Write a short note on heat stroke — types, pathophysiology, clinical features and management.

Definition

Heat stroke is a life-threatening emergency defined as a core body temperature above 40 °C (104 °F) accompanied by central nervous system dysfunction — confusion, delirium, seizures or coma — in the setting of heat exposure. It represents failure of thermoregulation, in contrast to fever, where the hypothalamic set-point is deliberately raised. It is of increasing importance in India, where severe summer heat waves cause substantial excess mortality.

Types

Pathophysiology

Heat gain exceeds heat loss and thermoregulatory compensation fails. Above 40 °C there is direct cytotoxic injury, with denaturation of proteins and enzyme dysfunction. This triggers a systemic inflammatory response with release of IL-1, IL-6 and TNF-α, causing endothelial injury and capillary leak — a picture closely resembling sepsis. Gut barrier failure permits endotoxin translocation, amplifying the response. The end result is multi-organ dysfunction: encephalopathy, rhabdomyolysis with myoglobinuric renal failure, hepatic necrosis, DIC and myocardial injury.

Clinical Features

• Core temperature > 40 °C measured rectally — oral and axillary readings are unreliable and dangerously underestimate core temperature.
• CNS dysfunction — irritability, confusion, ataxia, seizures, coma. This is the cardinal feature separating heat stroke from heat exhaustion.
• Hot skin, dry in classic and often sweaty in exertional heat stroke.
• Tachycardia, hypotension, tachypnoea; initially a hyperdynamic circulation.
• Nausea, vomiting, muscle cramps and tenderness.
• Complications: acute kidney injury, rhabdomyolysis, DIC with bleeding, hepatic failure, ARDS, arrhythmia.

Investigations

CBC, urea and electrolytes, creatine kinase (markedly raised in rhabdomyolysis), liver function, coagulation profile and D-dimer (DIC), arterial blood gas, blood glucose, urine for myoglobin, ECG, chest X-ray, and CT head where the diagnosis is uncertain or focal signs are present.

Management

Cooling is the single intervention that determines survival — begin immediately and do not delay for investigations or transfer.

• Remove from the heat source, strip clothing, and address airway, breathing and circulation.
• Cold water immersion is the most effective method and the treatment of choice in exertional heat stroke, achieving the fastest cooling rates.
• Where immersion is impractical (elderly, haemodynamically unstable, need for monitoring), use evaporative cooling — tepid water spray with continuous fanning — supplemented by ice packs to the neck, axillae and groins.
• Reduce core temperature to below 39 °C rapidly, then stop active cooling to avoid overshoot hypothermia. Monitor core temperature continuously with a rectal or oesophageal probe.
• Cold intravenous fluids and careful volume resuscitation; aggressive fluid therapy with urine output targets where rhabdomyolysis is present.
• Benzodiazepines for shivering and seizures — shivering generates heat and defeats cooling.
• Treat complications: rhabdomyolysis (fluids, renal replacement therapy if needed), DIC (blood products), and organ support in intensive care.

Prevention & Prognosis

Acclimatisation, adequate hydration, avoiding exertion during peak heat, light loose clothing, scheduling outdoor labour outside midday, and heat-wave action plans targeting the elderly and outdoor workers. Mortality is high and correlates directly with the duration and degree of hyperthermia before cooling begins, which is why pre-hospital and emergency-department cooling matters more than anything done later.