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Definition

Hypothermia is dangerously low body temperature, below 95°F (35°C).

Considerations

Other types of cold injuries that affect the limbs are called peripheral cold injuries. Of these, frostbite is the most common freezing injury. Nonfreezing injuries that occur from exposure to cold wet conditions include trench foot and immersion foot conditions. Chilblains (also known as pernio) are small, itchy or painful lumps on the skin that often occur on the fingers, ears, or toes. They are a type of nonfreezing injury that develops in cold, dry conditions.

You are more likely to develop hypothermia if you are:

• Very old or very young
• Chronically ill, especially people who have heart or blood flow problems
• Malnourished
• Overly tired
• Taking certain prescription medicines
• Under the influence of alcohol or drugs

Causes

Hypothermia occurs when more heat is lost than the body can make. In most cases, it occurs after long periods in the cold.

Common causes include:

• Being outside without enough protective clothing, especially in winter
• Falling into cold water of a lake, river, or other body of water
• Wearing wet clothing in windy or cold weather
• Heavy exertion, not drinking enough fluids, or not eating enough in cold weather

Symptoms

As a person develops hypothermia, they slowly lose the ability to think and move. In fact, they may even be unaware that they need emergency treatment. Someone with hypothermia also is likely to have frostbite.

The symptoms include:

• Confusion
• Drowsiness
• Pale and cold skin
• Slowed breathing or heart rate
• Shivering that cannot be controlled (although at extremely low body temperatures, shivering may stop)
• Weakness and loss of coordination

Lethargy (weakness and sleepiness), cardiac arrest, shock, and coma can set in without prompt treatment. Hypothermia can be fatal.

First Aid

Take the following steps if you think someone has hypothermia:

• If the person has any symptoms of hypothermia that are present, especially confusion or problems thinking, call 911 or the local emergency number right away.
• If the person is unconscious, check airway, breathing, and circulation. If necessary, begin rescue breathing or CPR. If the victim is breathing fewer than 6 breaths per minute, begin rescue breathing.
• Take the person inside to room temperature and cover with warm blankets. If going indoors is not possible, get the person out of the wind and use a blanket to provide insulation from the cold ground. Cover the person's head and neck to help retain body heat. If nothing else is available, natural material such as a thick layer of tree branches, pine needles, or leaves can help provide insulation from the ground.
• Victims of severe hypothermia should be removed from the cold environment with as little exertion as possible. This helps to avoid warmth from being shunted from the person's core to the muscles. In a very mildly hypothermic person, muscular exercise is thought to be safe, however.
• Once inside, remove any wet or tight clothes and replace them with dry, loose clothing. Cover the person with warm blankets if available.
• Warm the person. If necessary, use your own body heat to aid the warming. Apply warm compresses to the neck, chest wall, and groin. If the person is alert and can easily swallow, give warm, sweetened, nonalcoholic fluids to aid the warming.
• Stay with the person until medical help arrives.

Do Not

Follow these precautions:

• Do not assume that someone found lying motionless in the cold is already dead.
• Do not use direct heat (such as hot water, a heating pad, or a heat lamp) to warm the person.
• Do not give the person alcohol.

When to Contact a Medical Professional

Call 911 or the local emergency number anytime you suspect someone has hypothermia. Give first aid while waiting for emergency help.

Prevention

Before you spend time outside in the cold, do not drink alcohol or smoke. Drink plenty of fluids and get enough food and rest.

Wear proper clothing in cold temperatures to protect your body. These include:

• Mittens (not gloves)
• Wind-proof, water-resistant, many-layered clothing
• Two pairs of socks (avoid cotton)
• Scarf and hat that cover the ears (to avoid major heat loss through the top of your head)

Avoid:

• Extremely cold temperatures, especially with high winds
• Wet clothes
• Poor circulation, which is more likely from age, tight clothing or boots, cramped positions, fatigue, certain medicines, smoking, and alcohol

References

Prendergast HM, Erickson TB. Procedures pertaining to hypothermia and hyperthermia. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 7th ed. Philadelphia, PA: Elsevier; 2019:chap 65.

Sawka MN, O'Connor FG. Disorders due to heat and cold. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 95.

Zafren K, Danzl DF. Hypothermia, frostbite, and nonfreezing cold injuries. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 128.

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