Heat Stroke

Heat stroke first aid: cool first

1. Call 911 or your local emergency number.
2. Move the person into shade or air conditioning and remove excess clothing and equipment.
3. Cool them as fast as possible, aiming to bring temperature below about 39 °C (102 °F) within 30 minutes. The best method is to immerse the body up to the neck in a tub of cold or ice water, keeping the head supported. If there is no tub, rotate cold, wet towels or ice-water-soaked sheets over the whole body, put ice packs on the neck, armpits and groin, and fan while spraying with water.
4. Do not give anything to drink if the person is confused or not fully alert.
5. Place them on their side if they vomit or are unresponsive. Start CPR if they stop breathing.
6. Do not give acetaminophen (paracetamol) or aspirin. They do not lower heat stroke temperature and can harm the liver or worsen bleeding.

For exertional heat stroke, medical teams follow the principle "cool first, transport second" when cold water immersion is available on site, because each minute of high temperature adds to organ damage.

Heat stroke vs heat exhaustion

The defining difference is brain involvement. Any confusion in the heat should be treated as heat stroke.

Types of heat stroke

Classic (non-exertional) heat stroke

Develops over days during heat waves, mainly in:

• adults over 65
• infants and young children
• people with heart, lung or kidney disease, diabetes, obesity or dementia
• people who live alone, lack air conditioning, or are bedbound
• people taking medicines that impair heat loss (diuretics, beta blockers, anticholinergics, antipsychotics, some antidepressants)

Exertional heat stroke

Develops within hours during intense exercise or work in hot, humid conditions, in otherwise healthy people:

• athletes, especially football players in early-season practices and distance runners
• military recruits
• outdoor workers in construction and agriculture

Risk is higher with poor acclimatization, heavy clothing or gear, dehydration, recent illness, sleep deprivation, alcohol, and stimulants such as amphetamines.

Symptoms

• body temperature of 40 °C (104 °F) or higher
• confusion, disorientation, agitation or strange behavior
• slurred speech, unsteadiness
• seizures
• loss of consciousness
• hot, red skin, dry or sweating
• rapid, strong or weak pulse
• fast breathing
• headache, nausea and vomiting

What happens in the body

At very high temperatures, proteins and cell membranes are damaged, the gut lining leaks bacterial toxins into the blood, and widespread inflammation follows. This can cause:

• brain swelling and lasting neurological injury
• rhabdomyolysis (muscle breakdown)
• acute kidney injury
• liver failure
• disseminated intravascular coagulation (clotting and bleeding)
• heart damage and abnormal rhythms
• death, particularly with delayed cooling

Hospital treatment

• rapid cooling continued with immersion, evaporative cooling or cooling devices
• core temperature monitoring with a rectal or esophageal probe
• IV fluids with careful electrolyte management, including checking for low sodium from overdrinking
• treatment of seizures with benzodiazepines
• blood tests for kidney, liver, muscle and clotting damage
• intensive care support for organ failure

Recovery

Most people who are cooled quickly recover fully. Some have heat sensitivity for months. Athletes and workers should return to activity gradually under medical guidance, often over several weeks, with acclimatization. Prolonged high temperature before cooling raises the risk of lasting brain injury.

Prevention

• During heat waves, stay in air conditioning or visit a cooling center. Fans alone do not prevent heat illness when temperatures are very high.
• Check on older relatives and neighbors at least twice a day.
• Never leave children, older adults or pets in a parked car, even briefly.
• Drink fluids regularly, but do not overdrink. Watch urine color.
• Wear light, loose clothing and a hat. Schedule exercise and work for cooler hours.
• Acclimatize: increase activity in the heat gradually over 10 to 14 days.
• Follow work-rest cycles and heat safety plans at work and in sports.
• Ask your doctor whether any of your medicines increase heat risk.

Frequently asked questions

What are the signs of heat stroke?

The key signs are a very high body temperature, at or above 40 °C (104 °F), and changes in mental state: confusion, agitation, slurred speech, unsteadiness, seizures or collapse. The skin is usually hot and may be dry or sweaty. The pulse and breathing are fast.

What is the difference between heat stroke and heat exhaustion?

Heat exhaustion causes heavy sweating, weakness, dizziness, nausea and headache, with a normal mental state. Heat stroke involves a higher temperature and brain dysfunction such as confusion or collapse. Heat exhaustion can progress to heat stroke if the person is not cooled.

What should you do for someone with heat stroke?

Call 911 and start cooling immediately. The most effective method is immersing the body in cold or ice water. If that is not possible, use cold wet towels, ice packs on the neck, armpits and groin, and fanning. Do not give fluids if they are confused.

How long does it take to recover from heat stroke?

People who are cooled rapidly often recover within days. Others need longer hospital care for kidney, liver or muscle damage. Return to strenuous activity is usually gradual over weeks. Some people have lasting heat intolerance or neurological effects.

Who is most at risk of heat stroke?

Older adults, infants, people with chronic illnesses, people taking certain medicines, those without air conditioning, and people who exercise or work hard in the heat, especially if they are not acclimatized, are most at risk.