Exertional Heat Stroke: How to Recognise It and What to Do

Exertional heat stroke kills people who should have survived. Not because the condition is untreatable — it is, with near-100% survival when treated correctly — but because the right intervention is delayed, or the wrong one is used. Here is what the evidence says.

What is exertional heat stroke?

Exertional heat stroke (EHS) is a life-threatening emergency defined by a core body temperature above 40 °C combined with neurological dysfunction — confusion, ataxia, loss of consciousness, seizure. It differs from classic heat stroke in that it is triggered by intense physical exertion, regardless of ambient temperature. A runner in a 15 °C mountain race can develop EHS just as easily as a construction worker in a 40 °C industrial site.

EHS is not severe dehydration. It is not heat exhaustion. The mechanism is thermogenic: metabolic heat production overwhelms the body's thermoregulatory capacity, and core temperature escalates. Without immediate treatment, organ damage begins within minutes.

Clinical signs to recognise on the field

Identifying EHS quickly is critical. Watch for:

Confusion, disorientation, incoherent speech — the central neurological sign
Ataxia (unsteady gait, staggering, falling) — common in runners
Hot skin — sweating may be present or absent
Elevated heart rate, hypotension
Rectal temperature > 40 °C — the only reliable field measurement

Axillary or ear thermometry is not sufficient. The ACSM specifies that rectal thermometry is the gold standard for diagnosis and cooling monitoring in the field. If rectal temperature cannot be measured, treat as presumptive EHS if neurological signs are present.

Why the 30-minute window matters

Every minute above 40 °C accumulates organ damage. Walter & Carraretto (Critical Care, 2016) document the cascade: rhabdomyolysis, acute kidney injury, disseminated intravascular coagulation (DIC), hepatic failure, and irreversible cerebellar damage. The longer core temperature remains elevated, the less reversible the outcome.

The Korey Stringer Institute (Dr Douglas Casa, University of Connecticut) compiled data across 401 EHS cases treated with immediate cold water immersion: 100% survival when core temperature returned below 40 °C within 30 minutes. That rate falls significantly when cooling is delayed or inadequate.

The cooling options — and what the data says

Not all cooling methods are equivalent. The key metric is the cooling rate, expressed in degrees per minute.

Wet towels, ice packs, localised cold application Cooling rate: approximately 0.03 °C/min. Adequate for prevention and mild heat illness, not for EHS. Local vasoconstriction may even reduce heat transfer by limiting superficial blood flow.

Ice sheets / wet sheet method Cooling rate: 0.10–0.20 °C/min depending on body surface coverage. Better than ice packs, but still insufficient to bring a patient from 42–43 °C to below 40 °C within 30 minutes. Difficult to sustain in field conditions as sheets warm rapidly.

Evaporative cooling with forced ventilation Highly dependent on ambient humidity. In dry, windy conditions it can be reasonably effective. In hot, humid environments — precisely those most likely to produce EHS — effectiveness collapses. Not a reliable primary treatment.

Cold Water Immersion (CWI) Cooling rate: 0.35 °C/min (Casa DJ et al., Exercise and Sport Sciences Reviews, 2007). Water conducts heat approximately 25 times more effectively than air. Full-body immersion maximises the thermal exchange surface. This is the only method that reliably achieves the 30-minute target.

CWI is the unambiguous gold standard recommended by the ACSM (2023), the IOC (Hosokawa et al., BJSM 2021), and the SFAR. There is no evidence-based equivalent for EHS treatment.

The "Cool First, Transport Second" protocol

The most lethal mistake in EHS management is evacuating the patient before cooling. Every minute spent in an ambulance without immersion is a minute of ongoing organ damage.

The Cool First, Transport Second protocol, formalised by the ACSM and endorsed by the SFAR, is explicit: cool on site to 38.5 °C, then transport. Evacuation must never take priority over thermal treatment.

This requires that cooling equipment is available at the point of emergency — not only at the hospital. For event medical directors, fire & rescue teams, and EHS managers, this is a protocol and logistics question as much as a clinical one.

Bringing CWI to the field: the Kollder cooling tub

Cold water immersion has been the evidence-based standard for over two decades. The barrier to its widespread use has never been clinical — it has been operational. Standard immersion tubs are fixed, heavy, and infrastructure-dependent. They cannot follow athletes onto a mountain trail, be deployed at an industrial incident, or be staged at a field medical post.

The Kollder emergency cooling tub addresses this directly: a portable PVC and aluminium-frame tub (205 × 65 × 35 cm deployed) that is operational in under 30 seconds by a single person, on any terrain. It allows full patient immersion with complete medical access — rectal thermometry, IV access, airway management — without interrupting the cooling process.

For event medical directors, SDIS teams, military medical units, or industrial EHS managers looking to apply the recommended protocol in the field: kollder.com/#contact