Cold-Related Emergencies

Definition & Physiology

• Hypothermia: Core body temperature <35°C (95°F)
• Normal core temp: 37°C (98.6°F)
• Why it's dangerous: Low core temperature slows all metabolic processes. Heart becomes irritable, may develop ventricular fibrillation (deadly arrhythmia). Brain function impaired.

Heat Loss Mechanisms in Cold

• Conduction: Direct contact with cold surface (ground, water, cold object). Water conducts heat away 25x faster than air.
• Convection: Wind strips away insulating layer of warm air. "Wind chill" dramatically increases heat loss.
• Radiation: Body radiates heat to cold environment
• Evaporation: Wet clothing allows rapid evaporative heat loss
• Respiration: Breathing in cold air and exhaling warm air loses heat

Hypothermia Staging

Functional Field Staging

• Cold-stressed (not hypothermic): Alert, shivering, able to care for self → food, dry layers, exercise to rewarm.
• Mild: Alert but impaired, vigorous shivering → shelter, dry insulation, sugar/calories; keep moving only if fully alert.
• Moderate: Decreased consciousness, shivering weak or stopped → handle gently, no walking, insulate/wrap, external heat to the trunk, evacuate.
• Severe: Unconscious → treat as fragile, full hypothermia wrap, urgent evacuation, be prepared for CPR.

Numeric Reference Ranges

Mild Hypothermia (32-35°C / 90-95°F)

• Signs:
  • Shivering (GOOD sign — body still trying to warm itself)
  • Poor coordination (ataxia, clumsiness)
  • Slurred speech, confusion
  • Pale or cyanotic skin
  • Normal to slightly elevated blood pressure
• Patient awareness: Usually aware of condition, may seek shelter

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

• Signs:
  • Shivering STOPS (BAD sign — body has given up attempting to generate heat)
  • Increased confusion, poor judgment, may refuse to move or seek help
  • Ataxia (difficulty walking), loss of fine motor control
  • Bradycardia (slow heart rate), hypotension (low blood pressure)
  • Paradoxical undressing: patient feels warm and removes clothing (dangerous!)
• Mechanism of paradoxical undressing: Peripheral vasodilation from hypothermia confusion creates sudden sensation of warmth, but core is dropping. Patient undresses, accelerating heat loss.

Severe Hypothermia (<28°C / <82°F)

• Signs:
  • Unconscious or barely conscious
  • No shivering (muscle activity ceased)
  • Dilated pupils (appear dead)
  • Extreme bradycardia (pulse may be barely detectable, <30 bpm)
  • Extreme hypotension (may be unmeasurable)
  • May appear dead (but isn't!)
• Ventricular fibrillation risk: Heart may be in VF but is unresponsive to defibrillation until core temp is raised

Afterdrop: The Complication

What is afterdrop: Core temperature continues to fall even after the patient is removed from the cold source and rewarming begins

• Mechanism: Continued cooling of the core as heat conducts away into surrounding cold tissue, plus circulatory effects when the patient moves (cold peripheral blood mixing back toward the core)
• Rescue collapse (a distinct problem): Cardiovascular collapse around the time of rescue, triggered by rough handling or position changes (e.g., standing the patient up) — this is why gentle, horizontal handling matters
• How to minimize:
  • GENTLE, horizontal handling — avoid vigorous exercise, rough movement, or sitting/standing the patient up
  • Don't rub extremities vigorously
  • Avoid rewarming peripheral areas (arms/legs) before the core
  • Apply external heat to the trunk (chest, armpits, groin) not the extremities

Field Treatment by Stage

All Hypothermia Stages

• Remove wet clothing (if necessary to prevent continued evaporative loss)
• Insulate from the ground (sleeping pad, branches, packs) — this ground layer is insulation, not a vapor barrier
• Add insulation on top (sleeping bag, blankets, clothing)
• Add external heat sources:
  • Hot water bottles or heat packs (not too hot — wrap so they don't touch skin directly) against the trunk: groin, axillae, chest
  • Wrap in blankets or insulating materials
  • Skin-to-skin contact from another person mainly prevents further heat loss — it transfers little heat, so combine it with insulation and wrapped heat sources
• Offer warm sweet drinks if conscious and swallowing normally

Moderate Hypothermia (28-32°C)

• All steps above
• Handle GENTLY — avoid rough handling which can trigger VF
• Position supine (flat)
• NO alcohol
• Monitor airway carefully

Severe Hypothermia (<28°C)

• All steps above but EVEN MORE GENTLY
• Handle as if patient has unstable VF
• Protect airway; don't force oral intake
• CPR if pulseless (see below)
• Build a hypothermia wrap, layered from the patient outward:
  • Dry the patient (remove/replace wet clothing)
  • Vapor barrier (plastic sheet or tarp) against the clothing
  • Thick insulation all around, including underneath the patient
  • Windproof/waterproof outer shell
  • Head covered, face left exposed
  • Wrapped heat sources placed at the trunk
• Urgent evacuation (may need active core rewarming in hospital)

Hypothermic Cardiac Arrest: "No One is Dead Until Warm and Dead"

• Principle: Severely hypothermic patients may have no detectable pulse for extended periods but still be alive and resuscitable
• CPR guidelines:
  • Check carotid pulse for UP TO 60 SECONDS (hypothermia slows pulse)
  • If ANY pulse or sign of life is present after the 60-second check — even a very slow one — do NOT start chest compressions
  • If no pulse or sign of life: START CPR
  • Continue CPR throughout evacuation
  • Do NOT withhold CPR due to prolonged cardiac arrest if hypothermia suspected
  • Accepted exceptions — do not start or continue CPR if there is an obvious lethal injury, the chest is frozen solid/incompressible, the airway is packed with snow or ice, or there is a valid DNR order
• Defibrillation: Heart may be in VF but won't respond to defibrillation until core temp raised. Attempt defibrillation once if available, but don't repeat until core temp >30°C.
• Active core rewarming: Hospital provides warmed IV fluids, heated humidified oxygen, ECMO (extracorporeal membrane oxygenation) in severe cases. Some patients have recovered after hours without pulse if hypothermia was cause.

Frostbite: Freezing of Tissue

What: Ice crystal formation in tissue cells due to freezing temperatures

• Mechanism: Freezing occurs when tissue temperature drops below freezing and ice crystals form. Cold-induced vasoconstriction accelerates cooling but is not itself the cause of freezing. The ice crystals then damage cells mechanically and osmotically.
• Most common sites: Fingers, toes, nose, ears, cheeks
• Risk factors:
  • Wet skin/wet clothing
  • Wind chill
  • Immobility (can't move to generate heat)
  • Dehydration, malnutrition
  • Prior frostbite (skin loses cold tolerance)

Frostbite Stages

Frostnip (Superficial Cold Injury)

• What: Superficial tissue damage, NO actual freezing of deeper tissue
• Signs: Skin white or pale, numb, no blistering
• Recovery: Rapid and complete with rewarming (30 min). Full function returns.
• Treatment: Rewarm gently with body heat or warm water

Superficial Frostbite

• What: Skin is frozen, deeper tissue is soft
• Signs: White or waxy appearance during freezing. Clear blisters form after rewarming (serous fluid, less serious).
• Healing: Slower; may take weeks. Usually full recovery but possible permanent loss of cold tolerance.
• Treatment: Rewarm (see below)

Deep Frostbite (Full Thickness)

• What: Skin AND deep tissue frozen (muscle, bone). Most serious.
• Signs: Hard, wooden texture. Mottled blue/purple appearance. Blood-filled blisters after rewarming (indicates tissue death).
• Prognosis: Tissue death likely; permanent damage, may require amputation
• Treatment: Rewarm, then urgent evacuation for surgery

Rewarming Decision: CRITICAL

• Decision: If there's risk patient will refreeze, leave frostbitten area frozen
• Why: Refreezing causes massive additional tissue damage from ice crystal formation
• Example: Hiker with frozen toes deep in wilderness 8 hours from help. Better to walk out on frozen feet than thaw and refreeze during transport.

Rewarming Technique: When to Rewarm

• Method: Warm water immersion, NOT dry heat
• Temperature: 37-39°C (body temperature warm, NOT hot). Don't use boiling water.
• Duration: 30-45 minutes of immersion. Takes time for tissue to thaw.
• Pain: Rewarming is VERY PAINFUL. Acknowledge and provide comfort measures.
• Activity: Gentle — don't massage or rub tissue during rewarming

Post-Thaw Care

• DO NOT:
  • Rub the tissue (cells are fragile)
  • Apply direct heat (fire, stove)
  • Use alcohol or massage
• DO:
  • Leave ALL blisters intact in the field — including blood-filled (hemorrhagic) ones, which are left undisturbed
  • Protect blisters with dry, bulky dressings; any blister drainage is beyond field care
  • Elevate affected area to reduce swelling
  • Gentle padding/splinting for comfort
  • Pain management (ibuprofen helps reduce inflammation)
• Evacuation: All significant frostbite requires medical evaluation

Other Cold Injuries

Chilblain (Pernio)

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

Immersion Foot (Trench Foot)

• Prolonged wet + cold exposure (hours to days) without freezing
• Maceration (skin softening), pain, blisters, possible gangrene
• Treatment: clean, dry feet, rewarm slowly
• Prevention: keep feet dry during cold wet expeditions

Passive External Rewarming

• Mild hypothermia: May be sufficient
• Method: Insulate from cold with blankets, sleeping bag, clothing
• Allow body's own heat production: Shivering generates heat if insulation prevents heat loss
• Advantage: No risk of afterdrop from active rewarming

Active External Rewarming

• Methods:
  • Hot water bottles (wrapped, placed on core not extremities) — most accessible field method
  • Heat packs (chemical or stove-warmed rocks wrapped in cloth)
  • Warm drinks if patient is conscious and able to swallow
  • Skin-to-skin contact with a rescuer — mainly prevents further heat loss rather than transferring much heat; insulation plus wrapped external heat sources (warm water bottles/heat packs against the trunk) work better
• Target areas: Core (chest, armpits, groin) where major blood vessels are close to skin
• Caution: Gentle application; don't burn skin

Active Internal Rewarming

• Field options:
  • Warm oral fluids (if conscious and can swallow) — more effective if containing sugar for metabolic heat
  • Limited to field setting without advanced equipment
• Hospital options:
  • Warmed IV fluids
  • Heated humidified oxygen
  • ECMO (extracorporeal membrane oxygenation) for severe cases — most advanced

Rewarming Complications

• Afterdrop: Rapid core temperature drop after rewarming starts, from cold peripheral blood returning to the core
• Dehydration: Cold reduces fluid intake, but rewarming increases fluid loss from sweating
• Dysrhythmias: Heart may develop arrhythmias during rewarming
• Prevention: Gentle rewarming, core-first approach, monitor patient

Clothing: Layering System

• Layer 1 (Base): Moisture-wicking material (merino wool, synthetic) — NOT cotton. Cotton holds moisture and loses insulation when wet.
• Layer 2 (Insulation): Fleece, wool, or down. Traps air. Retains insulation even if damp (wool, fleece) or loses quickly (down if wet).
• Layer 3 (Shell): Windproof and waterproof outer layer. Prevents wind chill and wet.
• Extremities: Hat (prevents heat loss through head), gloves, socks, gaiters to keep snow out

Hydration & Nutrition

• Hydration: Cold suppresses thirst mechanism. Easy to become dehydrated in cold. Drink regularly.
• Nutrition: Metabolism is main heat production. Eat high-calorie foods to fuel heat production.
• Carbohydrates: Quick energy, metabolized to heat
• Fats: Sustained energy and insulation

Monitoring & Prevention

• Early signs in self: Uncontrollable shivering, poor coordination, confusion — seek shelter and warmth immediately
• Early signs in partner: Watch for: shivering, slurred speech, clumsiness, withdrawal. Hypothermia victim often doesn't recognize their own symptoms.
• Buddy system: Never hike alone in cold. Partners can recognize early signs and respond.
• Frequent breaks: Don't push through cold and fatigue. Take breaks in shelter to rewarm.
• Avoid alcohol: Causes vasodilation (increased heat loss), impairs judgment

Environmental Management

• Shelter: Get out of wind, precipitation. Even natural windbreak (rocks, trees) helps significantly.
• Insulation: Don't sit on cold ground. Use pad, branches, backpack as insulation barrier.
• Fire: If available and safe, provides critical warmth. But don't rely on fire alone; still need insulation.
• Avoid immersion: Stay dry. If wet, change into dry clothes immediately.