First aid treatment for heat exhaustion is a critical intervention.

Heat exhaustion is a precursor to the more serious, life-threatening type of heat-induced illness, heat stroke.

First Aid treatment for heat exhaustion is aimed at cooling the body in order to prevent heat stroke where brain damage, as well as damage to other vital organs, even death, can result. Exposure to high temperatures and humidity can induce heat cramps, heat exhaustion and/or heat stroke.

The optimum temperature in the human body is 36–37º C. Excessive variation to this will have detrimental effects.

What is heat exhaustion?

Heat exhaustion is caused by exertion accompanied by heat, high humidity and, often, dehydration.

[Heat exhaustion, unlike heat stroke, does not cause impaired mental function, confusion, or loss of consciousness. Internal body temperature does not go above 39° C (102°F).]

There are two types of heat exhaustion:

Water depletion – indicated by excessive thirst, weakness, headache, loss of consciousness. Salt depletion – indicated by nausea, vomiting, muscle cramps, dizziness. The body’s core temperature (internal temperature) is determined by factoring in the environmental heat and the body’s temperature. The normal core temperature is approximately 37° C (98.6° F). To maintain this, the body needs to regulate the heat gain from the environment (in cold weather, heat loss). Sweating — specifically the evaporation of sweat — is the body’s way of cooling itself. Hot, humid weather is not conducive to sweat evaporating, so the body is less able to cool itself efficiently, following over-exertion. Potential complications of heat exhaustion include:

• Severe kidney injury
• Rhabdomyolysis, which can cause kidney failure, tea-coloured urine from an increase in the muscle protein myoglobin, irregular heartbeat, muscle pain, vomiting
• Liver failure
• Arrhythmia – a heartbeat that is too fast or too slow
• Delirium or coma

Causes of Heat Exhaustion

The reason for frequent cases of heat exhaustion in urban areas during hot weather is that air quality is compromised in built-up areas where atmospheric conditions tend to stagnate. Night times offer little relief, as the heat continues to radiate from the concrete and asphalt.

To combat internal heat, the body will normally pump blood to the skin and release sweat. But the body’s ability to cool itself by sweating is hampered by summer humidity, as the already moist air is unable to absorb sweat from the skin.

The ability to sweat is reduced in a person who is dehydrated because they will be lacking in both the water and essential salts (electrolytes) to sweat. This inability to cool down by sweating can lead to heat exhaustion.

Heat Exhaustion Risk Factors

• High humidity – usually over 60%
• Liver or kidney conditions
• Intense physical work
• Underlying conditions that increase the chance of dehydration, such as diabetes or hyperglycaemia
• Injuries where part of the body is pinned down or compressed (crush injuries)
• Drug abuse

Age is another risk factor in heat-related illness. Adults over age 65, as well as infants and children up to age 4, are vulnerable. In the young, the body's ability to regulate its temperature isn’t fully developed. And in older adults, this ability is often eroded by illness, medications, or other factors. People who are unaccustomed to heat will be more susceptible to heat-related illnesses, such as heat exhaustion.

An early heatwave doesn’t offer an opportunity to acclimatise to higher temperatures. So too does travelling from a cold climate to a warm one increase the risk of heat-related illness. Also at risk are people who are sunburnt, underweight, or obese. Obesity affects the body’s ability to regulate its temperature and can cause it to retain more heat. Risk also increases with health conditions, such as diabetes, high blood pressure, sickle cell trait, and heart, lung, or kidney disease. Diabetics are notorious for underestimating their risk during heatwaves and can quickly find themselves in the emergency rooms. Other risk factors include alcoholism, mental illness, and conditions that cause fever.

The risk of heat-related illness is also increased by the following classes of medications:

• Beta blockers, diuretics for heart and blood pressure
• Antipsychotics for psychiatric conditions
• Antihistamines for reducing allergy symptoms
• Sedatives & stimulants

These are medications that affect the body’s ability to stay hydrated and to respond to heat appropriately. Illegal drugs, such as cocaine and amphetamines, can increase the body’s core temperature.

What are the symptoms of heat exhaustion?

Common signs of heat exhaustion include:

• irritable or aggressive behaviour
• rapid, shallow breathing
• red, flushed face
• cold, pale, damp skin, sometimes goosebumps
• nausea & vomiting
• excessive sweating
• cramps
• increased internal body temperature
• muscle weakness
• weak, rapid pulse
• headache
• low blood pressure or light-headedness when standing or bending over
• dizziness

Children who are old enough, might complain of stomach or leg cramps. Treat a child with heat exhaustion immediately.

How to treat heat exhaustion

Seek immediate medical attention if the person becomes confused or agitated, loses consciousness, or is unable to drink. Immediate cooling and urgent medical attention is essential if core body temperature (measured by a rectal thermometer) reaches or exceeds 40° C (104° F).

A person experiencing heat exhaustion should:

• Stop all activity & rest in a cooler place. An air-conditioned room is best for getting out of the heat and resting. If that’s not an option, find the nearest cool, shady place.
• Strip off excess clothing.
• Soak or spray with cool or cold water and if available, apply wrapped ice packs to the head, neck, groin and armpits.
• Fan vigorously, using whatever you can grab, e.g. a printed publication, a flipper (swimmer’s fin), a clipboard. While doing so, mist with cool water.
• Immerse. The most effective cooling means will be cool or ice-water immersion. Immerse the casualty up to their neck in a cool or ice bath (must be held at all times by multiple people to ensure airway) OR
• Cover all of their body with ice-soaked towels, swapping them frequently with fresh cold towels.
• Drink cool water or sports drinks once vomiting has ceased.
• Call 000 or 112 for emergency services if symptoms do not improve after 10 minutes of cooling treatment.

How long does heat exhaustion last?

Recovery, following quick and effective heat stroke treatment, will usually take a day or two in hospital. Generally there are few problems afterwards, although some heat stroke sufferers may be left with increased sensitivity to hot weather.

If organ damage is detected, recovery from heat stroke will be considerably longer. It may take 2 months to a year. This damage is caused by swelling and ranges from fair to poor. As complications increase, the prognosis changes dramatically for the worse. When permanent damage has impacted the brain, the lungs, liver, kidneys, the effects will be long-term.

How to prevent heat exhaustion

Staying hydrated and cool is the golden rule. Drink plenty of water or eletrolyte sports drink.

Making your own oral-rehydration solution is simple. Boil 5 cups (1 litre) of water then stir in 6 teaspoons of sugar and ½ teaspoon of table salt. Cool before drinking. Add flavourings, if you wish, in the form of fruit juices, honey, maple syrup.

Some rehydrating drinks and foods include:

• Banana puree mixed with water
• Carrot soup
• Fresh fruit juices, ideally orange, pear, peach
• Green coconut water
• Gruel (cooked cereal + water)
• Rice water or congee
• Weak, non-caffeinated tea

When the heat index is 33° C (91° F) or higher, it’s best to take precautions to keep cool. Stay inside in air conditioning if you can.

If you take medications, have a condition that increases your risk of heat-related problems, or a history of previous heat illness, be cautious. Avoid the heat and act quickly if you notice symptoms of overheating. Take it easy during the hottest times of the day. If you can’t avoid strenuous activity in hot weather, drink fluids and rest frequently in a cool spot.

Get acclimated. It can take several weeks for your body to adjust to hot weather. Do not leave anyone in a parked car in warm or hot weather, even if the windows are cracked or the car is in shade. The temperature in a car parked in the sun, can rise more than 11° C (20° F) in 10 minutes.

This is a common cause of heat-related deaths in children. Lock your car to prevent a child from getting inside. Schedule any strenuous activity for the early morning or evening. Stay hydrated when working in hot, humid environments, such as factories, laundry facilities, and kitchens. If you must go outdoors, wear lightweight, loose-fitting, light-coloured clothing and a wide-brimmed hat. Use sunscreen with an SPF of 30 or more. If strenuous sporting events or activities take place in hot weather, make sure medical services are available in case of a heat emergency. Drink extra fluids to prevent dehydration — water, fruit juice, or vegetable juice. During periods of extreme heat and humidity, an electrolyte-rich sports drink may be advisable to counter salt depletion. Your doctor can advise the best types of fluid and how much you should be drinking.

A general recommendation for people doing moderate- to high-intensity exercise, is to drink around half a litre of fluid, 2 to 3 hours before exercise. Consider adding a further quarter-litre of water or sports drink right before exercise.

During exercise, whether thirsty or not, around half a litre of should be consumed every 20 minutes. Drink a further quarter-litre of water or sports drink within a half hour after exercise. Be especially alert if you take medications that can affect your body's ability to stay hydrated and dissipate heat. People who are on fluid-restricted diets, or have a problem with fluid retention, should check with their doctor before increasing their fluid intake. The same applies to those who have have epilepsy or severe heart, kidney, or liver disease.

Avoid drinks containing caffeine or alcohol. Both substances will dehydrate and encourage heat exhaustion.

Disclaimer:This article is for informational purposes only. It does not constitute, replace, or qualify as any form of first aid training.

Other Resources

• Dehydration First Aid
• Heat-Induced Illness Poster
• Heat Cramps First Aid
• Heat Stroke First Aid