Hypothermia occurs when core body temperature drops below 35 degrees Celsius. This occurs when the body’s ability to generate heat by burning calories, muscle exertion and shivering is overwhelmed by heat loss. Heat is lost in four ways; radiation to a cold environment, conduction through contact with cold surfaces, convection from wind and water currents and evaporation of moisture. Improperly prepared or injured backcountry travellers can become hypothermic even in summer months.
The international commission on alpine rescue classifies hypothermia into five stages based on core body temperature. Each stage can also be differentiated by clinical findings in the field when core temperature reading may not be available.
HT I: Mild Hypothermia, 35-32 degrees
Normal or near normal consciousness, shivering
HT II: Moderate Hypothermia, 32-28 degrees
Shivering stops, consciousness becomes impaired
HT III: Severe Hypothermia, 24-28 degrees
Unconscious, may be difficult to detect vital signs
HT IV: Apparent Death, 15-24 degrees
HT V: Death from irreversible hypothermia
The goals of treating all stages of hypothermia are the same. Prevent further heat loss by radiation, convection, conduction and evaporation. This means changing wet for dry clothing, insulating the patient from the environment, providing shelter from the environment and arranging evacuation. If possible the patient should be provided with hot sweet drinks and food as fuel for their body to produce heat. Once patients move beyond mild hypothermia they will likely no longer be able to produce enough heat to warm themselves. Once further heat loss is prevented with adequate clothing, insulation and shelter, they require the addition of external sources of heat for warming.
https://www.northshorerescue.com/education/treating-hypothermia/
