and dissipation. Whereas in fever there is a physiological increase in the temperature setpoint of the body, in a heatstroke the hypothalamus setpoint remains normal. The young and elderly are at greatest risk because they do not take measures to prevent overheating (e.g., moving to a cooler environment or drinking more fluids). In addition to hot and humid weather, some drugs (e.g., vasoconstrictors, cocaine) and medical conditions (e.g., seizure, thyroid storm) can cause heatstroke. Affected individuals may present with a headache, nausea, hot skin without sweating, tender muscles, and varying degrees of neurological symptoms. Laboratory abnormalities 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, which include renal and hepatic failure with bleeding and possible coma and death. The best way to prevent heatstroke is to drink plenty of water, refrain from strenuous exercise in hot environments, and avoid clothing or substances that interfere with heat dissipation.

Nonexertional vs Exertional heatstroke [1]
Nonexertional heatstroke Exertional heatstroke
  • Children and elderly (> 70 years) are at highest risk
  • Healthy adolescents and adults are at highest risk
  • Particularly common in individuals with occupations that involve great exertion or exposure to heat (e.g., athletes, firefighters, military personnel)
Risk factors
  • Severe physical exertion and/or poor physicial fitness
  • Environmental factors (e.g., heavy protective clothing/equipment, high ambient temperatures and humidity )
Distinct clinical features
  • Usually hot, dry skin
Preferred rapid cooling technique
  • Evaporative or convecting techniques (e.g., spraying water, fanning, application of ice packs or wet gauze)
  • Immersion in ice water (most effective cooling modality)
  • Remove heavy/restrictive clothing

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

Heatstroke is mainly a clinical diagnosis.

Heatstroke Fever
  • Inability of the physiological response mechanisms to maintain a normal body temperature
  • Usually > 40°C (104 °F)
  • Usually < 40°C (104 °F)

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) [6]
    • 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 because of the risk of bleeding complications.

  • 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.
  1. Leyk D, Hoitz J, Becker C, Glitz KJ, Nestler K, Piekarski C. Health Risks and Interventions in Exertional Heat Stress.. Deutsches Arzteblatt international. 2019; 116 (31-32): p.537-544. doi: 10.3238/arztebl.2019.0537 . | Open in Read by QxMD
  2. Asmara IGY. Diagnosis and Management of Heatstroke.. Acta Med Indones. 2020; 52 (1): p.90-97.
  3. Gerrard D. Heat-Related Illness. Springer International Publishing ; 2019 : p. 45-55
  4. Trujillo MH, Fragachán G C. Rhabdomyolysis and Acute Kidney Injury due to Severe Heat Stroke.. Case reports in critical care. 2011; 2011 : p.951719. doi: 10.1155/2011/951719 . | Open in Read by QxMD
  5. Gagnon D, Lemire BB, Casa DJ, Kenny GP. Cold-water immersion and the treatment of hyperthermia: using 38.6°C as a safe rectal temperature cooling limit.. J Athl Train. undefined; 45 (5): p.439-44. doi: 10.4085/1062-6050-45.5.439 . | Open in Read by QxMD
  6. Epstein Y, Yanovich R. Heatstroke.. N Engl J Med. 2019; 380 (25): p.2449-2459. doi: 10.1056/NEJMra1810762 . | Open in Read by QxMD