ICU · Environmental

Acute heat stroke: exertional vs classic, rapid cooling, and 'sepsis from heat'

Also known as Heat stroke · Exertional heat stroke · Classic (non-exertional) heat stroke · Heat-related illness · Heatwave hyperthermia · Thermal injury multi-organ failure

Heat stroke is a life-threatening hyperthermic emergency defined by CORE TEMPERATURE >40C with CENTRAL NERVOUS SYSTEM DYSFUNCTION (confusion, agitation, delirium, seizures, coma) — it is the severe end of the heat-illness spectrum beyond heat cramps and heat exhaustion. TWO SUBTYPES: (1) CLASSIC (non-exertional) — elderly, chronic disease, anticholinergic/diuretic drugs, poor ventilation/air-conditioning, occurs EPIDEMICALLY during heatwaves (2003 European heatwave: >70,000 deaths); anhidrosis common (thermoregulatory failure). (2) EXERTIONAL — young, fit individuals (athletes, military recruits, miners, firefighters) performing intense exercise in hot/humid conditions; sweating usually PRESENT (profuse); rhabdomyolysis, DIC, AKI and lactic acidosis more severe. PATHOPHYSIOLOGY: core temp >40C → PROTEIN DENATURATION + membrane lipid peroxidation → direct cytotoxicity → systemic inflammatory response syndrome (cytokine cascade, endothelial activation, complement) indistinguishable from sepsis → gut translocation, DIC, ARDS, AKI, acute liver injury (hepatocyte necrosis) and rhabdomyolysis — 'heat stroke is like SEPSIS from heat'. The thermoregulatory set-point is NORMAL (unlike fever) — so ANTIPYRETICS (paracetamol/NSAIDs) are INEFFECTIVE and DANTROLENE is INEFFECTIVE (randomised trial showed no benefit; not malignant hyperthermia). MANAGEMENT: RAPID COOLING is the 1 priority — ideal cooling rates exceed 0.16C/min (0.08-0.15C/min still acceptable); GOLD STANDARD for exertional = COLD-WATER IMMERSION (water 1-17C; mean 0.22C/min in the Falmouth Road Race series, where all 274 cases cooled on site survived) — start ON-SITE before transport; alternatives: evaporative plus convective cooling (continual dousing + fanning — best-evidenced for classic), tarp-assisted cooling (~0.14C/min) when no tub is available, chilled IV crystalloid (30 mL/kg at 4C — supplement only), ice packs applied diffusely (strategic neck-axilla-groin packs NOT recommended as primary). No evidence-based endpoint temperature for cessation exists — in practice stop active cooling once core is below about 39C (hypothermia can occur during recovery). Control shivering (it hampers cooling — counter-warming, sedation). Treat complications: IV fluids for dehydration, lung-protective ventilation for ARDS, RRT for AKI, manage DIC, monitor CK/electrolytes for rhabdomyolysis. PROGNOSIS: classic high mortality (worse with age/comorbidity, Argaud Lyon cohort 28-day mortality 58%, 2-year 71%); exertional near-zero fatalities with immediate on-site immersion. Permanent cerebellar ataxia (Purkinje cell injury) is a classic sequela.