Hypothermia is defined as a drop in core temperature to less than 35C, and can occur even at warmer temperatures given the right circumstances. The head is a significant source of heat loss, especially in the cold: half of heat loss in colder temperatures is via radiation from the skin.
Dehydration and calorie depletion predispose to hypothermia. Measurement of temperature may be difficult in very cold situations. An oral electronic thermometer is close to pulmonary artery (core) measurements.
You may wish to carry a liquid thermometer backup and a spare electronic. Rectal temperatures may be a little higher and lag behind temperature drop.
Be aware of the Swiss Mountain Medicine field (clinical) definitions for Hypothermia:
Hypothermia I (Mild): alert, uncontrolled shivering: 35 – 32C (95 – 90F)
Shivering is most effective with removal from the cold. Limited exercise may help. Eat and drink.
Hypothermia II (Moderate): altered mentation, shivering stops: 32 – 28C (90 – 82F)
At this point the person must be actively warmed because they are unable to warm themselves.
Hypothermia III (Severe): unconscious: 28 – 24C (82 – 75F)
Handle carefully as the heart becomes progressively more irritable below 32C
Hypothermia IV: Not breathing: <24C (75F)
Shivering is an effective warming mechanism initially caused by skin temperature changes rather than changes in core temperature. Core temperature drop is caused by cold blood returning from limbs during rapid rewarming and can complicate rewarming efforts. Slower rewarming may reduce this complication.
The hypothermia wrap consists of layers: a waterproof sheet, several sleeping bags and warm items such as hand warmers and warm water bottles enclose the victim. The wrap can be carried in a litter. CPR is not recommended for Mod-Severe hypothermia due to cardiac irritability, unless definitive care is more than three hours away. Otherwise, provide respiratory support and evacuate. Check to see if the patient has a pulse for at least 2 minutes.
Evacuation is recommended for all but mild hypothermia.
Geoff Clover, MD
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