Overview
Heatstroke is a life-threatening emergency in which the body's temperature regulation fails and core body temperature rises to dangerous levels above 40°C. Unlike heat exhaustion, heatstroke causes confusion, loss of consciousness, and organ damage. It can be fatal without immediate treatment.
How common is it?
Heatstroke is uncommon in the UK but significant numbers of heat-related deaths occur during hot weather events. The elderly, young children, and athletes are at highest risk.
Causes and risk factors
The body normally loses heat through sweating and increased blood flow to the skin. In heatstroke, these mechanisms fail, either due to overwhelming heat exposure (classic heatstroke) or extreme physical exertion in heat (exertional heatstroke).
Common risk factors
- Extreme ambient temperature
- High humidity (prevents effective sweating)
- Strenuous exercise in hot conditions
- Age extremes (infants and elderly)
- Dehydration
- Medications: diuretics, anticholinergics, antipsychotics, some recreational drugs
- Obesity
- Previous history of heatstroke
Symptoms
- High body temperature above 40°C
- Hot, dry skin (in classic heatstroke) or wet skin (exertional)
- Confusion, disorientation, or bizarre behaviour
- Unconsciousness or seizure
- Nausea and vomiting
- Rapid, shallow breathing
- Rapid heartbeat
When to see a doctor
Call 999 immediately. Heatstroke is a medical emergency. Begin cooling the person immediately while waiting for emergency services.
Diagnosis
Clinical diagnosis in context of heat exposure. Rectal temperature measurement confirms hyperthermia. Blood tests assess organ function (kidney, liver, clotting), electrolytes, and blood glucose.
Treatments
Immediate aggressive cooling
Immersion in cold or ice water is the most effective cooling method. Evaporative cooling (wet skin with fanning) is used where immersion is not possible. Target temperature below 39°C within 30 minutes.
Intravenous fluid resuscitation
IV fluids correct dehydration and support blood pressure. Cooled IV saline provides additional cooling benefit.
Hospital monitoring and organ support
ICU monitoring for complications including rhabdomyolysis (muscle breakdown), kidney failure, coagulopathy, and liver damage.
Self-care and lifestyle
- Drink plenty of water before, during, and after physical activity in heat
- Avoid strenuous outdoor exercise during the hottest part of the day (10am to 4pm)
- Never leave children or pets in a car on warm days
- Acclimatise gradually to hot environments over 1 to 2 weeks
Prevention
Stay hydrated, avoid peak heat hours, wear light loose clothing, use air conditioning or fans, and check on elderly neighbours and relatives during hot weather spells.