Heat stroke

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Background

  • Severe, life-threatening end of the heat illness spectrum
  • Defined as core temperature >40°C (104°F) with CNS dysfunction
  • Universally fatal if untreated; mortality approaches 30% even with treatment[1]
  • Mortality directly correlates with duration and degree of elevated core temperature
  • Hallmark is multisystem organ dysfunction from heat-induced systemic inflammatory response

Types

  • Classic (nonexertional):
    • Insidious development over days
    • Seen in elderly, children, chronically ill, those on anticholinergic or diuretic medications
    • During heat waves
  • Exertional:
    • Rapid onset during exercise or physical exertion
    • Seen in otherwise young, healthy individuals (athletes, military, laborers)
    • Typically faster presentation and higher CK levels

Clinical Features

  • Core temperature >40°C (104°F) PLUS
  • CNS dysfunction[2]:
    • Altered mental status, confusion, agitation, slurred speech
    • Ataxia, seizures, coma
    • Inappropriate behavior may be earliest sign
  • Anhidrosis is frequently present but its absence does NOT rule out heat stroke
    • Sweating may still be present, especially in exertional heat stroke
  • Tachycardia, hypotension (high-output state → eventual cardiovascular collapse)
  • Tachypnea
  • Massive hematochezia may occur from intestinal ischemia[3]
  • Petechiae, purpura (DIC)

Differential Diagnosis

Template:Altered mental status and fever DDX Template:Environmental heat illness DDX

Evaluation

  • Core temperature (rectal or bladder probe preferred; tympanic/temporal unreliable)
    • Continuous monitoring essential (bladder temperature probe ideal)
  • Blood glucose (POC immediately)
  • ECG: most often sinus tachycardia; ischemic changes (ST depressions, TWI) may occur[4]
  • CBC: may show hemoconcentration initially; thrombocytopenia with DIC
  • BMP: electrolyte abnormalities (variable hypo/hypernatremia, hypokalemia), AKI
  • LFTs: transaminase elevation occurs in nearly all cases (peaks at 48-72h)
    • AST/ALT >1000 suggests severe liver injury
  • Coagulation studies: PT/INR, fibrinogen, D-dimer (DIC screening)
  • CK and myoglobin: rhabdomyolysis (exertional >> classic)
  • Lactate: marker of tissue hypoperfusion
  • VBG/ABG: metabolic acidosis
  • Urinalysis: myoglobinuria
  • CT head ± LP: if concern for CNS infection or hemorrhage

Management

Immediate

  • Cooling is THE priority — every minute of delay increases mortality
  • Remove from hot environment; remove clothing
  • Address ABCs; intubate if necessary for airway protection
  • Goal: reduce core temperature to 39°C (102.2°F) within 30 minutes
  • Cooling rate target: 0.15-0.25°C/min

Rapid Cooling Techniques

Cold Water Immersion (Treatment of Choice)

  • Most effective cooling method (cooling rate ~0.2°C/min)[5]
  • Immerse body to torso or neck in cold/ice water (1-17°C)
  • Best for exertional heat stroke in young/healthy patients
  • Also beneficial in elderly patients
  • Studies show up to 100% survival when initiated within 30 minutes of collapse[6]
  • Disadvantage: limited access to resuscitative measures during immersion

Evaporative/Convective Cooling

  • Spray lukewarm water (15°C / 59°F) continuously on patient while directing fans at exposed skin
  • Easier to apply while performing other interventions in ED
  • Slower cooling rate than immersion

Other Techniques

  • Cold IV fluids (4°C NS bolus) as adjunct (limited cooling on its own)
  • Ice packs to entire body surface (better than just neck/axillae/groin)
    • Ice packs only to neck, axillae, groin provides minimal cooling
  • Invasive lavage (bladder, gastric, thoracic) — limited data, reserved for refractory cases
  • ECMO — for refractory heat stroke

What NOT to Do

  • NO antipyretics (acetaminophen, NSAIDs) — thermoregulatory set point is normal; these are ineffective and may worsen liver/renal injury
  • NO dantrolene — not effective in heat stroke (heat stroke is not malignant hyperthermia)
  • AVOID peripheral vasoconstrictors (norepinephrine) — may redirect blood from skin and impair cooling
  • AVOID shivering (counterproductive) — treat with benzodiazepines if occurs during cooling

Supportive Care

  • IV fluid resuscitation:
    • Bolus 500-1000 mL NS if hypotensive
    • Titrate to UOP goal 1-2 mL/kg/hr (renal protection from rhabdomyolysis)
  • Seizures: benzodiazepines (lorazepam 2-4 mg IV)
  • Hypotension: small fluid boluses first; if refractory, consider dopamine or dobutamine
  • Correct electrolyte abnormalities
  • Treat DIC with blood products if clinically significant bleeding

Complications

  • Hepatic injury: almost always present; usually reversible but can progress to fulminant failure
  • Rhabdomyolysis → acute kidney injury (more common in exertional)
  • DIC and abnormal bleeding
  • ARDS
  • Persistent neurologic deficits: present in ~20% of survivors, associated with high mortality
  • Seizures
  • Myocardial injury

Disposition

  • All patients require admission (most to ICU)
  • Serial monitoring of core temperature, LFTs, coagulation studies, renal function, CK for 48-72h
  • LFTs may worsen for 2-3 days after presentation — repeat at 24-48h

See Also

References

  1. ↑ Gaudio FG, Grissom CK. Cooling Methods in Heat Stroke. J Emerg Med. 2016;50(4):563-72. PMID 26525947
  2. ↑ Becker JA, Stewart LK. Heat-related illness. Am Fam Physician. 2011;83(11):1325-30. PMID 21661715
  3. ↑ Lambert GP. Intestinal barrier dysfunction during exercise-heat stress. Med Sport Sci. 2008;53:61-73. PMID 19208999
  4. ↑ Mimish L. Electrocardiographic findings in heat stroke and exhaustion. J Saudi Heart Assoc. 2012;24(1):35-39. PMID 23960068
  5. ↑ Pryor RR, et al. Exertional heat illness: emerging concepts and advances in prehospital care. Prehosp Disaster Med. 2015;30(3):297-305. PMID 25959925
  6. ↑ Becker JA, Stewart LK. Heat-related illness. Am Fam Physician. 2011;83(11):1325-30. PMID 21661715
  • Hifumi T, et al. Heat stroke. J Intensive Care. 2018;6:30. PMID 29850022
  • Leon LR, Bouchama A. Heat stroke. Compr Physiol. 2015;5(2):611-647. PMID 25880507
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