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Heat Stroke: Detailed Overview and Management

Definition and Classification

1. Core body temperature >40°C (>104°F) - often >40.5°C (105°F) in full-blown cases
2. Central nervous system (CNS) dysfunction - confusion, delirium, ataxia, coma, or seizures

Note: The cessation of sweating is not the cause of heat stroke, and continued sweating does not exclude the diagnosis. - Rosen's Emergency Medicine, p. 2793

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Pathophysiology

1. Environmental heat + exercise → increased heat production / impaired dissipation
2. Cardiovascular challenge: high skin blood flow (peripheral pooling) diverts blood away from viscera
3. Splanchnic ischemia → endotoxemia, oxidative stress, systemic inflammatory response
4. Direct thermal tissue injury at >41°C - triggers heat shock proteins; cells undergo adaptation, injury, or apoptosis/necrosis
5. Reduced cerebral blood flow + abnormal local metabolism + coagulopathy → CNS dysfunction
6. Multi-organ dysfunction syndrome (MODS) - the terminal pathway

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Risk Factors and Predisposing Medications

• Extremes of age (elderly, infants)
• Obesity, poor physical conditioning, dehydration
• Cardiovascular disease, skin disorders (impaired sweating)
• Prior heat stroke episode (increased recurrence risk)
• Recent infection (proinflammatory cytokines deactivate heat shock protection)
• Lack of acclimatization

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Clinical Features

Prodromal symptoms (20% of cases, lasting minutes to hours):

• Weakness, dizziness, nausea/vomiting, anorexia
• Frontal headache, confusion, disorientation
• Muscle twitching, ataxia, signs of cerebellar dysfunction
• Anxiety, irritability, or frank psychosis

Classic presentation:

• Temperature: >40.5°C (105°F) rectally; may be lower in ED if pre-hospital cooling occurred
• CNS dysfunction: inappropriate behavior, confusion, delirium, ataxia, coma, seizures
• Skin: hot skin; sweating may or may not be present
• Other: tachycardia, hypotension, tachypnea

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Diagnostic Workup

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Differential Diagnosis

• CNS hemorrhage / stroke
• Meningitis / encephalitis
• Seizure disorder
• Sepsis with high fever
• Neuroleptic malignant syndrome (NMS) - "lead pipe" rigidity, hyperthermia, antipsychotic exposure
• Malignant hyperthermia - inhalational anesthetic or succinylcholine trigger
• Serotonin syndrome - triad of mental status changes + autonomic hyperactivity + clonus
• Thyroid storm - enlarged/nodular thyroid, elevated TFTs
• Drug toxicity - anticholinergic (key differentiator: mydriasis; heat stroke typically has miosis), cocaine, amphetamines
• Exercise-associated hyponatremia (no hyperpyrexia >40.5°C)

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Management

The overriding principle: Immediate cooling is the treatment - do not delay

• Degree of temperature elevation
• Duration before cooling is initiated
• Number of organ systems involved
• Death risk is substantially increased with anuria, coma, or cardiovascular failure at presentation

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Step 1 - Immediate Cooling (Primary Treatment)

A. Ice Water Immersion (most effective for EHS)

• Undress patient, submerge trunk and extremities in ice water tub
• Reduces temperature to <39°C within 10-40 minutes
• Best when pre-planned (e.g., at mass sporting events)
• Limitations: shivering, displaced monitoring leads, inability to defibrillate, logistical issues in ED

B. Evaporative Cooling (preferred in ED settings)

• Remove all clothing; spray cool water (~15°C) over body surface
• Direct fan over patient for continuous evaporation
• Use tepid (40°C) or warm air (45°C) with fans to prevent shivering and maintain vasodilation
• Makkah cooling unit: hammock with sprinklers + warm air fans - widely used for heat casualties during Hajj
• Limitations: less effective in very humid environments, electrode adherence difficult

C. Adjunctive Cooling Methods

• Ice packs to neck, axillae, and groin (high heat transfer areas) - useful supplement
• Cooling blankets - insufficient as sole method
• Cold IV saline
• Gastric/rectal lavage with cold irrigant - minimal heat exchange if used as primary method
• Cardiopulmonary bypass - reserved for refractory cases

• Antipyretics (NSAIDs, acetaminophen) have NO role - heat stroke is not fever from a raised set point
• Dantrolene has no established clinical benefit in heat stroke (unlike malignant hyperthermia)
• Shivering - treat with short-acting benzodiazepines (first line); phenothiazines (second line, caution: lower seizure threshold, anticholinergic effects)

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Step 2 - Resuscitation and Supportive Care

• Aspiration and seizures are common - secure airway early
• Hypoxemia may result from aspiration, pneumonitis, pulmonary hemorrhage, or edema
• Intubate if GCS is significantly impaired or airway unprotected

• IV crystalloid resuscitation (isotonic normal saline)
• Fluid requirements are modest: average ~1200 mL in the first 4 hours
• Avoid aggressive over-hydration - pulmonary edema is a recognized complication
• In elderly or cardiac patients: consider invasive monitoring (CVP, arterial line)
• Check glucose; treat hypoglycemia promptly (especially EHS)

• Target adequate urine output
• In rhabdomyolysis: aggressive fluids + consider urine alkalinization to protect kidneys

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Step 3 - Management of Specific Complications

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Complications of Heat Stroke

• Hypotension
• Hypothermic overshoot during cooling
• Hyperthermic rebound after cooling stops
• Rhabdomyolysis
• Delirium, coma, seizures
• Pulmonary edema, heart failure

• Cerebral edema, persistent neurologic deficit, encephalopathy
• Myocardial injury
• ARDS
• Renal failure
• Intestinal ischemia/infarction
• Pancreatic and hepatic injury
• DIC, thrombocytopenia
• Hyperkalemia, hypocalcemia, hyperuricemia

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Disposition

• All heat stroke patients require ICU admission
• Continue monitoring core temperature (rectal thermistor)
• Watch for rebound hyperthermia (can recur after initial cooling)
• Serial labs: LFTs, CK, coagulation, renal function q6-12h initially
• Patients with cardiovascular failure, anuria, or coma at presentation carry significantly worse prognosis

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Prevention and Acclimatization

• Acclimatization takes 10-14 days of progressive heat exposure; physiologically increases plasma volume, reduces heart rate, enhances sweating efficiency
• Avoid strenuous exercise during heat waves or periods of high heat index (temperature + humidity)
• Stay hydrated with electrolyte-containing fluids; avoid plain water over-hydration (hyponatremia risk)
• Protective clothing, shade, and rest breaks in high-risk occupational settings
• Check on elderly or isolated individuals during heat waves
• Individuals with prior heat stroke have increased recurrence risk and should be counseled

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• Tintinalli's Emergency Medicine, pp. 1389-1392
• Rosen's Emergency Medicine, pp. 2792-2795
• Goldman-Cecil Medicine, pp. 1104-1106