Hypothermia Dr Trisha Macnair Hypothermia, which can be fatal, occurs when the body's internal temperature drops below normal.

In this article

What are the symptoms? Who's affected?

How can it be prevented? What's the treatment?

Medical uses

Hypothermia is classified as a temperature below 35°C (96°F).

Watch out for the 'umbles': stumbles, mumbles, fumbles and grumbles. These are symptoms that show a gradual reduction in coordination of muscles and movement, and a falling level of consciousness.

Symptoms progress as the person's temperature drops:

• Initially, involuntary shivering, loss of complex motor skills (but still able to walk and talk), shutdown of blood vessels in the hands and feet.
• As temperature falls below 35°C (95°F), violent shivering, impaired consciousness, loss of fine-motor coordination, especially in the hands, slurred speech, illogical behaviour, loss of emotional cognition - an 'I don't care' attitude.
• As core temperature falls below 34°C (92°F), the effects becomes life threatening, shivering become intermittent and then stops, the person curls into the foetal position, muscles become rigid, pupils dilate, pulse rate drops.
• By 30°C (86°F) the person looks dead. Although still alive, they're in a state known as the 'metabolic icebox', breathing becomes shallow and erratic, consciousness is lost and the heart becomes vulnerable to deadly arrhythmias.

Shivering is one of several symptoms that can be used to assess hypothermia. If the person is able to stop themselves shivering, their hypothermia is only mild. If it can't be stopped voluntarily, the person has moderate to severe hypothermia.

Another quick test is to assess higher brain functioning by asking the person to count backwards from 100 in multiples of nine. This sort of cerebral ability is soon lost as temperature falls.

A sign of severe hypothermia is loss of the pulse at the wrist, a result of the circulation shutting down.

Babies and children, older people and people who are severely ill can easily become hypothermic, even indoors, and each year there are many deaths as a result.

Hypothermia is one of the greatest threats to people participating in outdoor sports, such as walking, mountaineering and sailing. The particular risks include:

• Cold and windy weather - windy conditions speed heat loss (wind chill)
• Failing to wear suitable clothing and equipment
• Getting wet - water conducts heat away from the body 25 times faster than air
• Fatigue and exhaustion
• Dehydration - fluid levels, fluid loss and heat loss are interconnected
• Inadequate food intake
• Lack of knowledge - alcohol causes vasodilation, for example, which aggravates heat loss

The Government offers extra support for some of the most vulnerable people in the form of winter fuel payments, to help keep their homes warm.

Other ways to prevent hypothermia include:

• Stay indoors as much as possible and limit your exposure to the cold
• Eat regularly and include plenty of carbohydrates (the body needs a reliable and constant energy supply to generate heat)
• Keep as active as possible
• Avoid alcohol - it causes dilation of peripheral blood vessel, increasing heat loss
• Avoid caffeine - it's a diuretic and increases the risk of dehydration, which aggravates heat loss
• Avoid nicotine - it constricts blood vessels and increases the risk of cold damage such as frostbite
• Wear multiple thin layers of clothing that help to trap heat, rather than one thick jumper
• If you go outside, always wear a hat (it can prevent as much as 20 per cent of heat loss) and gloves

Severe hypothermia needs urgent medical attention - call 999

Severe hypothermia needs urgent medical attention - call 999.

The basic principles are to stop heat loss and preserve the heat the person has, and provide body fuel to generate more heat. If a person is shivering, they can warm themselves at a rate of 2°C an hour.

Put on additional layers of clothing and replace wet clothes with dry. Get them moving to increase their activity and ensure their surroundings are as warm and still as possible.

Provide food, initially as hot liquids. Carbohydrates provide a rapid source of energy while fats can provide a prolonged source of fuel. Add warmth with a fire or heater, or by body-to-body contact.

In certain circumstances, doctors deliberately induce hypothermia, carefully lowering a patient's temperature to give surgeons more time to complete complex heart surgery, for example. Cooling reduces the oxygen needs of tissues, especially the brain.

This article was last medically reviewed by Dr Rob Hicks in January 2007.