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 five 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 oral temperature is 98.6°F (37°C). Accidental hypothermia occurs when there is an unintentional decrease of 3.6°F (2°C) or more from the normal core body temperature.

Heat is lost from the body to the environment by direct contact (conduction), air movement (convection), infrared energy emission (radiation), conversion of liquid sweat to a gas (evaporation), and exhalation of heated air from the lungs (respiration). It’s 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 ( Fig. 223 ) 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).

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 reaches its maximum effectiveness at generating heat by shivering.

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:

• 91.4°F to 98.6°F (33°C to 37°C ). Mild hypothermia. Sensation of cold; shivering; increased heart rate; urge to urinate; slight incoordination in hand movements; hunger; nausea; fatigue; dizziness; difficulty speaking; increased respiratory rate; increased reflexes (leg jerk when the knee is tapped); red face; muscular incoordination, stumbling gait, amnesia, maladaptive behavior, poor judgment; rapid heart rate converting to slow heart rate, apathy.

• 84.2°F to 91.4°F (29°C to 33°C ). Moderate hypothermia. Stupor progressing to unconsciousness; 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; low blood pressure; rapid breathing rate converting to shallow breathing; possibly nonreactive (to light) or dilated pupils; abnormal heart rhythms; diminished breathing; decreased neurological reflexes.

• 71.6°F to 84.2°F (22°C to 29°C ). Severe hypothermia. 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; fluid in the lungs; increased bleeding tendency; maximum risk for ventricular fibrillation. The victim no longer can control their body temperature and rapidly cools to the surrounding environmental temperature.

• Below 71.6°F (22 °C ). Profound hypothermia. Rigid muscles; barely detectable or absent blood pressure, heart rate, and respirations; dilated pupils; no response to pain; risk for ventricular fibrillation; heart stoppage; little or no brain activity; 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 (21°C) weather. Don’t use yourself as an indicator of warmth—you might 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 might become anxious, repeat themself, or even become delusional. Never leave a victim of even mild hypothermia to fend for themself.

• 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 40.6°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 might grossly understate how cold the victim really is and should be followed with a rectal measurement. Digital electronic eardrum (tympanic membrane) or forehead skin scanners used to measure temperature might also yield a false (compared to the core) reading.

  • Unless the victim has suffered a full cardiopulmonary arrest, the hypothermia itself might not be harmful. Unless tissue is frozen, cold is in many ways protective to the brain and heart. However, if a hypothermic victim is improperly transported or rewarmed, the process might 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.

Prevention of hypothermia

• 1.

  Carry adequate food. 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 Velcro, zipper, or button fly. Carry windproof and waterproof outer garments, mittens or gloves (with glove liners), socks, and a hat. Wear a hat to avoid heat loss 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. Adjust and vent layers frequently as needed.

• 3.

  Keep hands and feet dry. This is important to avoid frostbite as well. Hand Sense is a cream that can be applied to the hands to keep them dry by reducing perspiration. It was designed as a topical protectant and is not a moisturizer. For the feet, aluminum chlorohydrate–containing antiperspirant sprayed onto the skin can help control sweating. Do 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 don’t dry out easily.

• 4.

  Don’t exhaust yourself in cold weather.

• 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 PolarGuard, Quallofil, or down. Consider using a bag in which the down has been treated to achieve water repellency. Insulate hands and feet well, even when you are in your sleeping bag, which should be fluffed up before entry. Don’t enter a sleeping bag if you’re wet without drying off first if possible.

• 6.

  Don’t 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 (liters) per day. Ingesting snow is an inefficient way to replace water and may worsen hypothermia. Drink cold water from a stream in preference to eating snow. Don’t skip meals. Don’t consume alcoholic beverages. 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 water bottle with at least 1 quart (liter) of water (warm if possible), and sleep with it to keep it from freezing. Sleep with medicines (epinephrine, etc.) and batteries that need protection from freezing.

• 7.

  Consume adequate calories.

Mild hypothermia

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

Prevent the victim from becoming any colder. Get them 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, sleeping bags, cloth pads, or other suitable material. If the victim is coherent and can swallow without difficulty, encourage 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 use it. Try to keep the victim in a horizontal position until they is well hydrated. Don’t 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. They have ceased to shiver and shows signs of muscle stiffness. Unless you have a thermometer to measure this victim’s temperature, you must assume that they are severely hypothermic or will soon become so.

Follow the directions for mild hypothermia, with the added caution that it’s best not to allow this victim to walk about until they are fully alert; in addition, don’t give them fluids to drink until they become wide awake and understands what is going on. When the victim can purposefully and easily drink fluids, these should be sweetened with sugar to avoid the complication of low blood sugar (hypoglycemia). Some experts advise placing heated water bottles or padded heat packs in the armpits and groin areas and around the neck to assist with rewarming. Be very careful to not burn the victim’s skin. Wrap heated water bottles with insulation (e.g., fleece) to prevent burns.

Severe and profound hypothermia

Depending on the body temperature, a victim who appears to be asleep might 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. If the victim’s breathing is very shallow, you might not see a vapor trail. Feel for at least 1 minute at the groin (femoral artery) and neck (carotid artery) for a weak and/or slow pulse (see page 28).

If the victim shows any signs of life (movement, pulse, respirations), don’t initiate the chest compressions of cardiopulmonary resuscitation (CPR) . If the victim is breathing, even at a subnormal rate, their 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 might induce ventricular fibrillation. Administer supplemental oxygen (see page 431) by face mask 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 26) 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’re in doubt (about whether the victim is hypothermic, for instance), you should begin standard CPR (see page 30). 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, up to nearly 9 hours, presumably because of the protective effect of the cold. Remember, “no one is dead until they are warm and dead.” In the absence of an obvious fatal injury (such as decapitation), resuscitation and transport to a hospital should be undertaken. Fixed and dilated pupils, failure to identify a pulse or breathing, skin mottling, and stiff muscles all might be mistaken for the condition of death in the setting of hypothermia. A hospital that can provide sophisticated “extracorporeal” (such as heart-lung bypass, similar to what is used for heart surgery, to facilitated rewarming) life support might salvage a patient who suffers prolonged cardiac arrest with the initial appearance of death.

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. Continue CPR until the patient is brought to a hospital, the rescuers are fatigued, or the rescuers are endangered.

If you are the only person present, don’t bother with CPR, because you will not be able to resuscitate the victim until they are rewarmed. Your only hope is that the victim is in a cold-protected state (“metabolic icebox”) and that you can extricate them (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 them as gently as possible.

Rewarming and preparing a hypothermic victim for transport

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 18) and cervical spine (see page 33). Stabilize all other major injuries, such as broken bones. Cover open wounds.

• 3.

  Prevent the victim from becoming any colder. Provide shelter. Remove all their wet clothing and replace it with dry clothing. Don’t give away all of your clothing, however, or you might become hypothermic. Replace wet clothing with sleeping bags, insulated pads, bubble wrap, blankets, or even newspaper. Products from Blizzard ( www.blizzardsurvival.com ) or GrabberWorld ( www.grabberworld.com ) can be used to provide protection from the elements. These include familiar items such as the SPACE Brand Emergency Blanket. If a hypothermia prevention and management kit (containing a ready-heat blanket and heat-reflective shell) is available, use it. An excellent (but much more expensive) product is a hypothermic stabilizer bag. An improvised insulation wrap can be prepared ( Fig. 224 ).

  • Cover the victim’s head and neck. This is very important. Insulate the victim from above and below with blankets. Don’t change blankets unless necessary to keep the victim dry. Another technique is to use skin-to-skin contact by having a warm human rescuer lie inside a sleeping bag with the victim. But remember that in this situation, no heat is really contributed by the bag itself, these rescuers may be needed for other tasks, the healthy rescuer may become cold, and a sleeping bag will not work as well if unable to be zipped closed. Don’t count on a sleeping bag to be adequately prewarmed by a normothermic rescuer’s body heat. Another method 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. Don’t 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. A great deal of warmth can be conserved by using a thin liner bag inside a normal sleeping bag.

  

• 4.

  Don’t 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. If warm water (no hotter than 104°F [40°C]) is available and can be kept warm, the victim’s hands and feet can be immersed.

• 5.

  Keep the victim horizontal. Rapid rewarming or restoration of circulation will release cold, acid-laden blood from the limbs back to the core organs, which might cause a profound deterioration of the victim.

• 6.

  Seek assistance as soon as possible.

Cold water immersion

Water has a thermal conductivity approximately 25 times greater than that of air, and a person immersed in cold water rapidly transfers heat from their skin into the water and can suffer from immersion hypothermia. 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 316), which might lead to confusion, muscle spasm, aspiration of water, and loss of consciousness. Cold water rapidly cools muscles, and the victim loses their ability to swim or tread water. Muscles and nerves might 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.

If a victim is pulled from icy waters and appears to be clinically dead (fixed dilated pupils, no respirations, no detectable pulse), perform CPR until a qualified medical person is available to intervene or you become exhausted. Because of the physiology of cold-water immersion, the victim might be sufficiently protected to survive the event.