Heat stroke
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I now have comprehensive information to provide a thorough answer on heat stroke. Here is a synthesis from multiple authoritative sources.
Heat Stroke
Heat stroke is an acute, life-threatening emergency with high mortality if left untreated. It represents the most severe end of the heat illness spectrum (heat edema → heat cramps → heat exhaustion → heat stroke).
— Tintinalli's Emergency Medicine
Definition & Classification
Heat stroke is defined by two cardinal features:
- Hyperthermia (core temperature >40°C / >104°F)
- Altered mental status
There are two clinical subtypes:
| Feature | Classic (Nonexertional) Heat Stroke | Exertional Heat Stroke (EHS) |
|---|---|---|
| Population | Elderly, young children, chronically ill | Young healthy athletes, military recruits |
| Setting | Heat waves, poor ventilation | Intense exercise in hot environments |
| Sweating | Usually absent (anhidrosis) | Present in ~50% of cases |
| Rhabdomyolysis | Rare | Common |
| Acute renal failure | Rare | Common |
| Hypoglycemia | Less common | Can occur (↑ metabolism + hepatic damage) |
| Coagulopathy | Less common | Common |
The distinction between the two subtypes is not clinically important — immediate cooling is the therapeutic goal for both. Delay in cooling increases mortality.
— Tintinalli's Emergency Medicine, Rosen's Emergency Medicine
Pathophysiology
Heat stroke involves failure of the thermoregulatory system. The cerebellum is highly sensitive to heat, and neurologic injury is a direct function of maximum temperature reached and duration of exposure.
In classic heat stroke, skin blood vessels dilate to dissipate heat, producing low peripheral vascular resistance — this can persist even after temperature normalizes. High-output cardiac failure may result.
In exertional heat stroke, endogenous heat production overwhelms heat-dissipating mechanisms. Organ damage follows a progression: brain → intestine → kidney → liver → skeletal muscle.
— Goldman-Cecil Medicine, Rosen's Emergency Medicine
Clinical Features
Neurologic (CNS is the primary target):
- Ataxia (early sign — cerebellar sensitivity)
- Irritability, confusion, bizarre behavior, combativeness, hallucinations
- Hemiplegia, plantar responses, decorticate/decerebrate posturing
- Status epilepticus, coma
- Seizures are common, especially during cooling
Cardiovascular:
- Tachycardia (up to 180 bpm)
- Hyperdynamic circulation with low peripheral vascular resistance
- Hypotension
- Pulmonary edema (especially in classic heat stroke)
Other findings:
- Hot, dry skin (classic) or diaphoresis (exertional)
- Weakness, dizziness, nausea/vomiting, headache
— Miller's Anesthesia, Tintinalli's Emergency Medicine
Diagnosis
No single diagnostic test confirms heat stroke. Diagnosis is clinical — based on history, presentation, and exclusion of other causes.
Workup (directed at end-organ damage):
- CBC, comprehensive metabolic panel
- Arterial blood gas (PaCO₂ often <20 mmHg — hyperventilation; lactic acidosis in EHS)
- Coagulation profile (DIC possible)
- Creatine phosphokinase + myoglobin (rhabdomyolysis)
- Urinalysis
- Blood glucose (hypoglycemia may occur)
- ECG, chest X-ray
- Head CT ± lumbar puncture (to exclude other AMS causes)
Differential Diagnosis:
| Category | Examples |
|---|---|
| Infection | Sepsis, meningitis, encephalitis, malaria, typhoid, tetanus |
| Neurologic | Hypothalamic bleed/infarct, CVA, status epilepticus |
| Endocrine | Thyroid storm, pheochromocytoma, DKA |
| Toxicologic | Anticholinergic toxidrome, sympathomimetic OD, salicylate OD, serotonin syndrome, malignant hyperthermia, NMS, alcohol/benzo withdrawal |
— Tintinalli's Emergency Medicine
Medications That Predispose to Heat Stroke
| Drug Class | Examples |
|---|---|
| Anticholinergics | Atropine, benztropine, oxybutynin, scopolamine |
| Antidepressants | Tricyclics |
| Antiemetics | Metoclopramide, prochlorperazine, promethazine |
| Antiepileptics | Topiramate, zonisamide |
| Antihistamines | All |
| Antihypertensives | Beta blockers, calcium channel blockers |
| Antipsychotics | All |
| Diuretics | Hydrochlorothiazide, furosemide, spironolactone |
| Sympathomimetics | Amphetamines, cocaine, methylphenidate |
| Ergogenic aids | Anabolic steroids, creatine, ephedra |
— Rosen's Emergency Medicine
Treatment
Prehospital
- Remove patient from hot environment immediately
- Check point-of-care glucose
- Remove clothing; begin cooling (see methods below)
- IV normal saline 1–2 L bolus if hypotensive
ED Resuscitation
- Goal: reduce core temperature to ≤39°C (102.2°F) — avoid hypothermic overshoot
- IV fluids to maintain adequate urine output
- Monitor core temperature continuously (rectal thermometer, Foley thermometer probe, or esophageal thermometer)
- Invasive monitoring in elderly or those with cardiovascular disease
- Check and correct blood glucose
Cooling Techniques
| Method | Advantages | Key Notes |
|---|---|---|
| Evaporative cooling | Practical, well-tolerated, readily available | Spray cool water (~15°C) + fan; use tepid water (40°C) to prevent shivering; reduced efficacy in humid environments |
| Ice water immersion | Highly effective — gold standard for EHS | Problems: shivering, can't monitor/defibrillate, logistically difficult |
| Ice packs to neck/axillae/groin | Easy to apply | Less effective alone; useful as adjunct |
| Cold IV fluids | Simple | Not effective as sole treatment |
| Cooling blankets | Available | Work slowly; should not be sole treatment |
No method has been proven superior. Use what is most available and effective; switch if temperature is not dropping quickly.
Shivering during cooling: Treat with short-acting benzodiazepines (first-line); phenothiazines (second-line, but may lower seizure threshold, cause hypotension, and impair sweating via anticholinergic effects).
Antipyretics (aspirin, acetaminophen) are NOT effective in heat stroke — the hypothalamic set point is not elevated; this is a failure of heat dissipation, not a fever.
— Tintinalli's Emergency Medicine, Washington Manual of Medical Therapeutics
Complications
- Rhabdomyolysis → acute renal failure
- DIC / coagulopathy
- Hepatic injury
- ARDS / pulmonary edema
- Persistent neurologic deficits
- Death
Poor prognostic factors: Advanced age, hypotension, altered coagulation, lactic acidosis, need for endotracheal intubation on ED arrival.
— Rosen's Emergency Medicine, Tintinalli's Emergency Medicine
Heat stroke
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Here is a comprehensive overview of heat stroke drawn from authoritative medical textbooks.
Heat Stroke
Heat stroke is an acute, life-threatening emergency — fatal if left untreated. It is the most severe end of the heat illness spectrum (heat edema → heat cramps → heat exhaustion → heat stroke).
Definition & Classification
Two cardinal features define heat stroke:
- Hyperthermia — core temperature >40°C (>104°F)
- Altered mental status
Two clinical subtypes:
| Feature | Classic (Nonexertional) | Exertional (EHS) |
|---|---|---|
| Population | Elderly, very young, chronically ill | Young healthy athletes, military recruits |
| Setting | Heat waves, poor ventilation, no AC | Intense exercise in hot environments |
| Sweating | Usually absent | Present in ~50% |
| Rhabdomyolysis | Rare | Common |
| Acute renal failure | Rare | Common |
| Hypoglycemia | Less common | Common (↑ metabolism + hepatic damage) |
| Coagulopathy | Less common | Common |
| CVP | Often elevated | Variable |
The distinction is not clinically important — immediate cooling is the therapeutic goal for both. Delay in cooling directly increases mortality.
— Tintinalli's Emergency Medicine, Rosen's Emergency Medicine
Pathophysiology
Thermoregulatory failure leads to progressive organ damage. The sequence of organ involvement in exertional heat stroke: brain → intestine → kidney → liver → skeletal muscle.
- Classic heat stroke: Skin vasodilation causes low peripheral vascular resistance → high-output cardiac failure. This low PVR can persist after temperature normalizes.
- Exertional heat stroke: Endogenous heat production overwhelms heat dissipation mechanisms.
Metabolic acidosis (lactic acidosis) occurs in most severe cases of heat stroke, often accompanied by respiratory alkalosis (hyperventilation, PaCO₂ often <20 mmHg).
Key biochemical differences:
- Classic: hyperglycemia, hypophosphatemia
- Exertional: hyperphosphatemia, hypocalcemia, hypoglycemia
— Goldman-Cecil Medicine, Miller's Anesthesia
Clinical Features
Neurologic (CNS is the primary target organ):
- Cerebellum is highly heat-sensitive — ataxia is an early finding
- Irritability, confusion, bizarre behavior, combativeness, hallucinations
- Decorticate/decerebrate posturing, hemiplegia
- Status epilepticus, coma
- Seizures — common, especially during cooling
- A lucid interval may occur despite severe temperature elevation
Cardiovascular:
- Tachycardia (up to 180 bpm)
- Hypotension
- High-output cardiac failure (low PVR)
- Pulmonary edema
Other:
- Hot, dry skin (classic) or diaphoresis (exertional)
- Weakness, dizziness, headache, nausea/vomiting, syncope
Temperature range: typically 40°C–44°C, though values up to 47°C have been reported.
Anhidrosis is not a required diagnostic criterion — sweat is present in >50% of all heat stroke patients.
— Tintinalli's Emergency Medicine, Miller's Anesthesia
Diagnosis
No single diagnostic test confirms heat stroke. Diagnosis is clinical — history, presentation, and exclusion of other causes.
Core temperature monitoring: Rectal thermometer, Foley catheter temperature probe, or esophageal thermometer. Axillary, oral, and tympanic readings are unreliable during/after exercise in heat.
Workup — directed at end-organ damage:
- CBC, comprehensive metabolic panel
- ABG (lactic acidosis in EHS; PaCO₂ often <20 mmHg)
- Coagulation profile (DIC)
- CPK + myoglobin (rhabdomyolysis)
- Urinalysis (myoglobinuria, hematuria)
- Blood glucose
- ECG, chest X-ray
- Head CT ± lumbar puncture (exclude other AMS causes)
Differential Diagnosis:
| Category | Examples |
|---|---|
| Infection | Sepsis, meningitis, encephalitis, malaria, typhoid, tetanus |
| Neurologic | Hypothalamic bleed/infarct, CVA, status epilepticus |
| Endocrine | Thyroid storm, pheochromocytoma, DKA |
| Toxicologic | Anticholinergic toxidrome, sympathomimetic OD, salicylate OD, serotonin syndrome, malignant hyperthermia, NMS, alcohol/benzo withdrawal |
| Other | Exercise-associated hyponatremia (EAH) — presents similarly but without hyperthermia; requires Na⁺ correction |
Medications That Predispose to Heat Stroke
| Drug Class | Examples |
|---|---|
| Anticholinergics | Atropine, benztropine, oxybutynin, scopolamine |
| Antidepressants | Tricyclics |
| Antiemetics | Metoclopramide, prochlorperazine, promethazine |
| Antiepileptics | Topiramate, zonisamide |
| Antihistamines | All |
| Antihypertensives | Beta blockers, calcium channel blockers |
| Antipsychotics | All |
| Diuretics | Hydrochlorothiazide, furosemide, spironolactone |
| Sympathomimetics | Amphetamines, cocaine, methylphenidate |
| Ergogenic aids | Anabolic steroids, creatine, ephedra |
— Rosen's Emergency Medicine
Treatment
Prehospital
- Remove from hot environment immediately
- Remove clothing; begin cooling
- Check point-of-care glucose
- IV normal saline 1–2 L bolus if hypotensive
ED Resuscitation Goals
- Immediate cooling to ≤39°C (102.2°F) — avoid hypothermic overshoot
- Aggressive support of organ system function
- IV fluids to maintain adequate urine output
- Continuous core temperature monitoring
- Correct glucose and electrolytes
- Invasive monitoring in elderly or those with cardiovascular disease
Cooling Techniques
| Method | Key Points |
|---|---|
| Evaporative cooling | Spray cool water (~15°C) on body + fan; foundation of the Makkah cooling unit; reduced efficacy in high humidity |
| Ice water immersion | Highly effective, gold standard for EHS; problems: shivering, monitoring difficulty, defibrillation impossible, logistically demanding |
| Ice packs (neck/axillae/groin) | Easy adjunct; must use skin barrier to prevent cold injury; requires ongoing refreshment |
| Adhesive cold-water circulating pads | Continuous temperature gradient; need large area of intact skin |
| Invasive cooling | Bladder/gastric/colonic irrigation with cold saline, intravascular cooling catheters; reserved for refractory cases |
| Cold IV fluids | Not effective as sole treatment |
| Cooling blankets | Work slowly; not to be used alone |
No method has been proven superior. Target a cooling rate of ≥0.155°C/min. Switch methods if temperature is not dropping quickly.
Managing shivering during cooling:
- First-line: short-acting benzodiazepines
- Second-line: phenothiazines (caution — lower seizure threshold, cause hypotension, impair sweating via anticholinergic effects)
Pharmacologic Notes
- Antipyretics (NSAIDs, aspirin, acetaminophen) are NOT effective — the hypothalamic set point is not elevated; this is a heat dissipation failure, not a fever
- Acetaminophen is contraindicated in heat stroke (hepatic toxicity risk)
- Dantrolene is ineffective in heat stroke (unlike malignant hyperthermia)
Vasopressors for Hypotension
- If 20 mL/kg fluid bolus fails and CVP is low-to-normal: dopamine or dobutamine
- Avoid norepinephrine — α-adrenergic vasoconstriction redirects blood flow away from skin, impairing cooling
— Tintinalli's Emergency Medicine, Miller's Anesthesia
Complications
| Timing | System | Complication |
|---|---|---|
| Early | Vital signs | Hypotension, hypothermic overshoot, hyperthermic rebound |
| Muscular | Rhabdomyolysis | |
| Neurologic | Delirium, coma, seizures | |
| Cardiac | Heart failure | |
| Pulmonary | Pulmonary edema | |
| Renal | Oliguria | |
| Metabolic | Hypokalemia, hypernatremia, hyponatremia | |
| Late | Neurologic | Cerebral edema, persistent neurologic deficit |
| Cardiac | Myocardial injury | |
| Pulmonary | ARDS | |
| Renal | Renal failure | |
| GI | Intestinal ischemia/infarction, pancreatitis, hepatic dysfunction | |
| Metabolic | Hyperkalemia, hypocalcemia, hyperuricemia | |
| Hematologic | Thrombocytopenia, DIC |
Hepatic injury is common — delayed enzyme elevation peaks at 24–72 hours (centrilobular necrosis); almost always reversible.
Poor prognostic factors: Advanced age, hypotension on arrival, altered coagulation, lactic acidosis, need for endotracheal intubation.
Mortality: 3–5% in exertional heat stroke with prompt treatment; significantly higher in classic heat stroke and with delayed cooling.
— Tintinalli's Emergency Medicine, Miller's Anesthesia, Rosen's Emergency Medicine
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