Hypothermia
Introduction
Hypothermia happens when a person's body temperature drops below 35°C (95°F). Normal body temperature is around 37°C (98.6°F).
Hypothermia can quickly become life-threatening and should be treated as a medical emergency.
Hypothermia is usually caused by being in a cold environment. It can be triggered by a combination of things, including being exposed to the cold for a long time – this can be outdoors in cold conditions, in a poorly heated room or being in cold water.
When your body gets cold it will try to prevent losing more heat by:
- shivering (which keeps the major organs at normal temperature)
- restricting blood flow to the skin
- releasing hormones to generate heat
However, these responses use up energy and may not be enough to maintain body temperature if you're exposed to the cold for a long time.
When the body runs out of energy, it gradually begins to shut down. Shivering stops and your heartbeat starts to slow.
Signs of hypothermia
The symptoms of hypothermia vary depending on how low a person’s temperature has dropped.
Mild symptoms include shivering, tiredness and confusion. But as the temperature drops, shivering becomes more violent and a person is likely to become delirious, struggle to breathe and may end up unconscious.
When to get medical help
If someone you know has been exposed to the cold and they are distressed, confused, have slow, shallow breathing or they're unconscious, they may have severe hypothermia. Their skin may look healthy but feel cold. Babies may be limp, unusually quiet and refuse to feed.
You should seek medical help immediately if severe hypothermia is suspected. Dial 999 to request an ambulance.
If you're with someone with hypothermia while waiting for an ambulance, remove any wet clothing and wrap them in blankets or towels. If they're conscious, give them something warm (but not alcoholic) to drink. If they're unconscious, not breathing and you can't detect a pulse after feeling for 60 seconds at the carotid pulse in the neck, then cardio-pulmonary resuscitation (CPR) should be given if possible.
Read more about treating hypothermia.
Who's at risk?
People who are particularly at risk are those who are elderly or ill and have poorly heated accommodation or are unable to move around easily to generate heat. Each year in the UK, hypothermia is the main contributory factor in the deaths of more than 400 people who are over 65 years old.
Babies are also more prone to developing hypothermia because their bodies' ability to regulate their temperature isn't fully developed.
People who spend a considerable amount of time outside in cold weather conditions, such as climbers and skiers, are also at increased risk of getting hypothermia, particularly if they don't wear suitable clothing.
Read more about the causes of hypothermia.
Preventing hypothermia
There are several things you can do to prevent hypothermia. Simple measures can help, such as wearing appropriate warm clothing in cold weather and ensuring that children are well wrapped up when they go outside.
Whenever possible, keep an eye on elderly or ill neighbours and relatives to ensure that their home is warm during cold weather. The government offers a winter fuel allowance for older people living alone who are vulnerable to hypothermia. The Welsh Government run a campaign to promote keeping well, warm and safe in the winter - Keep Well this Winter.
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Symptoms
The symptoms of hypothermia can vary depending on whether it is mild, moderate or severe. The severity of hypothermia is determined by how low your body temperature has become.
Mild hypothermia
The early symptoms of hypothermia are often recognised by a parent or carer. This is because hypothermia can cause confusion, poor judgement and a change in behaviour which means the affected may not realise that they have it.
If someone has mild hypothermia (generally with a body temperature of 32-35°C), the symptoms aren't always obvious but they can include:
- constant shivering
- tiredness
- low energy
- cold or pale skin
- fast breathing (hyperventilation)
Moderate hypothermia
Moderate cases of hypothermia (generally with a body temperature of 28-32°C) can include symptoms such as:
- violent, uncontrollable shivering (although shivering can stop completely at lower temperatures as the body is unable to generate heat)
- being unable to think or pay attention
- confusion (some people don't realise they're affected)
- loss of judgement and reasoning (someone with hypothermia may decide to remove clothing despite being very cold)
- difficulty moving around
- loss of co-ordination
- drowsiness
- slurred speech
- slow, shallow breathing (hypoventilation)
The symptoms of severe hypothermia (a body temperature of below 28°C) can include:
- unconsciousness (comatose)
- shallow or no breathing
- weak, irregular or no pulse
- dilated pupils
The individual may in fact appear to be dead. However, under these circumstances the individual must be taken to hospital in order for it to be decided whether they have died, or are in a state of severe hypothermia. If this is the case, advanced medical intervention may still be able to resuscitate them.
Hypothermia in babies
Babies with hypothermia may look healthy but their skin will feel cold. They may also be limp, unusually quiet and refuse to feed.
When to seek medical attention
If you suspect hypothermia, seek medical attention. If you suspect that someone has severe hypothermia, dial 999 immediately to request an ambulance. Severe hypothermia is life threatening.
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Causes
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).
There are different types of hypothermia depending on how quickly the body loses heat. The three types are described by doctors as:
- acute or immersion hypothermia, which happens when a person loses heat very rapidly – for example, after falling into cold water
- exhaustion hypothermia – this happens when a person’s body is so tired it can no longer generate heat
- chronic hypothermia – heat is lost slowly over time; this is common in elderly people who live in poorly heated accommodation or in people sleeping rough
Hypothermia is most common in cold environments. You're more at risk if you don't wear enough layers to keep warm or you don't cover your head (a large amount of body heat is lost through your head).
It's also possible to get hypothermia in mild weather. For example, if you're soaked in the rain and don't dry off properly soon afterwards (particularly if there is a cool wind), the water evaporates from your skin and lowers your body temperature.
Who's at risk?
Certain groups, described below, have an increased risk of getting hypothermia because they're vulnerable to cold environments or they're unable to keep warm.
- Babies can lose heat quickly if they're left in a cold room because they can't regulate their body temperature as well as older children and adults. Newborn babies in particular are at risk for the first 12 hours of their life.
- Older people, particularly if they're 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 – these substances affect the body's ability to retain heat. The blood vessels stay widened (dilated), allowing heat to escape. Someone who is under the influence of drugs or alcohol may also not realise that they have hypothermia.
- People with a condition that affects their memory, such as Alzheimer's disease, may not be able to recognise the symptoms of hypothermia or recognise when they're cold.
- Someone who has fallen into cold water, which can cause the body's core temperature to fall very quickly.
- People who have suffered severe injury, particularly a head injury.
- People with certain health conditions, such as heart problems, severe arthritis or someone who has had a stroke. 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.
- People who spend long periods of time in cold weather conditions, such as climbers, walkers and skiers.
Read more about preventing hypothermia.
Perioperative hypothermia
It is also sometimes possible for hypothermia to occur during operations, when a person is under general anaesthetic and their body is unable to regulate its own temperature. This is known as perioperative hypothermia.
During operations, it's quite common for a patient’s temperature to fall even though healthcare professionals follow guidelines to ensure that all patients are kept warm.
You can read the NICE guidelines for more information about how hospitals keep patients warm before, during and after an operation.
Therapeutic hypothermia
In some cases, hypothermia is induced deliberately as a treatment. This is known as therapeutic hypothermia. There's 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 group of people includes those who have suffered a cardiac arrest due to a heart attack outside of hospital, but who have been successfully resuscitated and are in an intensive care unit.
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Treatment
Hypothermia is treated by preventing further heat being lost and by gently warming the patient. You should seek immediate medical attention if you suspect severe hypothermia, as it can be life-threatening.
Treating hypothermia home
If you're treating someone with mild hypothermia at home, or waiting for medical treatment to arrive, the following advice will help to prevent further heat loss.
- Move the person indoors or somewhere warm as soon as possible.
- Once the person is in a warm environment, carefully remove any wet clothing and dry the person.
- Wrap them in blankets, towels, coats (whatever you have available), protecting their head and torso first.
- Your own body heat can help someone with hypothermia. Gently hugging them can help to warm them up.
- Encourage the person to shiver if they're capable of doing so.
- If possible, give the person warm drinks (not alcohol) or high energy foods, such as chocolate, to help warm them up. However, it's important to only do this if they can swallow normally (ask them to give a cough to see if they can swallow).
- Once the person’s body temperature has increased, keep them warm and dry.
It's important to handle anyone with hypothermia very gently and carefully.
Things to avoid
There are certain things that you should not do when treating hypothermia because it may make the condition worse. You should not:
- put the cold person into a hot bath to warm them up – this will cause the blood vessels in the arms and legs to dilate (open up) too quickly and cause a fall in blood pressure to the vital organs such as the brain, heart, lungs and kidneys, possibly leading to cardiac arrest and death.
- give the person alcohol to drink because it will also cause the blood vessels in the arms, legs and throughout the surface of the skin to dilate too quickly
When to seek medical help
If someone you know has been exposed to the cold and they're distressed or confused, and they have slow, shallow breathing or they're unconscious, they may have severe hypothermia. Their skin may look healthy but feel cold. Babies may also be limp, unusually quiet and refuse to feed.
Cases of severe hypothermia require urgent medical treatment in hospital. You should call 999 to request an ambulance if you suspect that someone you know has severe hypothermia.
As the body temperature drops, shivering will stop completely. The heart rate will slow and a person will gradually lose consciousness. They won't appear to have a pulse or be breathing. If possible, cardio-pulmonary resuscitation (CPR) should be given while the person is being warmed. CPR is an emergency procedure that involves giving mouth-to-mouth resuscitation and chest compressions.
In some circumstances, advanced medical treatment can be used to temporarily withdraw blood from the body, warm it and then re-infuse it to warm the person. These techniques are only available in major hospitals that have specialist emergency services on site.
A person with severe hypothermia often stands a better chance of surviving if they're taken directly by the emergency services to one of these hospitals, even if it means bypassing a smaller hospital along the way.
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Prevention
There are simple measures you can take to prevent you, your child or elderly relatives getting hypothermia.
Staying warm inside
Keep an eye on any elderly or ill neighbours and relatives to ensure that they are keeping their house warm during cold weather. The Welsh Government runs a Keep Well this Winter campaign with useful information for older people including information on the winter fuel allowance and how to keep well, warm and safe. Keeping windows and internal doors closed will also help to trap heat.
If you have a baby, put a room thermometer in the room where they sleep in order to monitor the temperature. Keep it at 16-20°C (60.8-68°F).
If you're ill, visit your local pharmacy or GP to ensure that you're treated promptly and effectively. If you're taking regular medication, ask whether it affects your body's ability to regulate temperature.
Staying warm outside
Wear appropriate warm clothing in cold weather and make sure that your children are also well wrapped up when outdoors. A significant amount of body heat can be lost through the head, even if the rest of the body is covered up, so you and your children should wear a warm hat. Layers of clothing trap air, which helps to keep you warm. Waterproof and windproof clothing gives the best protection outdoors in the sort of weather conditions found in the British Isles (a temperate climate – cold, damp and wet).
A healthy diet with plenty of fluid, warm drinks and regular meals can help give you energy so that your body can generate heat. Avoiding alcohol, caffeine and nicotine can help as they all increase the rate at which the body loses heat.
Keep active when it's cold, but not to the point where you are sweating. If you exercise outdoors during the winter and you sweat after exercising, make sure that you dry off and put on warm clothes immediately afterwards. Wet clothes lose around 90% of their insulating power.
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