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Heatstroke

Last updated: September 20, 2021

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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.

Nonexertional vs Exertional heatstroke [1]
Nonexertional heatstroke Exertional heatstroke
Epidemiology
  • 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 physical 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 vs. fever

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

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
  • 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

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.
  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. 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
  5. 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
  6. Chen WT, Lin CH, Hsieh MH, Huang CY, Yeh JS. Stress-induced cardiomyopathy caused by heat stroke.. Ann Emerg Med. 2012; 60 (1): p.63-6. doi: 10.1016/j.annemergmed.2011.11.005 . | Open in Read by QxMD
  7. Epstein Y, Yanovich R. Heatstroke.. N Engl J Med. 2019; 380 (25): p.2449-2459. doi: 10.1056/NEJMra1810762 . | Open in Read by QxMD