What is frostbite?

Causes and Symptoms

The effect of cold on the human body is to reduce the circulation of blood to surface areas, such as the feet, hands, and face. This reduction restricts the amount of heat lost by the body and helps to prevent the development of hypothermia. Blood constriction may become so severe in severely chilled areas of the body, however, that circulation almost totally ceases. People with poorer circulation, such as the elderly and the exhausted, are not as resistant to low temperatures as are fitter or younger people.

If the skin’s temperature falls below -0.53 degrees Celsius, the tissue freezes and frostbite occurs. Rapid freezing causes ice crystals to form within a cell. These crystals rupture the cell wall and destroy structures within the cell, effectively killing it. If freezing is slow, ice crystals form between the cells and grow by extracting water from the cells. The tissue may be injured physically by the ice crystals or by dehydration and the resulting disruption of osmotic and chemical balance within the cells; however, tissue death following frostbite is more likely to be attributable to interruption of the blood supply to the tissue than to the direct action of freezing. Cold also damages the capillaries in the affected areas, causing blood plasma to leak through their walls, thus adding to tissue injury and further impairing circulation by allowing the blood to sludge (that is, clot because of an increase in red blood cells) inside the vessels. All sensation of cold or pain is lost as circulation becomes seriously impaired. Unless the tissue is warmed quickly, the skin and superficial tissues begin to freeze. With continual chilling, the frozen area enlarges and extends to deeper areas. This condition is known as frostbite.

Frostbite was common among soldiers during Napoleon’s campaign in Russia in the early nineteenth century, during World War II in Northern Europe, in the Korean War, and in fighting between Indian and Chinese troops in the Himalayas. Air crews, especially waist gunners in the US Air Force in World War II, were particularly prone to frostbite. In 1943, frostbite injuries among these bomber crews were more numerous than all other casualties combined.

Polar travelers before the 1920s suffered severely from frostbite. Mountain climbers are at risk from frostbite at higher elevations. Lower oxygen availability increases the danger of frostbite because the body cannot take in sufficient oxygen in this thinner air. The resulting condition, called hypoxia, reduces mental abilities, which may cause a person to either take inadequate precautions against the cold or neglect such precautions altogether. High winds, often experienced in the mountains, speed heat loss from exposed skin surfaces. This wind chill can be deadly to mountaineers and often leads to hypothermia, which increases the risk of frostbite, as heat is drawn away from extremities to protect the body’s core temperature. In addition, the insulating layer of subcutaneous fat decreases with longer periods of time spent at higher elevations, which in turn decreases the insulation of the surface areas of the body against freezing. Inadequate food intake while mountain climbing, often caused by poor appetite at high elevations, also increases the danger of frostbite, as the body does not have enough calories to keep its temperature constant. At higher elevations, most humans function at only about 60 percent of the physiological efficiency that they have at sea level. Women have more resistance to cold and may be less likely to experience frostbite than men.

Frostbite at high altitudes seems to be more common than at the same temperature at lower altitudes. More red blood cells are found in the blood of persons working at higher elevations, thickening the blood and reducing circulation to the extremities, thus lowering the temperature of these extremities. The basal metabolic rate and cardiac output of the body also decrease as one goes higher; both of these actions reduce the body’s ability to keep its feet, hands, and face warm.

Blood vessels move heat from the central body core to the skin, after which it radiates into the air from exposed surfaces. This heat loss is greatest in the hands, feet, and head, where the vessels are close to the skin’s surface. Respiration causes loss of body heat when cold air is inhaled into the lungs, body heat warms it, and the air is then exhaled. Evaporation, moisture leaving the skin’s surface, also draws heat from the body. In low temperatures, spilling gasoline on exposed skin will create frostbite because the fuel evaporates much faster than water, drawing heat away from the body quickly. Convection carries body heat away by wind currents. This wind-chill factor, calculated for Fahrenheit temperatures by subtracting two times the wind speed from the air temperature, determines the amount of heat energy lost from the body’s surface. Conduction transfers heat from one substance to another; for example, contact between the body and snow or metal will cause the skin to lose heat.

Although many people work and live in subzero temperatures, frostbite is uncommon. Nevertheless, an accident that prevents one from moving, loss of the ability to shiver in order to generate heat, or inactivity
may increase one's chances of developing frostbite. Frostbite can occur in any cold environment. Initial warning symptoms of frostbite include tingling and pain in the afflicted tissues. The skin may be slightly flushed before freezing. It then turns white or a blotchy blue in color and is firm and insensitive to the touch. Tissue that is first painful and then becomes numb and insensitive is frozen.

Treatment and Therapy

Slight cases of frostbite, often termed frostnip or superficial frostbite, can be treated outdoors or in the field with little or no medical help. Such cases are usually reversible, with no permanent damage, as only skin and subcutaneous tissues are involved. In cases of frostnip, also called first-degree frostbite, the frozen part, although white and frozen on the surface, is soft and pliable when pressed gently before thawing. The area is often a cheek or the tip of the nose or the fingers. The frozen area, usually small, can be warmed manually. A hand is placed over the frostnipped area if it is a cheek or nose, while frozen fingers can be placed under the armpit or on a partner’s bare stomach for warming. Tissue that has had only a minor amount of frostnip soon returns to normal color. A tingling sensation is felt when frostnipped tissue is thawed.

After thawing, areas that have had more serious superficial frostbite, also called second-degree frostbite, become numb, mottled, or blue or purple in color and then will sting, burn, or swell for a period of time. Small blisters, called blebs, may occur within twenty-four to forty-eight hours. Blistering is more common where the skin is loose. Blister fluid is absorbed slowly; the skin may harden and be insensitive to touch. Throbbing or aching may persist for weeks, and superficial gangrene may develop. With immediate treatment, second-degree frostbite will be mostly healed in two or three months and will not progress to the much more serious injury of deep frostbite.

Tissues vary in their resistance to frostbite. Skin freezes at -0.53 Celsius, and muscles, blood vessels, and nerves are also highly subject to freezing. Connective tissue, tendons, and bones are relatively resistant to freezing, however, which explains why the blackened extremities of a frostbitten hand or foot can be moved: the tendons under the gangrenous skin remain intact and functional.

Deep frostbite, also called third- or fourth-degree frostbite depending on severity, includes not only skin and subcutaneous tissue but also deeper structures, including muscle, bone, and tendons. The affected area becomes cold, mottled, and blue or gray in color and may remain swollen for months. With deep frostbite, the tissues become quite hard to the touch. The frozen part may be painless at first, but one to three days after thawing, the affected area becomes quite painful, and shooting and throbbing pains may continue for several months after. Blisters, initially small blebs and then large, coalescing ones, may take weeks to develop. Permanent loss of tissue is almost inevitable with deep frostbite. The affected extremity has a severely shriveled look. A limb may return to almost normal over some months, however, and
amputation should never be carried out until a considerable period, probably at least six to nine months, has elapsed.

In cases of frostbite, surgical intervention must be minimal. Blackened frostbitten tissue will gradually separate itself from healthy, unfrozen tissue without interference; no efforts should be taken to hasten separation. Most cases of deep frostbite seem to heal in six to twelve months, and the gangrenous tissue, if it has not become infected with bacteria, is essentially superficial and should be able to be removed without amputation. Many unnecessary amputations have been carried out because of impatience at the slow recovery rate of tissue that has suffered deep frostbite; amputation is only necessary when infection has set in and cannot be controlled with antibiotics.

If possible, deep frostbite should be treated under hospital care, not in the field or outdoors. The deep frozen tissue should remain frozen until hospital care is available. If frozen tissues are thawed, the patient will most likely be unable to move as the pain will be severe with any movement. Walking on feet that have been thawed after being frozen will cause permanent damage; however, walking on a frozen foot for twelve to eighteen hours or even longer produces less damage than inadequate warming. As frozen tissue thaws, cells exude fluid. If this tissue is refrozen, ice crystals form and cause more extensive, irreparable damage.

Rapid rewarming is the recommended treatment for deep frostbite and is a proven method of reducing tissue loss. Rubbing the frostbitten area with the hand or snow—akin to rubbing the area with broken glass—should never be done. This treatment does not melt the intracellular ice crystals or increase circulation to the frozen area, but it does break the skin and allow infection to enter into the system. Vasodilator agents do not improve tissue survival. Local antibiotics in aerosol form can be used, but it is unwise to rely on this method alone for combating infection. Sympathectomy, the removal or destruction of affected nerves, does not improve cell survival. The early use of the drug dextran to prevent sludging has limited benefit and may have dangerous side effects. The use of hyperbaric oxygen or supplementary oxygen may increase the tissue tension of oxygen and save some cells partially damaged by cold injury.

Rewarming should be carried out in a water bath with water temperatures ranging from 37.7 to 42.2 degrees Celsius (100 to 108 degrees Fahrenheit). Higher temperatures will further damage already-injured tissues. Rewarming in a large bathtub warms the frozen extremity more rapidly, resulting in less tissue loss in many cases, particularly where frostbite has been deep and extensive. A large container also permits more accurate control of the water temperature. If a bathtub is not available, a bucket, large wastebasket, dishpan, or other similar container can be used. During rewarming, hot water usually must be added to the bath occasionally to keep the temperature correct; in such cases, the injured extremity should be removed from the bath and not returned to it until the water has been thoroughly mixed and its temperature measured. An open flame must not come into contact with the area to which heat is applied, since sensation is lost as a result of the frostbite and the tissue could be seriously burned without the patient noticing.

For rewarming, the frostbitten extremity should be stripped of all clothing, and any constricting bands, straps, or other objects that might stop circulation should be removed. The injured area should be suspended in the center of the water and not permitted to rest against the side or bottom. Warming should continue for thirty to forty minutes. The frostbitten tissues may become quite painful during this process, so it may be necessary to give painkillers to the patient in order to reduce discomfort during or after thawing. Aspirin (as well as codeine, morphine, or meperidine, if needed) may be given for pain. Aspirin or an anticoagulant increases blood circulation by reducing red blood cell platelet formation and thus reducing sludging. Phenoxybenzamine reduces vasoconstriction.

Following rewarming, the patient must be kept warm and the injured tissue elevated and protected from any kind of trauma. One should avoid rupturing blisters that have formed. Blankets or bedclothes should be supported by a framework to avoid pressure on or rubbing of the injured area.

Subsequent care is directed primarily toward preventing infection. Cleanliness of the frostbitten area is extremely important. It should be soaked daily in a body-temperature water bath to which a germicidal soap has been added. If contamination of the water supply is a possibility, the bath water should be boiled and cooled before use. Dead tissue should not be cut or pulled away; the water baths remove such tissue more efficiently.

The afflicted area should be immobilized and kept sterile. Even contact with sheets can be damaging to a frostbitten limb. Sterile, dry cotton may be placed between the fingers or toes to avoid maceration. If infection appears present, as indicated by the area between the frostbitten tissue and healthy tissue becoming inflamed and feeling tender or throbbing, antibiotics such as ampicillin or cloxicillin should be given every six hours. Wet, antiseptic dressings should be applied if gangrene occurs in the damaged tissue. A
tetanus
toxoid booster shot, or human antitoxin if the patient has not been previously immunized against tetanus, should be given. Complete rest and a diet high in protein will help healing. Moderate movement of the afflicted area should be encouraged but should be limited to that done by a physical therapist, without assistance by the patient. Considerable reassurance and emotional support may be required by the patient, as the appearance of the frostbitten area can be alarming.

Amputation in response to infected, spreading gangrene may be needed eventually, but it should be delayed until the natural separation of dead from living tissue and bone has taken place. Radionucleotide scanning helps save frostbitten limbs by accurately demonstrating blood flow in frostbitten extremities, thus predicting what tissue will survive.

Perspective and Prospects

Frostbite is an injury that can affect anyone who works or plays in cold conditions. Increased knowledge about what causes this injury, better equipment, and techniques that minimize its effect have reduced its occurrence. Advances in medical knowledge regarding how the injury occurs within the afflicted tissues have produced treatment protocols that reduce the extent of permanent injury from frostbite.

Prevention is the most effective treatment for frostbite, which can occur only when the body lacks enough heat to keep the extremities above freezing. The overall body-heat deficit results from inadequate clothing or equipment, reduced food consumption, exhaustion, injury or inactivity causing a lack of body movement, or some combination of these factors. Those playing or working in a cold environment should know the conditions under which frostbite may develop. For frostnip to occur, the windchill index must exceed 1,400 and the air temperature must be below the freezing point of exposed skin (-0.53 degrees Celsius). An ambient temperature of -10 to -15 degrees Celsius is usually necessary for deep frostbite to develop.

Adequate clothing—especially boots that allow circulation to occur freely, mittens (not gloves) that cover the hands, and a head covering that protects the face, ears, and neck—must be worn. Boots should be well broken in and large enough to fit comfortably with several pairs of socks. The laces at the top of the boots should not be tight. Gaiters or overboots should be worn if deep or wet snow is anticipated. Windproof or insulated pants should be worn to protect the legs from cold and help keep the feet warm. Dry socks and mitten liners should be carried. Moisture greatly reduces the insulative value of clothing, so it is necessary to stay dry; if clothing becomes wet or damp, one should change into dry items. Plastic bags, worn over bare feet, provide a vapor barrier liner that is effective in helping keep one’s feet dry and warm under cold conditions. Adequate ventilation avoids dampness from excessive perspiration. Dressing in layers—having several light shirts, jackets, or a windbreaker—is better than wearing only one heavy jacket.

Heat production, resulting from exercise or the protective mechanism of shivering, is just as important as clothing in maintaining body temperature. Injuries that cause the victim to go into shock or lie immobilized predispose the victim to frostbite, even when adequate clothing is worn.

Eating high-energy foods and taking in 6,000 or more kilocalories (Calories) a day may be necessary to keep body temperatures constant under very cold or physically demanding conditions. Adequate rest, including eight or more hours of sleep, helps to reduce fatigue, which in turn increases the body’s ability to produce heat. Alcohol and tobacco should be strictly avoided. Alcohol dilates the blood vessels and, although this action temporarily warms the skin, results in increased loss of total body heat. Smoking constricts the blood vessels in the skin and so reduces heat flow to surface areas; this may be sufficient to initiate frostbite in exposed tissue. A person who has sustained frostbite in the past is usually more susceptible to more cold injury. Problems with arthritis may develop in extremities that have been frostbitten.

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