As we head into the colder part of the year, I thought I’d talk about the dangers of exposure to cold. On or off the grid, if you don’t take environmental conditions into account, you have made Mother Nature your enemy, and she is a formidable one, indeed.

Hypothermia is a condition in which body core temperature drops below the temperature necessary for normal body function and metabolism. The normal body core temperature is defined as between 97.5-99.5 degrees Fahrenheit (36.0-37.5 degrees Celsius). Symptoms related to cold exposure occur once the core temperature dips below 95 degrees (35 degrees Celsius).

HOW THE BODY LOSES HEAT

Besides simply breathing out warm air, the body loses heat in various ways:

Evaporation: The body perspires (sweats), which releases heat from the core. Heat loss through evaporation increases in dry, windy weather conditions.

Radiation: While the body makes efforts to maintain normal body temperatures, the body loses heat to the environment when the ambient (surrounding) temperature is lower than about 68 degrees F. Much lower temperatures cause heat loss more quickly.

Conduction: The body loses heat when its surface is in direct contact with cold temperatures, as in the case of someone falling from a boat into frigid water. Water, being denser than air, removes heat from the body much faster.

Convection: Heat loss where, for instance, a cooler object is in motion against the body core. The air next to the skin is heated and then removed, which requires the body to use energy to re-heat. Wind Chill is one example of air convection: If the ambient temperature is 32 degrees F but the wind chill factor is at 5 degrees F, you lose heat from your body as if it were actually 5 degrees F.

A surprising amount of heat is lost from the head area, due to its large surface area and tendency to be uncovered. Direct contact with anything cold, especially over a large area of your body, will cause rapid cooling of your body core temperature. When the Titanic sank in 1912, hundreds of people fell into near-freezing water. Within 15 minutes, they were probably beyond medical help.

GENERAL SYMPTOMS OF HYPOTHERMIA

The body, when it is exposed to cold, kicks into action to produce heat once the core cools down below 95 degrees F. The main mechanism to produce heat is shivering. Muscles shiver to produce heat, and this will be the first symptom you’re likely to see. As hypothermia worsens, more symptoms will become apparent if the patient is not warmed.

The diagnosis of hypothermia may be difficult to make with a standard glass thermometer because it doesn’t register below 94 degrees Fahrenheit. Unless you have a thermometer that can measure low ranges, it may be difficult to know for certain that you’re dealing with this problem.  You should assume that anyone with altered mental status encountered in cold weather is hypothermic until proven otherwise.

Aside from shivering, the most noticeable symptoms of hypothermia will be related to mental status. The victim may appear confused and uncoordinated. As the condition worsens, speech may become slurred. The patient will appear apathetic, lethargic, and uninterested in helping themselves; they may fall asleep. This occurs due to the effect of cooling temperatures on the brain; the colder the body core gets, the slower the brain works. Brain function is supposed to cease at a body temperature of about 68 degrees Fahrenheit, although there have been exceptional cases where people (usually children) survived even lower temperatures.

To learn about hypothermia in dogs, click here.

LEVELS OF HYPOTHERMIA

Some sources differentiate different levels of hypothermia body temperature:

MILD: (93-97 degrees F; 33.9-36.1 degrees C)

A person with mild hypothermia will usually still be awake and alert, but shivering. Hands and feet will be cold, and they may complain of pain or numbness in the extremities. Loss of dexterity is often noted.

MODERATE: (90-93 degrees F; 32.2-33.9 degrees C)

In moderate hypothermia, you’ll see all of the above, but mental status begins to alter and efforts to produce heat by shivering may decrease or even stop.

SEVERE HYPOTHERMIA: (82-90 degrees F; 27.8-32.2 degrees C)

The severely hypothermic person will stop shivering and mental status changes become clearly apparent. Expect to see confusion, lethargy, and memory loss. The victim’s muscles appear less flexible; they will be uncoordinated and speech will be slurred. An unusual apathy or denial regarding the seriousness of the situation is often noted.

CRITICAL HYPOTHERMIA (less than 82 degrees F (27.8° C))

Once less than 82 degrees F, the victim will likely be unconscious. Respirations will be impaired and the pulse slow and difficult to feel. Skin will be cold and cyanotic (blue) and muscles will be rigid. Pupils may be dilated.

Individual cases may vary somewhat.

TREATING HYPOTHERMIA

Immediate action must be taken to 1) prevent further heat loss and 2) reverse the ill effects of hypothermia. Important measures to take are:

Get the person out of the cold. Transport as soon as possible to a warm, dry location. If you’re unable to move the person out of the cold, shield them as much as possible. Be sure to place a barrier between them and the cold ground.

Exercise to produce heat in mild cases: In alert victims who can move without difficulty, mild exercise can help raise body temperature (as long as they stay dry). Avoid exertion in those with moderate hypothermia or worse, however, and in anyone with altered mental status.

Monitor breathing. A person with severe hypothermia may be unconscious. Verify that the patient is breathing and check for a pulse. If none, still assume the patient is revivable and begin CPR. Elevate the feet as you would for anyone in shock.

Take off wet clothing. If the person is wearing wet clothing, remove them gently. Ignore pleas of “leave me alone!” Cover them with layers of dry blankets, including the head, but leave the face clear (see image above).

Share body heat. There may be circumstances when it’s necessary to warm the person’s body by removing your clothing and making skin-to-skin contact. Then, cover both of your bodies with blankets. Some people may cringe at this notion, but it’s important to remember that you are trying to save a life. Gentle massage or rubbing may be helpful, but vigorous movements may cause unnecessary trauma.

Give warm oral fluids. If the affected person is alert and able to swallow, provide a warm, non-caffeinated beverage to help warm the body. Despite the image of St. Bernards saving alpine mountaineers with casks of brandy around their necks, alcohol is a bad idea. Alcohol may give you a “warm” feeling, but it actually causes your blood vessels to expand; this results in more rapid heat loss from the surface of your body and negates the body’s efforts to stay warm. Alcohol and recreational drugs also cause impaired judgment: Those under the influence might clothe inadequately for cold weather.

Use warm, dry compresses. First-aid “shake and break” warm compresses or warm (not hot) water in a plastic bottle will effectively apply heat to the body core if placed on the neck, chest wall or groin. Don’t use hot water, a heating pad or a heating lamp directly on the person. The extreme heat can damage the skin, cause strain on the heart, or even lead to cardiac arrest.

PREVENTION OF HYPOTHERMIA

An ounce of prevention is worth a pound of cure. To prevent hypothermia, you must anticipate the climate that you will be traveling through, including wind conditions and wet weather. Condition yourself physically to be fit for the challenge. Travel with a partner if at all possible, and have enough food and water available for the entire trip.

It may be useful to remember the simple acronym C.O.L.D. This stands for:  Cover, Overexertion, Layering, and Dry.

Cover: Protect your head by wearing a hat. This will prevent body heat from escaping from your head. Instead of using gloves to cover your hands, use mittens. Mittens are more helpful than gloves because they keep your fingers in contact with one another, conserving heat.

Overexertion:  Avoid activities that cause you to sweat a lot. Cold weather causes you to lose body heat quickly; wet, sweaty clothing accelerates the process. Rest when necessary; use rest periods to self-assess for cold-related changes. Pay careful attention to the status of your elderly or juvenile group members. Diabetics are also at high risk.

Layering: Loose-fitting, lightweight clothing in layers do the best job of insulating you against the cold. Use tightly woven, water-repellent material for wind protection. Wool or silk inner layers hold body heat better than cotton does. Some synthetic materials, like Gore-Tex, Primaloft, and Thinsulate, work well also. Especially cover the head, neck, hands and feet.

Dry: Keep as dry as you can. Get out of wet clothing as soon as possible. It’s very easy for snow to get into gloves and boots, so pay particular attention to your hands and feet.

If left untreated, hypothermia leads to complete failure of various organ systems and death.  People who develop hypothermia due to cold exposure are also vulnerable to other cold-related injuries, such as frostbite and immersion foot. We’ll discuss those and some specific clothing strategies in the near future.

Joe Alton MD

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