Hypothermia

Picture of the stages of frostbite

Hypothermia is defined as a body temperature (core, or internal body temperature) of less than about 95 F (35 C). Usually, hypothermia occurs when the body's temperature regulation is overwhelmed by a cold environment. However, in the medical and lay literature, there are essentially two major classifications, accidental hypothermia, and intentional hypothermia.

Accidental hypothermia usually occurs from exposure to cold that results in lowering the body temperature.

Intentional hypothermia is body temperature lowering induced usually for a medical procedure.

This article will focus on accidental hypothermia. Hypothermia is a medical emergency that, when quickly and appropriately treated, people can recover with little or no consequences.

Body temperature, when discussing hypothermia, is usually termed "core" temperature. This temperature is the temperature measured inside the body. It's a measurement that is most accurately done by a rectal thermometer, a rectal probe thermometer that has a constant temperature readout, or by a bladder or esophageal temperature device. Temperatures taken by other methods may not adequately measure core temperature.

The highest risk factor for hypothermia is losing body heat due to exposure to cold weather or partial or complete immersion in cold water. Examples include:

• Not dressing appropriately for cold weather
• Walking on a partially frozen body of water (rivers, lakes, ponds, etc.)

Other risk factors for hypothermia include:

• The young and elderly because their bodies cannot regulate body temperature efficiently
• People with mental illness
• People with alcohol or drug problems
• Some medications

Some medical diseases or conditions may decrease the body's ability to regulate its internal temperature, for example:

• Diabetes
• Spinal cord injuries
• Burns
• Hypothyroidism
• Parkinson's disease
• Malnutrition

The body parts most susceptible to injury in patients with hypothermia are those that may suffer from poor circulation or often have the least protection from the cold environment (feet, hands, nose, and ears). These extremities usually cool faster than the body's core. The internal organ most susceptible to hypothermia is the heart (dysrhythmias).

The cause of hypothermia is the inability of the body's temperature regulation system to keep the body's core temperature between 35.6 C and 37.5 C (96.08 F and 99.5 F), so any body temperature below about 35.6 C (96.08 F) is considered hypothermic by many doctors.

The body regulates the core temperature by either:

• generating heat
• cooling, or
• heat conservation. Heat conservation can be accomplished by peripheral vasoconstriction and by behavior; heat production is done by shivering and by increasing levels of thyroxine and epinephrine.

The signs and symptoms of hypothermia vary depending on how severe the hypothermia becomes. In general, there is a sequence of symptoms that can be roughly graded as mild, moderate, or severe (not all doctors agree with grading or fixed temperatures). However, the following is a list of symptoms that may occur as hypothermia progresses from mild to severe (temperatures are approximate and some symptoms may overlap).

Mild hypothermia symptoms (core temperature 32 C to 35 C [90 F to 95 F]) are:

• Shivering
• Fatigue
• Increased respiratory rate
• Hunger
• Nausea
• Mild confusion
• Some difficulty with speech and coordination

Moderate hypothermia (core temperature 28 C to 32 C [82 F to 90 F]) are:

• Increasing difficulty with all the symptoms (for example, inability to do simple tasks, slurred speech)

Severe hypothermia (core temperature below 28 C [82 F]) is:

• Shivering stops
• Extreme confusion (for example, removing clothing or extreme risk-taking behavior)
• A decline in consciousness
• A weak and/or irregular pulse
• Slow and shallow breathing
• Coma that can result in death

Newborns, infants, and young children are more likely to develop hypothermia because they have a larger surface area compared to body weight so they can lose body heat faster than older children and adults. WHO suggests slightly different temperature values for hypothermia levels in infants:

• Cold stress or mild hypothermia: 36.0 C to 36.4 C (96.8 F - 97.5 F)
• Moderate hypothermia: 32.0 C to 35.9 C (89.6 F to 96.6 F)
• Severe hypothermia: <32 C (89.6 F)

There may be some variation in these temperature values by some researchers, but these temperature levels can serve as guidelines in assessing hypothermia levels in infants and young children.

Since infants and young children either cannot or will not communicate with adults about hypothermia, parents, caregivers, and medical personnel rely on other clues or symptoms of hypothermia, which include:

• An accurate axillary (armpit) or rectal temperature below 36.4 C (97.5 F)
• A weak cry
• Low energy level
• Lethargic
• Reddish and cold skin
• The cool feeling of the extremities and abdomen
• Poor feeding
• Hypoglycemia (low blood sugar)
• Hypoxia (low levels of blood oxygen) or apneic (absence of breathing) episodes
• Heart arrhythmias

Some infants and children may experience chronic hypothermia and show symptoms of:

• weight loss,
• no weight gains, or
• failure to thrive.

Children and teens that can communicate have symptoms like those described for adults, but may occasionally have a combination of symptoms of those of a child or adult.

Yes, a person can become hypothermic indoors; however, the symptoms may develop slowly or not seem as obvious to family, friends, or even health care individuals unless a core body temperature is measured.

Individuals at risk for hypothermia indoors are the elderly or young living in unheated homes in cold temperatures or living in an over-air-conditioned home.

Any person that is at risk for hypothermia (see the previous section on risk factors) and has had exposure to cold weather or cold water immersion, and exhibits any symptoms of hypothermia should be seen in the emergency department. Individuals exhibiting intense shivering, numbness, clumsiness, confusion, and/or amnesia after exposure to cold should be seen immediately.

For many people, hypothermia is diagnosed by the patient's history and physical exam; especially pertinent is the patient's core temperature. As previously stated, any core temperature below 95 F or 35 C for an adult is considered to be hypothermic (for an infant, consider 36.4 C or 97.5 F).

Most individuals with hypothermia are considered to have a medical emergency so that diagnosis and treatment begin simultaneously. Some patients can develop bradycardia and show electrocardiogram (EKG, ECG) abnormalities.

For severe cases of hypothermia, treatment begins immediately in the field by careful handling of the patient to avoid developing ventricular fibrillation or any other cardiac dysrhythmia that hypothermic patients are prone to develop. Place the patient in an environment that is warm; remove all wet clothing and replace it with dry towels and blankets or sleeping bags. Simultaneously, be aware that the patient may have suffered other problems, like trauma and these problems may also need immediate attention (respiratory and/or cardiac failure).

External rewarming can begin before hospital arrival with warm packs (warm water bottles, warm chemical packs) placed on the person's armpits, groin, and abdomen. Be sure the warm packs (about 105.8 F or 41 C) are not hot to avoid skin burns. Do not attempt to warm extremities by rubbing them.

Core temperatures should be measured by a rectal, bladder, or esophageal thermometer. Do not use tympanic or skin thermometers. Hypothermic-induced dysrhythmias have been treated with bretylium, but this drug may not be available as it is no longer being manufactured.

After warming has begun with dry coverings, most guidelines recommend using warm humidified oxygen and heated intravenous saline (heated to about 113 F or 45 C) as additional treatments. In severe cases of hypothermia others also suggest instilling warm fluid into the patient's bladder. Thoracic lavage (flushing the thoracic [chest] region with warm water) with isotonic saline (pre-warmed to about 105.8 F or 41 C) has also been done.

Patients with mild to moderate hypothermia (95 F to 89.9 F or 35 C to 32.16 C) and no other injuries or problems require less drastic methods to rewarm. Patients whose body temperature normalizes by gradually rewarming in a warm, dry room with towels and blankets, usually do not need admission to the hospital. However, those with more severe hypothermia may need to be observed in the hospital.

Ideally, treatment will allow the body to return to its normal temperature. At normal temperature, the symptoms of hypothermia should gradually disappear. Consequently, the saying in most emergency departments that treat hypothermic patients is that "the hypothermic patient is not dead until they are warm and dead."

The best home remedy for hypothermia is simply to avoid those conditions that result in hypothermia such as not dressing appropriately for cold weather.

However, if you find someone that is possibly suffering from hypothermia the priority is to check for breathing, and a pulse and if necessary, begin cardiac resuscitation. If possible, help should be called (911). The next step is to rewarm the person as described above. If the person develops symptoms of moderate to severe hypothermia, they should be evaluated by a medical professional as soon as possible.

Preventing hypothermia is possible.

• Before participating in any cold-weather activities make sure that you are in the good physical condition and have the right clothing and nutrition before engaging in such activities.
• If you go camping or hiking in cold weather, travel with a partner for safety and let people know where you are going.
• Multiple layers of clothing that lose fitting and tend to remain dry are the best for cold-weather activities. Note that rain and wind can markedly increase the rate of heat loss from the body, so if these conditions develop, you need to be prepared to stay warm and dry.
• For individuals that have a higher risk for hypothermia (elderly and young children, for example), during wintry weather, keep homes heated to about 21.1 C (70 F), especially in the bedrooms at night.

If the person with mild hypothermia is treated quickly, does not require hospitalization, and has little or no residual problems, the prognosis is usually very good. However, some patients may suffer from extremity damage due to frostbite while others may be more prone to develop hypothermia in the future. People that have concurrent problems (alcoholism, psychiatric problems, advanced age or are homeless) have a worse prognosis, and their mortality rate is higher.