The Dangers of Heat and Cold: Hypothermia

Snow and Fence


Every chemical reaction has an optimal temperature range. Stray outside that given range and undesirable things happen; that’s why you may find your digital camera’s battery has mysteriously lost its power after a frigid night in the mountains. Everything that occurs inside your body is the result of chemical reactions. As such, it operates best under a particular set of conditions. Expose it to extreme temperatures and all sorts of problems may arise.

The human body’s ideal operating temperature is 98.6°F. As warm-blooded creatures, our bodies have a variety of mechanisms that 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.

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.

In either case, the body’s priority is keeping internal organs at that ideal operating temperature. Stray a few degrees too hot or too cold, and the chemical reactions that drive your internal organs will start to go haywire. It’s like giving a someone riding a unicycle a hard shove. If the change isn’t corrected organs will begin to shut down. Death may be the swift and unfortunate result.


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.

Kayaker traversing a waterfallIf 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.

2 Responses to “The Dangers of Heat and Cold: Hypothermia

  • My bf is at home refuses to go to the hospital so this really helped me out hes steadily getting better i tjink his hypothermia was in the begining stages his shivering is going away and i put a touque on his head along with three blankets
    Its the summer and he got caught in the rain so i will have to take away some of the blankets eventually which makes me nervous but i cranked the heat up in my house so i hope he’ll be okay

    • Paul Jones
      7 years ago

      Wow, I hope he’s okay! Did he recover? Hypothermia is scary business. It can definitely be an issue in the summer as well as the winter.

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