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Exertional Heat Stroke

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Other Names

  • Heat stroke
  • Exertional Heat Stroke (EHS)


  • This page refers to heat stroke, a condition characterized by extreme hyperthermia and CNS dysfunction[1]
    • This page primarily focuses on Exertional Heat Stroke (EHS) seen in athletes
    • The overlap with 'classic' heat stroke is significant



  • Mortality
    • Approaches 30% even with proper treatment (need citation)
    • Among the elderly, heat stroke deaths exceed 50%[2]
    • Less than <5% in young healthy athletes who receive prompt recognition, treatment[3]
  • Trending
    • Deaths appear to be on the rise
    • US Military reported an increase in exertional heat stroke cases (344) in 2014 compared with 2013[4]
    • Deaths from EHS were higher during the period from 2005 to 2009 than any other five year period over the past 35 years[5]


Epidemiologic and Clinical Features of Classic and Exertional Heatstroke..jpeg[6]
  • General
    • Severe end of heat related illness spectrum characterized by severe hyperthermia, neurologic dysfunction
    • This is a life threatening condition and medical emergency
    • Universally fatal if left untreated
    • The most critical interventions are to remove the patient from the heated environment to cool conditions
    • Subsequently, submersion in ice water to cool the patient
  • Timeline
    • In American football, most cases occur during summer practice where players are less fit, temperature and humidity are high


  • Heat stroke
    • Defined as "core temperature above 40°C (104°F) PLUS central nervous system involvement
  • Exertional Heat Stroke
    • Exertional heat stroke has the added component of a pathologic hyperthermia that occurs during strenuous activity
    • Triad: hyperthermia, neurologic dysfunction, recent physical exertion
  • Classic (Passive)
    • Seen in elderly and children
    • Due to exposure to environmental heat and poor heat-dissipation mechanisms
    • Typically occurs as an epidemic during a heat wave in those who can not care for themselves
  • Exertional
    • Associated with physical exercise
    • Results when excessive production of metabolic heat overwhelms physiological heat-loss mechanisms
    • Most often affects healthy young persons who receive prompt recognition, treatment
    • Can occur in first 60 minutes of exertion
    • Can be triggered without exposure to high ambient temperatures[7]

Environmental Evaluation

  • WBGT should be used to assess risk.


Pathophysiological Pathway Leading to Heat Stroke[6]
  • General
    • Occurs when the body's metabolic heat production exceeds its ability for heat transfer
    • Subsequently results in thermoregulatory dysfunction, metabolic disruption
  • Metabolic dysfunction
    • Interleukins's, cytokines, and heat shock proteins are released or disrupted resulting in pathophysiology similar to shock mechanisms.
    • For example, heat shock proteins become denatured, are no longer able to protect other proteins or enzymes from thermal destruction
    • Apoptosis and necrosis begin to occur at this level and begin to cause organ dysfunction.
  • Multiorgan dysfunction[8]
    • More pronounced in EHS than classic heat stroke
    • Peaks around 24 to 48 hours
    • Primarily to heat-induced necrotic and apoptotic cell death
    • Accompanying widespread microthrombosis, hemorrhage, and inflammatory injury

Associated Conditions

Three Phases

  • Hyperthermic–neurologic acute phase
    • Most critical to recognize
  • Hematologic–enzymatic phase
    • Peaking 24 to 48 hours after the event
  • Late renal–hepatic phase
    • If clinical symptoms are sustained for 96 hours or longer

Risk Factors Underlying Heat stroke (click to enlarge)[6]

Risk Factors

Differential Diagnosis

Differential Diagnosis Heat Illness

Differential Diagnosis Collapsed Athlete

Clinical Features

Signs and symptoms of exertional heat stroke[9]
  • History
    • In EHS, typically some sort of explanation for elevated core temperature
      • E.g. exercising outdoors, no access to air conditioning, landscaping
    • In most cases the athlete or laborer will collapse, prompting attention
  • Physical Exam
    • Hyperthermia with core temp greater 40°C (104°F)
    • CNS dysfunction (altered behavior, confusion, slurred speech, delirium, ataxia, coma, seizures)
      • Seizures and sphincter incontinence are more common in EHS (need citation)
    • Anhidrosis frequently present (absence does not exclude heat stroke)
    • Hematochezia (can occur from decreased intestinal perfusion, ischemia)
  • Special Tests


  • Primarily a clinical diagnosis
    • Based on triad of exposure or exertion, hyperthermia, CNS dysfunction
    • Workup (imaging, labs, EKG, etc) should not delay primary treatment of cooling



  • Should be obtained to exclude other causes


  • Blood glucose finger stick
  • Complete Blood Count
  • Metabolic Panel
  • Liver Function Tests
  • Blood Gas
  • Lactate
  • Coagulation studies
  • Creatinine phosphokinase, myoglobin
  • Urinalysis


  • There is no widely accepted classification system

Field management of suspected heat stroke[9]



  • Rapid Recognition
    • Typically triggered by collapse or near collapse of the athlete
    • Prehospital management is the most critical element to limiting morbidity and mortality[10]
    • Attempt to distinguish EHS from other forms of heat related illness
    • All patients suspected of having EHS should be transported to the hospital
  • ABCs/ Rapid Assessment
    • Confirm presence of pulse, spontaneous respirations
    • Patient may require airway management prehospital
    • Maintain oxygen saturation >90%
    • Patient should be given IVF bolus, especially if hypotensive
  • Rapid Cooling
    • The best outcomes for EHS involve rapid on-site whole-body cooling (need citation)
    • Cooling should be initiated as soon as EHS is suspected
    • Monitor temperature if possible
    • Remove from warm environment into air conditioned environment
Onsite whole-body cooling strategies for EHS casualties that are effective in the field.[9]
  • Cooling Techniques
    • Ice water tub immersion if possible[11]
    • Rotate ice-water soaked towels on trunk, extremities, head
    • Place ice packs in axilla, groin, behind knees
    • Douse body with ice water
    • Spray with tap water
  • EMS/ Tansport
    • Transport as soon as possible
    • Timing may depend somewhat on field resources, comfort of on-site team
    • EMS should actively cool en route to hospital


  • ABC
    • Patient may require intubation
  • Fluids
    • Bolus if hypotensive
    • Protects kidneys from highly likely rhabdomyolysis
    • Fluids should be cold
  • Complications
    • Hypotensive shock requiring pressors
    • Electrolyte dysfunction: hypo- or hyperkalemia, hyponatremia
    • Liver injury
    • Renal Failure
    • ARDS
    • Seizure: treat with benzodiazepines


  • General
    • Critical threshold is 40.5°C, above which mortality skyrockets
    • Cooling end point is 38-39°C (do not want to over-correct)
    • Cooling faster than 0.10°C is safe and desirable for improving prognosis[12]
    • Foley catheter for core temperature monitoring
    • No role for dantrolene, antipyretics
  • Cold Water Immersion
    • Treatment of choice
    • Immerse body to the level of torso or neck in ice water
    • Benefits: quickest decrease in core temperature, some studies have shown 100% survival when started early
      • Can cool as fast as 0.20°C to 0.35°C per minute
    • Disadvantages: immersion tub not available in most EDs, not well tolerated, hard to resuscitate
    • Ice packs to neck, axilla, groin, popliteal fossa similar benefit?
  • Evaporative/ Convective Cooling
    • Spray cold water on patient with fans directed at them
    • Can spray on skin or thin sheet
    • Benefits: Easier and quicker to apply in ED while performing other interventions
    • Disadvantage: slower than immersion, slightly higher morbidity and mortality
    • May be only option in austere environments where ice or transportation is not readily available
  • Invasive techniques with limited ata
    • Bladder lavage
    • Gastric lavagage
    • Tube thoracostomy with lavage
    • ECMO or cardiopulmonary bypass


Rehab and Return to Play


  • There are no clear rehabilitation guidelines

Return to Play/ Work

Example of staged return to play after exertional heat stroke (click to enlarge)[9]
  • No comprehensive guidelines
    • RTP or work decisions are challenging for physicians
    • At a minimum, clinical and laboratory findings need to return to baseline
    • Most athletes recover within a few weeks, especially if recognized and treated early[13]
  • American College of Sports Medicine[9]
    • Decision may involve medical staff, coaches, supervisors, athletic trainers, and/or family members
    • Athlete should go through a progressive increase in exercise intensity and duration in warm or hot conditions to assess recovery
    • If athlete can gradually regain preheat injury exercise tolerance and expected performance
    • Return to play is usually safe and advancing to full training and competition is acceptable
  • Heat Tolerance Testing (HTT)
    • May be required for athletes who are unable to advance activities in a reasonable time frame
    • Used by Israel Defense Force (IDF) Medical Corps 6 wk postexertional heat illness as part of the “return to duty” criteria[14]
      • Sensitivity (66.7%), specificity (77.7%), and diagnostic accuracy (77.2%) of the HTT[15]
      • Authors: risk of EHI recurrence is measurable and that a negative HTT result is associated with a substantial reduction of EHI risk
    • Note that this HTT has not been externally validated and requires more research

Complications and Prognosis


  • Rate of improvement/ recovery
    • If treatment is prompt, milder cases abate within a few days and most patients recover completely
    • Prognosis worsens if kidney and liver dysfunction are sustained for more than 96 hours
  • Risk of Death
    • Universally fatal if untreated
    • Mortality nearly 30% even if treated approrpiately[16]
    • Linear association between core temperature and risk of mortality
    • Study: risk of death months and years later remains higher than general population[17]


  • Persistent Neurological Deficit
    • Seen in 20% of of patients
    • Commonly affects cerebellum
  • Injury to autonomic nervous system
  • Injury to enteric nervous system

See Also


  1. Bouchama, Abderrezak, and James P. Knochel. "Heat stroke." New England journal of medicine 346.25 (2002): 1978-1988.
  2. Bouchama, Abderrezak, and James P. Knochel. "Heat stroke." New England journal of medicine 346.25 (2002): 1978-1988.
  3. Shapiro, Y., and D. S. Seidman. "Field and clinical observations of exertional heat stroke patients." Medicine and science in sports and exercise 22.1 (1990): 6-14.
  4. Armed Forces Health Surveillance Center (AFHSC. "Update: heat injuries, active component, US Armed Forces, 2013." Msmr 21.3 (2014): 10-13.
  5. Mueller, F., and R. Cantu. "Catastrophic sports injury research: twenty-sixth annual reports." University of North Carolina (2008).
  6. 6.0 6.1 6.2 Epstein, Yoram, and Ran Yanovich. "Heatstroke." New England Journal of Medicine 380.25 (2019): 2449-2459.
  7. Epstein, Y. O. R. A. M., et al. "Exertional heat stroke: a case series." Medicine and science in sports and exercise 31.2 (1999): 224-228.
  8. Roberts, George T., et al. "Microvascular injury, thrombosis, inflammation, and apoptosis in the pathogenesis of heatstroke: a study in baboon model." Arteriosclerosis, thrombosis, and vascular biology 28.6 (2008): 1130-1136.
  9. 9.0 9.1 9.2 9.3 9.4 Roberts, William O., et al. "ACSM expert consensus statement on exertional heat illness: recognition, management, and return to activity." Current sports medicine reports 20.9 (2021): 470-484.
  10. Belval LN, Casa DJ, Adams WM, et al. Consensus statement — prehospital care of exertional heat stroke. Prehosp. Emerg. Care. 2018; 22:392–7.
  11. Armstrong LE, Crago AE, Adams R, et al. Whole-body cooling of hyperthermic runners: comparison of two field therapies. Am. J. Emerg. Med. 1996; 14:355–8.
  12. McDermott, Brendon P., et al. "Acute whole-body cooling for exercise-induced hyperthermia: a systematic review." Journal of athletic training 44.1 (2009): 84-93.
  13. Laitano O, Leon LR, Roberts WO, Sawka MN. Controversies in exertional heat stroke diagnosis, prevention, and treatment. J. Appl. Physiol. 2019; 127:1338–48.
  14. Epstein Y. Heat intolerance: predisposing factor or residual injury? Med. Sci. Sports Exerc. 1990; 22:29–35.
  15. Schermann H, Craig E, Yanovich E, et al. Probability of heat intolerance: standardized interpretation of heat-tolerance testing results versus specialist judgment. J. Athl. Train. 2018; 53:423–30.
  16. Gaudio FG, Grissom CK. Cooling Methods in Heat Stroke. J Emerg Med. 2015 Oct 31.
  17. Wallace, Robert F., et al. "Prior heat illness hospitalization and risk of early death." Environmental research 104.2 (2007): 290-295.
Created by:
John Kiel on 30 June 2019 22:50:33
Last edited:
19 August 2022 07:03:49