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, 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
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 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 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.
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 40-42°C. 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 cardiac dysrhythmias. 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
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 tPa administered either intravenously or intraarterially may
decrease the likelihood of eventual need for amputation.
While extreme weather conditions increase the risk of frostbite it appears that certain
individuals and population groups appear more resistant to milder forms of frostbite, perhaps
due to longer term exposure and adaptation to cold weather environments.
References
External links Mayo Clinic
Definition of Frostbite, MedicineNet.com