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Q1: Definition and spectrum (2 min)
"Define heat stroke and place it in the heat-illness spectrum."
- Definition: core temperature above 40 degrees C (104 F) with central-nervous-system dysfunction (confusion, agitation, ataxia, seizures, coma), with or without anhidrosis and multi-organ failure.
- Spectrum: heat cramps (painful muscle cramps, afebrile, intact mental state) → heat exhaustion (core 37 to 40 C, sweating, headache, intact mental state, no end-organ damage) → heat stroke (core above 40 C + CNS dysfunction).
- The mental state and the temperature threshold are the lines — cross either and it is heat stroke.
- Key concept: heat stroke is a HYPERTHERMIA, not a fever — the hypothalamic set-point is normal — which is why antipyretics are useless.
Q2: Classic vs exertional (3 min)
"Distinguish classic from exertional heat stroke and tell me why it matters."
- Classic (non-exertional, epidemic): elderly, chronically ill, socially isolated; during heatwaves; polypharmacy (anticholinergics, diuretics, beta-blockers, antipsychotics); hot dry skin (anhidrosis); gradual onset; predominant complications DIC, hepatic, CNS; mortality over 50 per cent untreated. Cooling: evaporative (spray + fans).
- Exertional: young, fit; strenuous exercise in heat (athletes, military, firefighters); sweating often still present (early); abrupt collapse; predominant complications rhabdomyolysis, AKI, hyperkalaemia, hypoglycaemia; mortality under 5 per cent if cooled within 30 minutes. Cooling: cold-water immersion (gold standard).
- Why it matters: the cooling method follows the type; the population you screen differs; and a sweating athlete can still have exertional heat stroke (don't wait for anhidrosis).
- Drug precipitants: impair heat loss (anticholinergics, antipsychotics, beta-blockers, diuretics) vs increase heat production (MDMA, amphetamine, cocaine, salicylates).
Q3: Pathophysiology (3 min)
"Walk me through how heat stroke causes multi-organ failure."
- Heat-balance failure: environmental heat gain plus endogenous heat production exceed heat-loss capacity. Once ambient temperature exceeds body temperature, radiation/convection reverse into heat GAIN; high humidity abolishes evaporation (the main route in heat); wet-bulb above ~35 C is unsurvivable.
- Two-hit pathogenesis: (1) DIRECT HEAT INJURY — protein denaturation and lipid peroxidation above 41 to 42 C, mitochondrial failure; (2) SYSTEMIC INFLAMMATORY RESPONSE — intense splanchnic vasoconstriction → gut mucosal ischaemia → bacterial endotoxin translocation → cytokine storm (IL-1, IL-6, TNF-alpha) → a sepsis-like syndrome.
- Organ-specific: brain (heat-sensitive cerebellar Purkinje cells → ataxia), liver (centrilobular necrosis, transaminitis over 1,000), muscle (rhabdomyolysis, CK often over 1,000), kidney (acute tubular necrosis from myoglobin + hypovolaemia), coagulation (DIC, peaks 24 to 48 h), heart (arrhythmia, ischaemia), lung (ARDS).
- This is why the duration of hyperthermia predicts mortality — minutes matter.
Q4: Resuscitation and cooling (3 min)
"A collapsed athlete, core 41.5 C. Take me through your management."
- Cool first, transport second — begin cooling on site within 30 minutes; do NOT wait for tests/ICU/IV access.
- ABCDE: oxygen, IV access, intubate for coma/seizures; check capillary glucose (hypoglycaemia common in exertional); cooled IV fluids (4 C saline 30 mL/kg) titrated to BP and urine output.
- Cooling method: COLD-WATER IMMERSION (gold standard for exertional) — 2 to 15 C circulated water to the neck, agitate the water, monitor rectal temp continuously; rate 0.15 to 0.35 C/min; survival near 100% within 30 min. For classic heat stroke use EVAPORATIVE cooling (strip, spray lukewarm water + continuous fanning) — better tolerated in the elderly.
- TARGET: cool to below 39 C then STOP — avoid overshoot hypothermia.
- Seizures/agitation: IV lorazepam 4 mg or diazepam 10 mg — also suppresses shivering (which generates heat). Shivering counter-productive — suppress with benzodiazepines.
- Antipyretics and dantrolene do NOT work — no prostaglandin target, no trial benefit.
Q5: Complications, prognosis and pitfalls (3 min)
"Name the complications, the determinants of outcome, and three pitfalls."
- Complications: brain (cerebellar ataxia — may be permanent, seizures, coma), liver (acute liver failure), kidney (AKI), muscle (rhabdomyolysis, compartment syndrome), blood (DIC), heart (arrhythmia), lung (ARDS).
- Complications of cooling: overshoot hypothermia (stop at 39 C), shivering (suppress), cold-induced arrhythmia.
- Determinants of outcome: depth and DURATION of hyperthermia (strongest), speed of cooling, age/comorbidity, degree of multi-organ failure. Untreated classic over 50% mortality; exertional cooled within 30 min under 5%.
- Three pitfalls: (1) relying on oral/tympanic/temporal temperature (under-reads, misses the diagnosis — use rectal/core); (2) delaying cooling to wait for tests; (3) requiring anhidrosis for the diagnosis (exertional often still sweating). Others: giving antipyretics/dantrolene; missing the elderly 'confused' heatwave patient; not searching for precipitants (infection, drugs, dehydration).