Hypothermia

Beginner's Guide to Backpacking

I regard it as a point of professional pride that I never get cold in the mountains, even in the dead of winter. Of course, that's not to say my pride has never been wounded, sometimes quite uncomfortably so. Nonetheless, I've never actually been hypothermic, the condition in which the body's core temperature drops low enough to impair normal muscular and mental function. If you carry the clothing described earlier in Outfitting the Well-Burdened Clotheshorse and use it wisely, you'll never get in serious trouble from hypothermia. Your companion may not be as well-prepared or as conscientious about body maintenance as you, however, so you should know the symptoms of hypothermia.

Hypothermia begins with a sensation of chilliness, numb skin, shivering and loss of coordination and strength in the hands. It progresses to more severe shivering and loss of overall muscular coordination. Victims begin to stumble and fall frequently. Hands become numb, useless claws. Thought and speech slow to a crawl. Severely hypothermic victims lose the ability to walk and become incoherent and irrational. If cooling continues, death occurs because of heart failure.

Treatment for moderately hypothermic victims is simple: rewarming, starting with the trunk. Simply adding more clothing does not help, because hypothermia victims have lost the ability to rewarm themselves. Adding more clothing only serves to reduce the rate of heat loss; it does nothing to actually rewarm the body. To do that, external heat must be applied. The easiest way to do that in the field is to zip two sleeping bags together and have a warm rescuer climb inside with the victim. A conscious victim should drink warm liquids; however, you should never try to force an unconscious victim to drink. They're likely to choke. Severely hypothermic victims require hospital care.

The key to preventing hypothermia is staying dry. Good shell clothing will ward off rain and snow. Preventing sweat from soaking your clothing is more difficult. If you let yourself sweat while working hard in the cold, you'll get chilled when you stop. Despite the obvious threat of discomfort, however, sweating seems almost impossible to avoid. Why?

Perhaps because, in some primeval way, we like it. Researchers at Kansas State University's Institute for Environmental Research found that people exercising in a test chamber considered themselves more comfortable when they were sweating than when they weren't. The harder they worked, the more sweat they were producing when they declared themselves most comfortable, even though they had the option of cooling the test chamber until they stopped sweating completely.

We also sweat in the cold because the evaporation of sweat inside clothing rarely provides more than half the cooling of sweat evaporating off bare skin. The reason? Some sweat vapor inside a jacket condenses and gives up its heat before it can escape to the outside air. If you're sweating but not cooling, your body responds by producing more sweat in an accelerating cycle that can only be stopped by removing insulation.

In cold weather, you must consciously fight your natural tendency to sweat. That means dressing in layers that can be removed to prevent sweating when you're working hard and added to hold in heat when you stop moving. The human body generates about five times as much heat when hiking with a load as it does when at rest. Savvy backpackers adjust clothing as often as needed to remain comfortable.

Hypothermia cases are by no means limited to the winter months. In fact, hypothermia is actually quite common in the summer, when inexperienced and poorly prepared hikers get caught above timberline by a 40-degree rainstorm and 20-mph wind – a potentially lethal combination.

Next Page: Heat Exhaustion and Heat Stroke

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