Hypothermia and frostbite¶
Emergency numbers differ by country. This page uses 911, the number for the United States and Canada. Many other countries use 112, 999, or another number. Find the number for your country.
Cold emergencies represent a dual threat to human survival: systemic cooling of the core body temperature (hypothermia) and localized ice crystal formation within peripheral tissues (frostbite). Both conditions frequently occur together during winter storms, cold-water immersion, outdoor wilderness exposure, or residential heating failures. In severe hypothermia, the heart becomes exceptionally irritable, where rough physical handling can trigger fatal ventricular fibrillation.
This guide provides clinically validated emergency procedures based on directives from the Wilderness Medical Society (WMS), the International Commission for Mountain Emergency Medicine (ICAR MedCom), the American Heart Association (AHA), and international resuscitation councils to stage cold injuries, execute gentle rewarming, prevent afterdrop collapse, and preserve frozen extremities.
Do this now¶
If someone is suffering from severe cold exposure:
- Call your local emergency number immediately if the person is confused, slurring words, extremely drowsy, or has stopped shivering while still cold (911 in the United States and Canada, 112 in the European Union, 999 in the United Kingdom).
- Move the person out of the wind, rain, and snow into a warm shelter. Handle them with extreme gentleness; do not allow them to walk, stand, or exert themselves.
- Remove wet garments by cutting them away rather than roughly stripping them over limbs. Insulate the person immediately with dry blankets, sleeping bags, or an improvised hypothermia wrap, covering their head and torso while placing an insulating barrier between their body and the cold ground.
- If the person is conscious, alert, and able to swallow normally, provide warm, sweet, non-caffeinated and non-alcoholic drinks to supply caloric energy for metabolic shivering.
- If the person is unresponsive, check for breathing and a carotid pulse for a full 60 seconds before concluding cardiac arrest. If there is no breathing and no pulse, begin CPR immediately and attach an AED.
- For localized frostbite, protect the frozen tissue from friction, do not rub with snow, and never thaw tissue in the field if there is any possibility of refreezing before reaching hospital care.
Cold emergency clinical flowchart¶
PERSON EXPOSED TO FREEZING / COLD CONDITIONS
│
Is the person conscious and shivering?
│
┌────────────────────┴────────────────────┐
YES NO
│ │
┌───────────┴───────────┐ ┌───────────┴───────────┐
│ MILD (SWISS STAGE I) │ │ MODERATE TO SEVERE │
│ Core 32°C to 35°C │ │ (SWISS STAGE II - IV) │
│ (90°F to 95°F) │ │ Core < 32°C (< 90°F) │
└───────────┬───────────┘ └───────────┬───────────┘
│ │
1. Move to dry shelter 1. CALL EMERGENCY SERVICES
2. Replace wet clothing 2. HANDLE WITH EXTREME GENTLENESS
3. Warm sweet drinks 3. Immobilize horizontally
4. Active body movement 4. Multi-layer Burrito Wrap
5. Passive external rewarm 5. Warm torso only (No limb rub)
│ 6. Check pulse for 60 seconds
Monitored full recovery │
┌───────────┴───────────┐
│ Is there a pulse / │
│ normal breathing? │
└───────────┬───────────┘
│
┌────────┴────────┐
YES NO
│ │
Maintain airway Start gentle CPR
Continuous wrap Attach AED
Await transport Do not abandon
The Swiss clinical staging system for hypothermia¶
In field settings lacking esophageal or rectal core temperature probes, rescuers classify accidental hypothermia using the Swiss Clinical Staging System, established by the International Commission for Mountain Emergency Medicine:
THE SWISS CLINICAL STAGING SYSTEM
┌───────────┬─────────────────────┬──────────────────────────────────────────┐
│ Stage │ Core Temperature │ Clinical Symptoms and Presentation │
├───────────┼─────────────────────┼──────────────────────────────────────────┤
│ Stage I │ 32°C to 35°C │ Fully conscious, shivering vigorously, │
│ (Mild) │ (90°F to 95°F) │ normal or slightly impaired coordination │
├───────────┼─────────────────────┼──────────────────────────────────────────┤
│ Stage II │ 28°C to 32°C │ Impaired consciousness, apathy, confusion│
│ (Moderate)│ (82°F to 90°F) │ Shivering ceases; cardiac dysrhythmias │
├───────────┼─────────────────────┼──────────────────────────────────────────┤
│ Stage III │ 24°C to 28°C │ Unconscious, cold-stiffened muscles, │
│ (Severe) │ (75°F to 82°F) │ barely detectable respiration and pulse │
├───────────┼─────────────────────┼──────────────────────────────────────────┤
│ Stage IV │ < 24°C │ Apparent death; pulseless, apnoeic, │
│ (Deep) │ (< 75°F) │ fixed dilated pupils; warm before dead │
└───────────┴─────────────────────┴──────────────────────────────────────────┘
Stage I: Mild hypothermia¶
The body thermal defense mechanisms operate at maximum capacity. Shivering produces metabolic heat up to five times baseline levels. The person remains alert, oriented, and able to swallow. Management focuses on calorie replenishment, dry clothing, and shelter.
Stage II: Moderate hypothermia¶
As glycogen stores deplete and core temperature falls below 32°C (90°F), involuntary shivering ceases completely. The patient enters a state of hypothermic apathy: they may appear intoxicated, slur speech, stumble, or demonstrate paradoxical undressing (removing clothes because paralyzed cutaneous blood vessels suddenly dilate, giving a false sensation of extreme warmth). At this stage, external active heat to the torso is mandatory.
Stage III: Severe hypothermia¶
The victim loses consciousness. Peripheral reflexes vanish, pupils dilate, and muscles become rigid. Breathing slows to two or three shallow breaths per minute, and the pulse becomes thready and profound bradycardia sets in. The heart muscle is hyper-irritable.
Stage IV: Deep hypothermia (apparent death)¶
The patient appears dead: skin is icy cold, muscles are as stiff as rigor mortis, pupils are fixed and unreactive, and neither pulse nor breathing is detectable by ordinary exam. Rescuers must remember the foundational rule of wilderness medicine: "A hypothermic patient is not dead until warm and dead." The metabolic oxygen demand of the cold brain is reduced by up to 90 percent, allowing neurologically intact survival after hours of cardiac arrest. Resuscitative efforts must continue until the core temperature is elevated above 32°C (90°F) in a hospital setting.
The gentle handling doctrine¶
When managing Stage II, III, or IV hypothermia, rough physical movement is life-threatening:
- Ventricular fibrillation trigger: The hypothermic myocardium is chemically unstable and hypersensitive to mechanical stimulation. Jostling, sudden tilting, lifting a patient roughly, or allowing a victim to stand can precipitate intractable ventricular fibrillation (VF) or asystole.
- Horizontal immobilization: Keep the patient completely flat and motionless. Never permit a moderately or severely hypothermic person to walk or sit upright, as blood pressure collapses rapidly.
- 60-second pulse check: Because hypothermia causes profound sinus bradycardia (heart rates as low as 5 to 10 beats per minute) and severe vasoconstriction, take a full 60 seconds to palpate for a carotid pulse before deciding the heart has stopped. Starting chest compressions on a heart that is beating slowly can trigger cardiac arrest.
Rewarming shock and the afterdrop phenomenon¶
Improper external warming techniques can kill a hypothermic patient through a fatal physiological mechanism known as afterdrop:
THE AFTERDROP MECHANISM
Active heat applied directly to cold arms and legs
│
▼
Cutaneous vasodilation in peripheral vascular beds
│
▼
Cold, stagnant, acidic, potassium-rich venous blood
flushes from the extremities back into the thoracic core
│
▼
Core body temperature DROPS an additional 1°C to 2°C
Acidosis and hyperkalemia strike the cold heart
│
▼
REWARMING SHOCK, VENTRICULAR FIBRILLATION, AND CARDIAC COLLAPSE
How to prevent afterdrop and rewarming shock¶
- Warm the core only: Apply external heat sources (commercial heat packs, chemical warming blankets, warm water bottles wrapped in towels) exclusively to the central trunk: the chest, neck, armpits, and groin.
- Never apply active heat to extremities: Leave arms, hands, legs, and feet unheated. Allow the extremities to warm passively from the inside out as core cardiac output restores.
- Never massage or rub: Massaging cold limbs forces stagnant venous blood back to the heart and shreds fragile microvascular capillary beds.
- Never place a cold patient in a hot bath: Hot water immersion forces immediate peripheral vasodilation, resulting in massive hypovolemic shock as blood pools in the skin, depriving the brain and heart of pressure.
Field rewarming: the hypothermia burrito wrap¶
The standard non-invasive field treatment for accidental hypothermia is the multi-layered hypothermia wrap, designed to eliminate conductive, convective, radiative, and evaporative heat loss:
HYPOTHERMIA WRAP ARCHITECTURE
┌────────────────────────────────────────────────────────────────────┐
│ Outer Layer: Windproof and Waterproof Tarp / Plastic Bivy Sled │
│ ├────────────────────────────────────────────────────────────────┤ │
│ │ Insulation Layer: 2 to 3 Down/Synthetic Sleeping Bags or Quilts│ │
│ │ ├────────────────────────────────────────────────────────────┤ │ │
│ │ │ Active Heat Sources: Chemical Heat Packs on Torso / Groin │ │ │
│ │ │ ├────────────────────────────────────────────────────────┤ │ │ │
│ │ │ │ Vapor Barrier: Plastic Sheeting to Stop Evaporative Heat │ │ │ │ │
│ │ │ │ ├────────────────────────────────────────────────────┤ │ │ │ │
│ │ │ │ │ Patient in Dry Layer (Head Covered, Face Exposed) │ │ │ │ │ │
│ │ │ │ └────────────────────────────────────────────────────┘ │ │ │ │
│ │ │ └────────────────────────────────────────────────────────┘ │ │ │
│ │ └────────────────────────────────────────────────────────────┘ │ │
│ └────────────────────────────────────────────────────────────────┘ │
│ Base Layer: Closed-Cell Foam Sleeping Pad Insulating from Ground │
└────────────────────────────────────────────────────────────────────┘
- Ground insulation: Lay down two thick closed-cell foam pads or dry coats. Direct contact with snow or frozen ground drains body heat via conduction at high rates.
- Outer vapor and wind barrier: Spread a heavy waterproof tarp or plastic sheet over the ground pads.
- Thick insulation: Place two sleeping bags or thick wool blankets on top of the tarp.
- Vapor barrier: Place an impermeable plastic sheet directly inside the sleeping bag to trap evaporated sweat, preventing evaporative cooling.
- Torso heat packs: Position activated chemical warming pads or hot water bottles (wrapped in cloth to prevent contact burns) on the chest, armpits, and groin.
- Seal the wrap: Cocoon the patient completely, tucking all layers snugly around the neck and shoulders. Cover the head with a warm fleece or wool hat, leaving only the nose and mouth open for respiration.
Frostbite pathology and clinical staging¶
Frostbite is the localized thermal destruction of tissue caused by freezing ambient conditions, typically striking fingers, toes, ears, cheeks, and nose.
CLINICAL STAGING OF LOCALIZED TISSUE FREEZING
┌─────────────┬─────────────────────┬────────────────────────────────────────┐
│ Depth │ Tissue Involvement │ Physical Presentation and Prognosis │
├─────────────┼─────────────────────┼────────────────────────────────────────┤
│ Frostnip │ Superficial │ Transient numbness, blanching skin; │
│ (Reversible)│ epidermis │ softens with warming; no tissue loss │
├─────────────┼─────────────────────┼────────────────────────────────────────┤
│ 1st Degree │ Epidermis │ Erythema, central pallor, firm plaque; │
│ Frostbite │ │ desquamation; complete recovery │
├─────────────┼─────────────────────┼────────────────────────────────────────┤
│ 2nd Degree │ Epidermis and │ Clear, fluid-filled blisters within │
│ Frostbite │ superficial dermis │ 24 hours; good recovery with care │
├─────────────┼─────────────────────┼────────────────────────────────────────┤
│ 3rd Degree │ Full dermis and │ Hemorrhagic (purple/blood) blisters; │
│ Frostbite │ subcutaneous plexus │ severe throbbing pain; partial loss │
├─────────────┼─────────────────────┼────────────────────────────────────────┤
│ 4th Degree │ Deep muscle, tendon,│ Deep blue/gray, cold, woody, dry; │
│ Frostbite │ and bone │ ischemic necrosis, mummification, loss │
└─────────────┴─────────────────────┴────────────────────────────────────────┘
Frostnip versus true frostbite¶
- Frostnip: Superficial cold injury without architectural ice crystal formation. The skin feels numb, cold, and pale. When warmed against warm skin (such as placing cold fingers into an armpit), sensation and normal color return rapidly without blistering or permanent tissue destruction.
- True frostbite: Extracellular and intracellular ice crystals freeze solid at skin temperatures below -0.55°C (31°F). The ice crystals expand, mechanically puncturing cell membranes, while severe microvascular thrombosis occludes capillary perfusion.
The catastrophic freeze-thaw-refreeze cycle¶
The single greatest hazard in field frostbite management is the freeze-thaw-refreeze cycle: - Massive damage from refreezing: If frozen tissue is thawed in the field and subsequently refreezes during an evacuation march, the newly formed ice crystals are significantly larger and more jagged than the original crystals, causing complete necrosis of deep muscular and bony architecture. - Wilderness evacuation rule: Never thaw frozen feet or hands in the field if the victim must walk to safety or if freezing environmental conditions could refreeze the tissue. It is far safer for a patient to hike several kilometers on frozen, anesthetized feet than to walk on thawed, blubbery, blistered tissue that subsequently refreezes.
Clinical rewarming protocol for frostbite¶
Once the patient reaches a definitive, warm indoor medical facility or hospital where refreezing is impossible: 1. Warm water bath: Immerse the frozen extremity in circulating water maintained between 37°C and 39°C (98.6°F and 102.2°F). Water hotter than 40°C (104°F) will scald and destroy numb tissue. 2. Duration: Maintain immersion for 15 to 30 minutes, adding warm water periodically to maintain temperature, until the extremity becomes soft, pliable, and regains a reddish-purple hue. 3. Manage severe pain: Rewarming frozen tissue produces excruciating, agonizing reperfusion pain as nerve endings thaw. High-potency analgesic medications managed by healthcare clinicians are universally required. 4. Post-thaw dressing: Pat the skin dry with extreme care. Apply sterile aloe vera gel, place sterile gauze pads loosely between individual fingers and toes to prevent adherence, and wrap loosely with dry non-compressive bandages. 5. Elevate: Keep the thawed limb elevated above the level of the heart to minimize secondary ischemic edema. 6. Blister care: Do not rupture, pop, or debride clear or hemorrhagic blisters in the field; intact blister roofs provide a sterile biological dressing.
Resuscitation in hypothermic cardiac arrest¶
When managing cardiac arrest in deep hypothermia (Stage IV):
- Prolonged CPR: Continue cardiopulmonary resuscitation throughout evacuation. Patients who have been submerged in icy water or buried in avalanches have achieved complete neurological recovery after more than 6 hours of continuous mechanical chest compressions.
- Defibrillation rules: If the AED advises a shock, deliver one shock at maximum energy. If ventricular fibrillation persists, resume CPR and defer further shocks until the core temperature rises above 30°C (86°F), as a severely cold heart rarely responds to repetitive defibrillation.
- Withhold medications: Advanced life support medications (epinephrine/adrenaline and amiodarone) should be withheld or spaced at extended intervals when core temperature is below 30°C (86°F), as hepatic metabolism is stalled and drugs accumulate to toxic concentrations in the central circulation.
- Transport to ECMO centers: Severe hypothermic cardiac arrest patients must be transported directly to tertiary medical facilities equipped with Extracorporeal Membrane Oxygenation (ECMO) or cardiopulmonary bypass for rapid internal blood rewarming.
Cold weather safety and preparation checklist¶
- Dress in three technical layers:
- Base layer: Moisture-wicking synthetic (polyester/polypropylene) or merino wool; avoid cotton entirely ("cotton kills" because it absorbs moisture and loses all insulation).
- Middle insulating layer: Thick fleece, down, or high-loft synthetic batting.
- Outer shell layer: Windproof, waterproof, breathable membrane (such as Gore-Tex).
- Cover extremities: Wear insulated mittens instead of gloves (mittens keep fingers together, retaining heat), thick wool socks, and a windproof balaclava or winter hat.
- Maintain nutritional intake: Consume high-calorie, carbohydrate- and fat-dense snacks frequently during cold weather exertion to fuel metabolic shivering.
- Avoid alcohol and nicotine: Alcohol induces cutaneous vasodilation, creating a false sensation of warmth while rapidly dumping core heat into the environment; nicotine is a potent vasoconstrictor that accelerates frostbite in fingers and toes.
- Never sleep directly on snow or frozen earth: Always place an insulated foam pad beneath your sleeping bag.
First aid certification
Hands-on wilderness first aid training through the Red Cross, NOLS Wilderness Medicine, or St John Ambulance provides practical practice in hypothermia packaging, avalanche rescue, and frostbite wound stabilization.
Frequently asked questions¶
Why is rough handling dangerous for someone with severe hypothermia?¶
When body core temperature drops below 32°C (90°F), the heart muscle becomes hyper-irritable and unstable. Sudden jolts, rough transport, lifting someone into an upright position, or vigorous movement can trigger fatal ventricular fibrillation (a chaotic, uncoordinated heart rhythm) or immediate cardiac standstill. Rescuers must keep the patient flat, handle them with extreme gentleness, and minimize all physical manipulation.
What is the "afterdrop" phenomenon, and how do I prevent it?¶
Afterdrop occurs when active heat (like hot water or heating pads) is applied directly to cold arms and legs. The heat causes constricted blood vessels in the extremities to open up, sending cold, acidic, potassium-rich blood rushing back into the heart. This drives the core heart temperature down even further, triggering cardiac arrest. To prevent afterdrop, apply heat only to the center of the body (chest, neck, armpits, and groin) and never rub or heat the limbs.
Why shouldn't I thaw frostbitten hands or feet if they might freeze again?¶
Thawing and then refreezing causes catastrophic, irreversible tissue death. When thawed tissue refreezes, water crystals reform much larger and sharper, shredding cell walls, severing capillaries, and destroying muscle and bone architecture. It is medically much safer for a person to walk out of the cold on frozen, anesthetized feet than to walk on thawed tissue that subsequently refreezes. Only thaw tissue when you reach a warm facility where refreezing is impossible.
Can someone survive if they have no pulse and feel icy cold?¶
Yes. Deep hypothermia dramatically reduces the brain and vital organs need for oxygen, sometimes by more than 80 to 90 percent. Patients who appear dead, with stiff muscles, cold skin, and unreactive pupils, have made full neurological recoveries after hours of CPR and medical rewarming with heart-lung bypass machines. This is why emergency medicine follows the rule: "Nobody is dead until warm and dead."
Why should I avoid cotton clothing in cold weather?¶
Cotton fibers absorb water and sweat like a sponge and hold it directly against the skin. When wet, cotton loses nearly 100 percent of its insulating ability and conducts heat away from the body roughly 25 times faster than dry air. In the outdoors, this phenomenon is summarized as "cotton kills." Always choose moisture-wicking synthetic fabrics or merino wool for cold weather base layers.