Hypothermia

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Hypothermia

Hypothermia is a medical condition in which the victim's core body temperature has dropped to significantly below normal and normal metabolism begins to be impaired. This begins to occur when the core temperature drops below 35 degrees Celsius (95 degrees Fahrenheit). If body temperature falls below 32 °C (90 °F), the condition can become critical and eventually fatal. Body temperatures below 27 °C (80 °F) are almost uniformly fatal, though body temperatures as low as 14 °C (57.5 °F) have been known to be survivable. The opposite condition, where temperature is too high, is hyperthermia.

For unknown reasons, people who fall critically unconscious in very cold water can, in rare cases, be resuscitated, even though they would be expected to have died of drowning and/or hypothermia. See Mammalian diving reflex.

Types

There are three types of hypothermia, acute, subacute, and chronic.

Acute hypothermia is the most dangerous; the body temperature drops very swiftly, often in a matter of minutes, such as when a victim falls through an ice-covered lake.
Subacute hypothermia occurs on a scale of hours, most commonly by remaining in a cold environment for an extended period of time.
Chronic hypothermia is typically caused by an underlying disease.

Symptoms

Amnesia
Ataxia
Cold skin, even in torso
Confusion, progressing to delirium
Diuresis
Dysarthria
Gray complexion (pallor)
Hypokinesia
Increased muscle tone
Low blood pressure (hypotension)
Peripheral cyanosis
Rapid breathing (tachypnea) and heart rate (tachycardia), slowing and weakening as temperature decreases
Shivering
Tremor
Uncontrollable bleeding due to reduced coagulation enzyme activity
Weakness

Treatment

Treatment for hypothermia involves raising the core body temperature of the victim.

The first aid response to someone experiencing hypothermia, however, must be made with caution.

Do not rub or massage the casualty
Do not give alcohol
Do not give food or drink (this includes warm drinks)
Do not treat any frostbite
Do not allow the body to become vertical

Any of these actions will divert blood from the critical internal organs and may make the situation worse.

What you should do:

Call the emergency services
Get the patient to shelter
If possible, put the patient in a bath with medium-temperature water, with the clothes on
Place hot water bottles (wrapped in a cotton sock) in the patient's armpits and between their legs
Monitor the patient and be prepared to give Cardio-pulmonary resuscitation.
Remove wet clothing if and only if a dry change is available

If the hypothermia has become severe, notably if the patient is incoherent or unconscious, re-warming must be done by trained professionals. Bystanders should only remove the patient from the cold environment and call emergency services to get advanced medical care as quickly as possible.

Note
Moving a severely hypothermic person can, and most likely will cause ventricular fibrillation (heart attack), so if possible wait for trained emergency workers arrive. If help is over thirty minutes away, move the patient to an area that shelters them from the wind and cover or wrap them in a blanket.

Hospital treatment

In a hospital, warming is accomplished by external techniques (blankets, warming devices) for mild hypothermia and by more invasive techniques such as warm intravenous fluids or even lavage (washing) of the bladder, stomach, chest and abdominal cavities with warmed fluids for severely hypothermic patients. These patients are at high risk for arrhythmias (irregular heartbeats), and care must be taken to minimize jostling and other disturbances until they have been sufficiently warmed, as these arrhythmias are very difficult to treat while the victim is still cold. An important tenet of treatment is that a person is not dead until they are warm and dead - remarkable stories of recovery after prolonged cardiac arrest have been reported in patients with hypothermia. This is presumably because the low temperature prevents some of the cellular damage that occurs when blood flow and oxygen are lost for an extended period of time.

Prevention

In air, most heat is lost through the head, so hypothermia can be most effectively prevented by covering the head. Having appropriate clothing for the environment is another important prevention. Fluid-retaining materials like cotton can be a hypothermia risk if the wearer gets sweaty on a cold day, then cools down, they will have sweat soaked clothing in the cold air. For outdoor exercise on a cold day, it is advisable to wear fabrics which can wick away sweat moisture. These include wool or synthetic fabrics designed specifically for rapid drying.

Heat is lost much more quickly in water. Children can die of hypothermia in as little as two hours in water as warm as 16°C, typical of sea surface temperatures in temperate countries such as Great Britain. Many seaside safety information sources fail to quote survival times in water, and the consequent importance of diving suits, possibly because the original research into hypothermia mortality in water was carried out in wartime Germany on unwilling subjects. There is an ongoing debate as to the ethical basis of using the data thus acquired. Information on wetsuits and safety in water can be found here.

There is considerable evidence, however, that children that suffer near-drowning accidents in water near 0°C can be revived up to two hours after losing consciousness. The cold water also considerably lowers metabolism, allowing the brain to withstand a much longer period of hypoxia.

Medically induced

See induced hypothermia

External links

Diving medicine | Medical emergencies | Physiology | Causes of death

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