6. Frostbite

1. Definition

• Frostbite → local tissue injury from freezing, at tissue temperatures below −0.5 °C
• Non-freezing cold injuries:
  • Chilblains (pernio) → itchy red-purple skin lesions after repeated cold exposure
  • Trench (immersion) foot → prolonged cold, wet exposure above freezing
• Hypothermia → core temperature < 35 °C; general cold injury, often coexists

2. Aetiology and risk factors

• Low temperature, wind (wind chill), humidity, duration of exposure
• Most affected → toes, fingers, ears, nose, cheeks
• Tight shoes and clothing, wet clothing
• Alcohol intoxication, homelessness, psychiatric illness
• Smoking, peripheral arterial disease, diabetes
• Previous frostbite, immobility, exhaustion

3. Pathogenesis

Direct cellular injury (freezing phase)

• Ice crystals form in extracellular fluid
• Water drawn out of cells → cellular dehydration, electrolyte disturbance
• Intracellular ice (rapid freezing) → cell membrane rupture

Vascular injury (rewarming phase)

• Vasoconstriction and arteriovenous shunting during cooling
• Endothelial damage on rewarming → reperfusion injury
• Mediators → thromboxane A2, prostaglandin F2α
• Platelet aggregation, microvascular thrombosis, oedema
• Progressive dermal ischaemia → necrosis
• Repeated freeze-thaw cycles → most severe damage

Periods

1. Pre-reactive (latent) period → during cold exposure; pale, cold, numb skin; depth cannot be judged
2. Reactive period → after rewarming; inflammation, oedema, blisters, necrosis appear; depth becomes clear after days

4. Classification

Degrees of frostbite

1. First degree → epidermis; erythema, cyanosis, oedema, burning pain; recovers in 5–7 days with peeling
2. Second degree → epidermis and part of dermis; clear blisters within 24–48 h; heals in 2–3 weeks without scar
3. Third degree → full-thickness skin and subcutis; haemorrhagic blisters, black eschar; heals by granulation and scarring
4. Fourth degree → skin, muscle, tendon, bone; dry gangrene (mummification), demarcation, auto-amputation
5. Clinical grouping:
   • Superficial → first and second degree
   • Deep → third and fourth degree

5. Clinical picture

Symptoms

• Cold, numbness, clumsiness
• After rewarming → throbbing pain, burning, paraesthesia

Signs

• Pre-reactive → white or waxy, hard, insensate skin
• Reactive → hyperaemia, oedema, blisters, cyanosis
• Deep injury → haemorrhagic blisters, black dry eschar, line of demarcation after 3–4 weeks

6. Diagnosis

• Clinical, after rewarming
• Core temperature → exclude hypothermia
• Technetium-99m bone scan or magnetic resonance angiography (MRA) → assess tissue viability early, guides thrombolysis and amputation level
• Angiography → before thrombolysis

7. Differential diagnosis

• Chilblains
• Trench foot
• Raynaud's phenomenon
• Acute arterial occlusion

8. Treatment

First aid

• Move to a warm place; remove wet and tight clothing
• Treat hypothermia first → rewarm the core
• Do not rub the skin with snow or massage
• Do not rewarm if refreezing is possible → freeze-thaw-refreeze is worst
• Do not walk on frozen feet if avoidable

Conservative

• Rapid rewarming in circulating warm water at 37–39 °C for 15–30 min, until the skin is red and soft
• Analgesia → intravenous opioids; rewarming is very painful
• Ibuprofen → blocks thromboxane and prostaglandins
• Clear blisters → aspirate or debride; haemorrhagic blisters → leave intact
• Topical aloe vera, non-adherent dressings
• Elevation, splints, physiotherapy
• Tetanus prophylaxis
• Severe frostbite seen within 24 h → iloprost intravenously or thrombolysis with tissue plasminogen activator (tPA)
• Antibiotics only for infection

Surgical

• Fasciotomy → compartment syndrome
• Escharotomy → constricting circumferential eschar
• Delayed amputation after clear demarcation, 1–3 months
• Early amputation only for wet gangrene or sepsis
• Skin grafts and flaps for cover

9. Complications

• Wet gangrene, infection, sepsis
• Tetanus
• Amputation
• Cold hypersensitivity, chronic pain, neuropathy
• Hyperhidrosis, vasospasm
• Arthritis, growth plate damage in children