Overview
Heat Stroke
Quick Reference
Critical Alerts
- Core temperature >40°C (104°F) + CNS dysfunction = heat stroke
- Immediate cooling is life-saving: Every minute of delay increases mortality
- Exertional vs classic: Different populations, similar mortality if untreated
- Target temperature <39°C within 30 minutes: Aggressive cooling critical
- Multi-organ failure can occur: Rhabdomyolysis, DIC, liver/renal failure
- Antipyretics are INEFFECTIVE: Paracetamol/NSAIDs don't work for heat stroke
Key Diagnostics
| Test | Finding | Significance |
|---|---|---|
| Core temperature | >0°C (104°F) | Defines heat stroke |
| Mental status | Altered | Distinguishes from heat exhaustion |
| CBC | Leukocytosis, thrombocytopenia | Stress response, DIC |
| CMP | Elevated creatinine, LFTs | Organ dysfunction |
| CK | Markedly elevated | Rhabdomyolysis |
| Coagulation studies | Prolonged PT/aPTT | DIC |
| Lactate | Elevated | Tissue hypoperfusion |
Emergency Treatments
| Intervention | Method | Target |
|---|---|---|
| Cooling (gold standard) | Cold water immersion | Core temp <39°C in 30 min |
| Cooling (alternative) | Evaporative + convection | Continuous fanning + misting |
| Cooling (adjuncts) | Ice packs to neck/axilla/groin | Supplement other methods |
| IV fluids | 0.9% saline | 1-2L bolus; adjust to response |
| Shivering control | Midazolam | 2-5mg IV |
| Seizure | Benzodiazepines | Lorazepam 4mg IV |
Definition
Overview
Heat stroke is a life-threatening condition defined by core body temperature >40°C (104°F) with central nervous system dysfunction (altered mental status, seizures, coma). It represents failure of thermoregulation and requires immediate aggressive cooling to prevent death and permanent neurological injury.
Classification
| Type | Exertional Heat Stroke (EHS) | Classic Heat Stroke (CHS) |
|---|---|---|
| Population | Young, healthy, exercising | Elderly, chronically ill |
| Onset | During/shortly after exertion | Over hours to days |
| Skin | Often sweating | Usually hot and dry |
| Risk factors | Athletics, military, laborers | Heatwaves, medications |
| Mortality | 5-10% with treatment | 10-65% depending on population |
Heat Illness Spectrum
| Condition | Features | Temperature | Treatment |
|---|---|---|---|
| Heat cramps | Muscle cramps, sweating | Normal to mildly elevated | Rest, hydration, salt replacement |
| Heat syncope | Fainting with standing | Normal | Supine positioning, fluids |
| Heat exhaustion | Fatigue, headache, nausea | <40°C | Move to cool environment, fluids |
| Heat stroke | AMS + temp >0°C | >0°C | Aggressive cooling, ICU |
Epidemiology
- Incidence: ~600 deaths/year in US; underestimated
- Heatwaves: Can cause 1000+ excess deaths (European heatwave 2003: 70,000 deaths)
- Exertional heat stroke: 2-3 per 1,000 athletes/military during training
- Risk factors: Age extremes, chronic illness, medications, lack of acclimatization
Etiology and Risk Factors
Exertional Heat Stroke Risk Factors:
- Unacclimatized individuals
- High ambient temperature and humidity
- Strenuous exercise
- Dehydration
- Obesity
- Recent illness
- Sleep deprivation
- Overly insulating clothing
- Stimulant use (cocaine, amphetamines, MDMA)
Classic Heat Stroke Risk Factors:
| Category | Risk Factors |
|---|---|
| Age | >5 years, <4 years |
| Living conditions | No air conditioning, social isolation, top floor |
| Medical | Cardiovascular disease, diabetes, obesity, CNS disorders |
| Medications | Anticholinergics, beta-blockers, diuretics, antipsychotics, stimulants |
| Psychiatric | Schizophrenia, dementia (impaired recognition/response) |
| Alcohol | Impaired thermoregulation and judgment |
Pathophysiology
Normal Thermoregulation
- Heat production: Metabolism, exercise
- Heat dissipation: Radiation, conduction, convection, evaporation (sweating)
- Hypothalamic set point: ~37°C
Heat Stroke Mechanisms
- Heat accumulation: Production exceeds dissipation
- Thermoregulatory failure: Hypothalamus overwhelmed
- Cellular damage: Direct thermal injury begins >40°C
- Inflammatory cascade: Heat triggers cytokine release (similar to sepsis)
- Endothelial dysfunction: Increased vascular permeability
- Multi-organ failure: Cellular injury + hypoperfusion + coagulopathy
Organ-Specific Effects
| Organ | Pathophysiology | Clinical Manifestation |
|---|---|---|
| CNS | Direct thermal injury, edema | AMS, seizures, coma |
| Heart | Increased demand, direct injury | Arrhythmias, high-output failure |
| Liver | Thermal injury, hypoperfusion | Acute liver failure (may be delayed) |
| Kidneys | Hypoperfusion, rhabdomyolysis, DIC | AKI |
| Muscle | Thermal injury (exertional > classic) | Rhabdomyolysis |
| Coagulation | Endothelial injury, factor consumption | DIC |
| GI | Barrier breakdown | Endotoxemia, increased inflammation |
Why Duration of Hyperthermia Matters
- Outcomes directly related to duration above 40°C
- Mortality increases ~10% for every 30 min delay in cooling
- Target: Core temp <39°C within 30 minutes of arrival
Clinical Presentation
Cardinal Features
- Core temperature >40°C (104°F)
- Central nervous system dysfunction (altered mental status is mandatory)
History
Symptoms (If obtainable):
History to Obtain:
Physical Examination
Vital Signs:
| Parameter | Finding |
|---|---|
| Temperature | >0°C (104°F) - measure CORE (rectal, esophageal) |
| Heart rate | Tachycardia |
| Blood pressure | May be low (dehydration, vasodilation) |
| Respiratory rate | Tachypnea |
Important: Do NOT rely on oral/axillary temperature - significantly underestimates core temp
General Appearance:
Neurological (Key for Diagnosis):
| Finding | Frequency |
|---|---|
| Altered mental status | 100% (required) |
| Confusion, combativeness | Very common |
| Ataxia | Common |
| Seizures | 25-30% |
| Coma | Severe cases |
| Decorticate/decerebrate posturing | Very severe |
| Fixed dilated pupils | Poor prognosis |
Other Systems:
Intense heat sensation
Common presentation.
Dizziness, confusion (warning signs)
Common presentation.
Cessation of sweating (classic) or profuse sweating (exertional)
Common presentation.
Fatigue, weakness
Common presentation.
Nausea, vomiting
Common presentation.
Headache
Common presentation.
Muscle cramps
Common presentation.
Red Flags
Life-Threatening Complications
| Finding | Concern | Action |
|---|---|---|
| Core temp >1°C (106°F) | Extreme hyperthermia | Aggressive cooling, ICU |
| Coma or GCS <8 | Severe CNS injury | Airway protection, cooling |
| Seizures | CNS damage, increased heat production | Benzodiazepines, cooling |
| Hypotension refractory to fluids | Cardiogenic or distributive shock | Vasopressors, echo |
| DIC | Bleeding, thrombosis | FFP, platelets, cryoprecipitate |
| CK >0,000 | Severe rhabdomyolysis | Aggressive IV fluids |
| Oliguria/anuria | AKI from rhabdomyolysis/hypoperfusion | Fluids, consider RRT |
| AST/ALT >000 | Acute liver injury | Monitor, supportive care |
Prognostic Indicators of Poor Outcome
- Duration of hyperthermia before cooling
- Core temp >42°C
- Coma, seizures, posturing
- AST >3000 in first 24 hours
- DIC
- Lactate >6
Differential Diagnosis
Other Causes of Hyperthermia + AMS
| Diagnosis | Distinguishing Features | Key Evaluation |
|---|---|---|
| Sepsis | Infection source, rigors, may have hypothermia | Cultures, lactate, source workup |
| Neuroleptic malignant syndrome (NMS) | Antipsychotic exposure, rigidity, slow onset | Medication history, CK |
| Serotonin syndrome | Serotonergic drugs, clonus, hyperreflexia | Medication history |
| Anticholinergic toxicity | "Hot as a hare, blind as a bat" | Tox screen, history |
| Sympathomimetic toxicity | Cocaine, amphetamines, hypertension | Tox screen |
| Thyroid storm | Thyroid history, goiter, exophthalmos | TSH, free T4 |
| Malignant hyperthermia | Post-anesthesia, rigidity, metabolic acidosis | Anesthesia history, dantrolene response |
| Meningitis/encephalitis | Meningeal signs, fever preceding AMS | LP, CSF analysis |
| Status epilepticus | Witnessed seizures, post-ictal | EEG |
Diagnostic Approach
Immediate Assessment
Temperature Measurement:
- Rectal temperature is gold standard (or esophageal, bladder)
- Oral/axillary significantly underestimate
- Continuous monitoring recommended
Rapid Assessment:
- ABCs: Airway protection, breathing, circulation
- Core temperature
- Mental status (GCS)
- Rapid cooling initiation (don't delay for workup)
Laboratory Studies
| Test | Purpose | Expected Findings |
|---|---|---|
| CBC | Leukocytosis, thrombocytopenia | WBC elevated (stress); platelets may drop (DIC) |
| CMP | Renal function, electrolytes | Na+ variable, K+ elevated (rhabdo), elevated Cr/BUN |
| LFTs | Hepatic injury | AST/ALT elevated (may peak at 24-48h) |
| CK | Rhabdomyolysis | May be >0,000 in exertional |
| Coagulation (PT, aPTT, fibrinogen) | DIC | Prolonged PT/aPTT, low fibrinogen |
| D-dimer | DIC | Elevated |
| Lactate | Tissue hypoperfusion | Often elevated |
| ABG/VBG | Acid-base status | Metabolic acidosis |
| Urinalysis | Myoglobinuria | Positive blood on dipstick without RBCs |
| Glucose | Hypoglycemia | Variable; important to check |
Imaging
- CXR: If aspiration, ARDS suspected
- CT Head: If prolonged AMS or focal signs (rule out stroke, hemorrhage)
- Generally not priority if clear heat stroke presentation
Treatment
Principles of Management
- Immediate cooling: Single most important intervention
- Supportive care: Airway, breathing, circulation
- Treat complications: Rhabdomyolysis, DIC, organ failure
- Remove from heat source: Air-conditioned environment
- No antipyretics: They do not work; thermoregulatory failure is not fever
Cooling Methods
Gold Standard: Cold Water Immersion:
- Most effective for exertional heat stroke
- Immerse in ice water bath (2-4°C)
- Cool until core temp 38.5-39°C (risk of overshoot)
- Cooling rate: 0.20-0.35°C/min
Alternative: Evaporative Cooling (When immersion not possible):
- Remove clothing
- Continuous misting with tepid water
- High-velocity fans for convective heat loss
- Often used in hospital setting
- Cooling rate: 0.05-0.10°C/min (slower than immersion)
Adjunct Cooling Methods:
| Method | Notes |
|---|---|
| Ice packs to neck, axillae, groin | Large vessels; supplement other methods |
| Cooling blankets | Moderate effectiveness |
| Cold IV fluids | Limited cooling effect but helps volume |
| Gastric/bladder lavage with cold saline | Consider if refractory |
| Peritoneal lavage | Invasive; rarely needed |
| External cooling devices (Arctic Sun) | If available |
| ECMO/cardiopulmonary bypass | Last resort, refractory cases |
Important Considerations:
- Monitor continuously (rectal/esophageal probe)
- Stop active cooling at 38.5-39°C (afterdrop may continue)
- Manage shivering (increases heat production)
Control Shivering
Shivering generates heat and counteracts cooling efforts:
| Agent | Dose | Notes |
|---|---|---|
| Midazolam | 2-5mg IV | Also decreases seizure risk |
| Lorazepam | 1-2mg IV | Alternative benzodiazepine |
| Avoid chlorpromazine | - | Early studies used this; causes hypotension |
Fluid Resuscitation
- Initial bolus 1-2L isotonic crystalloid
- Adjust based on urine output, hemodynamics
- Avoid fluid overload (may develop pulmonary edema)
- Goal UO: 1-2 mL/kg/hr (especially if rhabdomyolysis)
Airway Management
- Intubate for GCS ≤8, inability to protect airway
- RSI with attention to hemodynamics
- Avoid succinylcholine (hyperkalemia from rhabdo)
Management of Complications
Rhabdomyolysis:
- Aggressive IV fluids (goal UO 1-2 mL/kg/hr)
- Monitor CK, potassium
- Consider continuous renal replacement therapy (CRRT) if AKI
DIC:
- Supportive: FFP, platelets, cryoprecipitate if bleeding
- Correct underlying hyperthermia
Acute Liver Failure:
- May be delayed 24-72 hours
- Monitor LFTs, INR, ammonia
- Consider N-acetylcysteine (off-label, evidence limited)
- Liver transplant consult for severe cases
Seizures:
- Benzodiazepines first-line
- Increase heat production; must control
Hypotension:
- Fluids first
- Vasopressors if refractory (norepinephrine)
Disposition
Admission Criteria
- All patients with heat stroke require admission
- Most require ICU-level care
- Continue monitoring even after cooling achieved (organ injury may manifest later)
ICU Criteria
- Core temp >41°C
- Coma, seizures, or GCS <12
- Hemodynamic instability
- Significant rhabdomyolysis (CK >10,000)
- Evidence of DIC
- Acute kidney injury
- Liver injury
- Respiratory distress or intubated
Discharge Criteria
Rarely applicable from ED for true heat stroke; requires period of observation and normal labs
Follow-Up
| Situation | Follow-Up |
|---|---|
| Post-discharge | PCP within 1 week |
| Athletes | Sports medicine, exercise physiologist for heat acclimatization |
| Elderly | Social services for heat safety planning |
| Recurrent | Investigate predisposing factors, medication review |
Patient Education
Prevention Strategies
General Public:
- Stay hydrated (don't wait until thirsty)
- Avoid strenuous activity during peak heat (10am-4pm)
- Wear lightweight, light-colored, loose-fitting clothing
- Use air conditioning; go to cooling centers if needed
- Never leave people/pets in parked vehicles
- Check on elderly neighbors during heatwaves
- Limit alcohol and caffeine
Athletes and Laborers:
- Gradual acclimatization over 10-14 days
- Frequent rest breaks in shade
- Adequate hydration before, during, and after activity
- Know early signs: dizziness, cramps, excessive fatigue
- Stop activity if symptoms develop
- Work/train with a partner
High-Risk Individuals:
- Ensure access to air conditioning
- Have someone check in daily during heatwaves
- Review medications with physician
- Know cooling strategies
Warning Signs to Recognize
- Heavy sweating suddenly stopping
- Confusion, bizarre behavior
- Dizziness, fainting
- Nausea, vomiting
- Rapid heartbeat
- Skin that feels dry and hot
Special Populations
Elderly
- Highest mortality group for classic heat stroke
- Impaired thermoregulation
- More likely on medications that impair heat dissipation
- Social isolation increases risk
- May not recognize or respond to symptoms
- Lower threshold for aggressive care
Athletes (Exertional Heat Stroke)
- Often previously healthy
- Higher rhabdomyolysis risk
- Cold water immersion is critical
- Return-to-play decisions require careful follow-up
- May have exercise-associated hyponatremia complicating picture
Pediatric
- Infants unable to escape heat
- Left-in-vehicle deaths tragically common
- Rapid cooling essential
- May present with seizures
Drug-Induced Hyperthermia
- Stimulants (cocaine, amphetamines, MDMA)
- Often exertional component (raves, dancing)
- Benzodiazepines helpful for agitation and hyperthermia
- Avoid antipsychotics in stimulant toxicity (lower seizure threshold)
Patients on Medications That Impair Thermoregulation
| Medication Class | Mechanism |
|---|---|
| Anticholinergics | Decrease sweating |
| Beta-blockers | Impair cardiac output response |
| Diuretics | Dehydration |
| Antipsychotics | Central thermoregulation impairment |
| Amphetamines/MDMA | Increase heat production |
Quality Metrics
Performance Indicators
| Metric | Target | Rationale |
|---|---|---|
| Core temperature measured not oral | 100% | Accurate diagnosis |
| Cooling initiated within 10 min of arrival | 100% | Reduces mortality |
| Core temp <39°C within 30 min | >0% | Optimal outcome |
| ICU admission for heat stroke | 100% | Monitoring for organ failure |
| DIC screening (coags) | 100% | Common complication |
| Rhabdomyolysis screening (CK) | 100% | Common complication |
Documentation Requirements
- Core temperature on arrival
- Method of temperature measurement
- Mental status on arrival (GCS)
- Cooling method and duration
- Time to target temperature
- Fluid resuscitation volume
- Laboratory trends (CK, LFTs, coags)
- Complications identified and treated
Key Clinical Pearls
Diagnostic Pearls
- AMS is required for diagnosis: Hyperthermia without AMS is NOT heat stroke
- Don't trust oral temps: Must measure core temperature
- Exertional patients may still be sweating: Absence of sweating not required
- Consider drug-induced causes: Especially in young patients at raves
- Delayed liver injury: LFTs may peak at 24-72 hours
- Think beyond heat stroke: Rule out sepsis, toxidromes, CNS pathology
Treatment Pearls
- Cool first, ask questions later: Every minute counts
- Cold water immersion is best: If available, use it
- Antipyretics don't work: Paracetamol and NSAIDs are ineffective
- Stop cooling at 38.5-39°C: Avoid overshoot and hypothermia
- Control shivering: It generates more heat
- Aggressive fluids for rhabdo: Target UO 1-2 mL/kg/hr
Disposition Pearls
- All heat stroke to ICU: Organ failure can be delayed
- Monitor liver for 72 hours: Peak injury is delayed
- Rhabdomyolysis monitoring: CK may continue to rise after cooling
- Athletes need clearance: Before returning to activity
- Prevention counseling: Essential for high-risk patients
References
- Leon LR, Bouchama A. Heat stroke. Compr Physiol. 2015;5(2):611-647.
- Bouchama A, Knochel JP. Heat stroke. N Engl J Med. 2002;346(25):1978-1988.
- Casa DJ, et al. National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses. J Athl Train. 2015;50(9):986-1000.
- Epstein Y, Yanovich R. Heatstroke. N Engl J Med. 2019;380(25):2449-2459.
- Gaudio FG, Grissom CK. Cooling Methods in Heat Stroke. J Emerg Med. 2016;50(4):607-616.
- Belval LN, et al. Practical Hydration Solutions for Sports. Nutrients. 2019;11(7):1550.
- McDermott BP, et al. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train. 2017;52(9):877-895.
- UpToDate. Severe nonexertional hyperthermia (classic heat stroke) in adults. 2024.