frostnip

関

凍傷

• 凍傷の初期段階

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/09/11 17:16:24」(JST)

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This article is about a medical condition. For other uses, see Frostbite (disambiguation).

Frostbite
Frostbitten toes two to three days after mountain climbing
Classification and external resources
Specialty	Emergency medicine, orthopedics
ICD-10	T33-T35
ICD-9-CM	991.0-991.3
DiseasesDB	31167
MedlinePlus	000057
eMedicine	emerg/209 med/2815 derm/833 ped/803
Patient UK	Frostbite
MeSH	D005627

Frostbite is the medical condition in which localized damage is caused to skin and other tissues due to freezing. 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.

Classification

There are several classifications for tissue damage caused by extreme cold including:

• Frostnip is a superficial cooling of tissues without cellular destruction.
• Chilblains are superficial ulcers of the skin that occur when a predisposed individual is repeatedly exposed to cold
• Frostbite involves tissue destruction.

Signs and symptoms

At or below 0 °C (32 °F), blood vessels close to the skin start to constrict, and blood is shunted away from the extremities via the action of glomus bodies. 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 four degrees of frostbite. Each of these degrees has varying degrees of pain.

First degree

This is called frostnip and only affects the surface of the skin, which is frozen. On the onset, there is itching and pain, and then the skin develops white, red, and yellow patches and becomes numb. The area affected by frostnip usually does not become permanently damaged as only the skin's top layers are affected. Long-term insensitivity to both heat and cold can sometimes happen after suffering from frostnip.

Second degree

If freezing continues, the skin may freeze and harden, but the deep tissues are not affected and remain soft and normal. Second-degree injury usually blisters 1–2 days after becoming frozen. The blisters may become hard and blackened, but usually appear worse than they are. Most of the injuries heal in one month, but the area may become permanently insensitive to both heat and cold.

Third and fourth degrees

Frostbite 12 days later

If the area freezes further, deep frostbite occurs. The muscles, tendons, blood vessels, and nerves all freeze. The skin is hard, feels waxy, and use of the area is lost temporarily, and in severe cases, permanently. The deep frostbite results in areas of purplish blisters which turn black and which are generally blood-filled. Nerve damage in the area can result in a loss of feeling. This extreme frostbite may result in fingers and toes being amputated if the area becomes infected with gangrene. If the frostbite has gone on untreated, they may fall off. The extent of the damage done to the area by the freezing process of the frostbite may take several months to assess, and this often delays surgery to remove the dead tissue.

Causes

Inadequate blood circulation when the ambient temperature is below freezing point leads to frostbite. This can be because the body is constricting circulation to extremities on its own to preserve core temperature and fight hypothermia. In this scenario the same factors that can lead to hypothermia (extreme cold, inadequate clothing, wet clothes, wind chill) can contribute to frostbite. Poor circulation can also be caused by other factors such as tight clothing or boots, cramped positions, fatigue, certain medications, smoking, alcohol use, or diseases that affect the blood vessels, such as diabetes.

Exposure to liquid nitrogen and other cryogenic liquids can cause frostbite as well as prolonged contact with aerosol sprays (see deodorant burn).

Risk factors

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

Treatment

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 are 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.

Warming can be achieved in one of two ways:

Passive rewarming 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.

Active rewarming 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. When performed, active rewarming seeks to warm the injured tissue as quickly as possible without burning. This is desirable, because the faster tissue is thawed, the less tissue damage occurs. Active rewarming is usually achieved by immersing the injured tissue in a water-bath that is held between 40 and 42 °C (104 and 108 °F). Warming of peripheral tissues can increase blood flow from these areas back to the body's core. This may produce a decrease in the body's core temperature and increase the risk of abnormal heart rhythms.

Surgery

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

Prognosis

3 weeks after initial frostbite

A number of long term sequelae can occur after frostbite. These include transient or permanent changes in sensation, paresthesia, increased sweating, cancers, and bone destruction/arthritis in the area affected.

Research

Evidence is insufficient to determine whether or not hyperbaric oxygen therapy as an adjunctive treatment can assist in tissue salvage. There have been case reports but there has not yet been a randomized control trial performed on humans.

Medical sympathectomy using intravenous reserpine has also been attempted with limited success. Studies have suggested that administration of tissue plasminogen activator (tPa) either intravenously or intraarterially may decrease the likelihood of eventual need for amputation.

While extreme weather conditions (cold and wind) increase the risk of frostbite it appears that certain individuals and population groups appear more disposed to frostbite.

References

External links

• Mayo Clinic
• Definition of Frostbite, MedicineNet.com

UpToDate Contents

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• 1. 凍傷 frostbite
• 2. 成人における偶発性低体温 accidental hypothermia in adults

English Journal

• Skin conditions in figure skaters, ice-hockey players and speed skaters: part II - cold-induced, infectious and inflammatory dermatoses.

• Tlougan BE1, Mancini AJ, Mandell JA, Cohen DE, Sanchez MR.
• Sports medicine (Auckland, N.Z.).Sports Med.2011 Nov 1;41(11):967-84. doi: 10.2165/11592190-000000000-00000.
• Participation in ice-skating sports, particularly figure skating, ice hockey and speed skating, has increased in recent years. Competitive athletes in these sports experience a range of dermatological injuries related to mechanical factors: exposure to cold temperatures, infectious agents and inflam
• PMID 21985216

• Cold exposure injuries to the extremities.

• Golant A1, Nord RM, Paksima N, Posner MA.
• The Journal of the American Academy of Orthopaedic Surgeons.J Am Acad Orthop Surg.2008 Dec;16(12):704-15.
• Cold exposure injuries comprise nonfreezing injuries that include chilblain (aka pernio) and trench, or immersion, foot, as well as freezing injuries that affect core body tissues resulting in hypothermia of peripheral tissues, causing frostnip or frostbite. Frostbite, the most serious peripheral in
• PMID 19056919

• National Athletic Trainers' Association position statement: environmental cold injuries.

• Cappaert TA1, Stone JA, Castellani JW, Krause BA, Smith D, Stephens BA; National Athletic Trainers' Association.
• Journal of athletic training.J Athl Train.2008 Oct-Dec;43(6):640-58. doi: 10.4085/1062-6050-43.6.640.
• OBJECTIVE: To present recommendations for the prevention, recognition, and treatment of environmental cold injuries.BACKGROUND: Individuals engaged in sport-related or work-related physical activity in cold, wet, or windy conditions are at risk for environmental cold injuries. An understanding of th
• PMID 19030143

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