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A 21-year-old army recruit collapses 8 km into a route march on a 39-degree-C afternoon in May. On arrival at the medical tent he is confused, aggressive and ataxic. Core (rectal) temperature is 41.4 degrees C, pulse 132 per minute, blood pressure 92/54, respiratory rate 28, SpO2 96 per cent on room air. His skin is hot and he is still sweating profusely. Capillary glucose is 2.6 mmol/L. A rectal thermistor is in place and an ice-water tub is available on site.
Questions
a) What is the diagnosis, and why is the profuse sweating NOT against it? (2 marks)
Diagnosis: exertional heat stroke — core temperature above 40 degrees C (41.4 C) WITH central nervous system dysfunction (confusion, aggression, ataxia), during strenuous exertion in heat.
Profuse sweating is not against the diagnosis: in early exertional heat stroke the athlete is often still sweating at the moment of collapse. Anhidrosis (hot dry skin) is the textbook picture of classic heat stroke late in its course, but it is NOT required for the diagnosis. Waiting for dry skin is a classic lethal error. The ataxia reflects heat-sensitive cerebellar Purkinje-cell injury, an early hallmark.
b) Outline the immediate resuscitation, including the cooling method, the target, and the rule on transport. (4 marks)
Immediate bundle:
- Remove from the heat; remove all clothing. Protect the airway — he is confused and aggressive; prepare for possible intubation if his conscious level falls.
- High-flow oxygen; IV access.
- Check and correct hypoglycaemia — give IV dextrose (e.g. 50 mL of 50 per cent dextrose) for the 2.6 mmol/L reading; this is common in exertional heat stroke (glycogen depletion plus hepatic failure).
- RAPID COOLING by COLD-WATER IMMERSION — the gold standard for exertional heat stroke. Immerse in ice and water at 2 to 15 C up to the neck, circulate/agitate the water, and monitor core temperature continuously with the rectal probe. Cooling rate 0.15 to 0.35 C per minute.
- 'Cool first, transport second' — begin cooling on site within 30 minutes before transfer; survival approaches 100 per cent when cold-water immersion is begun within 30 minutes.
- Cooling TARGET: remove from the water when the core temperature reaches below 39 C (allow for a small afterdrop) then STOP active cooling to avoid overshoot hypothermia.
- Continuous core-temperature and ECG monitoring; IV fluids (cooled 0.9 per cent saline if available) titrated to blood pressure and urine output.
c) Explain why antipyretics (paracetamol, NSAIDs) and dantrolene are NOT used in heat stroke. (2 marks)
Heat stroke is a hyperthermia, not a pyrexia. In fever, pyrogens (IL-1, IL-6, TNF-alpha) drive prostaglandin-E2 synthesis in the hypothalamus, raising the thermoregulatory set-point, and antipyretics work by lowering it back via COX inhibition. In heat stroke the set-point is NORMAL — the body is doing everything it can to lose heat, but environmental heat gain plus endogenous heat production exceed its capacity. There is no prostaglandin excess to inhibit, so paracetamol and NSAIDs are inert (and paracetamol adds toxicity to a heat-injured liver).
Dantrolene (the ryanodine-receptor blocker effective in malignant hyperthermia) shows no outcome benefit in heat stroke in randomised trials, because heat stroke is not a primary calcium-mediated muscle syndrome. The only effective treatment is physical heat removal.
d) Over the next 12 hours he develops dark 'cola' urine, a creatine kinase of 52,000 U/L, and potassium of 6.9 mmol/L. Outline the management of these complications. (2 marks)
The picture is rhabdomyolysis with myoglobinuria and life-threatening hyperkalaemia (a hallmark of exertional heat stroke):
- Aggressive IV fluid resuscitation to a target urine output of 1 to 2 mL/kg/h to flush myoglobin and prevent cast nephropathy/acute tubular necrosis.
- Treat the hyperkalaemia immediately — calcium gluconate 10 mL of 10 per cent IV (membrane stabilisation), insulin-dextrose (10 units in 50 mL of 50 per cent dextrose IV), nebulised salbutamol 10 to 20 mg, and sodium bicarbonate if acidotic.
- Renal replacement therapy for established acute kidney injury or refractory hyperkalaemia.
- Serial monitoring of CK, potassium, creatinine and urine output; watch for compartment syndrome in severe rhabdomyolysis.