Frostbite and frostnip

Definition

Frostbite is damage to the skin and other tissues caused by freezing. Frostnip is a mild form of this cold injury.

Description

Skin exposed to temperatures a little below 32°F (0°C) can take hours to freeze, but very cold skin can freeze in minutes or seconds. Nevertheless, under extreme conditions, even warm skin exposed to subzero temperatures and high wind chill factors can freeze rapidly. Air temperature, wind speed, humidity, and altitude all affect how cold the skin becomes. A strong wind can lower skin temperature considerably by dispersing the thin protective layer of warm air that surrounds the body. Wet clothing readily draws heat away from the skin because water is a potent conductor of heat. The evaporation of moisture on the skin also produces cooling. For these reasons, wet skin or clothing on a windy day can lead to frostbite even if the air temperature is above freezing.

The extent of permanent injury, however, is determined not by how cold the skin and the underlying tissues become but by how long they remain frozen. When skin is exposed to freezing temperatures, three things happen. The skin begins to freeze, causing ice crystal formation, damage to capillaries (the tiny blood vessels that connect the arteries and veins), and other changes that damage and eventually kill cells. Much of this harm occurs because the ice produces pressure changes that force water (crucial for cell survival) out of the cells.

Tissue hypoxia, or oxygen deficiency, occurs next as a survival mechanism in the body kicks in, causing the blood vessels in the hands, feet, and other extremities to narrow in response to cold. Among its many tasks, blood transfers body heat to the skin, which then dissipates the heat into the environment. Blood vessel narrowing is the body's way of protecting vital internal organs at the expense of the extremities by reducing heat flow away from the center of the body. However, blood also carries life-sustaining oxygen to the skin and other tissues, and narrowed vessels result in oxygen starvation. Narrowing also causes acidosis (an increase in tissue acidity) and increases blood viscosity (thickness). Ultimately, blood stops flowing through the capillaries) and blood clots form in the arterioles and venules (the smallest arteries and veins). Damage also occurs to the endothelial cells that line the blood vessels.

Hypoxia, blood clots, and endothelial damage lead, in turn, to the release of inflammatory mediators. These are substances that act as links in the inflammatory process, which promote further blood vessel damage, hypoxia, and cell destruction. Tissue damage is greatest when skin is exposed to freezing slowly or over a long period of time. More damage can occur when rewarming is slow or the affected area is warmed and refrozen.

Demographics

In North America, frostbite frequently occurs in Alaska, Canada, and the northern states, which have extremely cold winter temperatures. Frostbite, however, can occur almost anywhere, given the right conditions. Though there has been in the early 2000s a substantial decline in the number of frostbite cases in the United States, due to better winter clothing and footwear and greater public understanding of how to avoid cold-weather dangers, these cases are rising among the homeless who do not have adequate clothing or shelter. Frostbite has thus become an urban as well as a rural public health concern. The growing popularity of outdoor winter activities has also expanded the at-risk population.

Children are at a higher risk of experiencing frostbite and frostnip than adults because they experience heat loss from their skin more rapidly. Those children with disorders that affect circulation, such as diabetes, may be even more susceptible to frostbite and frostnip. Children who have had a recent injury, surgery, or blood loss are at risk, as well as teenagers who might be smoking , drinking alcohol, or taking beta-blockers for high blood pressure or a heart condition. Also, children who have had a frostbite injury in the past are more prone to having a recurrence in the same location. In addition, children from tropical climates may not be able to withstand cold temperatures as well as their cold-climate counterparts, making them more susceptible to frostbite and frostnip at higher temperatures.

Causes and symptoms

Causes

Skin damage from frostbite and frostnip occurs because of freezing, either by extremely cold weather, wet clothing in cold temperatures, or through chemical exposures, such as dry ice or highly compressed gases. Most children encounter frostbite when they participate in outdoor sports , camp in winter, get wet and cannot change their clothing immediately, or do not dress according to the weather conditions. Frostnip and frostbite are associated with ice crystal formation in the tissues.

Symptoms

In frostnip, no tissue destruction occurs and the ice crystals dissolve as soon as the skin is warmed. Frostnip affects areas such as the earlobes, cheeks, nose, fingers, and toes. The skin turns pale, and the person experiences numbness or tingling in the affected part until warming begins.

Frostbite, by contrast, has a range of severity. Most injuries affect the hands and feet, but about 10 percent of all frostbite cases affect the nose, cheeks, ears, and even the penis. Frostbite is classified by degree of injury (first, second, third, or fourth), or simply divided into two types, superficial (corresponding to first- or second-degree injury) and deep (corresponding to third- or fourth-degree injury). Frostnip is sometimes labeled a first-degree frostbite case.

Once frostbite sets in, the affected part begins to feel cold and, usually, numb. This condition is followed by a feeling of clumsiness. The skin turns white or yellowish. Many patients experience severe pain in the affected part during rewarming treatment and an intense throbbing pain that arises two or three days later and can last days or weeks. As the skin begins to thaw during treatment, edema (excess tissue fluid) often accumulates, causing swelling. In frostbite injuries of second-degree or higher, blisters appear. Third-degree cases produce deep, blood-filled blisters and a hard black eschar (scab). Fourth-degree frostbite penetrates below the skin to the muscles, tendons, nerves, and bones. Septicemia or blood poisoning and infection may also be present, as well as the possible need for amputation (the surgical removal of appendages such as fingers, toes, foot, or leg).

When to call the doctor

If a child's clothing has been wet for a long period of time or the child has been exposed to freezing temperatures, shows skin discoloration, and complains of feeling numb, the child should be seen by a doctor. In most cases, the child will be hospitalized to monitor the rewarming process and to do the necessary tests needed to determine the extent of the frostbite. Prolonged exposure to extreme temperatures can also produce hypothermia (lowered body temperature), which can be life threatening.

Diagnosis

Initial diagnosis is usually made based on the environmental conditions. Physical examination of the skin reveals that the skin is extremely cold and may have white, red, blue, or black areas on it. The patient may report feeling numb or a tingling sensation.

Frostbite diagnosis may also include conventional radiography (x rays), angiography (x-ray examination of the blood vessels using an injected dye to provide contrast), thermography (use of a heat-sensitive device for measuring blood flow), and other techniques for predicting the course of injury and identifying tissue that requires surgical removal. During the initial treatment period, however, a physician cannot judge how a case may progress. Diagnostic tests only become useful three to five days after rewarming, once the blood vessels have stabilized.

Treatment

Frostnip

Frostnipped fingers are helped by blowing warm air on them or holding them under one's armpits. Other frostnipped areas can be covered with warm hands. The injured areas should never be rubbed.

Frostbite

Emergency medical help should always be summoned whenever frostbite is suspected. While waiting for help to arrive, one should, if possible, remove wet or tight clothing and put on dry, loose clothing or cover with a blanket. Rubbing the area with snow or anything else is dangerous because it can cause tissue damage. The key to prehospital treatment is to avoid partial thawing and refreezing, which releases more inflammatory mediators and makes the injury substantially worse. For this reason, the affected part must be kept away from heat sources such as campfires and car heaters. Experts advise rewarming in the field only when emergency help will take more than two hours to arrive and refreezing can be prevented.

Because the outcome of a frostbite injury cannot be predicted at first, all hospital treatment follows the same routine. Treatment begins by rewarming the affected part for 15 to 30 minutes in water at a temperature of 104–108°F (40–42°C). This rapid rewarming halts ice crystal formation and dilates narrowed blood vessels. Aloe vera (which acts against inflammatory mediators) is applied to the affected part, which is then splinted, elevated, and wrapped in a dressing. Depending on the extent of injury, blisters may be debrided (cleaned by removing foreign material) or simply covered with aloe vera. A tetanus shot and, possibly, penicillin, are used to prevent infection, and the patient is given ibuprofen to combat inflammation. Narcotics are needed in most cases to reduce the excruciating pain that occurs as sensation returns during rewarming. Except when injury is minimal, treatment generally requires a hospital stay of several days, during

which hydrotherapy and physical therapy are used to restore the affected part to health. Experts recommend a cautious approach to tissue removal and advise that 22 to 45 days must pass before a decision on amputation can safely be made.

Alternative treatment

Alternative practitioners suggest several kinds of treatment to speed recovery from frostbite after a person leaves the hospital. Bathing the affected part in warm water or using contrast hydrotherapy can help enhance circulation. Contrast hydrotherapy involves a series of hot and cold water applications. A hot compress (as hot as the patient can stand) is applied to the affected area for three minutes followed by an ice-cold compress for 30 seconds. These applications are repeated three times each, ending with the cold compress.

Nutritional therapy to promote tissue growth in damaged areas may also be helpful. Homeopathic and botanical therapies may also assist recovery from frostbite. Homeopathic Hypericum ( Hypericum perforatum ) is recommended when nerve endings are affected (especially in the fingers and toes) and Arnica ( Arnica montana ) is prescribed for shock. Cayenne pepper ( Capsicum frutescens ) can enhance circulation and relieve pain. Drinking hot ginger ( Zingiber officinale ) tea also aids circulation. Other possible approaches include acupuncture to avoid permanent nerve damage and oxygen therapy.

Prognosis

The rapid rewarming approach to frostbite treatment, pioneered in the 1980s, has proved to be much more effective than older methods in preventing tissue loss and amputation. A study of 56 first-, second-, and third-degree frostbite patients treated with rapid rewarming between 1982 and 1985 found that 68 percent recovered without tissue loss, 25 percent experienced some tissue loss, and 7 percent needed amputation. In a comparison group of 98 patients, treatment using older methods resulted in a tissue loss rate of nearly 35 percent and an amputation rate of nearly 33 percent. Although the comparison group included a higher proportion of second- and third-degree cases, the difference in treatment results was determined to be statistically significant.

The extreme throbbing pain that many frostbite sufferers endure for days or weeks after rewarming is not the only prolonged symptom of frostbite. During the first weeks or months, people often experience tingling, a burning sensation, or a sensation resembling shocks from an electric current. Other possible consequences of frostbite include skin-color changes, nail deformation or loss, joint stiffness and pain, hyperhidrosis (excessive sweating), and heightened sensitivity to cold. For everyone, a degree of sensory loss lasting at least four years, and sometimes a lifetime, is inevitable.

Prevention

With the appropriate knowledge and precautions, frostbite can be prevented even in the coldest and most challenging environments. Appropriate clothing and footwear are essential. To prevent heat loss and keep the blood circulating properly, clothing should be worn loosely and in layers. Covering the hands, feet, and head is also crucial for preventing heat loss. Children especially should wear hats that cover their heads and ears, mittens, and coats that are wind and water resistant. Wet clothing and footwear must be removed as quickly as possible and replaced with dry clothing and shoes.

Alcohol and drugs should be avoided because of their harmful effects on judgment and reasoning. Experts also warn against alcohol use and smoking in the cold because of the circulatory changes they produce.

Parental concerns

Parents should pay close attention to weather reports before sending children out to play or to take part in long-exposure outdoor activities such as sledding, skiing, and winter camping. Listening to winter driving warnings and road reports is also important before taking trips in the winter or in the mountains.

In addition, parents should keep a close eye on their children when the children play outdoors in winter around lakes, streams, and other water sources. Even older children and teenagers can slip on ice or snow and fall in. The risk of hypothermia and frostbite is too great to ignore. Sometimes, even a child's getting his or her shoes wet and then continuing to play in the cold can produce serious frostbite.

See also X rays .

Resources

BOOKS

Danzl, Daniel F. "Disturbances Due to Cold." In Conn's Current Therapy , ed. Robert E. Rakel. Philadelphia: W. B. Saunders Co., 1996.

McCauley, Robert L., et al. "Frostbite and Other Cold-Induced Injuries." In Wilderness Medicine: Management of Wilderness and Environmental Emergencies , ed. Paul S. Auerbach. St. Louis: Mosby, 1995.

WEB SITES

Bjerke, H. Scott, and Amit Tevar. "Frostbite." Available online at http://www.emedicine.com/med/topic2815.htm (accessed October 25, 2004).

"Frostbite Fact Sheet." Available online at http://www.mckinley.uiuc.edu/handouts/frostbit/frostbit.html (accessed October 25, 2004).

"Frostbite." KidsHealth for Parents. Available online at http://www.kidshealth.org/parent/firstaid_safe/emergencies/frostbite.html (accessed October 25, 2004).

Janie Franz Howard Baker