Heat Stroke

Heat stroke is a core temperature over 40 degrees Celsius with central nervous system dysfunction (confusion, delirium, seizures or coma), caused by failure of thermoregulation in a hot environment or during intense exertion.

Two forms exist

• Classic (nonexertional): occurs in heat waves among the elderly, young children and people with chronic illness. Mortality is 20 to 60%.
• Exertional: occurs in athletes, soldiers and laborers. Mortality is 3 to 5% when cooling is immediate, and far higher with delay.

Mechanism: direct thermal cytotoxicity, gut barrier failure with endotoxin translocation, a systemic inflammatory response, endothelial injury and coagulopathy. Organ damage depends on the duration of temperature above about 40.5 degrees Celsius.

Risk factors: age extremes, obesity, dehydration, lack of acclimatization, high humidity, cardiovascular disease, alcohol, and drugs that impair sweating or heat loss (anticholinergics, antipsychotics, diuretics, beta blockers, stimulants). Complications: rhabdomyolysis, acute kidney injury (25 to 35%), hepatic injury peaking at 2 to 3 days (and sometimes liver failure), disseminated intravascular coagulation, acute respiratory distress syndrome, myocardial injury and lasting cerebellar ataxia.

• Temperature over 40 degrees Celsius with altered mental state: confusion, irritability, delirium, ataxia, seizures or coma
• Hot dry skin in classic heat stroke, and sweating in many exertional cases
• Tachycardia, tachypnea, hypotension, vomiting and diarrhea
• Muscle tenderness and dark urine in exertional disease
• Red flags: Glasgow coma score of 8 or lower, seizures, hypotension, jaundice, bleeding and oliguria

1. Core temperature by rectal probe at once (oral, axillary and tympanic readings are unreliable). Do not delay cooling for any test.
2. Bedside glucose, then blood tests: electrolytes (sodium, potassium, calcium, phosphate), creatinine, creatine kinase, liver tests (AST and ALT may exceed 1000 units/L), lactate, arterial blood gas, full blood count, coagulation studies and fibrinogen.
3. Urinalysis for myoglobin, ECG and troponin.
4. Exclusion of other causes: cultures and lumbar puncture when meningism is present, malaria test in endemic regions, toxicology screen, thyroid function, and CT head for focal signs.
5. Repeat blood tests at 6 to 12 hours, since coagulopathy and liver injury evolve.

Differentials: sepsis, meningoencephalitis, malaria, thyroid storm, drug-induced hyperthermia, neuroleptic malignant syndrome and status epilepticus.

Immediate cooling is the treatment, and every minute of delay raises the risk of organ damage. The aim is a core temperature under 39 degrees Celsius within 30 minutes of collapse.

1. Cold water immersion (water at 1 to 5 degrees Celsius, up to the neck) is the most effective method for exertional heat stroke, cooling at 0.15 to 0.2 degrees Celsius a minute. Stir the water, monitor the rectal temperature continuously, and stop at 38.5 to 39 degrees Celsius.
2. Alternatives when immersion is impossible (and for classic heat stroke in the elderly): ice-water-soaked sheets changed every 3 minutes, ice packs to the neck, axillae and groin, or evaporative cooling with 15 degrees Celsius water spray and a fan. Cold IV 0.9% saline 1 to 2 L at 4 degrees Celsius.
3. Airway and breathing: oxygen, and intubation for Glasgow coma score of 8 or lower.
4. Fluids: IV 0.9% saline 500 mL bolus, then titrated to blood pressure and urine output of 1 to 2 mL/kg/h. Avoid over-hydration, because of hyponatremia and pulmonary edema.
5. Seizures and shivering: lorazepam 2 to 4 mg IV (children 0.1 mg/kg) or diazepam 5 to 10 mg IV (children 0.2 mg/kg).
6. Do not give paracetamol, aspirin or dantrolene (no benefit).
7. Complications:
   • Hyperkalemia: calcium chloride 1 g IV, and insulin 10 units IV with 50 mL of 50% dextrose.
   • Rhabdomyolysis: IV 0.9% saline to keep urine output over 1 mL/kg/h. Do not treat asymptomatic hypocalcemia (rebound hypercalcemia follows).
   • Disseminated intravascular coagulation: fresh frozen plasma 15 mL/kg, platelets for counts under 20 × 10^9/L (under 50 with bleeding) and cryoprecipitate for fibrinogen under 1.5 g/L.
   • Hypoglycemia: 50% dextrose 25 to 50 mL IV.
   • Acute kidney injury: renal replacement therapy for hyperkalemia, acidosis or overload.
   • Acute liver failure: transplant assessment for rising INR with encephalopathy.
8. Observation: intensive care for at least 24 to 48 hours, with repeated creatine kinase, creatinine and liver tests.
9. Return to exertion: only after at least 1 week without symptoms and with normal creatine kinase, creatinine and liver tests, then a gradual 2 to 4 week return with acclimatization.

Prevention: acclimatize over 10 to 14 days, drink to thirst and avoid overdrinking, limit exertion in the heat of the day, review heat-impairing drugs, and arrange cooled shelter and checks on elderly people during heat waves.