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BASICS

Description

  • Heat illness is a continuum of increasingly severe disorders caused by dehydration, electrolyte imbalance, and thermoregulatory failure due to environmental heat exposure.
  • Heat exhaustion: mild to moderate, dehydration symptoms with normal or elevated temperature (<104°F).
  • Heat stroke: core temperature >104°F (40°C) with CNS abnormalities; medical emergency.
  • Can be exertional (physical activity related) or nonexertional (environmental exposure).
  • Systems affected: endocrine/metabolic, nervous, hepatic, hematologic.

Epidemiology

  • More common in children and elderly.
  • Incidence ~20 per 100,000 per season; increasing with rising global temperatures.
  • Approximately 600 deaths/year in the U.S.

Etiology and Pathophysiology

  • Excess heat causes direct cellular toxicity and triggers inflammatory cytokine imbalance, endothelial damage, and multi-organ dysfunction.
  • Failure of heat dissipation mechanisms combined with heat stress and exaggerated inflammatory response.

Risk Factors

  • Poor acclimatization and conditioning
  • Dehydration, salt loss
  • Obesity
  • Acute febrile or GI illnesses
  • Chronic diseases (diabetes, HTN, cardiac disease)
  • Substance abuse (alcohol, drugs)
  • High heat/humidity, poor ventilation
  • Heavy, restrictive clothing
  • Certain medications (anticholinergics, diuretics, β-blockers, antipsychotics, etc.)
  • Nutritional supplements (ephedra)

General Prevention

  • Activity modification and adequate hydration.
  • Proper acclimatization and conditioning.
  • Wear loose, light-colored, breathable clothing.
  • Avoid leaving children/pets unattended in vehicles.
  • Seek air-conditioned environments during heat waves.

DIAGNOSIS

Clinical Features

Heat Exhaustion

  • Symptoms: fatigue, lethargy, weakness, dizziness, nausea, vomiting, myalgias, headache, profuse sweating, tachycardia, hypotension, thirst, hyperventilation.
  • Core temperature: normal or elevated but <104°F (40°C).
  • Skin: cool, clammy.

Heat Stroke

  • Core temperature >104°F (>40°C).
  • CNS dysfunction: delirium, confusion, coma.
  • Skin: hot, flushed, dry (sweating may be absent in nonexertional heat stroke).
  • Rapid onset in exertional type; gradual onset in classic type (elderly, chronically ill).

History

  • Heat cramps: muscle spasms with sweating.
  • Heat exhaustion: sweating, fatigue, dizziness, nausea.
  • Heat stroke: altered mental status.

Physical Exam

  • Rectal temperature preferred.
  • Heat exhaustion: tachycardia, cool/clammy skin.
  • Heat stroke: elevated core temp, hot/dry skin, neurologic abnormalities.

Differential Diagnosis

  • Febrile illnesses, sepsis
  • Drug-induced dehydration
  • Cocaine intoxication
  • Neuroleptic malignant syndrome
  • Malignant hyperthermia

Diagnostic Tests

  • Labs: electrolytes (especially sodium), BUN, creatinine, liver and muscle enzymes (CPK), CBC (hemoconcentration), urinalysis.
  • Monitor for DIC, rhabdomyolysis, renal/hepatic dysfunction.

TREATMENT

General Measures

  • Immediate whole-body cooling in heat stroke (ice water immersion preferred).
  • Remove clothing, wet patient, apply ice packs to neck, groin, axillae.
  • For heat exhaustion: evaporative cooling with water spray and fans, cold water immersion of hands/forearms, ice packs.
  • Fluid and electrolyte replacement with isotonic saline; avoid hypotonic fluids.
  • Monitor serum sodium and hemodynamics; consider CVP monitoring.

Medications

  • No specific drugs initially; rehydrate with isotonic fluids.
  • Antipyretics are ineffective and not recommended for heat illness.
  • Corticosteroids may be considered in ICU for severe cases.
  • Manage DIC with appropriate blood products if present.

Admission & Nursing

  • Cool immediately upon suspicion or diagnosis.
  • Monitor airway, breathing, circulation, core temperature, and labs closely.
  • ICU care for severe heat stroke.

ONGOING CARE

Follow-Up Recommendations

  • Rest with legs elevated.
  • Monitor rectal temperature until stable below 102°F (38.9°C).
  • Manage fluids and electrolytes carefully.
  • Continue monitoring for organ dysfunction.

Diet

  • Cool or cold clear liquids; avoid caffeine.
  • No sodium restriction needed unless specific indications.

Patient Education

  • Importance of hydration and acclimatization.
  • Recognize early signs of heat illness: fatigue, headache, dizziness.
  • Use sun protection; wear appropriate clothing.

Prognosis

  • Heat exhaustion usually resolves within 24-48 hours with treatment.
  • Heat stroke mortality ranges 10-80%, dependent on severity and rapidity of cooling.
  • Early recognition and cooling critical to reduce mortality.

Complications

  • Multi-organ failure (renal, hepatic, CNS)
  • Cardiac arrhythmias, myocardial infarction
  • Pulmonary edema, ARDS
  • Rhabdomyolysis
  • Disseminated intravascular coagulation (DIC)
  • Seizures, coma

Clinical Pearls

  • Exertional heat stroke is a medical emergency; immediate ice water immersion saves lives.
  • Rectal temperature measurement is gold standard; avoid oral temperature.
  • Start cooling before transport when possible (sports events, wilderness).
  • Avoid antipyretics; focus on physical cooling and rehydration.

References

  1. Roberts WO, Armstrong LE, Sawka MN, et al. ACSM expert consensus statement on exertional heat illness: recognition, management, and return to activity. Curr Sports Med Rep. 2021;20(9):470-484.
  2. Gauer R, Meyers BK. Heat-related illnesses. Am Fam Physician. 2019;99(8):482-489.
  3. Bouchama A, Abuyassin B, Lehe C, et al. Classic and exertional heatstroke. Nat Rev Dis Primers. 2022;8(1):8.