Hypothermia

Page last reviewed: 13/07/2011

Hypothermia occurs when a person's normal body temperature of around 37°C (98.6°F) drops below 35°C (95°F).

It is usually caused by being in a cold environment. It can be triggered by a combination of things, including prolonged exposure to cold (such as staying outdoors in cold conditions or in a poorly heated room for a long time), rain, wind, sweat, inactivity or being in cold water.

Types of hypothermia

There are different types of hypothermia, which depend on how quickly the body loses heat.

  • Acute or immersion hypothermia occurs when a person loses heat very rapidly, for example by falling into cold water.
  • Exhaustion hypothermia occurs when a persons body is so tired it can no longer generate heat.
  • Chronic hypothermia is when heat loss occurs slowly over time. This is common in elderly people living in a poorly heated house, or in people sleeping rough.

When your body gets cold, the normal response is to warm up by becoming more active, putting on more layers or moving indoors. But if exposure to the cold continues, your body's automatic defence system will try to prevent any further heat loss by:

  • shivering (which keeps the major organs at normal temperature),
  • restricting blood flow to the skin, and
  • releasing hormones to generate heat.

After prolonged exposure to the cold, these responses are not enough to maintain body temperature, as they also drain energy.

When the body's energy is exhausted, it slowly starts to shut down. Shivering stops and your heartbeat begins to slow. This life-threatening stage can develop very quickly, so it is vital that hypothermia is treated as a medical emergency.

 

Who is most at risk?

Elderly people and those who are ill and unable to move around easily are especially vulnerable to hypothermia. This can be due to poorly heated accommodation, not eating enough or not being active enough to generate energy.

People who spend a lot of time in extreme weather conditions, such as climbers and skiers, are at a higher risk, especially if they are not wearing suitable clothing.

Babies are also more prone to hypothermia because their body's ability to regulate its temperature is not fully developed. They lose heat quickly if left in a cold room for too long.

Blood

Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

Page last reviewed: 13/07/2011

The symptoms of hypothermia depend on how cold the environment is and how long you are exposed for.

Severe hypothermia needs urgent medical treatment in hospital. Shivering is a good guide to how severe the condition is. If the person can stop shivering on their own, the hypothermia is mild, but if they cannot stop shivering, it is moderate to severe.

Mild cases

In mild cases, symptoms include:

  • shivering,
  • feeling cold,
  • low energy, or 
  • cold, pale skin

Moderate cases

The symptoms of moderate hypothermia include:

  • violent, uncontrollable shivering,
  • being unable to think or pay attention,
  • confusion (some people don't realise they are affected),
  • loss of judgement and reasoning,
  • difficulty moving around or stumbling (weakness),
  • feeling afraid,
  • memory loss,
  • fumbling hands and loss of coordination,
  • drowsiness,
  • slurred speech,
  • listlessness and indifference, or
  • slow, shallow breathing and a weak pulse.

Severe cases

The symptoms of severe hypothermia include:

  • loss of control of hands, feet, and limbs,
  • uncontrollable shivering that suddenly stops,
  • unconsciousness,
  • shallow or no breathing,
  • weak, irregular or no pulse,
  • stiff muscles, and
  • dilated pupils.

Babies with hypothermia may look healthy but their skin will feel cold. They may also be limp, unusually quiet and refuse to feed.

Although hypothermia is defined as occuring when the body temperature drops below 35°C (95°F), mild hypothermia can start at higher body temperatures.

Glossary

Drowsiness
Drowsiness is when someone feels extremely tired and uncontrollably near to sleep.

Page last reviewed: 13/07/2011

Hypothermia is caused by getting too cold. The body loses more heat than it can generate and the body temperature drops below 35°C (95°F).

This is most common in cold environments, and the risk is increased if you are not wearing enough layers to keep warm, or do not have your head covered (a large amount of body heat is lost through your head).

Hypothermia is also possible in mild weather. For example, if you get soaked in a rain shower and do not dry off properly soon afterwards, particularly if there is also a cool wind. The water evaporating from your skin brings down your body temperature.

Certain groups are at a higher risk of hypothermia:

  • Babies, who can lose heat quickly if left in a cold room. This is because they cannot regulate their body temperature as well as older children and adults.
  • People who spend a lot of time in extreme weather conditions, such as climbers, walkers and skiers.
  • Older people, particularly if they are not very active, do not eat enough, have other illnesses or take medication that can interfere with the body's ability to regulate temperature.
  • Homeless people who are unable to find shelter.
  • Heavy drug and/or alcohol users, as these substances affect your body's ability to retain heat. The blood vessels stay dilated (widened), allowing heat to escape. You may not be able to tell when you are cold.
  • People with mental illnesses such as Alzheimer's disease may not be able to recognise the symptoms of hypothermia or when they are cold.
  • People who have fallen into cold water, which can cause the body's core temperature to drop very quickly.
  • People recovering from accidents.
  • People with certain health conditions, such as heart problems, untreated hypothyroidism, a stroke and severe arthritis. These conditions can change the body's ability to respond to temperature changes, for example by affecting the fingers and toes (where you may first feel cold).
  • People taking sedatives, which can interfere with the body's ability to regulate temperature.

Perioperative hypothermia

It is also possible for hypothermia to occur during operations, when a person is under general anaesthetic and the body is unable to regulate its own temperature. This is known as perioperative hypothermia. It is defined as a temperature at or below 36ºC.

It is quite common during operations for patients to drop below this temperature even though healthcare staff follow guidelines to try to ensure all patients are kept warm. But it is very unusual for patients' bodies to become as cold as 35ºC.

Deliberate hypothermia

In some cases hypothermia is induced deliberately as a treatment. There is evidence to suggest that, in some circumstances, inducing a state of hypothermia in the body can reduce the risk of death and increase the chances of a good recovery. This includes patients who have brain injuries or who have had severe heart attacks and are in a coma.

Glossary

Blood vessels
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
Heart
The heart is a muscular organ that pumps blood around the body.

Page last reviewed: 13/07/2011

Hypothermia is usually diagnosed on the basis of typical symptoms and environment. If a person has been exposed to cold, is distressed or confused and has slow, shallow breathing, you should suspect hypothermia and get medical help urgently.

If your child is unusually quiet after playing in the cold for a long time, or appears slightly confused, they may have hypothermia. The skin may look healthy but feel cold, and babies may be limp, unusually quiet and refuse to feed. If you suspect that your child has hypothermia, get medical help.

If possible, a doctor will take a history of exposure to work out where a patient has been and why they may have hypothermia. The core body temperature will be measured from the ear or the forehead but sometimes it is necessary to put the thermometer into the person's rectum (anus). For diagnosis of hypothermia, body temperature has to be below 35°C (95°F).

Page last reviewed: 13/07/2011

As hypothermia can be a life-threatening condition, seek medical attention as soon as possible.

Hypothermia is treated by preventing further heat being lost and by gently warming the patient.

If you are treating someone with mild hypothermia at home, or waiting for medical treatment to arrive, follow the advice below to prevent further loss of heat.

Things to do for hypothermia:

  • Move the person indoors, or somewhere warm, as soon as possible.
  • Once sheltered, gently remove any wet clothing and dry the person.
  • Wrap them in blankets, towels, coats (whatever you have), protecting the head and torso first.
  • Your own body heat can help someone with hypothermia. Hug them gently.
  • Increase activity if possible, but not to the point where sweating occurs, as that cools the skin down again.
  • If possible, give the person warm drinks (but not alcohol) or high energy foods, such as chocolate, to help warm them up.
  • Once body temperature has increased, keep the person warm and dry.

It is important to handle anyone that has hypothermia very gently and carefully.

Things you should NOT do:

  • Don't warm up an elderly person using a bath, as this may send cold blood from the body's surfaces to the heart or brain too suddenly, causing a stroke or heart attack.
  • Don't apply direct heat (hot water or a heating pad, for example) to the arms and legs, as this forces cold blood back to the major organs, making the condition worse.
  • Don't give the person alcohol to drink, as this will decrease the body's ability to retain heat.
  • Don't rub or massage the person's skin, as this can cause the blood vessels to widen and decrease the body's ability to retain heat. In severe cases of hypothermia there is also a risk of heart attack.

Severe hypothermia needs urgent medical treatment in hospital. Shivering is a good guide to how severe the hypothermia is. If the person can stop shivering of their own accord, hypothermia is mild, but if they cannot stop shivering, it is moderate to severe.

As the body temperature decreases further, shivering will stop completely. The heart rate will slow and a person will gradually lose consciousness. When unconscious, a person will not appear to have a pulse or be breathing. Emergency assistance should be sought immediately and CPR provided while the person is warmed. CPR is an emergency procedure, consisting of mouth-to-mouth resuscitation and chest compression.

Medical treatment warms up the body from the inside. Doctors do this by giving warm fluids intravenously (through a vein). In very rare and severe cases, haemodialysis or cardiopulmonary bypass may be used. This is a treatment to take blood out of the body, warm it up, and return it. The blood is filtered through an artificial kidney, much like dialysis treatment for people with kidney failure.

Glossary

Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Dialysis
Dialysis is a way of removing unwanted waste and water from the body. Waste is drawn from the kidneys into a liquid solution, which is then removed fr
Vein
Veins are blood vessels that carry blood from the rest of the body back to the heart.
Heart attack
A heart attack happens when there is a blockage in one of the arteries in the heart.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Heart
The heart is a muscular organ that pumps blood around the body.
Kidney
Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.
Intravenously
Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein.

Page last reviewed: 13/07/2011

Below are things you can do to avoid hypothermia:

  • If the weather is cold, dress appropriately before you go outside. Even if the rest of the body is covered up, significant amounts of body heat can be lost through the head, so wear a warm hat.
  • Children do not always realise how cold they are when playing outdoors, so wrap them up well.
  • Layers of clothing trap air, which helps to keep you warm. Tightly woven, waterproof clothes are best when outside.
  • If you have a baby, put a room thermometer where they sleep to monitor the temperature. Keep it at16-20°C (60.8-68°F).
  • Drink plenty of fluids and hot drinks (not alcohol) and eat regular, balanced meals to give you energy.
  • Keep active when it is cold, but not to the point where you are sweating. If you exercise outdoors in the winter and get sweaty from this, make sure you dry off and put on warm clothes immediately after.
  • Keep dry and change out of wet clothes as soon as possible. Wet clothes lose about 90% of their insulating power.
  • Cut down on alcohol, caffeine and nicotine as all three aggravate heat loss.
  • Keep your house warm during cold weather. If you are concerned about heating costs, you could try just keeping one room in the house warm. Keeping windows and doors closed also helps to trap heat.
  • Visit your GP regularly to manage any illnesses effectively. If you are taking regular medication, ask whether it affects your body's ability to regulate your temperature.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

Browse Health A-Z