INJURIES AND ILLNESSES DUE TO COLD

HYPOTHERMIA (LOWERED BODY TEMPERATURE)

The body generates heat through metabolic processes that can be maximized with involuntary shivering to roughly 5 times the basal level (up to 10 times with maximum exercise). However, shivering is abolished after a few hours of exposure, because of exhaustion and depletion of muscle energy supplies. When a victim loses the ability to shiver, the cooling process becomes quite rapid. Skin, surface fat, and superficial muscle layers then act as an insulating “shell” for the core of vital organs (heart, lungs, liver, kidneys, and so on). People are tropical beings—that is, when they are naked and at rest, the environmental temperature at which body heat is neither gained nor lost is 82°F (28°C). Normal skin temperature in cool weather is 90°F to 93°F (32.2°C to 33.9°C); this can drop to 70°F to 73°F (21.1°C to 22.8°C) before core cooling begins. Accidental hypothermia occurs when there is an unintentional decrease of 3.6°F (2°C) from the normal core (measured rectally) body temperature of 98.6°F to 99.9°F (37°C to 37.7°C). Normal oral temperature is 98.6°F (37°C). Mild hypothermia is considered to occur when the core temperature is between normal and 91.4°F (33°C); moderate hypothermia is core body temperature below 91.4°F (33°C) down to 85.2°F (29°C); severe hypothermia is core body temperature below 85.2°F (29°C) down to 71.6°F (22°C); and profound hypothermia is below 71.6°F (22°C).

Heat is lost from the body to the environment by direct contact (conduction), air movement (convection), infrared energy emission (radiation), the conversion of liquid (sweat) to a gas (evaporation), and the exhalation of heated air from the lungs (respiration). It is important to note that the rate of heat loss via conduction is increased 5-fold in wet clothes and at least 25-fold in cold-water immersion. Windchill (Figure 176) refers to the increase in the rate of heat loss (convection) that would occur when a victim is exposed to moving air. This chill can be compounded further if the victim is wet (conduction, convection, and evaporation).

Figure 176 Windchill determination. To determine windchill, find the ambient air temperature on the top line, and then read down the column to the line that corresponds with the current wind speed. Example: When the air temperature is 10°F and the wind speed is 20 mph, the rate of heat loss is equivalent to −9°F under calm conditions. To convert to metric or Celsius, use the following: 1 mile = 1.61 kilometers; C = 5/9 (F − 32).

At a core body temperature of 96.8°F (36°C), metabolic rate, blood pressure and preshivering muscle tone increase. At 95°F (35°C), the body cannot be any more effective at generating heat by shivering.

Immersion hypothermia refers to the particular case in which a victim has become hypothermic because of sudden immersion into cold water. Again, water has a thermal conductivity approximately 25 times greater than air, and a person immersed in cold water rapidly transfers heat from his skin into the water. The actual rate of core temperature drop in a human is determined in part by these phenomena and in part by how quickly heat is transferred from the core to the skin, skin thickness, the presence or absence of clothing, the initial core temperature, gender, fitness, water temperature, drug effects, nutritional status, and behavior in the water.

A sudden plunge into cold water causes the victim to hyperventilate (see page 300), which may lead to confusion, muscle spasm, and loss of consciousness. The cold water rapidly cools muscles and the victim loses the ability to swim or tread water. Muscles and nerves may become ineffective within 10 minutes. Over the ensuing hour, shivering occurs and then ceases. Anyone pulled from cold water should be presumed to be hypothermic. In terms of survival, the aphorism is that when a person is plunged into very cold water (32°F or 0°C), he or she has 1 minute to control breathing (e.g., to stop hyperventilating from the “gasp reflex”), 10 minutes of purposeful movement before the muscles are numb and not responsive, 1 hour before hypothermia leads to unconsciousness, and 2 hours until profound hypothermia causes death.

The progression of hypothermia leads to predictable physiological responses, which roughly correspond to different body temperatures. Although not invariable, the signs and symptoms are as follows:

91.4°F to 98.6°F (33°C to 37°C). Sensation of cold; shivering; increased heart rate; urge to urinate; slight incoordination in hand movements; increased respiratory rate; increased reflexes (leg jerk when the knee is tapped); red face; muscular incoordination, stumbling gait, maladaptive behavior, rapid heart rate converting to slow heart rate, apathy.

85.2°F to 91.4°F (29°C to 33°C). Stupor; decreased or absent shivering; weakness; apathy, drowsiness, and/or confusion; poor judgment; slurred speech; inability to walk or follow commands; paradoxical undressing (inappropriate behavior); complaints of loss of vision; amnesia; rapid heart rate converting to slow heart rate; rapid breathing rate converting to shallow breathing; loss of shivering; possible nonreactive or dilated pupils, abnormal heart rhythms, diminished breathing.

71.6°F to 85.2°F (22°C to 29°C). Minimal breathing; coma; decreased respiratory rate; decreased neurologic reflexes progressing to no reflexes; no voluntary motion or response to pain; very slow heart rate, low blood pressure; maximum risk for ventricular fibrillation. The victim no longer can control his body temperature and rapidly cools to the surrounding environmental temperature.

Below 71.6°F (22°C). Rigid muscles; barely detectable or absent blood pressure, heart rate, and respirations; dilated pupils; risk for ventricular fibrillation; appearance of death.

The first principle of therapy is to suspect hypothermia. Any person who is found in a cold environment should be suspected of suffering from hypothermia. The definition of “cold environment” is variable. Someone who is wet, improperly dressed, and intoxicated with alcohol can become hypothermic in 70°F weather. Do not use yourself as an indicator of warmth—you may be perfectly comfortable while your companion is lapsing into hypothermia.

Unless the victim is found frozen in a block of ice or has been recently pulled from frigid waters, the most likely clue to a hypothermic state is altered mental status. The winter hiker who gradually loses interest and lags behind the group (“Just leave me behind—I’ll catch up”), who dresses inappropriately for the weather or begins to undress, or who begins to stumble and make inappropriate remarks should be immediately evaluated for low body temperature. A hypothermic individual may become anxious, repeat himself, or even become delusional. Never leave a victim of even mild hypothermia to fend for himself.

The second principle of therapy is to measure the victim’s temperature. This should be done, if possible, with a thermometer calibrated to read below 94°F (34.4°C), which is the cutoff for most standard oral thermometers. Hypothermia thermometers with a range of 75°F to 105°F (23.9°C to 40.5°C) are available. Temperature ideally should be measured rectally, although this is often impractical. Oral and axillary (armpit) temperatures are unreliable in this situation, and should be used only to screen for low body temperature. That is, if they are normal, the victim will have at least a normal body temperature, but could be hotter. However, if they are low, they may grossly understate how cold the victim really is, and should be followed with a rectal measurement. Digital electronic eardrum scanners used to measure temperature may also yield a false (compared to the core) reading.

Unless the victim has suffered a full cardiopulmonary arrest, the hypothermia itself may not be harmful. Unless tissue is actually frozen, cold is in many ways protective to the brain and heart. However, if a hypothermic victim is improperly transported or rewarmed, the process may precipitate ventricular fibrillation, in which the heart does not contract, but quivers in such a fashion as to be unable to pump blood. The burden of rescue is to transport and rewarm the victim in a way that does not precipitate ventricular fibrillation.

The following general rules of therapy apply to all cases:

1. Handle all victims gently. Rough handling can cause the heart to fibrillate (cause a cardiac arrest). Secure the scene and avoid creating additional victims via unstable snow, ice, or rock fall.

2. If necessary, protect the airway (see page 22) and cervical spine (see page 37). Stabilize all other major injuries, such as broken bones.

3. Prevent the victim from becoming any colder. Provide a shelter. Remove all his wet clothing and replace it with dry clothing. Don’t give away all of your clothing, however, or you may become hypothermic. Replace wet clothing with sleeping bags, insulated pads, bubble wrap, blankets, or even newspaper. The “blizzard pack” from Blizzard Protection Systems, Ltd. (www.blizzardpack.com) can be used to provide protection from the elements. The Pro-Tech Extreme bag or vest, SPACE brand emergency bag, SPACE brand all-weather blanket, and SPACE brand emergency blanket, all from MPI Outdoors (www.mpioutdoors.com), are other options for this purpose.

Cover the victim’s head and neck. Insulate the victim from above and below with blankets. Do not change blankets unless necessary to keep the victim dry. If possible, put him in a sleeping bag sandwiched between two warm rescuers. But remember that in this situation, no heat is really contributed by the bag itself. Do not count on a sleeping bag to be adequately prewarmed by a normothermic rescuer’s body heat. Another technique is to blow warm air from an electric hair dryer into the bag with the victim. Hot water in bottles, well insulated with clothing to prevent skin burns, may be placed next to the victim in areas of high heat transfer, such as the neck, chest wall, and groin. A great deal of warmth may be conserved by using a thin liner bag inside a normal sleeping bag.

4. Do not attempt to warm the victim by vigorous exercise, rubbing the arms and legs, or immersing in warm water. This is “rough handling” and can cause the heart to fibrillate if the victim is severely hypothermic.

5. Seek assistance as soon as possible.

Mild Hypothermia

The victim of mild hypothermia is awake, can answer questions intelligently, and complains of feeling cold. He may or may not be shivering.

Prevent the victim from becoming any colder. Get him out of the wind and into a shelter. If necessary, build a fire or ignite a stove for added warmth. Gently remove wet items of clothing and replace them with dry garments. This is very important, even if the victim will be very briefly exposed out in the open. If no dry replacements are available, the clothed victim should be covered with a waterproof tarp or poncho to prevent evaporative heat loss. Cover the head, neck, hands, and feet. Insulate the victim above and below with blankets. If the victim is coherent and can swallow without difficulty, encourage the ingestion of warm sweetened fluids. Good choices include warm gelatin (Jell-O), juice, or cocoa, because carbohydrates fuel shivering. If only cool or cold liquids are available for drinking, this is fine. Avoid heavily caffeinated beverages. If a dry sleeping bag is available, one or more rescuers should climb in with the victim and share body heat. However, this technique may not be very effective, and great care must be taken not to cause the victim to become wet (e.g., from the rescuer’s sweat). Do not apply commercial heat packs, hot-water-filled canteens, or hot rocks directly to the skin; they must be wrapped in blankets or towels to avoid serious burns. Try to keep the victim in a horizontal position until he is well hydrated. Do not vigorously massage the arms and legs, because skin rubbing suppresses shivering, dilates the skin, and does not contribute to rewarming.

Moderate Hypothermia

The victim of moderate hypothermia has become apathetic and mildly confused, wishes to be left behind, and is uncooperative. Speech is often slurred, and logic is on the wane. The victim rapidly becomes uncoordinated and clumsy, often stumbling. He has ceased to shiver, and shows signs of muscle stiffness. Unless you have a thermometer to measure this victim’s temperature, you must assume that he is severely hypothermic or will soon become so. Follow the directions for mild hypothermia, with the added caution that it is best not to allow this victim to walk about until he is fully alert; in addition, do not give him fluids to drink until he becomes wide awake and understands what is going on.

Severe Hypothermia

Depending on the body temperature, a victim who appears to be asleep may be in a complete coma. Below 86°F (30°C), humans become poikilothermic, like a snake, and take on the temperature of the environment.

Examine the victim carefully and gently for signs of life. Listen closely near the nose and mouth and examine chest movement for spontaneous breathing. Feel at the groin (femoral artery) and neck (carotid artery) for a weak and/or slow pulse (see page 33).

If the victim shows any signs of life (movement, pulse, respirations), do not initiate the chest compressions of cardiopulmonary resuscitation (CPR). If the victim is breathing regularly, even at a subnormal rate, his heart is beating. Because hypothermia is protective, the victim does not require a “normal” heart rate, respiratory rate, and blood pressure. Pumping on the chest unnecessarily is “rough handling,” and may induce ventricular fibrillation. Administer supplemental oxygen (see page 431) by facemask if it is available.

If the victim is breathing at a rate of less than 6 to 7 breaths per minute, you should begin mouth-to-mouth breathing (see page 29) to achieve an overall rate of 12 to 13 breaths per minute.

If help is on the way (within 2 hours) and there are no signs of life whatsoever, or if you are in doubt (about whether the victim is hypothermic, for instance), you should begin standard CPR (see page 32). If possible, continue CPR until the victim reaches the hospital. Rescue breathing should take priority over chest compressions, particularly in the victim of cold-water immersion. There have been documented cases of “miraculous” recoveries from complete cardiopulmonary arrest associated with environmental hypothermia after prolonged resuscitation, presumably because of the protective effect of the cold. Remember, “no one is dead until he is warm and dead.” However, all of these victims were ultimately resurrected in the hospital, after they had been fully rewarmed.

A victim of severe hypothermia cannot be rewarmed in the field. If a hypothermic victim suffers what you determine to be a cardiac arrest in the wilderness, transport should be the first priority. If enough rescuers are present to allow CPR and simultaneous transport, do both. If you are the only person present, do not bother with CPR, because you will not be able to resuscitate the victim until he is rewarmed. Your only hope is that the victim is in a cold-protected state (“metabolic icebox”) and that you can extricate him (as gently as possible!) to sophisticated medical attention.

In any case of severe hypothermia, transport should be undertaken as soon as possible. Take care to cover the victim with dry blankets and to handle him as gently as possible. Rapid rewarming or restoration of circulation will release cold, acid-laden blood from the limbs back to the core organs, which may cause a profound deterioration of the victim.