Sun stroke
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Sunstroke (Heat Stroke)
Definition
Sunstroke, or heat stroke, is an acute, life-threatening medical emergency defined by the combination of:
- Core body temperature >40°C (>104°F)
- Altered mental status (AMS)
It is fatal if untreated. A delay in cooling directly increases the mortality rate.
- Tintinalli's Emergency Medicine, p. 1389
Types
| Type | Setting | Key Feature |
|---|---|---|
| Classic (Non-exertional) | Elderly, sedentary individuals in hot weather; no air conditioning | Often involves anhidrosis (dry skin), though sweat IS present in >50% of cases |
| Exertional (EHS) | Athletes, soldiers, manual workers during intense physical activity | More likely to present with sweating; rhabdomyolysis and lactic acidosis common |
The clinical distinction between the two is NOT important because immediate cooling is the goal in both types.
Pathophysiology
Heat stress triggers a cascade:
- Physical stress - high ambient temperature, humidity, exercise, heavy clothing
- Physiological strain - cardiovascular challenge, reduced tissue perfusion, hyperthermia, oxidative stress
- Pathology:
- Increased gut permeability
- Endotoxemia
- Systemic Inflammatory Response Syndrome (SIRS)
- Coagulopathy (DIC)
- Multi-organ cell necrosis/apoptosis
Organs at risk: Brain, intestine, kidney, liver, skeletal muscle.
At temperatures above 42°C, potassium channel dysfunction can trigger ventricular tachycardia or fibrillation. Sustained temperatures at or above 42°C may cause permanent brain injury.
- Goldman-Cecil Medicine, p. 1105-1106
- Plum and Posner's Stupor and Coma, p. 405-406
Risk Factors
- Elderly individuals (impaired thermoregulation, living alone, no AC)
- Infants and young children
- Athletes and military personnel
- Outdoor workers
- Drugs that impair thermoregulation:
- Anticholinergics (older antipsychotics, antihistamines)
- Diuretics
- Beta-blockers
- Sympathomimetics (cocaine, amphetamines)
Clinical Features
Cardinal features:
- Hyperthermia >40°C
- Altered mental status (confusion, combativeness, coma)
CNS findings (the cerebellum is highly heat-sensitive):
- Ataxia (early sign)
- Irritability, confusion, bizarre behavior, hallucinations
- Hemiplegia, decorticate/decerebrate posturing
- Status epilepticus
- Coma
Other symptoms:
- Nausea, vomiting, diarrhea
- Dizziness, weakness, headache
- Tachycardia, hypotension
- Flushed hot skin (wet or dry)
Note: Anhidrosis (absence of sweating) is NOT required for diagnosis - sweat is present in over half of heat stroke patients.
- Tintinalli's Emergency Medicine, p. 1389
Spectrum of Heat Illness
Minor to severe, in order of severity:
- Heat rash (miliaria rubra) - sweat duct occlusion
- Heat syncope - peripheral vasodilation + pooling in extremities
- Heat cramps - muscle cramps from dehydration and electrolyte loss
- Heat exhaustion - temp usually ≤40°C, minor CNS symptoms only, primarily cardiovascular
- Heat injury - end-organ damage (liver, kidney, rhabdomyolysis) without major CNS changes
- Heat stroke - temp >40°C + significant AMS - the most severe form
Diagnosis
There is no specific diagnostic test. Diagnosis is clinical - based on history, presentation, and exclusion of other causes.
Workup includes:
- CBC, comprehensive metabolic panel, ABG
- Coagulation profile (watch for DIC)
- Creatine phosphokinase (CPK) and myoglobin (rhabdomyolysis)
- Urinalysis
- Blood glucose (hypoglycemia possible, especially in exertional)
- ECG (risk of arrhythmia at extreme temperatures)
- Chest X-ray
- CT head and lumbar puncture if needed to exclude other AMS causes
Typical labs in exertional HS:
- Lactic acidosis
- Hypoglycemia
- PaCO2 often <20 mmHg (hyperventilation)
- Elevated CPK
Differential Diagnosis
| Infectious | Neurologic | Endocrine | Toxicologic |
|---|---|---|---|
| Sepsis, meningitis, encephalitis, malaria, typhoid, tetanus | Hypothalamic bleed/infarct, CVA, status epilepticus | Thyroid storm, pheochromocytoma, DKA | Anticholinergic toxidrome, serotonin syndrome, malignant hyperthermia, NMS, sympathomimetic OD |
Treatment
Prehospital
- Remove patient from hot environment immediately
- Remove clothing
- Check point-of-care glucose
- Begin cooling (see below)
- IV normal saline 1-2 L bolus if hypotensive
Emergency Department Resuscitation
Goal: Cool to approximately 39°C (102.2°F) - avoid overshooting into hypothermia
Two large-bore IV lines for fluid resuscitation. Give isotonic fluids (normal saline) - even if the patient appears hypernatremic, rapid sodium correction can be dangerous.
ECG immediately - at 42°C, ventricular arrhythmias become a real risk.
Cooling methods:
| Method | Notes |
|---|---|
| Evaporative cooling | Spray cool water (~15°C) on skin + fan airflow. Practical, well-tolerated. First-line in most settings |
| Ice-water immersion | Most effective for exertional HS in young, healthy patients. Difficult to monitor patient |
| Ice packs | Applied to neck, axillae, groin. Adjunct method |
| Cold IV fluids | Helpful adjunct |
| Intravascular cooling | For refractory cases; allows controlled temperature modulation |
Key point: No single cooling method has been proven superior. Use whichever is available, accessible, and effective. If one isn't working, try another.
Shivering (a complication of rapid cooling) is treated with short-acting benzodiazepines (first-line). Phenothiazines are second-line - caution: they lower seizure threshold and impair sweating via anticholinergic effects.
Antipyretics (aspirin, acetaminophen) are NOT effective - heat stroke is not a fever, it is a failure of thermoregulation, so antipyretics do not work.
Complications
- Rhabdomyolysis and acute kidney injury
- Disseminated Intravascular Coagulation (DIC) - a major cause of death
- Liver failure (transaminases often dramatically elevated)
- Pulmonary edema / ARDS
- Cerebral edema and permanent brain damage (especially with sustained temps ≥42°C)
- Cardiac arrhythmias (VT/VF)
- Seizures (common during and after cooling)
Prognosis
- Mortality is high without treatment
- Neurologic injury is a function of maximum temperature reached and duration of exposure
- Most patients who survive the initial event regain cognitive function rapidly
- Sustained temperatures ≥42°C can cause permanent brain injury
Prevention
- Stay hydrated (increase fluid intake in heat)
- Avoid strenuous activity in peak heat (10 AM - 4 PM)
- Wear light, breathable clothing
- Never leave children or elderly in parked cars
- Gradual acclimatization to heat before strenuous activity
- Access to cool/air-conditioned spaces for high-risk individuals
Sources: Tintinalli's Emergency Medicine, p. 1389-1394; Goldman-Cecil Medicine, p. 1105-1106; Plum and Posner's Diagnosis and Treatment of Stupor and Coma, p. 405-406
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