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Heat Exhaustion and Heat Stroke
Sean C. Robinson, MD
Brian Frank, MD
image BASICS
  • A continuum of increasingly severe heat illnesses caused by dehydration, electrolyte losses, and failure of the body's thermoregulatory mechanisms when exposed to elevated environmental temperatures.
    • Heat exhaustion is a mild to moderate form of heat illness displaying dehydration type symptoms with a normal to elevated temperature < 104°F (1).
    • Heat stroke is characterized by an elevated core temperature >104°F with central nervous system abnormalities (1,2).
  • System(s) affected: endocrine/metabolic, nervous, hepatic, hematologic
  • Synonym(s): heat illness; heat injury; hyperthermia; heat collapse; heat prostration
Geriatric Considerations
Elderly persons are more susceptible.
Pediatric Considerations
Children are more susceptible.
Pregnancy Considerations
Pregnant women may be more susceptible to volume depletion with heat stress.
  • Predominant age: more likely in children or elderly
  • Predominant sex: male = female
  • Depends on intensity of heat; estimate of 20/100,000 persons per season (3)
  • Concern for increasing incidence of disease if ambient environmental temperatures continue to rise
  • Depends on predisposing conditions in combination with environmental factors
  • Roughly 600 deaths/year in the United States
  • Direct cellular toxicity of heat, imbalance between inflammatory and anti-inflammatory cytokines, and vascular endothelial damage causing end-organ dysfunction
  • Interplay between failure of heat-dissipating mechanisms, an overwhelming heat stress, and an exaggerated acute-phase inflammatory response
  • Poor acclimatization to heat or poor physical conditioning
  • Salt or water depletion
  • Obesity
  • Acute febrile or GI illnesses
  • Chronic illnesses: uncontrolled diabetes mellitus or hypertension, cardiac disease
  • Alcohol and other substance abuse
  • High heat and humidity, poor air circulation in environment
  • Heavy, restrictive clothing
  • Nutritional supplementation that includes ephedra (2)
  • Medications (&agr;-adrenergics, anticholinergics, antihistamines, antipsychotics, benzodiazepines, &bgr;-blockers, calcium channel blockers, clopidogrel, diuretics, laxatives, neuroleptics, phenothiazines, thyroid agonists, tricyclic antidepressants) (1)
  • The most important factor in preventing heat stress is adequate fluid replacement.
  • Allow acclimatization to hot weather through proper conditioning and activity modification.
  • Dress appropriately with loose-fitting, open-weaved, light-colored clothing.
  • Avoid dehydration by consuming a proper amount of fluids during activity or exercise.
  • Never leave children unattended in cars during hot weather.
  • Try to gain access to air-conditioned environments during hot weather.
  • The prognosis is good when mental function is not altered and when serum enzymes are not elevated; recovery is within 24 to 48 hours in most cases.
  • The mortality rate for heat stroke (10-80%) is directly related to the duration and intensity of hyperthermia, as well as to the speed and effectiveness of diagnosis and treatment (3).
  • Heat exhaustion: Symptoms are milder than in heat stroke, with no severe CNS derangements:
    • Fatigue and lethargy
    • Weakness
    • Dizziness
    • Nausea, vomiting
    • Myalgias
    • Headache
    • Profuse sweating
    • Tachycardia
    • Hypotension
    • Lack of coordination
    • Agitation
    • Intense thirst
    • Hyperventilation
    • Paresthesias
    • Core temperature usually elevated but can be normal, if elevated < 104°F (40°C)
  • Heat stroke: divided into two categories, classic and exertional:
    • Classic: caused by environmental exposure, primarily in elderly or chronically ill patients, and may develop gradually over days
      • Delirium
      • Confusion
      • Coma
      • Core temperature >104°F (>40°C)
      • Hot, flushed, dry skin
    • Exertional: typically younger, very active patients; rapid onset
      • Exhaustion
      • Confusion, disorientation
      • Delirium
      • Coma
      • Hot, flushed skin, typically with sweating
      • Core temperature >104°F (>40°C) (1,2)
  • Other causes of elevated temperature, dehydration, or circulatory collapse
  • Febrile illnesses, sepsis
  • Drug-induced fluid loss
  • Cardiac arrhythmia or infarction
  • Acute cocaine intoxication
  • Neuroleptic malignant syndrome
  • Malignant hyperthermia (an autosomally inherited disorder of skeletal and cardiac muscle in which patients have abnormal muscle metabolism on exposure to halothane or skeletal muscle reactants)

Used primarily to detect end-organ damage
Initial Tests (lab, imaging)
  • Electrolytes, urinalysis
  • Creatinine, BUN
  • Liver enzymes, muscle enzymes (creatine phosphokinase)
  • CBC
  • Increased urine-specific gravity
  • Results of these studies may indicate hypernatremia, hyperchloremia, and hemoconcentration.
  • Drugs that may alter lab results: diuretics
Diagnostic Procedures/Other
Rectal temperature monitoring (do not rely on oral temperature) (1,2)[A]
  • Fluid and electrolyte replacement with normal saline gradually; avoid hypotonic fluids (1,2)[C].
  • Consider CVP monitoring.
  • Body immersion in ice water, careful consideration of airway protection (1,3)[C]
  • Evaporative cooling: spraying water over the patient and facilitating evaporation and convection with the use of fans (1,3)[C]
  • Immersing the hands and forearms in cold water (3)[C]
  • Use of ice or cold packs on the neck, groin, and axillae (1,2)[C]
  • No clear superiority of any one method (1).
First Line
No medications are required in the initial management. Use isotonic saline solution to rehydrate (1,3)[C].
Second Line
  • Consider immunomodulators such as corticosteroids.
  • Iced gastric, bladder, or peritoneal lavage (3)[C]
  • In DIC, consider appropriate replacement therapy.
Admission Criteria/Initial Stabilization
  • Important to cool patient before transport if you suspect heat stroke
  • Rapid cooling: Remove clothing, wet patient down, and apply ice packs.
  • Emergency treatment; best in a hospital setting
Rest with legs elevated (3)[C].
Patient Monitoring
  • Rectal temperature monitoring: Cooling may be discontinued when the core temperature drops to 102°F (38.9°C) and stabilizes.
  • Heat stroke patients may require airway management, hemodynamic monitoring, and careful fluid and electrolyte administration and monitoring.
  • Consider CVP monitoring.
  • Cool or cold clear liquids only (noncarbonated)
  • Avoid caffeine.
  • Unrestricted sodium
  • The key to prevention is proper hydration.
  • Stress the importance of proper conditioning and acclimatization.
  • Instruct patients to recognize heat stress signs and symptoms.
  • Maintain as much skin exposure as possible in hot, humid conditions while using proper sunblock protection.
1. Lipman GS, Eifling KP, Ellis MA, et al. Wilderness Medical Society practice guidelines for the prevention and treatment of heat-related illness: 2014 update. Wilderness Environ Med. 2014;25(4 Suppl):S55-S65.
2. Becker JA, Stewart LK. Heat-related illness. Am Fam Physician. 2011;83(11):1325-1330.
3. Yeo TP. Heat stroke: a comprehensive review. AACN Clin Issues. 2004;15(2):280-293.
Additional Reading
  • Armstrong LE, Casa DJ, Millard-Stafford M, 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.
  • Atha WF. Heat-related illness. Emerg Med Clin North Am. 2013;31(4):1097-1108.
  • Bouchama A, Dehbi M, Chaves-Carballo E. Cooling and hemodynamic management in heatstroke: practical recommendations. Crit Care. 2007;11(3):R54
  • Smith JE. Cooling methods used in the treatment of exertional heat illness. Br J Sports Med. 2005;39(8):503-507.
  • T67.5XXA Heat exhaustion, unspecified, initial encounter
  • T67.0XXA Heatstroke and sunstroke, initial encounter
  • T67.3XXA Heat exhaustion, anhydrotic, initial encounter
Clinical Pearls
  • The diagnosis of heat stroke relies on both hyperthermia and CNS dysfunction (e.g., irritability, ataxia, confusion, seizures, or coma).
  • Start the cooling process immediately when heat exhaustion or heat stroke is recognized, beginning with wetting the skin with a cool mist and giving oral rehydration solutions containing saline, if the patient is alert and oriented.
  • If in the field (e.g., sporting events, wilderness), cooling should be priority prior to transport
  • Do not rely on oral temperature.