Frostbite
Classification and external resources
Hands, feet, noses, legs and ears are most likely to be affected by frostbite.
ICD-10	T33.-T35.
ICD-9	991.0-991.3
DiseasesDB	31167
MedlinePlus	000057
eMedicine	emerg/209 med/2815 derm/833 ped/803
MeSH	D00562

Frostbite (congelatio in medical terminology) is the medical condition wherein localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas. The initial stages of frostbite are sometimes called "frostnip".

[edit] Classification

Cold injuries can result in a number of distinct conditions including:

• Frostnip is a superficial cooling of tissues without cellular destruction.^[1]
• Chilblains are superficial ulcers of the skin that occur when a predisposed individual is repeatedly exposed to cold
• Frostbite, on the other hand, involves tissue destruction.
• Hypothermia is a decrease in core body temperature below 35 C.
• Trench foot or immersion foot is due to repetitive exposure to wet non-freezing temperatures.

[edit] Mechanism

Frostbitten hands

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At or below 0 °C (32 °F), blood vessels close to the skin start to constrict. The same response may also be a result of exposure to high winds. This constriction helps to preserve core body temperature. In extreme cold, or when the body is exposed to cold for long periods, this protective strategy can reduce blood flow in some areas of the body to dangerously low levels. This lack of blood leads to the eventual freezing and death of skin tissue in the affected areas. There are three stages of frostbite. Each of these stages have varying degrees of pain.

• Stage 1

First degree frostbite causes skin to appear yellow or white. There may also be slight burning sensations. This stage of frostbite is relatively mild and can be reversed by the gradual warming of the affected area.

• Stage 2

Second degree frostbite develops after continued exposure. This stage is characterized by the disappearance of pain and the reddening and swelling of the skin. Treatment in this stage may result in blisters and it may also peel the skin.

• Stage 3

Third degree frostbite results in waxy and hard skin. It is at this stage that the skin dies and edema may occur as a result of the lack of blood.

If third degree frostbite is not treated immediately then the damage and the frostbite becomes permanent, nerve damage will occur due to oxygen deprivation. Frostbitten areas will turn discolored, purplish at first, and soon turn black. After a while nerve damage becomes so great that feeling is lost in the frostbitten areas. Blisters will also occur. If feeling is lost in the damaged area, checking it for cuts and breaks in the skin is vital. Infected open skin can lead to gangrene and amputation may be needed.

[edit] Risk factors

Risk factors for frostbite include using beta-blockers and having conditions such as diabetes and peripheral neuropathy.

[edit] Prevention

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Factors that contribute to frostbite include extreme cold, inadequate clothing, wet clothes, wind chill, and poor circulation. Poor circulation can be caused by tight clothing or boots, cramped positions, fatigue, certain medications, smoking, alcohol use, or diseases that affect the blood vessels, such as diabetes.

People working in chemical laboratories should take precautions to wear gloves and other safety equipment as liquid nitrogen and other cryogenic liquids can cause frostbite even with brief exposure.

It is important to find shelter early if caught in a severe snowstorm or other outdoor situation in very cold weather. This is especially important if the weather is windy, as wind chill can greatly reduce the time it takes for frostbite to set in. Even a small cave, ditch, hollow tree, or vehicle can help reduce the chances of frostbite. It is also important to increase physical activity to maintain body warmth, especially in the hands and feet. If without gloves or with inadequate gloves, hands should be kept inside clothing next to the body to stay warm. Extra clothing such as scarves or underwear can be placed around the toes. The face, especially the nose, should be covered with a scarf or other garment. Contrary to popular belief sharing a sleeping bag or blanket with one or more other people, or even dogs, doesn't help to keep warm.

People susceptible to frostbite should wear woolen socks, gloves, and caps in extreme cold. For frostbite in the feet, keeping feet in warm saline water will provide relief. Diabetes can also sometimes lead to frostbite, so diabetics should take precautions as to avoid trips to ice-cold places.^[2]

[edit] Treatment

Treatment of frostbite centers on rewarming (and possibly thawing) of the affected tissue. The decision to thaw is based on proximity to a stable, warm environment. If rewarmed tissue ends up refreezing, more damage to tissue will be done. Excessive movement of frostbitten tissue can cause ice crystals that have formed in the tissue to do further damage. Splinting and/or wrapping frostbitten extremities is therefore recommended to prevent such movement. For this reason, rubbing, massaging, shaking, or otherwise applying physical force to frostbitten tissues in an attempt to rewarm them can be harmful.^[3] Caution should be taken not to rapidly warm up the affected area until further refreezing is prevented. Warming can be achieved in one of two ways:

Passive rewarming^[4] involves using body heat or ambient room temperature to aid the person's body in rewarming itself. This includes wrapping in blankets or moving to a warmer environment.^[5]

Active rewarming^[6] is the direct addition of heat to a person, usually in addition to the treatments included in passive rewarming. Active rewarming requires more equipment and therefore may be difficult to perform in the prehospital environment.^[7] When performed, active rewarming seeks to warm the injured tissue as quickly as possible without burning them. This is desirable as the faster tissue is thawed, the less tissue damage occurs.^[8] Active rewarming is usually achieved by immersing the injured tissue in a water-bath that is held between 40 - 42 C. Warming of peripheral tissues can increase blood flow from these areas back to the bodies core. This may produce a degree in the bodies core temperature and increase the risk of cardiac dysrhythmias.^[9]

[edit] Surgery

Debridement and or amputation of necrotic tissue is usually delayed. This has led to the adage "Frozen in January, amputate in July".^[10] With exceptions only being made for signs of infections or gas gangrene.^[11]

[edit] Prognosis

A number of long term sequela can occur after frost bite. These include: transient or permanent changes in sensation, electric shocks, increased sweating, cancers, and bone destruction / arthritis in the area affected.^[12]

[edit] History

During the second world war Nazi Germany and Japan conducted numerous cold experiments on prisoners. see Nazi human experimentation and Unit 731

[edit] Research

Evidence is insufficient to determine whether or not hyperbaric oxygen therapy as an adjunctive treatment can assist in tissue salvage.^[13] There have been case reports but few actual research studies to show the effectiveness.^{[14][15][16][17][18]}

Medical sympathectomy using intravenous reserpine has also been attempted with limited success.^[19]

[edit] References

[edit] External links

• NIH
• eMedicine
• Mayo Clinic
• Article on how keep feet warm to avoid frostbite
• DDB 31167
• CRISP Thesaurus 00001790
• A Home-Made Steam Bath for Frozen Feet, Popular Science monthly, February 1919, page 35, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PA35