CHAPTER 304

Cold Injuries

The skin and the tissues under it are kept at a constant temperature (about 98.6° F, or 37° C) by the circulating blood and other mechanisms. The blood gets its heat mainly from the energy given off by cells when they burn (metabolize) food—a process that requires a steady supply of food and oxygen. A normal body temperature is necessary for proper functioning of all the cells and tissues in the body. In a person with low body temperature, most organs, especially the heart and brain, become sluggish and eventually stop working.

Body temperature falls when the skin is exposed to colder surroundings. In response to this fall in temperature, the body uses several protective mechanisms to generate additional heat. For example, the muscles produce additional heat through shivering. Also, the small blood vessels in the skin narrow (constrict), so that more blood is diverted to vital organs, such as the heart and brain. However, as less warm blood reaches the skin, body parts such as the fingers, toes, ears, and nose cool more rapidly. If body temperature falls much below about 88° F (about 31° C), these protective mechanisms stop working, and the body cannot warm itself. If body temperature falls below 83° F (about 28° C), death is likely.

Cold injuries are less likely to occur, even in extremely cold weather, if the skin, fingers, toes, ears, and nose are well protected or are exposed only briefly. The risk of cold injuries increases when the flow of blood is too slow, when food intake is inadequate, or when insufficient oxygen is available, as occurs at high altitudes. Keeping warm in a cold environment requires several layers of clothing— preferably wool or synthetics such as polypropylene, because these materials insulate even when wet. Because the body loses a large amount of heat from the head, a warm hat is essential. Eating enough food and drinking enough fluids (particularly warm fluids) also help. Food provides fuel to be burned, and warm fluids directly provide heat and prevent dehydration. Alcoholic beverages should be avoided, because alcohol widens (dilates) blood vessels in the skin, which makes the body temporarily feel warm but actually causes greater heat loss.

Cold injuries include hypothermia, frostnip, chilblains, immersion foot, and frostbite. Other problems related to the cold include Raynaud’s syndrome (see page 426) and allergic reactions to the cold (see page 1121).

Did You Know…

Drinking alcoholic beverages actually makes the body colder because the widening of blood vessels that makes a person feel warm allows more heat to escape from the body.

Hypothermia

Hypothermia is a dangerously low body temperature.

Being surrounded by too cold of an environment, having certain disorders, being unable to move, or a combination can cause body temperature to become too low.

The person shivers but then may become confused and lose awareness.

Getting warm and dry can lead to recovery unless the body temperature is very low.

If the body temperature is very low, doctors may warm the person with warmed oxygen and heated fluids given intravenously or passed into the abdominal or chest cavity through plastic tubes. Doctors also provide heat to the outside of the body.

Hypothermia results when the body loses more heat than can be replaced by increasing metabolism (through exercise) or by increasing warming from external sources, such as a fire or the sun. Wind increases heat loss, as does sitting or lying on a cold surface or being immersed in water. Sudden immersion in very cold water may cause fatal hypothermia in 5 to 15 minutes. However, a few people, mostly infants and young children, have survived for as long as 1 hour completely submerged in ice water. The shock can shut off all systems, essentially protecting the body. Hypothermia may also occur after prolonged exposure in only moderately cool water.

SPOTLIGHT ON AGING

Aging takes a toll on the body’s ability to adapt to the cold. With aging, the body becomes less efficient at shivering and at diverting blood away from the surface of the body. Also, the layer of fat just under the skin thins, so there is less insulation to prevent heat loss.

The body’s ability to produce heat is decreased by disorders that commonly affect older people, such as hypothyroidism. The body’s ability to retain heat is decreased by disorders such as diabetes. A person who is less able to move around because of an injury or a disorder such as a stroke or arthritis is also at a greater risk of dangerous cooling, because the decreased movement generates less heat-producing muscle activity. Alcohol and certain drugs, such as antidepressants, increase the risk as well.

Hypothermia is almost always preventable. Older people are advised to take the following precautions:

Maintain a warm environment. Older people sometimes keep their home at a lower-than-desirable temperature as a means of saving money, but the thermostat should be set at 68° F or higher. It is especially important that the bedroom be kept warm. Fuel assistance programs and home winterization programs may help defray costs.

Wear several layers of clothing. Clothing made of wool or synthetic materials such as polypropylene are especially useful because these materials insulate even when they become wet. Because the body loses a large amount of heat from the head, wearing a hat is important. Fingers and toes must also be protected.

Eat warm foods and drink warm fluids. Food provides the body with fuel to be burned, and warm fluids provide heat and prevent dehydration.

Avoid alcoholic beverages. Alcohol dilates blood vessels in the skin, which makes the body temporarily feel warm but actually causes greater heat loss.

Exercise regularly. Exercise can increase the body’s production of heat.

People at greatest risk are those who are lying immobile in a cold environment—such as people who have had a stroke or a seizure or who are unconscious from intoxication, a low blood sugar level, or an injury. Because they are not moving, these people generate less heat and also are unable to leave the cold environment. Such people are at risk of becoming hypothermic even when the surrounding temperature may be only as cold as 55 or 60° F (about 13 to 16° Celsius [C]). The very young and the very old are at particular risk. People in these age groups often do not compensate for cold as well as young adults and are dependent on others to anticipate their needs and keep them warm. Very old people quite often become hypothermic while indoors from sitting immobile in a cold room for hours. Infants lose body heat rapidly and are particularly susceptible to hypothermia. Sometimes a disorder, such as a widespread infection or an underfunctioning thyroid gland, causes or contributes to hypothermia.

Symptoms

Initial symptoms include intense shivering and teeth chattering. As body temperature falls further, shivering stops and movements become slow and clumsy, reaction time is longer, thinking is blurred, and judgment is impaired. These symptoms may develop so gradually that people, including companions of the affected person, do not realize what is happening. People may fall, wander off, or simply lie down to rest. When shivering stops, people become more sluggish and slip into a coma. The heart and breathing rates become slower and weaker. Eventually the heart stops.

The lower the body temperature is, the higher the risk of death. Death may occur at body temperatures below 88° F (about 31° C) but is most likely to occur below 83° F (about 28° C).

Diagnosis

Doctors diagnose hypothermia by measuring body temperature, typically with a rectal thermometer. Conventional thermometers do not record below 94° F (about 34° C). Thus, special thermometers are needed to measure temperatures in severe hypothermia. Blood and sometimes other tests are done to see whether a disorder caused hypothermia.

Treatment

In the early stages, drying the body, changing into warm dry clothing, being covered with warm blankets, and drinking hot beverages can bring about recovery. In people who are found unconscious, further heat loss is prevented by wrapping them in a warm dry blanket and, if possible, removing wet clothing and moving them to a warm place while arrangements are made for immediate transportation to a hospital. Cardiopulmonary resuscitation (CPR) is only recommended outside of a hospital after very careful consideration for the following reasons:

It is difficult for untrained people to detect very faint respirations and heartbeats.

Often, even if no pulse can be felt and no heartbeat can be heard, the heart may be beating. Applying chest compressions to a cold beating heart often disturbs heart rhythm, resulting in death.

A severely hypothermic person must be handled gently, because a sudden jolt may cause an irregular heart rhythm, (arrhythmia) that could be fatal.

In the hospital, doctors warm the person with warmed oxygen and heated fluids given intravenously or passed into the abdominal or chest cavity through plastic tubes inserted into those areas. In addition, the blood may be warmed through the process of hemodialysis (in which the blood is pumped out of the body, through a filter with a heating attachment, and back into the body) or with a heart-lung machine (which pumps blood out of the body, heats the blood, adds oxygen, and then returns the blood to the body).

Because some people with hypothermia who have arrived at the hospital with no signs of life have recovered, doctors may continue resuscitation efforts until the person is warmed but still shows no signs of life. If certain blood test results are extremely abnormal, the person is already dead.

Nonfreezing Tissue Injuries

In nonfreezing tissue injuries, parts of the skin are chilled but not frozen.

Nonfreezing tissue injuries include frostnip, immersion foot, and chilblains.

Frostnip: Frostnip is a cold injury in which the chilled areas of skin become numb, swollen, and red. The only treatment needed is warming the area for a few minutes. During warming, the area may hurt or itch intensely. No permanent damage results, although sometimes the area is particularly sensitive to cold for months or years afterward.

Immersion Foot: Immersion foot (trench foot) is a cold injury that develops when a foot is kept in wet, cold socks and boots for several days. The foot is pale, clammy, swollen, and cold. After warming, the foot becomes red and painful to the touch. Sometimes blisters develop, which may open and become infected. The skin may become overly sensitive to changes in temperature. Treatment consists primarily of the following measures:

Gently warming, drying, and cleaning the foot

Elevating the foot

Keeping the foot dry and warm

Some doctors give antibiotics to prevent infection. A tetanus booster is given if the person’s tetanus vaccination is not current. Rarely, this type of injury occurs in the hands. Immersion foot can often be prevented by changing socks and drying the feet at least daily.

Chilblains: Chilblains (pernio) is an uncommon reaction that may occur with repeated exposure to cold. Symptoms include itching, pain, redness, swelling, and, in rare cases, discolored areas or blisters on the affected area (usually the leg or fingers). The condition is uncomfortable and recurrent but not serious. Preventing exposure to cold is the best treatment. The drug nifedipine, taken by mouth, sometimes relieves symptoms.

Frostbite

Frostbite is a cold injury in which an area of the body is frozen.

Extreme cold may freeze tissues, destroying them and sometimes surrounding tissues.

The area may be numb, white, swollen, blistered, or black and leathery.

The area is rewarmed in warm water as soon as possible.

Most areas heal over time, but sometimes surgery is required to remove dead tissue.

The damage caused by frostbite results from a combination of factors. Freezing kills some cells: others survive. Because cold causes blood vessels to narrow, tissue that is near the frozen area but not itself frozen may be damaged as a result of the decreased blood flow. Sometimes cold also causes clots to form in small blood vessels in this tissue. These clots may limit blood flow so much that the tissue dies. When blood flow returns to the affected area, the damaged tissues release a number of chemical substances that promote inflammation. Inflammation worsens the damage caused by the cold. In addition, toxic substances are released into the bloodstream as frozen tissue is warmed.

Exposure to below-freezing temperatures puts any part of the body at risk of frostbite. The risk of frostbite damage depends on how cold it is and how long the part was exposed. People at greatest risk of developing frostbite are those who have poor circulation because of diabetes or arteriosclerosis, blood vessel spasm (which may be caused by smoking, some neurologic disorders, or certain drugs), or constriction of blood flow by gloves or boots that are too tight. Exposed hands and feet and an exposed face are most vulnerable. Contact with wetness or metal accelerates freezing and is particularly dangerous.

Symptoms

Symptoms vary with the depth and amount of tissue frozen. Shallow frostbite results in a numb white patch of skin that peels after warming. Slightly deeper frostbite causes blisters and swelling of the affected area. Deeper freezing causes the extremity to feel numb, cold, and hard. The area is pale and cold. Blisters often appear. Blisters filled with clear fluid indicate milder damage than do blisters filled with blood-stained fluid.

The extremity may become gray and soft (wet gangrene). If wet gangrene develops, in many cases the extremity must be amputated. More frequently, the area becomes black and leathery (dry gangrene).

Diagnosis

Frostbite is diagnosed by its typical appearance and occurrence after significant exposure to cold. Sometimes frostbite appears the same as nonfreezing injuries for the first few days. After a period of time, frostbitten tissue develops characteristics that differentiate it from nonfreezing injuries.

Treatment

Outside of the Hospital: People who have frostbite should be covered with a warm blanket because they may also have hypothermia. When possible, warming of the frostbitten area should begin immediately. The area is immersed in warm water that is no hotter than can be comfortably tolerated by the caregiver (100 to 104° F or about 40° Celsius [C]). Rubbing the area (particularly with snow) leads to further tissue damage. Because the area has no sensation, people cannot tell if a burn is developing. Thus, the area should not be warmed in front of a fire or with a heating pad or electric blanket.

It is more damaging to thaw and refreeze tissue than to allow it to remain frozen. Thus, if people with frostbite must be re-exposed to freezing conditions, particularly if they must walk on frostbitten feet, the tissue should not be thawed. Thawed feet are more vulnerable to damage from walking. If people must walk on frostbitten feet to reach help, the feet should not be thawed first. Also, every effort should be made to protect the damaged tissue from rubbing, constriction, or further damage. The feet are cleaned, dried, and covered. People are kept warm and given an analgesic if possible. They are taken to a hospital as soon as possible.

In the Hospital: In the hospital, warming is begun or continued. Full rewarming takes about 15 to 30 minutes. The frostbitten area becomes extremely painful as it is warmed, so an injection of an opioid analgesic may be necessary. Blisters should not be broken. If blisters break, they should be covered with antibiotic ointment.

Once the tissue is warmed, the frostbitten area should be gently washed, dried, wrapped in sterile bandages, and kept meticulously clean and dry to prevent infection. Anti-inflammatory drugs, such as ibuprofen by mouth, or aloe vera gel applied topically helps relieve the inflammation. Infection requires use of antibiotics, although some doctors try to prevent infection from occurring by giving antibiotics to all people with deep frostbite. Some doctors also use drugs given intravenously to improve circulation to the affected area, although these forms of treatment are beneficial only in the first few days after injury.

After Hospital Discharge: Whirlpool baths with warm water (about 98.6° F, or 37° C) three times per day followed by gentle drying, rest, and time are the best ongoing treatments. Most people slowly improve over several months, although amputation is sometimes necessary to remove the dead tissue. Because frostbite may appear to affect a larger area and to be more severe than it will weeks or months later, the decision to amputate is usually postponed for several months until the area has had time to heal. Sometimes an imaging test, such as magnetic resonance imaging (MRI), radio-nuclide scanning, microwave thermography, or a laser-Doppler flow study, helps determine which areas may recover and which will not. Areas that will not recover require amputation. Some people develop numbness or oversensitivity to cold after frostbite heals.