Heat Marathon -canstockphoto24918889Heat-related illnesses comprise a continuum of disorders ranging from the minor heat edema, heat rash, heat cramps, and heat exhaustion to the more life-threatening condition known as heat stroke. As a general rule, it is involves a process whereby heat gain overwhelms the body’s mechanisms of heat loss. Often it is caused by an impairment of the body’s cooling and adaptive mechanism to effectively transfer heat to the environment, thus leading to a rise in core temperature. 1

Risk Factors 1,2

  • Extremes of age (<4 years and >75 years)
  • Strenuous exercise
  • Ambient temperature
  • Cardiovascular disease
  • Dehydration
  • Obesity
  • Psychiatric illnesses
  • Medications

Although mostly preventable, heat stroke has a mortality rate of 10-20% even with treatment.3 Therefore, it is essential for its early recognition and intervention. This post will outline how to effectively approach and handle heat stroke in the emergency department.

What is Heat Stroke 1–3

  • Core body temperature ≥40ºC (104ºF) with associated altered mental status
  • Two types:
  1. Classic Heat Stroke (non-exertional)
    • Interference with thermoregulation or cooling strategies
    • Typically occurs over days
    • Examples: extremes of age, poverty, heat wave, lack of air conditioning, immobility, confined spaces (cars, attics, boiler rooms), cardiovascular disease, obesity, anhidrosis, physical disability, psychiatric conditions, medications, alcoholism, or recreational drugs
  2. Exertional Heat Stroke
    • Typically occurs within minutes to hours
    • Occurs in otherwise healthy individuals who perform heavy exercise in high temperature settings, such as young athletes, military recruits, and fire/police trainees

Distinctions between heat stroke and heat exhaustion3

Heat Exhaustion Heat Stroke
Temperature <40C (104F) ≥40C (104F)
Mental Status Normal mental status
Brief period of mild confusion
Brief syncope
Altered mental status – hallmark of heat stroke (confusion, poor attention, poor memory, agitation, delirium, confusion, hallucinations, coma, seizures)
Airway & Breathing Clear airway
May be tachypneic
Airway may be compromised
Tachypneic
Circulation Tachycardic
Normal BP
Mild-moderate dehydration
Tachycardic
Hypotension/ wide pulse pressure
Moderate-severe dehydration
Skin Sweating Dry skin (classic heat stroke)
Sweating (exertional heat stroke)
Other Nausea/vomiting
Headache
Generalized fatigue
Weakness
Hypo/hypernatremia
Nausea/vomiting
Diarrhea
DIC
Rhabdomyolysis
Renal failure
Cardiogenic shock
Liver failure

 Differential Diagnosis for Hyperthermia4

  • Environmental
    • Heat-related illnesses
  • Drugs and medications
    • Malignant hyperthermia
    • Alcohol withdrawal
    • Salicylate toxicity
    • Neuroleptic malignant syndrome
    • Stimulant toxicity (cocaine, phencyclidine, amphetamine)
    • Anti-cholinergic toxicity
  • Infectious
  • Neurologic
    • Hypothalamic stroke
    • Status epilepticus
    • Cerebral hemorrhage
  • Endocrine
    • Thyroid storm
    • Pheochromocytoma
  • Oncologic
    • Lymphoma
    • Leukemia

Diagnostic Workup 1–3

  1. Core temperature with frequent monitoring
    • Rectal temperature is the most reliable assessment of core temperature 1 – level C evidence (based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series)
  2. Laboratory studies
    • Compete blood count (CBC)
    • Electrolytes
    • Arterial or venous blood gas
    • Glucose
    • Blood urea nitrogen (BUN)/creatinine
    • Creatinine kinase (CK)
    • Liver enzymes
    • Coagulation studies
    • Urinalysis
    • Urine myoglobin
  3. Electrocardiogram (ECG), if history of syncope or cardiovascular disease
  4. Chest radiograph to rule out aspiration or pulmonary infection
  5. Consider for CT brain ± lumbar puncture, based on clinical suspicion

Treatment and Disposition 2

  1. Basic supportive measures
    • Airway protection
    • Cardiac monitoring
    • IV fluid therapy with normal saline or lactated Ringer solution
      • Goal: maintain mean arterial pressure >60 mmHg
      • Correct electrolyte abnormalities
  2. Rapid cooling
    • Target temperature:
      • A range of target temperatures have been recommended at 37-40.1ºC. 5 Often 39-40ºC is recommended to avoid overshoot hypothermia.
    • Rapid accessibility to cooling is the most effective method to prevent heat-related mortality4
    • Although the literature is sparse on the ideal cooling method for EXERTIONAL heat stroke, consider cold water immersion — associated with lowest morbidity and mortality 1 (Level C evidence)
    • Evaporative cooling with mist and fan is also effective
      • Avoid ice water as shivering may induce thermogenesis
      • Other cooling methods: ice pack cooling to groin and axilla, cooling blanket, thoracic/peritoneal lavage
      • Do not use antipyretics!
  3. Pharmacotherapy
    • Manage seizures and severe shivering with short acting benzodiazepine
    • Treat rhabdomyolysis
      • IV fluid resuscitation and sodium bicarbonate (3 ampules of 50 mL of 8.4% bicarbonate in 1 L 5% D5W at 250 mL/hr)
      • Consider furosemide if inadequate urine output.
      • Consider antibiotics IF and ONLY IF infection is high on list of possible etiologies.
  4. Complications/Disposition
    • Major complications: rhabdomyolysis, liver failure, renal failure, heart failure, cardiovascular collapse, pulmonary edema, or disseminated intravascular coagulation (DIC)
    • Admit to the intensive care unit for further observation

Take Home Messages About Heat Stroke

  • Heat stroke is a medical emergency that requires prompt recognition and treatment.
  • It is characterized by altered mentation and hyperpyrexia as a result of thermoregulatory dysfunction, leading to multi-organ failure and tissue damage.
  • Treatment includes stabilization of ABCs, rapid cooling, managing fluid and electrolyte imbalances, and treating secondary complications.
  • Important: Antipyretics are NOT effective in reducing core body temperature in heat stroke! Use cold water immersion, evaporative methods, or other cooling methods along with benzodiazepines to reduce shivering when necessary.

Image: (c) Can Stock Photo

1.
Becker J, Stewart L. Heat-related illness. Am Fam Physician. 2011;83(11):1325-1330. [PubMed]
2.
Tran TP. Heat emergencies. In: Ma OJ, Cline DM, ed. Emergency medicine manual. 6th ed. McGraw-Hill, NY: 2004:564-565.
3.
Glazer J. Management of heatstroke and heat exhaustion. Am Fam Physician. 2005;71(11):2133-2140. [PubMed]
4.
American C, Armstrong L, Casa D, et al. American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc. 2007;39(3):556-572. [PubMed]
5.
Bouchama A, Dehbi M, Chaves-Carballo E. Cooling and hemodynamic management in heatstroke: practical recommendations. Crit Care. 2007;11(3):R54. [PubMed]
Katherine Li

Katherine Li

Medical student
University of Ottawa Faculty of Medicine
Katherine Li

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