Heat stroke — clinical features, diagnostic criteria, differential diagnosis and treatment

Definition and diagnostic criteria — the classic triad. Heat stroke is defined as a failure to maintain body temperature and is characterised by a core temperature above 40.6°C (105°F), severe central nervous system dysfunction — psychosis, delirium, coma — and anhidrosis with hot, dry skin. The two groups primarily affected are older adults who are chronically ill, and the young undergoing strenuous exercise — that is, classic (non-exertional) and exertional heat stroke. Mortality is as high as 80% once this syndrome is manifest.

Predisposing factors in older adults. There are multiple predisposing factors for heat stroke in older adults, but most often there is a prolonged heat wave. Add the age-related and iatrogenic contributors: reduced thirst and impaired water conservation, reduced sweating capacity, impaired cardiovascular compensation, immobility and dependence on carers, social isolation, dementia, absence of air conditioning, and drugs — anticholinergics and antihistamines (impair sweating), antipsychotics and antidepressants (impair thermoregulation), diuretics (volume depletion), beta blockers (blunt the cardiac response), and alcohol. Chronic cardiac, respiratory, renal and neurological disease all raise the risk.

Clinical features — early and late. The diagnosis requires a high level of suspicion. Early manifestations of heat exhaustion are non-specific: dizziness, weakness, a sensation of warmth, anorexia, nausea, vomiting, headache and dyspnoea. Later, severe central nervous system dysfunction and anhidrosis develop — psychosis, delirium, coma, and hot, dry skin. In older adults the presentation is frequently just confusion, a fall or collapse, and the history of heat exposure must be sought actively.

Differential diagnosis. The differential is essentially every cause of hyperthermia with altered mental state: sepsis and meningoencephalitis (the commonest and most important alternative — and heat stroke may be complicated by infection); neuroleptic malignant syndrome (antipsychotics, lead-pipe rigidity, raised CK); serotonin syndrome (serotonergic drugs, clonus, hyperreflexia); malignant hyperthermia (anaesthetic exposure); anticholinergic toxicity (hot, dry skin, dilated pupils, urinary retention); thyroid storm; drug withdrawal states; status epilepticus; cerebrovascular event affecting the hypothalamus; and stimulant or cocaine toxicity. The distinguishing features are the environmental history, the drug history and the muscle findings.

Complications — the multi-organ failure that determines outcome. Myocardial damage, congestive heart failure and arrhythmias; renal failure in 20–25%; cerebral oedema and seizures with diffuse and focal findings; hepatocellular necrosis, jaundice and liver failure; rhabdomyolysis with myoglobinuria; bleeding diathesis and disseminated intravascular coagulation; electrolyte disturbances; metabolic acidosis with respiratory alkalosis; infection including aspiration pneumonia and sepsis; and dehydration with shock. Once the full syndrome has developed for any length of time the prognosis is very poor.

Treatment — cool first, and cool fast. Management at this stage requires intense multisystem care, but the key is rapid specific therapy consisting of cooling to 38.9°C (102°F) within the first hour. Ice packs and ice-water immersion are superior to convection cooling with alcohol sponge baths or electric fans. Alongside cooling: secure the airway, give oxygen, obtain a rectal core temperature, resuscitate with intravenous crystalloid guided by cardiac status, treat seizures with benzodiazepines, give generous fluids and monitor CK and urine output for rhabdomyolysis, correct electrolytes and coagulopathy, and treat infection. Antipyretics — paracetamol and NSAIDs — are useless because the hypothalamic set point is normal, and are potentially harmful given hepatic and renal injury; dantrolene has no role. In view of the poor survival, efforts must be directed towards prevention: older patients should be cautioned about the dangers of hot weather, and for those at particularly high risk, temporary relocation to more protected environments should be considered. Prevention appears to be the most appropriate approach to management of temperature dysregulation in older adults — through education about susceptibility, appropriate behaviour in extreme temperatures, and close monitoring of the most vulnerable. Heat exposure + core temperature >40°C + altered mental state = HEAT STROKE ↓ COOL FIRST, TRANSPORT SECOND — begin cooling immediately, before and during transfer ↓ Preferred If immersion unavailable Ice-water immersion (1–5°C) or cold- Ice packs to neck, axillae, groin · wet water immersion (9–12°C) sheets with fanning · cold IV fluids ↓ Target <39°C within 30 minutes · continuous rectal temperature monitoring · stop cooling at 38.5–39°C to avoid overshoot hypothermia ↓ Then: airway and oxygen · IV crystalloid · benzodiazepines for seizures and shivering · monitor CK, creatinine, LFT, coagulation, electrolytes · treat rhabdomyolysis, DIC, AKI · exclude and treat sepsis · no antipyretics, no dantrolene LATEST UPDATE (2023–PRESENT) — 1 POINT

The Society of Critical Care Medicine published the first formal Guideline for the Treatment of Heat Stroke (Crit Care Med 2025), and India's NCDC issued a national emergency cooling protocol (March 2024). The SCCM guideline makes active cooling recommended over passive cooling, with cold- or ice-water immersion achieving the fastest cooling rate and to be prioritised where available — ice-water immersion at 1–5°C or cold-water immersion at 9–12°C. Its good-practice statements are precise and highly quotable: clinicians may use similar strategies for either classic or exertional heat stroke; cooling methods should reach the target temperature within 30 minutes of recognition; and modalities achieving a cooling rate of at least 0.155°C per minute should be prioritised. It also states that there is no evidence to support pharmacological interventions affecting temperature control, so they should be avoided. In India, the NCDC/NPCCHH "Emergency Cooling for Severe Heat-Related Illnesses" (March 2024) operationalises this for Indian emergency departments, including improvised cold-water immersion using a body bag or tarpaulin where a tub is unavailable, and the NDMA Heat Action Plans — with the Ahmedabad Heat Action Plan as the model, credited with a substantial reduction in heat mortality — provide the preventive framework: early-warning alerts, cool shelters, rescheduled outdoor work, and active check-in on isolated older people during heatwaves and power cuts, which is the single highest-yield preventive measure for this population.