Exertional Heat Illness / Heat Stroke

A young athlete who collapses during exertion, confused and very hot, has exertional heat stroke until proven otherwise. Exertional heat stroke is the life-threatening end of the heat-illness spectrum: strenuous activity producing severe hyperthermia, with a core temperature over about forty degrees, together with central nervous system dysfunction - confusion, agitation, collapse or seizures. The CNS dysfunction with severe hyperthermia is what distinguishes it from heat exhaustion, which has relatively preserved mental status and a lower core temperature, and importantly exertional heat stroke can strike young, healthy individuals even in temperate climates, so I would not be falsely reassured by mild conditions. My immediate priority is rapid, aggressive cooling on site - the principle is 'cool first, transport second', because outcome is driven by how long the core temperature stays dangerously high. The gold-standard method is whole-body cold-water immersion, which I would start without delay and continue until a safe core temperature is reached, while securing the airway, breathing and circulation and measuring the core temperature, ideally rectally. I would only then transport. In hospital, care continues cooling if needed and manages the complications, which include acute kidney injury, coagulopathy, liver dysfunction, rhabdomyolysis and neurological injury. Prevention at events - acclimatisation, hydration, work-rest cycles and wet-bulb-globe-temperature-based heat policies - reduces the risk.