First Aid Certificate Training and Courses

Hyperthermia and Hypothermia Emergencies

Hypothermia and Hyperthermia Emergencies

Humans and other mammals are able to maintain a relatively constant body temperature despite widely ranging environmental temperatures. Although the average human body temperature is 36.7°C, this temperature varies depending on individual differences, time of day, the stage of sleep and the ovulatory cycle in women. Thermoregulation is the balance between heat production mechanisms and heat loss mechanisms that occur to maintain a constant body temperature. When the body is too hot, it decreases heat production and increases heat loss and when the body is too cold, it increases heat production and decreases heat loss. Body temperature is regulated by a system of sensors and controllers across the body that sends signals to the brain.


Hypothermia is a potentially life-threatening condition, which occurs when body temperature falls below 35°C. The normal function of most human body systems and organs requires the body’s temperature to be controlled within the narrow limits of 36.5°C to 37.5°C. As the body’s temperature falls, systems and organs progressively fail until death occurs, usually from cardiac arrest. Infants and elderly are at greater risk of developing hypothermia.

Common Causes of Hypothermia

Environmental – exposure to cold water and conditions.

Trauma – trauma, immobility, burns.

Systemic Illness – malnutrition, severe infections.

Neurological – stroke, altered consciousness.

Endocrine – impaired metabolism.

Drugs – alcohol, sedatives.

Mild Hypothermia


Pale, cool skin.

Impaired coordination.

Slurred speech.

Responsive but with apathy or confusion.

Slow pulse.

Infants will be quiet and refuse to eat.


Moderate to Severe Hypothermia

Reduced or absence of shivering.

Pale, cool skin becoming blue and cold.

Increasing muscle stiffness.

Progressive decrease in consciousness.

Slow irregular pulse.

Breathing is slow or not able to be detected.


Casualty may appear dead.

Call 000 for an ambulance urgently.

Remove from cold environment and protect from wind, rain, cold, wet ground.

Remove cold and wet clothing – do not remove if there is no other cover available.

Warm casualty by drying wet skin then wrapping in blanket, “space blanket”, sleeping bag.

If fully conscious, give warm fluids to drink (preferably sugary drinks).

DO NOT give alcohol.

If the casualty is not shivering, cautiously apply an external source of heat such as a heat pack or body to body contact. Ensure any heat source is only warm and not hot to avoid burns.

DO NOT place the casualty in a warm bath.

Be prepared for sudden collapse and the need to commence CPR.


Hyperthermia describes a group of heat illnesses that include dehydration, heat cramps, heat exhaustion and heat stroke.


On warm, humid or hot days:

Keep infants and the elderly in cool, ventilated areas and provide plenty of fluids.

Wear light coloured, loose-fitting clothing during physical activity.

Wear a hat when outside.

Consume plenty of fluids during exertion.

For participants in sporting events

Allow six weeks for acclimatisation with progressive exercise before competition.

Avoid vigorous exercise during a viral illness.

Plan events to be held in the early morning or late evening and in the cooler months of the year.

Provide regular water stations.

Never leave children and elderly persons unattended in parked cars.


Dehydration is when a casualty has an excessive loss of body fluid. This condition occurs when the amount of water leaving the body is greater than the amount being taken in. The percentage of the human body that is water varies between 55% to 78% depending on a person’s age and sex; this makes adequate consumption of water essential. The causes of dehydration include prolonged exposure to heat and humidity, diseases of the gastrointestinal tract that cause vomiting and/or diarrhoea, prolonged vigorous exercise (e.g. in a marathon), kidney disease and certain medications (diuretics). Although we lose water routinely a balance must be maintained to avoid dehydration which can lead to shock and be life-threatening particularly in young children and the elderly.

The body routinely loses water through:

Breathing and humidified air leaving the body.

Perspiring to cool the body.

Urination or having a bowel movement to rid the body of waste products.

Follow the DRSABCD emergency action plan.

Cease activity and remove from hot environment.

Rest in shade.

Remove unnecessary clothing.

Give cool sips of water.

Seek medical advice once recovered.

If casualty does not improve or condition deteriorates call 000 for an ambulance.

Heat Cramps

Heat cramps are painful muscle spasms in the abdomen, arms or legs following strenuous activity. Heat cramps often are caused by a lack of salt in the body, but salt replacement should not be considered without advice from a medical professional. Heat cramps usually affect people who sweat a lot during strenuous activity. The sweating depletes the body’s salt and moisture. Heat cramps may also be a symptom of heat exhaustion.

Painful muscle cramps in the limbs or abdomen.

Uncontrolled spasms of affected limbs.

Pale, clammy skin.

Nausea and/or vomiting.

Tiredness, dizziness or weakness.

Sweating if associated with exertion.

Cease activity and remove casualty to a cool place to rest.

Lay the casualty down with legs slightly elevated.

Gently stretch the affected muscles.

Remove unnecessary clothing.

Apply a cold compress to affected muscles.

Replace lost fluid with sips of cool water; give slowly if casualty is nauseated.

DO NOT rub or massage the affected limb.

DO NOT perform any further exercise.

Heat Exhaustion

Heat exhaustion is the body’s response to an excessive loss of water and salt contained in sweat. It is a warning that the body is getting too hot and generally develops after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. Those most susceptible to heat exhaustion are elderly people, people with high blood pressure and people working or exercising in a hot environment.

Cramps in the limbs and/or abdomen.

Profuse and prolonged sweating.

Persistent headache.

Thirst, nausea and/or vomiting.

Giddiness and fainting.

Exhaustion and lethargy.

Rapid breathing and shortness of breath.

Pale, cool, clammy skin.

Rapid, weak pulse.


  Follow the DRSABCD emergency action plan.

Remove casualty to a cool environment to rest.

Lay the casualty down.

Reassure the casualty.

Remove unnecessary clothing.

Moisten the skin with a moist cloth or atomiser spray.

Cool by fanning.

Give frequent small sips of water if fully conscious and not nauseated.

Call 000 for an ambulance.

Monitor the casualty, if casualty becomes unconscious follow DRSABCD.

If dehydration or heat exhaustion is left untreated they may lead to heatstroke.

Heat Stroke

Heat stroke is a form of hyperthermia, an abnormally elevated body temperature with accompanying physical and neurological symptoms. Unlike heat cramps and heat exhaustion, heat stroke is a true medical emergency that can be life-threatening if not treated promptly and appropriately.

The body normally generates heat as a result of metabolism, and is usually able to dissipate the heat by either radiation of heat through the skin or by evaporation of sweat. However, in extreme heat, high humidity, or vigorous exertion under the sun, the body may not be able to dissipate the heat and the body temperature rises, sometimes up to 41.1°C or higher. Another cause of heat stroke is dehydration. A dehydrated person may not be able to sweat fast enough to dissipate heat, which causes the body temperature to rise.

Heat Stroke can be caused by:

Hot climates.

Infection and illnesses.

Insufficient fluid intake.

Overdressing for the climate.

Physical exercise.


Nausea and/or vomiting

Flushed, hot, dry skin (no sweating).


Visual disturbances.

Irritability, mental confusion, aggression.

Staggering gait, fatigue.



Body temperature 40°C or more.

Strong pounding rapid pulse, gradually weakening.

Collapse, unconsciousness leading to coma.

Call 000 for an ambulance urgently.

Follow the DRSABCD emergency action plan.

Remove casualty to a cool environment to rest.

Loosen and remove any unnecessary clothing.

Moisten the skin with a moist cloth (cover with a wet sheet) or atomiser spray and fan repeatedly.

Apply wrapped ice packs to neck, groin and armpits.

Continue until body feels cool to the touch, and then stop.

Give casualty sips of cool fluid if fully conscious. DO NOT give if the casualty is semi-conscious or unconscious. Re-hydration will need to be via intravenous fluids administered by the ambulance or medical personnel.

Monitor the casualty and be prepared to commence CPR.

Scroll to Top