Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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First Climber Found

One of the three climbers lost on Mt. Hood has been found, perished in a snow cave high on the mountain. He succumbed to hypothermia, which represents the second such tragedy in as many weeks, with perhaps more to follow.

As for all such situations, our hearts go out to the family and friends of the climber found and those still missing.

In the northern hemisphere, it is now winter, and so hypothermia and frostbite become serious medical concerns to a greater degree than during other seasons. What follows is a brief primer on the effects of hypothermia:

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). The rate of heat loss via conduction is increased 5-fold in wet clothes and at least 25-fold in cold-water immersion. Windchill refers to the increase in the rate of heat loss (convection) that would occur when a victim is exposed to moving air.

During prolonged exposure to severe cold environmental temperatures, 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. Normal skin temperature in cool weather is 90 to 93° F (32.2 to 33.9° C); this can drop to 70 to 73° F (21.1 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 body temperature of 98.6 to 99.9° F (32.7 to 37.7° C). Thus, hypothermia is felt to occur when the core temperature is at or below 95° F (35° C); mild hypothermia transitions to moderate hypothermia as the core body temperature descends from 95° F (35° C) to 90° F (32.2° C); severe hypothermia is defined as a core body temperature of less than 90° F (32.2° C).

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

95 to 98.6° F (35 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.

90 to 95° F (32.2 to 35° C). Increased muscular incoordination; stumbling gait; decreased or absent shivering; weakness; apathy, drowsiness, and/or confusion; slurred speech.

85 to 90° F (29.4 to 32.2° C). Loss of shivering; confusion progressing to coma; inability to walk or follow commands; paradoxical undressing (inappropriate behavior); complaints of loss of vision; decreased respiratory rate; decreased reflexes.

Below 86° F (30° C). Rigid muscles; decreased blood pressure, heart rate, and respirations; dilated pupils; appearance of death. The victim no longer can control his body temperature and rapidly cools to the surrounding environmental temperature.

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. In the absence of obvious hypothermia, 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.

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).

2. If necessary, protect the airway and cervical spine.

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. 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, or SPACE brand emergency blanket, all from MPI Outdoors, 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 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.

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. 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. 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. 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.

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 sufficiently allow purposeful swallowing in order to prevent choking on the ingested liquids.

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.

If the victim shows any signs of life (movement, pulse, respirations), do not initiate the chest compressions of CPR. If the victim is breathing regularly, even at a subnormal rate, then 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.

If the victim is breathing at a rate of less than 6 to 7 breaths per minute, you should begin mouth-to-mouth breathing 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. 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 can rarely 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, then 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.

Prevention of Hypothermia

1. Carry adequate food and thermal wear, such as Thermax, Capilene, and/or polypropylene (“polypro”) or wool undergarments. Anticipate the worst possible weather conditions. Dress in layers so that you can adjust clothing for overcooling, overheating, perspiration, and external moisture. Use a foundation layer to wick moisture from the body to outer layers. The first layer (such as CoolMax) should keep the skin cool and dry (to avoid perspiration). Add an insulation layer to provide incremental warmth. For shirts, use wool, fleece, Capilene, or polypropylene. Consider a turtleneck or neck gaiter. For pants, wear wool or pile, with a fly. Carry windproof and waterproof outer garments, mittens or gloves (with glove liners), socks, and a hat. In very cold weather, up to 70% of generated heat may be lost by radiation from the uncovered head. Boots should be large enough to accommodate a pair of polypropylene socks (“liner socks”) plus at least one pair of heavy wool socks without cramping the toes.

2. Stay dry. Avoid sweating.

3. Keep hands and feet dry. This is important to avoid frostbite as well. For the feet, aluminum chlorohydrate–containing antiperspirant sprayed onto the skin can help to control sweating. Dr. Murray Hamlet recommends doing this three times a week for the first week of winter, then once a week after that. Avoid leather boots that become soaked with moisture and do not dry out easily.

4. Do not exhaust yourself in cold weather. Do not sit down in the snow or on the ice without insulation beneath you.

5. Seek shelter in times of extreme cold and high winds. Don’t sit on cold rocks or metal. Insulate yourself from the ground with a pad, backpack, log, or tree limb. Carry a properly rated (for the cold) sleeping bag stuffed with Hollofil II, Quallofil, or down. Insulate hands and feet well, even when you are in your sleeping bag, which should be fluffed up prior to entry. Do not enter a sleeping bag if you are wet without drying off first if possible.

6. Do not become dehydrated. In the cold, dehydration is caused by evaporation from the respiratory tree, increased urination, and inadequate fluid intake. Drink at least 3 to 4 quarts (liters) of fluid daily. During extreme exercise, drink at least 5 to 6 quarts per day. Ingesting snow is an inefficient way to replace water, because it worsens hypothermia. Drink cold water from a stream in preference to eating snow. Do not skip meals. Do not consume alcoholic beverages in cold weather. They cause an initial sensation of warmth because of dilation of superficial skin blood vessels, but this same effect contributes markedly to heat loss. At night, fill a canteen or Nalgene water container with at least 1 quart (liter) of water, and sleep with it to keep it from freezing.

7. Consume adequate calories.

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photo of Makalu by Chris Pizzo
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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.