Absence of shivering in a patient with hypothermia is a bad sign and should be attended to immediately said Dr. KK Aggarwal, President, Heart Care Foundation of India.

Hypothermia is defined as a core temperature below 35ºC (95ºF), and can be further classified by severity:

1. Mild hypothermia: core temperature 90 to 95ºF. Symptoms include confusion, increased heart rate and increased shivering.

2. Moderate hypothermia: temperature 82 to 90ºF; and symptoms include lethargy, low heart rate, irregular pulse, loss of eye pupillary reflexes, and reduced or absent shivering.

3. Severe hypothermia: below 82ºF; and findings include coma, low blood pressure, irregular pulse, pulmonary edema, and rigidity

The factors contributing to the development of hypothermia include outdoor exposure, cold water submersion, medical conditions like hypothyroidism, sepsis, toxins like ethanol abuse, and drugs like oral anti diabetics, sedative hypnotics. Risk is highest in the elderly as the ability to autoregulate core temperature is impaired.

The diagnosis is done by the use of a low reading thermometer as many standard thermometers only read down to a minimum of 93ºF. A rectal or esophageal temperature probe is preferred for severe hypothermia.

The initial treatment of hypothermia is directed toward heat resuscitation, assessment of the extent of injury, and rewarming.

Passive external rewarming is the treatment of choice for mild hypothermia and is a supplemental method in patients with moderate to severe hypothermia.

1. Remove the wet clothing.

2. Cover with blankets.

3. Maintain room temperature at approximately 24ºC (75ºF).

4. Do active external rewarming in patients with moderate to severe hypothermia. It consists of combination of warm blankets, radiant heat, or forced warm air applied directly to the patient's skin.

5. Rewarm the trunk first BEFORE the extremities to minimize hypotension and acidemia due to arterial vasodilation and core temperature afterdrop.

6. For severe hypothermia, treat with less invasive rewarming techniques (eg, warmed IV crystalloid), and progressively adding more invasive ones (eg, warmed pleural lavage) as needed.

Rough handling of the moderate or severe hypothermic patient can precipitate arrhythmias, including ventricular fibrillation, that are often unresponsive to defibrillation and medications. Cardiopulmonary resuscitation (CPR) should continue until the patient is rewarmed to 30 to 32ºC (86 to 90ºF), at which point renewed attempts at defibrillation and resuscitation with ACLS medications are undertaken.