Frostbite

What is frostbite?

Frostbite is an injury that is caused by exposure of parts of the body to the cold. The cold causes freezing of the skin and underlying tissue. The fingers, toes and feet are most commonly affected but other 'extremities' including the nose, ears, and the cheeks can also develop frostbite.

What causes frostbite?

Usually your blood carries oxygen to all parts of your body so that your body tissues are kept healthy. As a protective response, when your body is exposed to extreme cold, blood vessels constrict (narrow) so that blood (and oxygen) is diverted away from your extremities to your vital organs to keep your body alive. After some time, this lack of blood supply and oxygen to the skin can start to cause damage to the cells.

In areas of the body affected by frostbite, ice crystals form and cells and blood vessels become damaged. Blood clots can also form in small blood vessels which further reduces the chance of blood and oxygen getting to the affected tissues.

The likelihood of frostbite is increased the longer that you are exposed to the cold temperatures. Also, if the cold temperatures are accompanied by wind (producing wind chill which brings the temperature down further) or high altitude.

How common is frostbite and who gets it?

Frostbite is uncommon in the UK. Frostbite most commonly affects the following groups of people:

• Soldiers
• People who work outdoors in the cold
• Homeless people
• Winter outdoor sports enthusiasts such as skiers and climbers

However, it can affect anyone who is exposed to low temperatures (below freezing). In particular, if your wear inadequate clothing.

If you have underlying health problems such as peripheral vascular disease (narrowing of the arteries, mainly occurring in the legs) or diabetes, you have an increased risk of developing frostbite. Also, if you take certain drugs that constrict (narrow) your blood vessels, for example nicotine in cigarettes, or beta-blockers, your risk is increased. People who have Raynaud's phenomenon (a condition where the small blood vessels of the fingers constrict) also have an increased risk of developing frostbite. See separate article called 'Raynaud's Phenomenon (Cold Hands)' for more detail.

The different degrees of frostbite

Rather like burns, frostbite injuries tend to be classified by the degree of injury. The degree of frostbite basically refers to how deep the frostbite injury goes.

The skin has two layers - the epidermis and the dermis. Beneath the dermis is a layer of fat, and then the deeper structures such as muscles and tendons.

• First-degree frostbite just affects the epidermis (the outer layer of the skin).
• Second-degree frostbite may affect the epidermis and part of the dermis.
• Third-degree frostbite affects the epidermis, the dermis and the fatty tissue beneath the dermis.
• Fourth-degree frostbite affects the full thickness of the skin, the tissues that lie underneath the skin, and also deeper structures such as muscles, tendons and bone.

What are the symptoms of frostbite?

Frostbite can cause feelings of cold and firmness in the affected area, such as the fingers or toes. Stinging, burning and numbness can also occur. You may experience pain, throbbing, burning or an electric current-like sensation when the affected area is rewarmed.

In first-degree frostbite, the affected area of skin becomes white and feels numb. It may also feel hard or stiff. If it is treated quickly, the skin usually recovers fully. First-degree frostbite is sometimes called 'frost nip'.

In second-degree frostbite, the affected skin is also often white, or may become blue. It feels frozen and hard. Blisters filled with a clear or milky fluid appear on the skin.

In third-degree frostbite, skin can be white or blue or 'blotchy'. Blisters also develop and are filled with blood. Over some weeks, black thick scabs form. The skin feels hard and cold. In fourth-degree frostbite, there is damage to the full thickness of the skin and also the underlying tissues such as muscle, tendons and bone.

For some pictures of frostbite see www.dermis.net/dermisroot/en/43133/diagnose.htm

How is frostbite diagnosed?

Frostbite is usually diagnosed by the typical symptoms in someone who has been exposed to extreme cold weather. Frostbite can happen very quickly so you need to be aware of the symptoms and signs. If you are aware of the early symptoms of frostbite, and shelter from the cold, you can prevent more severe symptoms and the possibility of permanent damage.

Special scans are sometimes used to assess the degree of frostbite and to determine how much tissue is damaged.

What is the initial treatment for frostbite?

First aid treatment

Some basic first aid for frostbite injuries includes:

• You must get shelter from the cold.
• Change wet clothing for dry clothing to reduce the chance of further heat loss from your body.
• Don't rub the affected area as this can cause further tissue damage.
• If your hand or a foot is affected by frostbite, wrap it in a blanket for protection.
• If possible, avoid walking on frostbitten feet as fractures can occur as well as chipping of the affected tissue.

Rewarming treatment

The aim is to start this as soon as possible. However, particularly if someone has been in the mountains and has developed frostbite, they may have other life-threatening problems that need to be treated first. Rewarming may be done either in a bath or placing the affected area in a tub of water. The water temperature should be 40-42°C. The affected area should not be massaged, as this can cause further injury.

Drug treatment

Painkillers are usually needed to treat pain. Rewarming can be very painful. Some other drugs have also been used. Examples include drugs such as dextran, heparin and tissue plasminogen activator (tPA) given intravenously (via a cannula in a vein). The idea is that these drugs may help to increase the blood supply to injured tissues.

What happens next with frostbite?

When a body part with frostbite is thawed out, the skin turns red, may blister and can be very painful. It can also become swollen. Eventually, dead blackened tissue that forms scabs can develop.

If frostbite is superficial, over time, new pink skin will form underneath the scabs. It can take up to six months for the area to recover. There can be full recovery but some people have permanent problems including pain, numbness and stiffness in the affected area.

However, if frostbite is deep, tissue damage can be permanent and tissue loss can occur. For example, the end of a finger or toe can gradually separate off. Sometimes surgery is needed to remove dead tissue. Amputation of, for example, fingers or toes may be needed. However, surgery should be delayed for as long as possible (usually 3-4 weeks). This gives affected tissues a chance to recover and the full extent of the injury can be seen.

Can frostbite be prevented?

The most important way of preventing frostbite is to get out of the cold. If you are exposed to the cold, make sure that you wear appropriate warm clothing. Mittens are better than gloves. Your head, neck and face need to be covered if it is windy. Wear waterproof clothing so that your body is kept dry. Multiple layers of clothing are best. Layers act as extra insulation by trapping air that warms to your body's temperature. A warm pair of boots is also needed. You need to increase your fluid and calorie intake in cold weather. At high altitudes, a lot of heat can be lost through breathing. This means that any activity that you do needs to be adjusted to minimise your work of breathing. The use of oxygen by mountain climbers can reduce their chance of developing frostbite.