What is Hypothermia?

Hypothermia is a condition in which the core body temperature drops to below 32.2°C to 35°C (90°F to 95°F). Hypothermia is more commonly a cause of death in older people, or those over 65 years. Deaths among males outnumber those among females by a ratio of 2.5 to 1.

Causes of hypothermia

Causes of hypothermia include:

• exposure to cold
• metabolic disorders such as hypothyroidism or adrenal insufficiency
• toxins
• infections
• endocrine insufficiency
• disorders of the central nervous system
• medical illnesses which involve loss of heat through injured areas of the skin, as following extensive burns, psoriasis and other exfoliative disorders
• neurologic causes, which include spinal injury and head trauma, and
• sepsis.

In urban areas, exposure, and drowning associated with intoxication or mental illness are important causes.

Other less frequent causes

Accidental exposure is gaining in importance with the growing interest in wilderness adventure holidays. Rarely, medical treatment may result in hypothermia, as for instance, following too aggressive infusion of intravenous fluids, or during the cooling-down treatment of heat stroke.

Symptoms

The manifestations of hypothermia are varied. This condition may occur in the mild, moderate or severe form, and is progressive without prompt and adequate treatment.

Common symptoms of mild hypothermia include shivering, peripheral vasoconstriction, and a rise in the blood pressure, respiratory rate and heart rate, which are all the outcome of the body’s attempts to recover its normal temperature. Later signs include dulling of the mental processes, loss of finer motor movements, clumsiness, cold diuresis and poor judgment.
As the temperature falls further, moderate hypothermia sets in, and the body functions slow down. The drop in the rate of breathing, heart rate and blood pressure signal the increasing coldness of the body core, while the patient may drift into unconsciousness. Shivering ceases, and reflexes become slow.

Finally, at a body temperature below 28°C, severe hypothermia occurs. Breathing is almost absent, the pupils no longer react to light, and the patient is in a coma, with a flat EEG. The heart ventricles show fibrillation or have ceased to contract.

Secondary complications include rhabdomyolysis, acute tubular necrosis and renal failure.

Diagnosis and treatment

Hypothermia is best diagnosed with the use of a rectal thermometer, which reflects core temperature. It is important to keep in mind that no patient with hypothermia should be given up for dead until the body temperature has risen to above 30°C to 32°C (89.6°F) without signs of life.

Initially, the patient should be brought into shelter, and put under warm dry blankets after removing cold or wet clothing. Movements should be gentle and limited to the minimum required, and nasogastric intubation avoided, to prevent the onset of ventricular fibrillation. Glucose and thiamine administration are almost always warranted as they are useful in glycogen-depleted patients and alcoholic patients, respectively, and do not cause any harm in almost all cases. Core rewarming is useful to reduce the time spent in hypothermia.

Coagulopathies and arrhythmias are both common complications of hypothermia, but require no specific treatment, since they usually resolve with rewarming. The only exception is ventricular fibrillation, the deadly arrhythmia which requires the use of defibrillation, both before and after rewarming the patient if initial attempts are unsuccessful.

Other complications that follow rewarming include:

• core temperature afterdrop
• pneumonia,
• pulmonary edema
• ventricular arrhythmias
• myoglobinuria and renal failure, and
• seizures.

Treatment

• Non-invasive, such as passive external warming, which includes getting the victim under shelter, and replacing cold wet clothes with warm dry coverings.
• Active external rewarming, such as the use of an electric blanket.
• Active core rewarming, by infusion of warmed electrolyte solutions, administration of warmed humidified oxygen, lavage of the body cavities with warmed isotonic fluids, and extracorporeal blood warming.

References

• http://www.aafp.org/afp/2004/1215/p2325.html
• http://www.ncbi.nlm.nih.gov/pubmed/8434836
• http://www.ncbi.nlm.nih.gov/pubmed/14728949