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Outdoor First Aid

How to Prevent, Recognize, and Treat Hypothermia

Don't be fooled: Hypothermia can happen in the summer or the winter. Learn how to prevent and treat a dropping core body temp.

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Cold can be more than uncomfortable: Under the right circumstances, it can turn into hypothermia, a potentially-fatal lowering of the human body’s core temperature. It can happen in summer in the Smokies just as easily as in winter in the Rockies, and it can affect anyone from the sick or injured to the young and fit. Recognizing the signs and symptoms of this common outdoor affliction is one of the most important things you can do to keep yourself and your hiking partners safe when the mercury drops.

What is hypothermia and what causes it?

Hypothermia is when the human body’s temperature drops abnormally low, generally below 95 degrees Fahrenheit. Our bodies are constantly losing heat, radiating it out through our skin and losing it to evaporation as wind dries sweat or rain on our skin. Under normal circumstances, that isn’t a problem as our bodies thermoregulate, producing heat to keep our temperatures stable. If we lose heat faster than we’re able to produce it, our body temperature begins to creep downward. The result is hypothermia.

How cold does it need to be for me to get hypothermia?

Not as cold as you think. If the weather is rainy and windy, you can get hypothermia in 50 F temperatures, or even warmer if you’re immersed in water for a long period of time. The colder it gets, the bigger the risk: At -30 F, a person who isn’t dressed for the cold can begin to experience symptoms of hypothermia in 10 minutes or less. Children, older people, and hikers with certain medical conditions may be more prone to hypothermia, but anyone can be at risk.

Recognizing and Treating Hypothermia

With timely treatment, most people with hypothermia recover. Know the signs and symptoms, and what to do about them, before you head outside.

Mild Hypothermia

When core body temperature drops below 95°F, 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 93°F, 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°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°F, person stops shivering.
  • When core body temperature drops below 86°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°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.

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 compressions should be done at one-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

How to Prevent Hypothermia

The best way to treat hypothermia? Don’t get it.

  • Read the weather forecast before you leave and make sure you’re equipped and dressed for it, including sufficient insulation and an outer layer to keep moisture at bay. Consider carrying an extra layer or a survival blanket.
  • Eat enough—calories fuel the furnace. Fats are good for long-term energy, simple carbohydrates for a quicker boost.
  • As the saying goes, cotton kills: It dries slowly, and saps body heat when wet. Instead, pick synthetics or wool.