Frostbite results from a freezing injury. It is most commonly seen with hypothermia or abnormally low body temperature, below 95 Fahrenheit (below 35 Celsius).
The time it takes to suffer from frostbite depends on ambient temperature and wind speed or windchill.
Treatment of frostbite is based first on rewarming and then on the preservation of tissue to prevent subsequent injuries.
Treatment includes analgesics, aloe vera, elevation and splinting, antibiotics as needed for infection, and carefully selected debridement or amputation if needed.
Frostbite occurs when there is freezing and crystallization of the body fluids inside and between the cells from prolonged exposure to low temperatures. Frostbite can occur not only from cold temperatures but from wind exposure, which causes the blood vessels to constrict.
Most commonly, frostbite occurs first in the extremities such as the fingers, toes, tip of the nose, ears, and lips. Naturally, frostbite occurs more in the winter, but it can also affect homeless people, mountaineers, paragliders, hang gliders, kite skiers, and winter sports enthusiasts.
The goals of the treatment of frostbite are to preserve as much good, healthy tissue as possible. This may include conservative medical treatments and surgery, as appropriate.
How long does it take to suffer from frostbite?
As a general rule, it takes about 30 minutes to suffer from frostbite if the ambient temperature is 0 degrees Fahrenheit (F) (-18 degrees Celsius) below with no wind. There are readily available charts that can estimate wind chill temperatures based on air temperature and wind speed. These estimates can provide predictions of the minutes of exposure that are likely to result in frostbite.
Using Fahrenheit examples, it takes hours for frostbite to occur in temperatures above 10 degrees, no matter how much the wind is blowing. When it is 5 degrees and the wind is fierce, over 30 miles per hour (mph), then frostbite can happen faster than you expect.
What happens during frostbite?
Our blood flow plays the primary role in the prevention of frostbite and thermal homeostasis. Our skin tends to lose heat better than it stays warm. That is why we are better at adjusting to heat better than cold environments.
The effects of skin temperature can be dramatic on cutaneous blood flow. Normally, the blood flow in our skin is 200 to 250 mL/minute. At 59 degrees F (15 degrees C), we have maximal vasoconstriction. Below 59F, our vasoconstriction is disrupted as much as three to five times per hour. People who are more used to the cold can acclimate to this vasoconstriction and become less susceptible to frostbite.
We have all experienced our hands or toes getting numb when it gets below only 50F (10C). This is called neurapraxia.
When the temperatures go below 32F (0C), things get more serious. The minimal amount of blood flow in our skin allows the skin to freeze. Skin temperature can begin dropping quickly. Smaller blood vessels are at more risk first, then larger blood vessels can stop flowing. Direct damage begins to occur to the cells and ice crystals will form.
The deeper tissues can progress through stages beginning with pre-freeze or superficial cooling. Next comes the freeze-thaw stage when ice crystals form. Vascular stasis occurs when there is an alternating between vasoconstriction and vasodilation to keep oxygen and nutrients flowing to the cells and tissues. Lastly, the cells and tissues may die from ischemia, low oxygen, and eventually tissue necrosis (death).
How is frostbite treated?
The goals of treatment of frostbite are to return to normal function, salvage tissue, and prevent complications. These goals are achieved through rewarming.
Rewarming begins with removing the person from the cold environment. Then, if needed, using a pad or splint on the affected area helps reduce the chances of injury. Of course, removing any wet clothing and wrapping the person with warm dry clothing is vital. It is important to avoid trauma to the affected areas, including walking on frostbite tissue. Try to avoid warming affected tissue only then to allow it to be exposed to the same cold conditions again. Do not rub frostbitten tissue since it can cause tissue damage. Using a fire or heating element to warm affected tissues can cause trauma as well.
Rewarming is best accomplished by immersing the frostbitten areas in water that is heated to body temperature or slightly higher (98.6 to 102.6F or 37 to 39C). Careful attention should be given to not allowing the water to get too hot or too cold. Whirlpool baths are preferred because of the ability to circulate the water.
Be sure not to stop the rewarming too soon. Be aware that the person will have pain so that should be treated with analgesics, if possible. It is important to avoid inadvertently slow rewarming or becoming too overzealous and using water that is too hot. Secondary burns can occur either from hot water or exposure of the frostbitten tissue to external heat or flames. Usually, it takes about 20 to 40 minutes for superficial frostbite injuries to responding. It can take an hour or more for deep frostbite injuries.
Using antiseptic solutions such as chlorhexidine and povidone-iodine can be particularly helpful in preventing infection.
After the skin has undergone safe rewarming and thawing, it is vital to prevent any further injury, especially re-exposure to the cold environment that caused the problem in the first place.
Elevation and splinting of the extremity are recommended. Using sterile, non-adherent bandages are preferred, if possible, with local wound care if there are open sores. All frostbitten areas are susceptible to infection, so the dressings should be monitored closely. Some frostbitten areas will develop blisters. It is controversial as to what to do with the blisters. Some healthcare professionals advocate aspiration and debridement of clear blisters. Those blisters that are hemorrhagic (blood-filled) should not be disturbed unless they are affecting the movement of a joint.
If there is evidence of a concurrent fracture or dislocation, those should be treated conservatively until the tissue has been thoroughly rewarmed and thawed.
Topical aloe vera cream is recommended every six hours for frostbitten areas. Also, a tetanus shot is advocated. As a general rule, antibiotic prophylaxis is not recommended at first. If the person develops signs of infection, then oral antibiotics are used and directed toward what the wound culture reveals.
Other treatments such as infusion of low-molecular-weight dextran, intravenous use of tissue plasminogen activator (tPA), and other ancillary modalities such as buflomedil (an alpha blocker) to increase blood flow, hyperbaric oxygen, and vitamin C are still controversial and not well studied in humans.
In some instances, if the frostbite causes permanent tissue damage, surgical treatment is necessary. The last resort is amputation. Fortunately, this is rare.