Heat stroke

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
• 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:
  • 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
• Petechiae, purpura (DIC)

Differential Diagnosis

• Key diagnoses to consider:
  • Sepsis / meningitis / encephalitis
  • Thyroid storm
  • Neuroleptic malignant syndrome
  • Serotonin syndrome
  • Malignant hyperthermia
  • Anticholinergic toxicity
  • Sympathomimetic toxicity (cocaine, amphetamines)
  • Alcohol withdrawal / benzodiazepine withdrawal

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
• 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)
• 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
• 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

• Heat emergencies
• Heat exhaustion
• Rhabdomyolysis
• Malignant hyperthermia
• Neuroleptic malignant syndrome

References

• 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