Cold-Related Emergencies

Definition and physiology

• Hypothermia: core body temperature under 35°C (95°F)
• Normal core temp: 37°C (98.6°F)
• Why it's dangerous: a low core temperature slows every metabolic process. The heart gets irritable and can slip into ventricular fibrillation (VF), a deadly arrhythmia. Brain function suffers too.

How the body loses heat in the cold

• Conduction: direct contact with something cold, like the ground, water, or a cold object. Water pulls heat away 25 times faster than air.
• Convection: wind strips away the insulating layer of warm air next to the body. Wind chill sharply increases heat loss.
• Radiation: the body radiates heat into the cold around it
• Evaporation: wet clothing lets heat escape fast through evaporation
• Respiration: breathing in cold air and breathing out warm air costs heat

Hypothermia staging

Functional field staging

• Cold-stressed (not hypothermic): alert, shivering, able to look after themselves → food, dry layers, exercise to rewarm.
• Mild: alert but impaired, shivering hard → shelter, dry insulation, sugar and calories; keep moving only if fully alert.
• Moderate: decreased consciousness, shivering weak or stopped → handle gently, no walking, insulate and wrap, external heat to the trunk, emergent evacuation.
• Severe: unconscious → treat them as fragile, full hypothermia wrap, emergent evacuation, be ready for CPR.

Numeric reference ranges

Mild hypothermia (32-35°C / 90-95°F)

• Signs:
  • Shivering, which is a good sign. The body is still trying to make heat.
  • Poor coordination (ataxia, clumsiness)
  • Slurred speech, confusion
  • Pale or bluish (cyanotic) skin
  • Normal to slightly high blood pressure
• Patient awareness: usually aware of their condition, and may look for shelter

Moderate hypothermia (28-32°C / 82-90°F)

• Signs:
  • Shivering stops without rewarming. That's a bad sign. The body has quit trying to make heat.
  • More confusion and poor judgment. They may refuse to move or to get help.
  • Trouble walking (ataxia) and lost fine motor control
  • Slow heart rate (bradycardia) and low blood pressure (hypotension)
  • Paradoxical undressing, where the patient feels warm and starts stripping off clothes in the cold
• How paradoxical undressing happens: the peripheral vessels dilate, and the confused patient feels a sudden rush of warmth while the core keeps dropping. They undress, and heat loss speeds up.

Severe hypothermia (<28°C / <82°F)

• Signs:
  • Unconscious or barely conscious
  • No shivering (the muscles have stopped)
  • Dilated pupils (they can look dead)
  • Extreme bradycardia: the pulse may be barely detectable, under 30 bpm
  • Extreme hypotension, possibly unmeasurable
  • May look dead, and may not be
• Ventricular fibrillation risk: the heart may be in VF and may not respond to defibrillation until the core temperature comes up

Afterdrop: the complication

What afterdrop is: core temperature keeps falling even after the patient is out of the cold and rewarming has started

• Mechanism: the core keeps cooling as its heat conducts out into the cold tissue around it. Movement adds a circulatory effect, as cold blood from the limbs mixes back toward the core.
• Rescue collapse (a separate problem): cardiovascular collapse around the time of rescue, triggered by rough handling or position changes, like standing the patient up. Gentle, horizontal handling is how you avoid it.
• How to minimize it:
  • Gentle, horizontal handling. No vigorous exercise, no rough movement, no sitting or standing them up.
  • Don't rub the arms and legs hard
  • Don't rewarm the arms and legs before the core
  • Put external heat on the trunk (chest, armpits, back), not the arms and legs

Field treatment by stage

All hypothermia stages

• Remove wet clothing, if that's what it takes to stop ongoing evaporative loss
• Insulate them from the ground first (sleeping pad, branches, packs). Insulation underneath matters most, because cold ground pulls heat faster than air. This ground layer is insulation, not a vapor barrier.
• Add insulation on top (sleeping bag, blankets, clothing). Wrap the torso and the legs, and cover the head.
• Add external heat:
  • Hot water bottles or heat packs against the trunk (chest, armpits or axillae, back). Keep them from getting too hot, and wrap them so they never sit directly on skin.
  • Wrap them in blankets or other insulating material
  • Skin-to-skin contact from another person mostly prevents further heat loss. It transfers little heat, so pair it with insulation and wrapped heat sources.
• Offer warm, sweet drinks and food only if they're fully alert and swallowing normally

Moderate hypothermia (28-32°C)

• Everything above
• Handle them gently. Rough handling can trigger VF.
• Lay them flat on their back (supine)
• No alcohol
• Watch the airway carefully

Severe hypothermia (<28°C)

• Everything above, but even more gently
• Handle them as if they're in unstable VF
• Protect the airway. Nothing by mouth.
• CPR if they're unresponsive and not breathing (see below)
• Build a hypothermia wrap (a "burrito," in trail slang), layered from the patient outward:
  • Dry the patient (remove or replace wet clothing)
  • Vapor barrier (plastic sheet or tarp) against the clothing
  • Thick insulation all the way around, including underneath the patient
  • Windproof, waterproof outer shell
  • Head covered, face left exposed
  • Wrapped heat sources placed at the trunk
• Emergent evacuation. They may need active core rewarming in a hospital.

Hypothermic cardiac arrest: "No one is dead until warm and dead"

• Principle: a severely hypothermic patient can go a long time with no detectable pulse and still be alive and resuscitable
• CPR guidelines:
  • Watch for breathing and any sign of life for up to 60 seconds. Hypothermia can slow breathing way down.
  • If there's any breathing or sign of life in that minute, even very slow, do not start chest compressions
  • Unresponsive and not breathing (or only gasping): start CPR. No pulse check first.
  • Keep CPR going through the whole evacuation
  • If you suspect hypothermia, do not withhold CPR because the arrest has gone on a long time
  • Accepted exceptions: don't start or continue CPR if there's an obvious lethal injury, the chest is frozen solid and can't be compressed, the airway is packed with snow or ice, or there's a valid DNR order
• Defibrillation: the heart may be in VF and may not respond to defibrillation until core temp comes up. If an AED is available, use it and follow its prompts, and keep CPR going between shocks.
• Active core rewarming: the hospital has warmed IV fluids, heated humidified oxygen, and ECMO (extracorporeal membrane oxygenation) for severe cases. Some patients have recovered after hours without a pulse when hypothermia was the cause.

Frostbite: frozen tissue

What: ice crystals forming in tissue cells at freezing temperatures

• Mechanism: tissue freezes when its temperature drops below freezing and ice crystals form. Cold-induced vasoconstriction speeds the cooling, but it isn't what freezes the tissue. The ice crystals then damage cells, both mechanically and osmotically.
• Most common sites: fingers, toes, nose, ears, cheeks
• Risk factors:
  • Wet skin or wet clothing
  • Wind chill
  • Immobility (can't move to make heat)
  • Dehydration, malnutrition
  • Prior frostbite (the skin loses cold tolerance)

Frostbite stages

Frostnip (superficial cold injury)

• What: superficial cold injury, with no actual tissue freezing
• Signs: skin white or pale, numb, no blisters
• Recovery: rapid and complete with rewarming (30 min). Full function comes back.
• Treatment: rewarm gently with body heat or warm water

Superficial frostbite

• What: the skin is frozen, and the deeper tissue is still soft
• Signs: white or waxy while frozen. Clear blisters (serous fluid) form after rewarming. They're the less serious kind.
• Healing: slower, and it can take weeks. Usually a full recovery, though cold tolerance may be permanently reduced.
• Treatment: rewarm (see below)

Deep frostbite (full thickness)

• What: skin and deep tissue frozen (muscle, bone). The most serious kind.
• Signs: hard and wooden to the touch. Mottled blue or purple. Blood-filled blisters after rewarming, which point to tissue death.
• Prognosis: tissue death is likely. Expect permanent damage, and it may mean amputation.
• Treatment: rewarm only if it can't refreeze (see below), then urgent evacuation for surgery

The rewarming decision

• Decision: if there's a risk the tissue will refreeze, leave the frostbitten area frozen
• Why: refreezing causes massive additional tissue damage as ice crystals form again
• Example: a hiker with frozen toes, deep in the backcountry, 8 hours from help. Walking out on frozen feet beats thawing them and having them refreeze on the way.
• Once feet are thawed, they don't walk. Never walk on thawed feet. From that point the patient gets carried.

Rewarming technique: when to rewarm

• Method: warm water immersion, not dry heat
• Temperature: 37-39°C, body-temperature warm, not hot. No boiling water.
• Duration: 30-45 minutes of immersion. Thawing takes time.
• Pain: rewarming is very painful. Acknowledge it, and do what you can to keep them comfortable.
• Activity: gentle. Don't massage or rub the tissue while it rewarms.

Post-thaw care

• Don't:
  • Rub the tissue (the cells are fragile)
  • Apply direct heat (fire, stove)
  • Use alcohol or massage
• Do:
  • Leave every blister intact in the field, including the blood-filled (hemorrhagic) ones
  • Protect blisters with dry, bulky dressings. Draining a blister is beyond field care.
  • Elevate the affected area to reduce swelling
  • Pad or splint it gently for comfort
  • Pain relief (ibuprofen also helps reduce inflammation)
• Evacuation: all significant frostbite needs medical evaluation

Other cold injuries

Chilblain (pernio)

• Chronic exposure to cold and wet at non-freezing temperatures
• Itchy, red or purple lesions on the ears, fingers, and toes
• Treatment: rewarm and keep dry

Immersion foot (trench foot)

• Long wet, cold exposure (hours to days) without freezing
• Maceration (softened, waterlogged skin), pain, blisters, possible gangrene
• Treatment: clean and dry the feet, and rewarm slowly
• Prevention: keep feet dry on cold, wet expeditions

Passive external rewarming

• Mild hypothermia: this may be enough
• Method: insulate them from the cold with blankets, a sleeping bag, clothing
• Let the body make its own heat: shivering generates heat, as long as the insulation holds it in
• Advantage: no risk of afterdrop from active rewarming

Active external rewarming

• Methods:
  • Hot water bottles, wrapped and placed on the core, not the arms and legs. The most accessible field method.
  • Heat packs (chemical, or stove-warmed rocks wrapped in cloth)
  • Warm drinks if they're fully alert and able to swallow
  • Skin-to-skin contact with a rescuer. It mostly prevents further heat loss rather than transferring much heat. Insulation plus wrapped external heat (warm water bottles or heat packs against the trunk) works better.
• Target areas: the trunk (chest, armpits, back), not the arms and legs. Never directly on skin.
• Caution: go gently, and don't burn the skin

Active internal rewarming

• Field options:
  • Warm oral fluids (only if they're fully alert and can swallow). They work better with sugar in them, which fuels metabolic heat.
  • That's about the limit in the field, without advanced equipment
• Hospital options:
  • Warmed IV fluids
  • Heated humidified oxygen
  • ECMO (extracorporeal membrane oxygenation) for severe cases, the most advanced option

Rewarming complications

• Afterdrop: a rapid drop in core temperature after rewarming starts, as cold blood from the limbs returns to the core
• Dehydration: cold cuts fluid intake, and rewarming adds fluid loss through sweating
• Dysrhythmias: the heart can develop arrhythmias during rewarming
• Prevention: rewarm gently, core first, and keep monitoring

Clothing: the layering system

• Layer 1 (base): moisture-wicking material (merino wool, synthetic), not cotton. Cotton holds moisture and loses its insulation when wet.
• Layer 2 (insulation): fleece, wool, or down. It traps air. Wool and fleece keep insulating when damp; down loses it quickly once wet.
• Layer 3 (shell): a windproof, waterproof outer layer. It keeps out the wind chill and the wet.
• Extremities: a hat (cuts heat loss through the head), gloves, socks, gaiters to keep snow out

Hydration and nutrition

• Hydration: cold blunts the thirst mechanism, so it's easy to get dehydrated. Drink regularly.
• Nutrition: metabolism is the main source of heat. Eat high-calorie food to fuel it.
• Carbohydrates: quick energy, burned for heat
• Fats: sustained energy and insulation

Monitoring and prevention

• Early signs in yourself: shivering you can't control, poor coordination, confusion. Get to shelter and warmth immediately.
• Early signs in a partner: shivering, slurred speech, clumsiness, withdrawal. Someone getting hypothermic often doesn't recognize their own symptoms.
• Buddy system: never hike alone in the cold. A partner can spot the early signs and act on them.
• Frequent breaks: don't push through cold and fatigue. Take breaks in shelter to rewarm.
• Avoid alcohol: it causes vasodilation (more heat loss) and impairs judgment

Environmental management

• Shelter: get out of the wind and precipitation. Even a natural windbreak (rocks, trees) helps a lot.
• Insulation: don't sit on cold ground. Put a pad, branches, or a pack under you.
• Fire: if you have one and it's safe, it's a major source of warmth. Don't rely on fire alone; you still need insulation.
• Avoid immersion: stay dry. If you get wet, change into dry clothes immediately.