Overview
Heat Emergencies
Quick Reference
Critical Alerts
- Heat stroke is life-threatening: Core temp >40°C (104°F) + CNS dysfunction
- Rapid cooling is essential: Target under 39°C within 30 minutes
- Classic vs Exertional heat stroke: Different populations, same emergency
- Cold water immersion is gold standard: For cooling
- Antipyretics do NOT work: Hypothalamic setpoint is normal
- Multiorgan failure can develop: DIC, rhabdo, renal failure
Heat Exhaustion vs Heat Stroke
| Feature | Heat Exhaustion | Heat Stroke |
|---|---|---|
| Temperature | under 40°C (104°F) | ≥40°C (104°F) |
| CNS | Intact or mild symptoms | Altered mental status (defining) |
| Sweating | Present | May be absent (classic) or present (exertional) |
| Treatment | Remove from heat, fluids, rest | EMERGENT COOLING + ICU |
| Prognosis | Good | Mortality 10-50% if delayed cooling |
Emergency Treatments
| Condition | Treatment |
|---|---|
| Heat cramps | Oral or IV fluids, rest, salt |
| Heat exhaustion | Remove from heat, IV fluids, cooling |
| Heat stroke | Cold water immersion, IV fluids, ICU |
Definition
Overview
Heat emergencies are a spectrum of disorders caused by failure of thermoregulation during heat exposure. Heat stroke is defined by core temperature ≥40°C (104°F) with central nervous system dysfunction. It is a medical emergency requiring immediate cooling. Delayed treatment leads to multiorgan failure and death.
Classification
Heat Illness Spectrum:
| Condition | Features |
|---|---|
| Heat cramps | Muscle cramps, no fever |
| Heat exhaustion | Fatigue, weakness, headache, temp under 40°C, preserved mentation |
| Heat stroke | Temp ≥40°C + altered mental status (confusion, seizure, coma) |
Heat Stroke Types:
| Type | Population | Sweating |
|---|---|---|
| Classic (non-exertional) | Elderly, chronic illness, medications | Often absent |
| Exertional | Young, athletes, military, laborers | Usually present |
Epidemiology
- Heat-related deaths increasing: Climate change
- Classic heat stroke: Elderly during heat waves
- Exertional heat stroke: Athletes, military recruits, laborers
- Mortality without treatment: Up to 80%
- Mortality with prompt cooling: 10-20%
Etiology
Risk Factors:
| Factor | Notes |
|---|---|
| Environmental | High ambient temperature, humidity |
| Exertion | Exercise, labor |
| Age extremes | Elderly, infants |
| Medications | Anticholinergics, diuretics, beta-blockers, antipsychotics |
| Chronic illness | Cardiovascular, diabetes, obesity |
| Dehydration | Reduced sweating capacity |
| Drugs | Amphetamines, cocaine, MDMA |
| Lack of acclimatization | New to hot environment |
Pathophysiology
Thermoregulation Failure
-
Normal cooling mechanisms:
- Radiation, convection, evaporation (sweating)
- Hypothalamus regulates setpoint
-
Heat stroke:
- Heat production exceeds dissipation
- Core temperature rises
- Cellular damage begins >40°C
- Inflammatory cascade, coagulopathy
Organ Damage
| System | Effect |
|---|---|
| CNS | Confusion, seizures, coma |
| Cardiovascular | High-output failure, hypotension |
| Hepatic | AST/ALT elevation, liver failure |
| Renal | Acute kidney injury, rhabdomyolysis |
| Hematologic | DIC, thrombocytopenia |
| Muscle | Rhabdomyolysis |
Clinical Presentation
Heat Exhaustion
| Symptom | Notes |
|---|---|
| Temperature | under 40°C (104°F) |
| Mental status | Normal or mildly impaired |
| Weakness, fatigue | Prominent |
| Headache | Common |
| Nausea, vomiting | Common |
| Diaphoresis | Present |
| Tachycardia | Compensatory |
Heat Stroke
| Finding | Description |
|---|---|
| Temperature | ≥40°C (104°F) |
| Altered mental status | REQUIRED for diagnosis (confusion, agitation, ataxia, seizure, coma) |
| Skin | Hot; dry (classic) or sweating (exertional) |
| Tachycardia | Often severe |
| Hypotension | Late |
| Tachypnea | |
| Vomiting, diarrhea |
History
Key Questions:
Physical Examination
| Finding | Significance |
|---|---|
| Core temperature | Rectal preferred; ≥40°C = Heat stroke |
| Mental status | Altered = Heat stroke |
| Skin | Hot; dry or wet |
| Vital signs | Tachycardia, hypotension (late) |
| Neurological | Ataxia, seizures, posturing |
Environmental exposure (heat wave, exercise)
Common presentation.
Duration of exposure
Common presentation.
Fluid intake
Common presentation.
Medications
Common presentation.
Underlying medical conditions
Common presentation.
Substance use (amphetamines, cocaine)
Common presentation.
Acclimatization status
Common presentation.
Red Flags
Life-Threatening Signs
| Finding | Concern |
|---|---|
| Temp ≥40°C + Altered mental status | Heat stroke |
| Seizures | Severe CNS dysfunction |
| Coma | Severe heat stroke |
| Hypotension | Circulatory collapse |
| Anuria | Renal failure |
| DIC | Coagulopathy |
Differential Diagnosis
Other Causes of Hyperthermia
| Diagnosis | Features |
|---|---|
| Sepsis | Infection source, WBC abnormalities |
| Neuroleptic malignant syndrome | Antipsychotic use, rigidity |
| Malignant hyperthermia | Anesthetic exposure |
| Serotonin syndrome | Serotonergic drugs, clonus |
| Thyroid storm | Thyrotoxicosis history |
| Drug toxicity | Cocaine, amphetamines, MDMA |
| Anticholinergic toxicity | Dry, flushed, mydriasis |
Diagnostic Approach
Clinical Diagnosis
- Heat stroke is a clinical diagnosis
- Core temp ≥40°C + Altered mental status + Environmental exposure
Core Temperature Measurement
- Rectal temperature is gold standard
- Oral, axillary, tympanic underestimate core temp
Laboratory
| Test | Expected Findings |
|---|---|
| CBC | Hemoconcentration, thrombocytopenia (DIC) |
| BMP | Hypernatremia or hyponatremia, elevated creatinine, electrolyte abnormalities |
| LFTs | AST/ALT elevation (may be severe) |
| Coags | Elevated PT/INR, PTT (DIC) |
| CK | Elevated (rhabdomyolysis) |
| Lactate | Elevated |
| Urinalysis | Myoglobinuria |
| ABG | Respiratory alkalosis initially, metabolic acidosis later |
Treatment
Principles
- Remove from heat
- Initiate rapid cooling immediately: Goal under 39°C in 30 min
- IV fluids for volume resuscitation
- Monitor for and treat complications
- ICU admission for heat stroke
Heat Exhaustion
| Intervention | Details |
|---|---|
| Remove from heat | Cool, shaded environment |
| Rest | |
| Oral fluids | If tolerated; electrolyte solutions |
| IV fluids | NS or LR if unable to take PO |
| Monitor | For progression to heat stroke |
Heat Stroke (EMERGENCY)
Cooling Methods (In Order of Effectiveness):
| Method | Notes |
|---|---|
| Cold water immersion | GOLD STANDARD; submerge to neck |
| Evaporative cooling | Spray water + fans |
| Ice packs | Axillae, groin, neck |
| Cold IV fluids | Adjunct; 4°C NS |
| Cooling blankets | Less effective |
Cooling Target:
- Goal: Core temp under 39°C (102.2°F) within 30 minutes
- Once under 39°C, stop active cooling to avoid hypothermia
Do NOT Use:
- Antipyretics (acetaminophen, NSAIDs): Ineffective; hypothalamic setpoint is normal
Fluid Resuscitation:
| Agent | Dose |
|---|---|
| Normal saline | 1-2 L bolus, titrate to hemodynamics |
| Monitor for fluid overload |
Seizure Management:
| Agent | Dose |
|---|---|
| Benzodiazepines | Lorazepam 4 mg IV, repeat PRN |
Shivering Management:
| Agent | Dose |
|---|---|
| Benzodiazepines | Midazolam, lorazepam |
| Magnesium sulfate | Adjunct |
Avoid: Dantrolene (not effective in heat stroke; only in malignant hyperthermia)
Rhabdomyolysis Management
| Intervention | Details |
|---|---|
| Aggressive IV fluids | Target UOP 200-300 mL/hr |
| Monitor CK, renal function | |
| Avoid bicarbonate | Unless severe acidosis |
Disposition
Heat Exhaustion
- May discharge if symptoms resolve, tolerating PO, reliable follow-up
- Observe for 4-6 hours minimum
Heat Stroke
- All patients require ICU admission
- Continuous temperature monitoring
- Watch for delayed organ failure
Referral
| Indication | Referral |
|---|---|
| Renal failure | Nephrology |
| Hepatic failure | GI/Hepatology |
| DIC | Hematology |
| Rhabdomyolysis | Nephrology |
Patient Education
Condition Explanation
- "Your body overheated and couldn't cool itself down."
- "We are cooling you rapidly to prevent organ damage."
- "You will need close monitoring in the ICU."
Prevention
- Stay hydrated in hot weather
- Avoid strenuous activity during peak heat
- Wear light, loose clothing
- Take breaks in cool, shaded areas
- Never leave children or pets in parked cars
- Acclimatize gradually to hot environments
- Know your medications that increase risk
Warning Signs
- Confusion, dizziness
- Nausea, vomiting
- Rapid heartbeat
- Hot, dry skin or excessive sweating
- Muscle cramps
Special Populations
Elderly
- Higher risk of classic heat stroke
- May have blunted thirst response
- Medications increase risk
Athletes/Military
- Exertional heat stroke
- Aggressive cooling essential
- Cold water immersion is standard
Medications That Increase Risk
| Class | Examples |
|---|---|
| Anticholinergics | Antihistamines, antipsychotics |
| Diuretics | Fluid depletion |
| Beta-blockers | Reduced cardiovascular response |
| Phenothiazines | Impaired thermoregulation |
| Stimulants | Increased heat production |
Quality Metrics
Performance Indicators
| Metric | Target | Rationale |
|---|---|---|
| Rectal temp measured | 100% | Accurate core temp |
| Cooling initiated in under 10 min | 100% | Survival |
| Temp under 39°C in under 30 min | >0% | Outcome improvement |
| ICU admission for heat stroke | 100% | Monitoring |
Documentation Requirements
- Environmental exposure history
- Core temperature (rectal)
- Mental status
- Cooling method and duration
- Temperature during cooling
- Complications and management
Key Clinical Pearls
Diagnostic Pearls
- Heat stroke = ≥40°C + Altered mental status: This is the definition
- Rectal temp is gold standard: Other methods underestimate
- Classic heat stroke may have DRY skin: Elderly
- Exertional heat stroke usually has SWEATING: Young, athletes
- Check for rhabdo, DIC, renal failure, liver failure
- Differential includes NMS, serotonin syndrome, thyroid storm
Treatment Pearls
- Cool FIRST, workup SECOND: Cooling is life-saving
- Cold water immersion is most effective: Submerge to neck
- Evaporative cooling if immersion not available: Spray + fans
- Target under 39°C within 30 minutes: Stop cooling at that point
- Antipyretics do NOT work: Don't give them
- Manage shivering with benzos: Shivering generates heat
Disposition Pearls
- All heat stroke to ICU: Delayed organ failure occurs
- Heat exhaustion may discharge if resolves: After observation
- Organ failure may develop hours later: Monitor labs
- Educate on prevention: Critical for at-risk patients
References
- Bouchama A, et al. Heat stroke. N Engl J Med. 2002;346(25):1978-1988.
- Epstein Y, Yanovich R. Heatstroke. N Engl J Med. 2019;380(25):2449-2459.
- Casa DJ, et al. Cold water immersion: the gold standard for exertional heatstroke treatment. Exerc Sport Sci Rev. 2007;35(3):141-149.
- Lipman GS, et al. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Heat Illness. Wilderness Environ Med. 2019;30(4S):S33-S46.
- Leon LR, et al. Heat stroke: role of the systemic inflammatory response. J Appl Physiol. 2015;119(12):1420-1427.
- CDC. Heat-Related Illness. 2024.
- Tintinalli JE, et al. Heat Emergencies. Tintinalli's Emergency Medicine. 9th ed. 2020.
- UpToDate. Severe hyperthermia (heat stroke) in adults. 2024.