Hypothermia — Recognition and Rewarming Techniques

Hypothermia occurs when the body's core temperature drops below 35°C (95°F). It is a systemic emergency — not just cold skin or cold extremities, but a drop in the temperature of the body's vital organs. At sufficiently low core temperatures, the heart's electrical system fails, causing cardiac arrest.

Hypothermia kills through two mechanisms: direct physiological failure at low temperatures, and the acute circulatory collapse that can be triggered by incorrect rescue manoeuvres. Understanding both the condition and the hazards of incorrect treatment is essential for anyone in cold environments.

Recognition — Signs by Temperature

Hypothermia presents differently at different core temperatures:

Core Temperature	Stage	Signs
35–32°C (95–89.6°F)	Mild	Shivering; slurred speech; poor coordination; confusion; increased heart rate
32–28°C (89.6–82.4°F)	Moderate	Shivering stops; increasingly confused; drowsy; rigid muscles
28–24°C (82.4–75.2°F)	Severe	Unconscious; very slow pulse; very slow breathing; pupils may be dilated
< 24°C (< 75.2°F)	Profound	No detectable pulse; no breathing; appears dead

Critical point: A person who appears dead in a cold environment may not be dead. Cardiac arrest from hypothermia is potentially reversible if the person is rewarmed correctly — there are documented cases of people surviving with core temperatures below 20°C. The principle: "Not dead until warm and dead."

⚠️ Do not assume death without professional medical assessment in a hypothermic person. Begin CPR and continue until hospital care is available if the person shows no signs of life but the cause is hypothermia.

Identifying the Stage Without a Thermometer

In most field situations, a thermometer capable of measuring low temperatures will not be available. Clinical signs approximate the stage:

Field Observation	Likely Stage
Shivering, speaking coherently, walking	Mild
Shivering stopped; slow, confused speech	Moderate
Not shivering; unresponsive; barely moving	Severe
No pulse found; not breathing	Profound / cardiac arrest

Shivering is actually a positive sign — it is the body's metabolic warming mechanism. When shivering stops (as it does in moderate hypothermia), the person is worse, not better.

Field Management — Preventing Further Heat Loss

Before rewarming, stop the loss:

1. Remove wet clothing — wet clothing accelerates heat loss approximately 25 times compared to dry clothing
2. Insulate from the ground — conduction to cold ground is a major heat loss route; place insulating material underneath the person before above
3. Wind protection — convection is a major heat loss route; shelter from wind
4. Cover the head — up to 40% of heat loss in a cold person can be through the uncovered head
5. Vapour barrier — wrapping the person in a waterproof layer (space blanket, plastic sheet, bin liner) over insulating layers traps humid warm air around the body

Rewarming Approach by Stage

Stage	Rewarming Approach
Mild	Passive rewarming: shelter, dry clothing, warm environment, warm drinks if conscious
Moderate	Passive rewarming + insulation; handle extremely gently; no hot drinks
Severe	Passive external rewarming; gentle handling; hospital rewarming (core rewarming) required
Profound / arrest	CPR; hospital for extracorporeal rewarming (ECMO or bypass)

Passive Rewarming (Mild Hypothermia)

For mild hypothermia, the body still has the metabolic capacity to rewarm itself if the heat loss is stopped:

• Dry warm clothing
• Warm shelter
• Warm sweet drinks if fully conscious (not sedated)
• Calorie-dense food to fuel shivering
• Warm water bottles wrapped in cloth to axilla (armpits) and groin

The Handling Hazard — Rescue Collapse

One of the most dangerous aspects of hypothermia is "rescue collapse" — sudden cardiac arrest triggered by inappropriate movement or rewarming of a severely hypothermic person:

• In severe hypothermia, the heart is beating very slowly and the electrical system is fragile
• Movement can trigger ventricular fibrillation (cardiac arrest)
• Rapid rewarming of the extremities causes cold blood from the arms and legs to flow to the core, causing a paradoxical further drop in core temperature

Handling rules for moderate to severe hypothermia:

1. Handle gently and horizontally — avoid sudden movements, bending, or lifting that jerks the body
2. Keep the person horizontal — sitting them upright can cause blood to pool in the legs, reducing cardiac output further
3. Do not give alcohol — causes peripheral vasodilation, increasing heat loss and bringing cold blood to the core
4. Do not rub extremities vigorously — this brings cold blood centrally
5. No hot baths — too rapid peripheral rewarming

Severe and Profound Hypothermia — CPR Considerations

For a person with no detectable pulse and not breathing from hypothermia:

1. Check pulse for at least 60 seconds — in severe hypothermia, the heart rate can be as low as 4–6 beats per minute; a short pulse check misses this
2. If no pulse after 60-second check: begin CPR
3. Continue CPR — do not stop; in profound hypothermia, CPR maintains cerebral and cardiac perfusion until hospital rewarming is possible
4. AED if available: apply; the device may not recommend shock (hypothermic heart does not typically respond); continue CPR
5. Hypothermia patients are not declared dead in the field — hospital rewarming via ECMO (extracorporeal membrane oxygenation) can warm the blood directly; this has revived patients with no detectable heartbeat

After Field Rewarming (Mild Hypothermia)

Even when the person appears recovered from mild hypothermia:

• Medical review is advisable
• Monitor for persistent confusion or cardiac abnormalities
• Reinforce rewarming and nutrition
• Seek medical care if signs of moderate hypothermia were present at any point

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Quick Reference

Stage	Core Temp	Key Sign	Field Action
Mild	35–32°C	Shivering; confused	Shelter; dry clothes; warm sweet drinks
Moderate	32–28°C	Shivering stopped; drowsy	Insulate; handle gently; horizontal; hospital
Severe	28–24°C	Unconscious; barely breathing	Very gentle handling; passive rewarming; hospital
Profound	< 24°C	No pulse or breathing	CPR; hospital for ECMO
Key rule	—	Not dead until warm and dead	Do not assume death; continue CPR
Never	—	Hot bath; alcohol; rough handling; upright position	Worsens outcome; causes rescue collapse