Hypothermia 101

As the temperature dips, hypothermia can threaten survival for backwoods adventurers unaware of its warning signs.
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As the temperature dips, hypothermia can threaten survival for backwoods adventurers unaware of its warning signs.

Hypothermia is an abnormally low body-core temperature caused by exposure to a cold environment.

How to Recognize Hypothermia

Mild Hypothermia

When core body temperature drops below 95ºF, mild hypothermia sets in.

  • Person feels cold and shivers at maximum level.
  • Person maintains normal consciousness level, remains alert, and has normal or slightly impaired coordination.
  • When core body temperature drops below 93ºF, the person develops slurred speech, memory loss, poor judgment, and carelessness.

Mild Hypothermia Treatment

  1. Move the person from the cold environment to a sheltered environment.
  2. Replace any wet clothing with dry, insulated garments.
  3. Give the person warm food and lots of sugary hot fluids (an average-size adult needs about 60 kilocalories of hot drinks or about 2 quarts of highly sugary liquids such as drink mixes) to elevate core temperature 10 F.
  4. Slow heat loss by wrapping the person in a sleeping bag, plastic bag, or tarp. Huddling with the person in a sleeping bag will help slow heat loss.
  5. Resist the urge to use hot water bottles or heat packs. They can turn off the body's shivering mechanism, and they add very little heat to the body core. Instead, bring water to a boil and have the person inhale the steam, or build a fire.

Profound Hypothermia

When core body temperature drops below 90 degrees F, profound hypothermia develops.

  • The person becomes weak and lethargic.
  • The person has an altered mental state (is disoriented, confused, combative or irrational, or in a coma).
  • The person is uncoordinated.
  • When core body temperature drops below 88 degrees F, person stops shivering.
  • When core body temperature drops below 86 degrees F, person's heart pumps less than two thirds the normal amount of blood. Pulse and breathing are half their normal rates.
  • When core body temperature drops below 83 degrees F, the heart is very irritable and unstable, and likely to develop abnormalities. The person is in danger of cardiac arrest. Rough handling of the person increases the potential for cardiac arrest.

Sobriety Test for Hypothermia: An excellent test to determine if someone is developing profound hypothermia is to have the person try to walk a straight line, heel-to-toe, as in a sobriety test. If the person cannot perform this task and is not intoxicated, it indicates the progression from mild to profound hypothermia.

Profound Hypothermia Treatment

Treatment in the backcountry is aimed at stabilizing the person and preventing any further cooling.

  1. Handle the person very gently. Rough handling may cause his heart to fail.
  2. Place the person in a sleeping bag, or place blankets or clothing underneath and on top of him. Any heat that you can provide will probably not rewarm the person but will help prevent further cooling.
  3. A person with significantly altered mental state should not be allowed to eat or drink because of the potential for choking or vomiting.
  4. Rewarming is best done in a hospital, because of the potential complications associated with profound hypothermia. Professional assistance is usually needed to evacuate a profoundly hypothermic person.

Caution: First-aid management of hypothermic victims should not be based solely on measurements of body temperature because it is often difficult to obtain an accurate temperature in the field.

It may be difficult to distinguish whether a person is profoundly hypothermic or dead. The profoundly hypothermic person may have a pulse and respirations that are barely detectable. Double-check carefully, feeling for the carotid pulse (it is found on either side of the center of the throat where the carotid artery goes to the head). Check this for at least one minute since the heart rate may be very slow. Place a glass or plastic surface next to the person's mouth to see if it fogs up.

When to perform CPR: If the person is breathing or has any pulse, no matter how slow, do not initiate CPR, as this may cause the heart to stop beating completely. If there is no sign of a pulse or breathing after one minute, what to do next depends on your situation:

  1. If you are alone or with only one other person, cover the hypothermic person and place him in a protected shelter (place insulation beneath and on top of him). Both rescuers should go for help and stay together for safety.
  2. If there are multiple rescuers, and it is safe to stay with the victim, begin CPR. Chest conpressions should be done a t on-half the normal rate. At least two people should go for help and stay together for safety.
  3. If the person can be easily transported out of the backcountry in an improvised stretcher, the rescuers may elect to do this while performing CPR during the transport as best as possible.

Never assume that a profoundly hypothermic person is dead until his body has been warmed thoroughly and there are still no signs of life. It is possible, though rare, that one without detectable signs of life will recover when rewarmed.

Adapted from Wilderness 911: A Step-by Step Guide for Medical Emergiencies and Improvised Care in the Backcountry, Eric A. Weiss, MD (The Mounaineers, 1-800-553-4453, www.backpacker.com/bookstore, $16.95).