Heatstroke

Heatstroke is an illness characterized as a core body temperature exceeding 40°C (104°F) with accompanying neurological symptoms including ataxia, seizures, and/or delirium. Heatstroke is usually due to the body’s inability to regulate its temperature when challenged with an elevated heat load. The illness can be classified as exertional or non-exertional. Management involves emergent stabilization, cooling, and supportive care. Early recognition and intervention are important to prevent complications or organ failure.

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Overview

Definition

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.

Epidemiology

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
  • Dementia 
  • Physical exercise in a hot, humid environment
  • Medications that impair heat response:
    • Anticholinergics
    • Antihistamines
    • Diuretics 
    • Neuroleptics 
    • Antihypertensives
    • Phenothiazines
    • Tricyclic antidepressants

Etiology

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:
    • Elderly
    • Disabled
    • Neurological disorders
    • Psychiatric disorder
    • Recreational drug use
  • Exertional heatstroke affects patients who perform strenuous activities in exceedingly hot or humid conditions, such as:
    • Athletes
    • Military personnel
Table: Types of heatstroke
Classic heatstrokeExertional heatstroke
AgeElderlyYoung
Health statusDebilitated with chronic medical conditionsHealthy
Predisposing factorsMedications, poor housingAthletic competition, training
OccurrenceDuring heatwavesSporadic
SkinAnhidrosisDiaphoresis
GlucoseNormalLow
Lactic acidosisAbsentOften severe
CoagulopathyMildSevere, DIC
RenalOliguriaAcute kidney injury
RhabdomyolysisAbsent or mildOften severe
DIC: disseminated intravascular coagulation

Pathophysiology

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
      • Sweating
  • 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:
      • Hypernatremia
      • Hyperkalemia
      • Brain edema
    • Rhabdomyolysis (muscle breakdown):
      • Weakness
      • Kidney damage
    • Coagulopathies:
      • Strokes
      • Seizures
Pathophysiology chart of heatstroke

Pathophysiology of heatstroke

Image by Lecturio.

Diagnosis

History and physical exam

  • History of exposure to elevated temperatures in high humidity
  • Symptoms:
    • Lethargy
    • Weakness
    • Nausea/vomiting
    • Dizziness
  • Signs: 
    • Vital signs:
      • Elevated body temperature
      • Low blood pressure
      • Tachycardia
      • Tachypnea
      • Widened pulse pressure
    • Cutaneous findings:
      • Anhydrosis: classic heat stroke
      • Diaphoresis: exertional heat stroke
    • Neurological findings:
      • Delirium 
      • Seizures
      • Diffuse weakness

Workup

Lab testing is for monitoring of progression of symptoms and cure.

  • Continuous core temperature monitoring (rectal probe or Foley catheter)
  • Lab testing:
    • CBC
    • CMP
    • Blood glucose
    • Clotting studies
    • Blood gasses 
    • Serum creatine phosphokinase (CPK)
    • Urine myoglobin
  • ECG: in setting of electrolyte imbalance

Management

Morbidity and mortality are directly related to the duration of core temperature elevation.

Classic heatstroke

  • 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.

Exertional heatstroke

  • Rapid cooling (cold-water immersion, misting with fan)
  • Repletion of glucose and electrolytes 
  • Maintain high-volume urine output for rhabdomyolysis.

Differential Diagnosis

  • 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.

References

  1. Gaudio FG, Grissom CK. Cooling Methods in Heat Stroke. (2016). J Emerg Med. https://pubmed.ncbi.nlm.nih.gov/26525947/ 
  2. Adams T, Stacey E, Stacey S, Martin D. Exertional heat stroke. (2012). Br J Hosp Med (Lond). https://pubmed.ncbi.nlm.nih.gov/22504748/

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