Hypothermia & Heat Retention 101

Educational content only — seek certified wilderness-first-aid training for clinical instruction.

1) The Biology of Cooling

Core temperature below 35 °C (95 °F) defines hypothermia. As skin and core temperatures drop, vasoconstriction limits peripheral blood flow to conserve core heat. Shivering thermogenesis increases metabolic heat output, but at high energy cost—up to 600 kcal per hour.

• Mild (35–32 °C): shivering, fine-motor loss.
• Moderate (32–28 °C): halted shivering, slowed pulse and breathing.
• Severe (<28 °C): arrhythmias, unconsciousness, cardiac arrest risk.

2) Mechanisms of Heat Loss

• Conduction: direct contact with cold ground or metal; fastest loss when wet.
• Convection: wind removes boundary-layer warmth; mitigated by shell layers.
• Evaporation: sweat or wet clothing—latent heat drain.
• Radiation: infrared emission from uncovered skin.
• Respiration: each breath exhales warm, humid air; use scarf or buff to trap moisture.

3) Safe Rewarming Methods

1. Stop further cooling: remove wet clothing; insulate from ground with foam, branches, or pack.
2. Passive rewarming: add dry layers, shelter from wind; body heat rebounds naturally if mild.
3. Active external warming: apply heat packs to armpits, chest, groin — core before limbs.
4. Active internal: warm sweet liquids (no caffeine/alcohol); carbohydrates fuel shivering.

Never rub cold limbs or immerse a person in hot water. Handle the person gently, rewarm the core slowly, and activate emergency medical services for suspected hypothermia.

4) Immediate Field Priorities

1. Move the person out of wind and precipitation, then insulate them from the ground.
2. Remove wet clothing with as little unnecessary movement as possible and replace it with dry insulation.
3. Warm the chest, neck, head, and groin gradually. Do not apply direct high heat to bare skin.
4. Monitor breathing and responsiveness while arranging evacuation. Give warm, sweet, nonalcoholic fluids only if the person is fully alert and able to swallow.

Medical references: CDC hypothermia guidance · American Red Cross first aid

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