Introduction

Every chemical reaction has an ideal temperature at which it takes place. Temperatures outside a given range can make undesirable things happen in a reaction; that’s why you may find your digital camera’s lithium battery has mysteriously lost all its power after a frigid night in the mountains. Everything that happens inside your body is the result of complex chemical reactions; therefore your body operates best under a particular set of conditions. Expose it to extremes of temperature and a host of problems can arise.

The ideal temperature for the human body is 98.6°F. As warm-blooded creatures, our bodies have mechanisms in place to maintain a core temperature very close to that number. If you get too cold you shiver. Your muscles rapidly contract and relax, burning calories and generating heat. In addition, a chemical process called oxidative phosphorylation revs up inside your cells. Fats and sugars are burned like molecular logs on a fire in order to warm you up. Blood is redirected from the cold extremities to the internal organs, preserving body heat and preventing excessive cooling of the body's blood supply.

If you get too hot, on the other hand, blood is redirected to the outer surfaces of the body where it can be cooled by radiation of heat into the surrounding environment and by evaporating sweat.

In either case, the body's goal is to keep its internal organs at that ideal operating temperature, 98.6 degrees. Stray a few degrees too hot or too cold, and chemical reactions that drive your internal organs will start to go haywire. If the change isn't corrected or gets worse organs will begin to shut down. Death may be the swift and unfortunate result.

Hypothermia is estimated to cause over 600 deaths each year in the United States. Early detection is paramount. One of the first signs is uncontrollable shivering. Individuals suffering from mild hypothermia are usually alert, but may show signs of disorientation, irritability, apathy, or confusion.

Hypothermia

According to the Centers for Disease Control (CDC), hypothermia is defined as a “preventable lowering of the core body temperature to or below 95 degrees Fahrenheit.” Hypothermia is estimated to cause over 600 deaths each year in the United States. The elderly are at the highest risk of hypothermia, but there are a host of other predisposing factors. These include things such as drug use, alcohol intoxication, and most notably, wet or insufficient clothing.

Alcohol is a significant risk factor. It causes the blood vessels to widen, allowing greater blood flow to the extremities and all throughout the body. This action is known as vasodilation (vaso = blood vessel, dilation = to widen). The result is that the victim may feel warmer, while at the same time losing more heat to his surroundings. Many types of drugs, both illegal and legal, impair one's ability to deal with their surroundings. Even a prescribed pain-killer such as a narcotic may dull a person's ability to accurately assess her condition and take the appropriate steps for survival.

Clothing provides insulation from cold weather by trapping warm air that has been heated by the body. Air is trapped between the skin and clothing, as well as among the fibers of the clothing itself. Wind and water significantly reduce a material's insulating capacity. Outdoor enthusiasts should be constantly vigilant for signs and symptoms of hypothermia, especially in friends or group-members who have been exposed to a cold, wet environment. River rafters who have been submerged in water have been known to contract hypothermia even on relatively warm, sunny days.

One of the first signs of hypothermia is uncontrollable shivering. Individuals suffering from mild hypothermia are usually alert, but may begin to show signs of disorientation, irritability, apathy, or confusion. If a member of your group is showing early signs of hypothermia, begin talking to her immediately and assess her reactions. If she denies having the symptoms of hypothermia or feeling cold, trust your observations rather than her assertions.

In cases of moderate hypothermia, the situation worsens rapidly. The victim is sliding down a slippery slope, and the situation is already a serious emergency. Confusion and disorientation progressively worsen; the victim's speech may become slow and slurred. The victim may have difficulty walking straight and staying balanced, a condition known as ataxia. These signs and symptoms occur as the blood vessels constrict and circulation slows. Heart rate and breathing become depressed; the victim may complain of feeling drowsy. He may even insist on being left alone or allowed to sleep.

In late stages of hypothermia, brain function deteriorates even further, predisposing the victim to poor decisions. An individual with hypothermia may inexplicably begin stripping off layers of clothing, increasing their risk and exposure. A person suffering from hypothermia may become irritable and combative as well, making them difficult to deal with.

Once severe hypothermia sets in the victim may appear profoundly drunk or lose consciousness. All coordination is gone, resulting in an inability to walk or move. Breathing becomes so shallow that it may be difficult to detect. The body may become rigid, and the eyes dilated. The skin will feel cold to the touch and appear cyanotic, having a bluish tint.

Hypothermia must be managed as soon as possible. While mild hypothermia can be effectively managed in the field, moderate or severe hypothermia requires immediate hospitalization. Improper or aggressive rewarming of victims suffering from severe hypothermia can result in an abundance of other problems, including heart failure. Remember that in cases of moderate or severe hypothermia, the victim must be evacuated and treated by a medical professional if at all possible. Field treatment of moderate and severe hypothermia should remain a last resort.

If hypothermia is detected while still in it's initial stage, or if evacuation is not a possibility, the condition should be managed as effectively as possible in the field. When managing hypothermia, the first step is isolating the victim from exposure to the environmental factors that led to the problem in the first place, followed by gradual and controlled rewarming. If the problem was brought about by a cold, driving wind, create an effective windbreak or set up a tent. If it's raining, get out of the rain by finding or making shelter. If the person experiencing hypothermia was submerged in cold water, remove the wet clothing and begin rewarming with dry clothes or a sleeping bag.

Mild hypothermia can usually be managed with passive rewarming. This method relies on the victim's own production of heat to rewarm the body. After wet clothing has been removed and the skin dried, the victim should be wrapped in a sleeping bag, blankets, towels, or whatever else is available.

Moderate hypothermia is often treated first with active rewarming followed by passive rewarming. Active rewarming involves applying an external source of heat to the skin. This can involve placing water that has been warmed on a campstove or fire into a bottle or hydration bladder and placing it inside the sleeping bag or blanket with the victim. Another human body may also act as a source of active rewarming for a hypothermia victim.

Severe hypothermia requires active internal rewarming. There are several types of active internal rewarming; they all require an appropriately equipped medical facility. Cardiopulmonary bypass involves circulating the patient's blood through a rewarming device then returning it to the body. However, many hospitals are not equipped to offer this treatment. Another treatment option involves having the patient breathe pre-warmed air. Both of these methods are designed to raise the core body temperature in a controlled and gradual manner in order to avoid heart failure and other problems associated with aggressive rewarming. Hypothermia treatment in a medical facility can also include the use of antibiotics and fluid replacement therapy.

As with many topics in wilderness medicine, the best course of action is prevention. If you're outdoors, remain constantly vigilant. If you or anyone else in your group has been exposed to circumstances that could lead to hypothermia, take appropriate action and pay close attention. Hypothermia is a quick and silent killer. In particular, be alert for individuals complaining of being profoundly cold, exhibiting signs of confusion, slurred speech, or drowsiness. Watch for unusual behavior including irritability, denial, and lack of coordination.

Frostbite

Exposure to cold temperatures causes blood vessels near the surface of the body to constrict, reducing blood flow and thus loss of heat to the surroundings. This serves as one of the body's protective measures against hypothermia, or cooling of the core body temperature. Sometimes there is an unfortunate side-effect of this mechanism, especially in sub-freezing temperatures. It is known as frostbite. When the temperature of the skin or extremities dips below freezing, the water and liquids inside and between cells begin to crystallize. As the water freezes, the microscopic ice crystals rupture and kill cells, causing irreversible tissue damage.

In the past doctors have advocated multiple and sometimes confusing classification systems for assessing the severity of frostbite. Recently some experts have moved towards describing frostbite as either “superficial” or “deep.” Since it's simple, easy to remember, and effective, we'll use this method.

The symptoms of superficial frostbite begin with stinging or pain in the affected area, followed by a feeling of numbness and cold. Superficial frostbite may appear as a white or gray patch of skin with surrounding redness. As the condition worsens clear blisters may form in the affected area. Upon palpation, the skin will still feel soft and malleable. If pressing a finger against the affected skin leaves an indentation, there is still healthy tissue underneath the damaged skin.

If the skin is hard to the touch, frostbite may have already reached the deeper tissues. Deep frostbite is also often accompanied by black hemorrhagic blisters and dry, black, necrotic tissue.

Frostbitten limbs or appendages should be rewarmed by immersion in luke-warm or tepid water (about 100°F). However, rewarming should only take place if there is no risk of refreezing. Partial thawing followed by refreezing results in more damage than extended freezing alone. If warmth cannot be maintained, avoid rewarming frostbitten extremities until such a time that continued warmth can be guaranteed. After rewarming, frostbite victims experience severe throbbing pain and redness. Many victims also complain of a persistent prickling or tingling feeling that can last for weeks. Long-term symptoms include cold sensitivity, numbness, and excessive perspiration.

Rubbing or massaging frostbitten areas of the body is not recommended, since it will only worsen the condition of the already-damaged tissues. Pressure dressings or elastic bandages reduce circulation and are not recommended unless necessary to stop bleeding from another injury. In any case of frostbite, medical attention should be sought out as soon as possible, preferably at a burn or trauma center. In severe cases of frostbite there is an extremely high risk of infection, gangrene, and other complications.

As always, the first and most important step in managing frostbite is prevention. Gaining the appropriate knowledge and training is a big step in the right direction. Be aware that extremities such as toes, fingers, ears, lips, and the nose are at the highest risk for frostbite. If you will be pursuing an activity where cold weather is a possibility, always pack for the worst-case scenario. Make sure you'll have a spare change of dry, warm clothes available, including gloves, socks, and something to cover the head, ears, and face.

Heat Exhaustion and Heat Stroke

As soon as the ambient temperature rises above that of the body, the body can no longer lose heat through radiation. Instead it begins to gain heat from the surrounding environment, and must therefore lose that heat through other methods. Evaporation works best in a dry climate. As humidity approaches 100%, however, the body also loses its ability to dissipate heat through evaporation.

Heat exhaustion is the most common form of heat-related illness. It results when the body generates more heat than it is able to dissipate. If heat exhaustion isn't controlled, it can eventually result in a more serious situation, heat stroke. Predisposing factors for heat exhaustion and heat stroke include heat (obviously), humidity, heavy physical activity, dehydration, and hyponatremia (a low salt-concentration in body fluids). Add a few of these circumstances together and you have a recipe for heat injury.

Fortunately the human body is a remarkable machine which has the ability to adapt to its surroundings. People who live and work in hot climates can adapt to a certain extent. Their bodies tend to retain more water. They sweat more profusely and earlier than others who are not acclimatized to heat. This doesn't mean that someone who lives in Phoenix, Arizona, isn't going to get heat stroke—according to the CDC the number of heat-related deaths in Arizona is 3-7 times higher than the national average. It just means that you should be additionally careful if you or someone in your group isn't used to hot conditions.

The signs and symptoms of heat exhaustion can be difficult to nail down. Usually they include nausea and vomiting, headache and muscle pain, dizziness, irritability, weakness, and fainting.

In cases of heat exhaustion, body temperature will be less than 106 degrees Fahrenheit, and may even be normal. As the situation worsens, the body's heat regulation systems begin to break down. This can result in a steady and uncontrolled rise in temperature.

Once core body temperature rises past 106 degrees Fahrenheit, the cells of the body can only last for a short period of time (sometimes as short as 45 minutes) before beginning to sustain damage. If the temperature gets hot enough, or the condition lasts long enough, cells begin to die and organs will shut down. This condition is referred to as heat stroke and it can be accompanied by a wide variety of symptoms.

If heat stroke is suspected, immediately begin evacuation for hospitalized care. The longer a case of heat stroke remains untreated or unmanaged, the worse the long-term prognosis becomes for the victim. Heat stroke can easily result in debilitating organ dysfunction or death.

Signs and symptoms of heat stroke include all the signs and symptoms of heat exhaustion. In addition, victims may experience confusion, altered mental status, hallucinations, or coma. Victims may also exhibit shock-like symptoms including rapid heart rate and rapid breathing. The victim may or may not be sweating. Perspiration, or lack thereof, is no indication of whether or not heat stroke is occurring. The victim's skin may feel warm and dry or cold and moist.

In cases of heat exhaustion or heat stroke, the victim must be moved out of the heat as quickly as possible. If an air-conditioned vehicle or building is not available, move the victim to a shaded area and remove excess clothing. If ice is available, gently apply ice packs to the neck, armpits, and groin. This facilitates rapid cooling since the carotid, brachial, and femoral arteries approach the surface of the body in these areas. If ice is not available apply small amounts of water and fan the body in order to speed up evaporative cooling. Alternatively, you may lay a wet sheet or towel loosely across the victim's body.

Using the above methods of management, heat exhaustion should resolve within two or three hours at most. If the victim's condition is not improving as quickly as it should, evacuate and seek out professional medical attention.

If heat stroke is suspected, immediately begin evacuation for hospitalized care. Be sure to facilitate cooling during transportation. Use an air-conditioned vehicle if possible, or roll down the windows and apply water to the victim. The longer a case of heat stroke remains untreated or unmanaged, the worse the long-term prognosis becomes for the victim. Heat stroke can easily result in debilitating organ dysfunctions or death.

Heat-related illness is one of the more preventable types of injury experienced in the wilderness. First and foremost, avoid heavy activity in hot environments. For example, if you're backpacking in southern Utah in the month of July, you may want to avoid hiking during the hottest hours of the day. Dress appropriately. Wear light, loose clothing, and remember that dark colors absorb heat from the sun. Last, stay well-hydrated at all times. People engaging in physical activity in hot weather can require up to one liter of water per hour in order to remain well hydrated. If you will be hiking or backpacking in desert regions devoid of water sources, a common recommendation is to bring at least one gallon of water per person, per day.

Summary

Surviving in the wilderness is mostly a matter of being observant and using your head. Take responsibility for your own safety, and those in your group as well. It's true that injury and death in the backcountry are sometimes the result of unfortunate, unpredictable accidents. Far more often, however, a bit of forethought and preparatory knowledge are all you need to remain alive and unhurt.