Heatstroke

Cool first. Transport second. In that order, not the other way round.

ACT

The sign that decides everything: altered consciousness. Confusion, incoherent speech, odd behaviour, unusual aggression, staggering, drowsiness. Combined with burning-hot skin, it's heatstroke, and it's life-threatening.

1. Get the person out of the heat. Shade, a cool indoor space, a draught. Immediately.
2. Undress them. Every layer removed is heat that can finally escape.
3. Cool them hard, right now, on the spot. Immersing the whole body in the coldest water available, with the head held above water, is the reference method. A river, a bathtub, a basin, a drinking trough, a container. Keep stirring the water around the body: water that sits against the skin warms up and stops cooling.
4. If immersion is impossible, combine everything you have: continuous dousing, wet cloths changed non-stop, strong fanning, cold packs on the neck, armpits and groin. It's much less effective, so you have to do much more of it.
5. Have someone call for help while you cool them, never instead of cooling.
6. Stop active cooling when the person becomes clear-headed again and their skin is clearly cooler, or after about fifteen minutes if you can't measure anything. The goal is to get back below 39 °C (102 °F).
7. Only give them something to drink if their consciousness is completely normal and they aren't vomiting. Otherwise, nothing by mouth.

Don't transport them before cooling them, unless the transport itself lets you keep cooling. It's the major reversal in recent guidelines: time spent moving without cooling is time lost, and it's the time spent above the critical threshold that determines lasting damage.

Two exceptions to immersion: cardiac arrest, where resuscitation comes first, and seizures, where immersion becomes dangerous.

ADAPT

It's exertional heatstroke. It strikes young, healthy people training or working, including in mild or cool weather. This is the form where cold-water immersion has the strongest evidence, and where speed changes everything: the data show excellent survival rates when the temperature is brought back below the critical threshold within the first half hour.

It's an elderly person during a heatwave. The deadliest form, and the quietest. They sweat less, feel less thirst, and can tip over without complaining first. New confusion is sometimes the only sign. Prevention means visiting regularly, not waiting for a call.

It isn't heatstroke yet. Cramps, headache, nausea, intense fatigue, heavy sweating but normal consciousness: that's heat exhaustion, serious but not yet critical. Rest in the shade, remove clothing, cool down, and drink small sips regularly. This is the stage where everything can still be stopped. The water must be safe: see Making water safe to drink.

The person loses consciousness. Move straight to Unconscious person: breathing comes before cooling.

You have almost no water. Wetting a piece of clothing and exposing it to the wind cools by evaporation with very little water. The effect is small but real, and it's what you have.

You have to keep moving in intense heat. Travel at dawn and dusk, rest through the hot hours in the shade and off ground that has heated up, cover up in loose, light-coloured clothing rather than stripping off, and drink before you're thirsty. These choices follow the same logic as Se déplacer de nuit.

UNDERSTAND

The body gets rid of heat mainly through the evaporation of sweat. This mechanism has two limits, and both are reached quickly.

Humidity. When the air is already saturated, sweat no longer evaporates: it drips. It then stops cooling entirely, while still draining the body of water. That's why humid heat is far more dangerous than dry heat at the same temperature.

Available water. Without rehydration, sweating drops and then stops. Skin that has become dry and burning hot in intense heat means the cooling system has stopped working. It's a major sign of severity.

Beyond a certain threshold, the body's proteins start to break down. The brain is affected first, hence the disturbed consciousness — which often comes before anyone measures the temperature, and is the best warning sign available without a thermometer.

What determines lasting damage isn't the peak reached, but the time spent above the threshold. That explains the whole sheet: it isn't how powerful the cooling is that counts, it's how early it starts. Immersion far outperforms other methods because it cools several times faster than a wet cloth or an ice pack — water conducts heat about twenty-five times better than air, the same physical property that makes immersion so dangerous in Hypothermia, used this time in the right direction.