Hypothermia: Causes, Symptoms and Treatments


MNT Knowledge Center

Prior to the onset of hypothermia the body maintains a relatively stable temperature whereby heat production is balanced by heat loss.

When the outside environment gets too cold or the body’s heat production decreases, hypothermia occurs (hypo=less + thermia=temperature).

Contents of this article:

  1. What is hypothermia?
  2. Symptoms of hypothermia
  3. Causes of hypothermia
  4. Diagnosis of hypothermia
  5. Treatment of hypothermia
  6. Preventing hypothermia

Fast facts on hypothermia

Here are some key points about hypothermia. More detail and supporting information is in the main article.

  • Hypothermia is the opposite of hyperthermia.
  • If untreated, hypothermia can lead to organ failure and death.
  • Hannibal lost half of his army to hypothermia in 218 BC.
  • Early symptoms include dilated pupils and drowsiness.
  • Between 20% and 50% of hypothermia deaths are due to removal of clothing.
  • Older people are more at risk of hypothermia.
  • Hypothermia can be diagnosed simply by taking the patient’s temperature.
  • Depending on severity, treatment ranges from hot water bottles to intravenous heated liquid.

What is hypothermia?

[Man with frozen beard]
Hypothermia occurs when the body can no longer maintain a temperature equilibrium

Body temperature is controlled in the part of the brain called the hypothalamus, which is responsible for recognizing alterations in the body temperature and responding appropriately.

The body produces heat through the metabolic processes in cells that support vital body functions. Most heat is lost at the skin surface by convection, conduction, radiation, and evaporation.

If the environment gets colder, the body may need to generate more heat by shivering (increasing muscle activity that promotes heat formation). But if heat loss is greater than the body’s ability to make more, then the body’s core temperature will fall.

As the temperature falls, the body shunts blood away from the skin and exposure to the elements. Blood flow is increased to the vital organs of the body including the heart, lungs, kidney, and brain. The heart and brain are most sensitive to cold, and the electrical activity in these organs slows in response to cold. If the body temperature continues to decrease, organs begin to fail, and eventually death will occur.

In a side note, historically hypothermia has played a major role in the success or failure of many military campaigns from Hannibal’s loss of nearly half his men in 218 BC to the near destruction of Napoleon’s armies in Russia in 1812. Loss of life to hypothermia continued through the first and second world wars. Civilian examples of deaths caused by hypothermia are found during the sinking of the RMS Titanic and RMS Lusitania.

Hypothermia is the opposite of hyperthermia which is present in heat exhaustion and heat stroke.

Symptoms of hypothermia

A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.

As people develop hypothermia, their abilities to think and move are often lost slowly. In fact, they may even be unaware that they need emergency treatment. A number of skin conditions may be associated with hypothermia or may occur with normal body temperature. These include cryopedis and frostbite.

The body starts to slow as the temperature drops. Aside from the cold that is felt and the shivering that may occur, mental function is most affected initially. A particular danger of hypothermia is that it develops gradually, and since it affects thinking and reasoning, it may go unnoticed.

Initial hunger and nausea will give way to apathy as the core body temperature drops. This is followed by confusion, lethargy, slurred speech, loss of consciousness, and coma.

Often the affected person will lie down, fall asleep, and die. In some cases, the patient will paradoxically remove their clothes just before this occurs.

The decrease in brain function occurs in direct relationship to the decrease in body temperature (the colder the body, the less the brain function). Brain function stops at a core temperature of 68 F (20 C).

The heart is subject to abnormal electrical rhythms as hypothermia progresses. Ventricular fibrillation, a disorganized rhythm in which the heart is unable to pump, may occur at core temperatures below 82.4 F (28 C). This is one type of cardiac arrest.

On the next page, we look at the causes, diagnosis, treatment and prevention of hypothermia.


MNT Knowledge Center

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Causes of hypothermia

Twenty to fifty percent of hypothermia deaths are associated with paradoxical undressing. This typically occurs during moderate to severe hypothermia, as the person becomes disoriented, confused, and combative. They may begin discarding their clothing, which, in turn, increases the rate of heat loss.

Heat is lost more quickly in water than on land. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia. A water temperature of 10 °C (50 °F) often leads to death in one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. Water at a temperature of 26 °C (79 °F) will, after prolonged exposure, lead to hypothermia.

Patients who are indoors in warm environments may develop hypothermia secondary to air conditioning or ice baths. These indoor patients with hypothermia tend to be elderly, and they may present initially to their regular physician with vague complaints of mental and/or motor skill deterioration.

The subtle symptoms of early mild to moderate hypothermia are less obvious in indoor patients. However, indoor patients have a significantly higher mortality rate than their outdoor counterparts, most likely secondary to increased age and later time of discovery and diagnosis.

Other causes of hypothermia include metabolic disorders that are linked to a decreased basal metabolic rate and can be related to dysfunction of the thyroid, adrenal, or pituitary glands.

Diagnosis of hypothermia

[Person breathing in the cold]
The easiest way to diagnose hypothermia is by taking the patient’s temperature.

To figure out whether someone is suffering from hypothermia, temperature is taken with a thermometer. If the temperature appears to be below 96° F (35.5° C) or it can’t be read on an oral thermometer, the person’s temperature can be taken again using a rectal thermometer for a more exact reading.

If the thermometer still does not show the temperature or is below 96 degrees F, one should immediately see a doctor. The only way to tell accurately if a person has hypothermia is to use a special thermometer that can read temperatures below 94° F (34° C). Most hospitals have these thermometers.

Treatment of hypothermia

Aggressiveness of treatment is matched to the degree of hypothermia. Treatment ranges from noninvasive, passive external warming, to active external rewarming, to active core rewarming.

Passive external rewarming involves the use of a person’s own heat generating ability through the provision of properly insulated dry clothing and moving to a warm environment.

Active external rewarming consists of applying warming devices externally such as hot water bottles or warmed forced air. In austere environments this is often done by placing a hot water bottle in both armpits. Another method is to place the person in a tub with hot water (of 44°C), and place their arms and legs outside of the tub/hot water.

Active core rewarming is the use of intravenous warmed fluids, irrigation of body cavities with warmed fluids (the thorax, peritoneal, stomach, or bladder), use of warm humidified inhaled air, or use of extracorporeal rewarming such as via a heart lung machine.

In severe cases resuscitation begins with simultaneous removal from the cold environment and concurrent management of the airway, breathing, and circulation. Rapid rewarming is then commenced. A minimum of patient movement is required as aggressive handling may increase risks of a dysrhythmia.

Preventing hypothermia

Hypothermia is a devastating and potentially avoidable condition, making education and preparation the cornerstones of prevention.

The Centers for Disease Control and Prevention (CDC) recommend creating a winter survival kit for indoor safety, including nonperishable food, blankets, a first aid kit, water, and necessary medications.

Other measures, such as weather stripping and insulated doors, are important, especially for elderly persons. If persons are stranded in a motor vehicle, they should move all items from the trunk into the interior of the vehicle to conserve heat.

When persons are outdoors, multiple layers of clothing should be worn, with the innermost layers made of wool, silk, or polypropylene because these materials retain heat better than cotton. Layering clothing traps in multiple layers of air, thereby minimizing convective heat loss. Wearing a hat or heavy scarf on the head helps to minimize heat loss caused by radiation.

If signs or symptoms of mild hypothermia are evident, a person should return indoors immediately to prevent progression to a life-threatening condition.

Recent developments on hypothermia from MNT news

Therapeutic hypothermia can help in range of cardiac arrests

Lowering body temperature in cardiac arrest patients with “non-shockable” heart rhythms increases survival rates and brain function, according to new research in the journal Circulation.

Hypothermia in organ donors could improve kidney transplants

Kidney transplantation could be made more efficient by simply cooling the body of a deceased organ donor by just 2°C from normal body temperature, according to the findings of a new study.