Recognizing and Treating Hypothermia in the Field

Step-by-Step Instructions

1. 01

   Know the four stages and what to look for

   Hypothermia occurs when core body temperature drops below 95°F (35°C). Normal core temp is 98.6°F. The four stages and their core temperature: Stage 1 — Mild (89–95°F / 32–35°C): shivering, goosebumps, impaired coordination, slurred speech beginning, pale skin. The victim usually knows something is wrong. Stage 2 — Moderate (82–89°F / 28–32°C): shivering stops (this is a warning sign, not improvement), muscle stiffness, severely impaired coordination, confusion, drowsiness. Victim may appear drunk. Stage 3 — Severe (68–82°F / 20–28°C): unconscious or nearly so, very slow or absent shivering, dilated pupils, very slow heartbeat, paradoxical undressing (victim removes clothing due to nerve confusion — seen in 20–50% of hypothermia deaths). Stage 4 — Death (<68°F / 20°C): cardiac arrest, no detectable pulse. Hypothermia victims in Stage 4 have survived with immediate hospital rewarming — the rule is "not dead until warm and dead."

   Warning: When shivering stops, most people assume the victim is improving. The opposite is true. Shivering is your body's last active warming mechanism. When it stops in a cold environment, the victim has moved into moderate-to-severe hypothermia and is in serious danger.
2. 02

   Treat mild hypothermia immediately

   Mild hypothermia (shivering, alert, responsive) is reversible with field treatment if you act immediately. Step 1: Remove from the cold environment. Get out of wind, rain, and cold ground. A tent, vehicle, or dense tree cover all help. Step 2: Remove wet clothing. Wet fabric conducts heat away from the body 25× faster than dry fabric. Even if you have nothing dry to replace it with, removing wet clothing and wrapping in a space blanket is better than leaving wet clothes on. Step 3: Insulate from the ground first. Cold ground steals heat faster than cold air. Layer under the victim — sleeping pad, dry leaves, extra packs, anything that creates an air gap between them and the ground. Step 4: Wrap the victim in dry insulation. A sleeping bag (get inside with them if needed), wool blanket, or multiple space blankets. Cover the head — it is responsible for up to 30% of heat loss. Step 5: Apply heat packs to the core, not the extremities. Armpits, groin, and neck are the locations where blood vessels are closest to the surface. Warming hands and feet first drives cold blood toward the core and can trigger afterdrop (see below).

   Warning: Never give alcohol to a hypothermia victim. Alcohol causes vasodilation — it feels warming but rapidly increases heat loss. It also impairs judgment, masking symptoms.
3. 03

   Treat moderate-to-severe hypothermia with extreme care

   A victim in Stage 2+ (confused, shivering stopped, unresponsive) requires evacuation to a hospital. Your job in the field is to prevent further cooling and transport safely — not to aggressively rewarm. Why: rapid external rewarming of a severely hypothermic patient can trigger afterdrop (cold blood from the extremities floods the core when peripheral blood vessels dilate, further dropping core temperature) and rewarming cardiac arrest (the cold, sluggish heart is at high risk of ventricular fibrillation during rough handling or rapid temperature changes). In the field: (1) Handle the victim GENTLY. Do not jostle or force movement. (2) Keep them horizontal — do not raise them upright (orthostatic hypotension can cause cardiac arrest). (3) Check for breathing and pulse for 60 seconds before assuming absent — hypothermic pulse is extremely slow and faint. (4) Wrap in as much insulation as available: sleeping bag, space blanket, extra clothing. (5) If you have warm IV fluids (rare in field situations), they help. (6) Evacuate immediately, continuously monitoring breathing.

   Warning: CPR in hypothermic cardiac arrest: start CPR if you confirm no pulse after 60 seconds, and continue until the victim is at a hospital and rewarmed. A hypothermic heart can often be resuscitated at temperatures that would mean irreversible death in a normothermic patient. "Not dead until warm and dead" is a genuine medical principle.
4. 04

   Understand afterdrop — the hidden danger during rewarming

   Afterdrop is the continued fall in core body temperature even after you begin rewarming. It happens because: when the body is severely cold, peripheral blood vessels constrict to protect the core. When rewarming begins, these vessels dilate. Cold blood that was pooled in the arms and legs suddenly flows back toward the core, dropping core temperature further before it starts to rise. Afterdrop is responsible for many deaths of patients who "seemed to be improving." How to minimize afterdrop risk: (1) Rewarm core first, always — armpits, groin, neck. Never hands and feet first. (2) Keep the victim horizontal — sitting or standing accelerates afterdrop. (3) Rewarm passively and gradually for severe cases — your body heat plus insulation, not hot water immersion or heating pads. (4) If using chemical heat packs, wrap them in cloth before applying — direct contact can cause burns on cold skin that has lost sensation.

5. 05

   The five things you must NOT do

   These mistakes kill people who would otherwise have survived: (1) Do NOT rub or massage cold extremities. Mechanical stimulation of cold tissues drives cold blood toward the heart and can trigger cardiac arrest. (2) Do NOT give alcohol. It feels warm, causes dangerous vasodilation and heat loss, and impairs the victim's ability to signal worsening. (3) Do NOT put a moderately-to-severely hypothermic victim in a hot bath. Rapid peripheral rewarming maximizes afterdrop and causes cardiac arrhythmias. (4) Do NOT have the victim exercise to "warm up." In Stage 1 shivering this is borderline acceptable. In Stage 2+ it forces cold blood to the core. (5) Do NOT leave a confused victim alone to "rest." Confusion is a Stage 2 symptom, not fatigue. An unmonitored Stage 2 victim can progress to unconsciousness and cardiac arrest within an hour.

   Warning: Paradoxical undressing — when a victim removes their clothing despite the cold — occurs in 20–50% of hypothermia deaths. It is caused by a nerve sensation malfunction, not conscious choice. If you find a victim undressed in a cold environment, treat for hypothermia immediately, even in above-freezing temperatures.
6. 06

   Prevent hypothermia before it starts

   Prevention is the only first aid that has a 100% success rate. The core principle: stay dry and stay fueled. Wet cotton kills — avoid cotton as a base layer in any cold or wet environment. Choose synthetic (polyester, nylon) or merino wool for everything next to your skin. The hypothermia prevention checklist: (1) Dress in layers (wicking base, insulating mid, waterproof shell). (2) Eat and drink regularly — hypothermia progresses fastest in caloric deficit and dehydration. (3) Rest before you are exhausted — exhaustion drops core temperature faster. (4) Know the wind chill — 35°F in 20 mph wind feels like 19°F and kills in hours. (5) Have a dry set of clothes sealed in a waterproof bag that you do not open until you need them. (6) Never ignore shivering. Shivering is your body telling you it is losing the thermal balance. Stop, assess, and rewarm before it progresses. The window between Stage 1 and Stage 2 can be as short as 30 minutes in wet, windy conditions.