Heatstroke is a temperature-related illness caused by the body’s failure to maintain temperature homeostasis. Heatstroke is characterized by body temperatures approaching and exceeding 40ºC (104ºF) and neurological symptoms including seizures, delirium, and ataxia.
Incidence in the United States is difficult to determine due to lack of reporting:
- Estimated annual incidence: 1.34 ED visits per 100,000
- Incidence increases with age.
- Male > female
- More common in spring and summer months
- More common in southern states
- Approximately 3,332 deaths from 2006–2010
Risk factors for heatstroke:
- Advanced age or immobility
- Psychiatric disease
- Physical exercise in a hot, humid environment
- Medications that impair heat response:
- Tricyclic antidepressants
Heatstroke can be divided based on its etiology as classic or exertional.
- Classic (non-exertional) heatstroke affects patients who, due to illness or situation, cannot thermoregulate or act to remedy exposure to excessive environmental heat:
- Neurological disorders
- Psychiatric disorder
- Recreational drug use
- Exertional heatstroke affects patients who perform strenuous activities in exceedingly hot or humid conditions, such as:
- Military personnel
|Classic heatstroke||Exertional heatstroke|
|Health status||Debilitated with chronic medical conditions||Healthy|
|Predisposing factors||Medications, poor housing||Athletic competition, training|
|Lactic acidosis||Absent||Often severe|
|Renal||Oliguria||Acute kidney injury|
|Rhabdomyolysis||Absent or mild||Often severe|
Under normal conditions, the body can thermoregulate extremely efficiently (undergoing a 1°C (1.8°F) change in core temperature for every 25–30°C (45–54°F) change in environmental temperature). Heatstroke is the product of a failure to thermoregulate.
- Normal temperature regulation:
- Body temperature is regulated by the CNS.
- Hypothalamus monitors body temperature and activates mechanisms to dissipate heat:
- Increased cardiac output
- Vasoconstriction of splanchnic circulation
- Situations in which heat dissipation fails:
- Existing pathology disrupts hemostasis mechanisms.
- Inadequate hydration to produce sweat
- Ambient humidity > 75% disrupts evaporation of sweat
- Sequelae of heatstroke arise:
- Severe dehydration:
- Brain edema
- Rhabdomyolysis (muscle breakdown):
- Kidney damage
- Severe dehydration:
History and physical exam
- History of exposure to elevated temperatures in high humidity
- Vital signs:
- Elevated body temperature
- Low blood pressure
- Widened pulse pressure
- Cutaneous findings:
- Anhydrosis: classic heat stroke
- Diaphoresis: exertional heat stroke
- Neurological findings:
- Diffuse weakness
- Vital signs:
Lab testing is for monitoring of progression of symptoms and cure.
- Continuous core temperature monitoring (rectal probe or Foley catheter)
- Lab testing:
- Blood glucose
- Clotting studies
- Blood gasses
- Serum creatine phosphokinase (CPK)
- Urine myoglobin
- ECG: in setting of electrolyte imbalance
Morbidity and mortality are directly related to the duration of core temperature elevation.
- Rapid cooling (evaporative methods are preferred):
- Ice-water immersion may be used.
- Stop when core temperature reaches 39°C (102.2°F).
- Volume resuscitation: careful monitoring of electrolytes
- Avoid vasoconstrictors (treat dysrhythmia with cooling, not drugs).
- Antipyretics are not indicated and may be harmful.
- Rapid cooling (cold-water immersion, misting with fan)
- Repletion of glucose and electrolytes
- Maintain high-volume urine output for rhabdomyolysis.
- Fever: elevation of core body temperature induced by cytokine (mainly prostaglandin E2) activation during inflammation. Regulation occurs at level of hypothalamus. Usually occurs in response to infection and resolves with treatment of same.
- Thyroid storm: an acute exacerbation of hyperthyroidism marked by fever, profuse sweating, tachycardia and/or arrhythmia (atrial fibrillation), hypertension, agitation, nausea, vomiting, diarrhea, confusion, seizures, delirium, and coma. Treatment involves rehydration, beta-blockers, iodide, antithyroid drugs, sedatives for agitation, antipyretic medication, and cooling blankets.
- Serotonin syndrome: a group of symptoms that may occur if certain serotonergic medications are combined. Marked by autonomic instability, muscle rigidity, and altered mental status.
- Neuroleptic malignant syndrome: a rare, idiosyncratic, and potentially life-threatening reaction to a neuroleptic (i.e., antipsychotic) drug. Marked by high temperature (above 38°C (100.4°F)), alteration in level of consciousness, autonomic dysregulation, and severe muscular rigidity (typically, lead-pipe rigidity).
- Malignant hyperthermia: a rare complication triggered by certain anesthetics and, if not treated, lethal in 70%–80% of cases. Characterized by a rapid increase in body temperature, tachycardia, dysrhythmia, hypercapnia, and rigid or painful muscles.