Frostbite

Background

• Results from the freezing of tissue
• It is a disease of morbidity, not mortality
• Risk correlated with temperature and wind speed
  • Risk is <5% when ambient temperature (includes wind chill) is > –15C (5F)
  • Most often occurs at ambient temp < –20C (–4F)
• Can develop w/in 2-3sec when metal surfaces that are at or below –15C (5F) are touched
• Most commonly affects distal part of extremities, face, nose, and ears
• High-risk groups: outdoor workers, elderly, homeless, drug or alcohol abusers, psychiatric disease

Pathophysiology

• Freezing alone is usually not sufficient to cause tissue death
  • Thawing contributes markedly to the degree of injury
  • Endothelial damage, beginning at the point of thaw, is the critical event in frostbite
    • Resulting damage results in swelling, platelet aggregation, vessel thrombosis

Zones of Injury

1. Zone of Coagulation
   • Most severe and usually most distal
   • Damage is irreversible
2. Zone of Hyperemia
   • Least severe and usually most proximal
   • Generally recovers w/o treatment in <10d
3. Zone of Stasis
   • Middle zone characterized by severe, but possibly reversible, cell damage
   • It is this zone for which treatment may have benefit

Clinical Features

Classification

• Visual determination of tissue viability is difficult in first few weeks
• Classify early injuries as superficial or deep
• First degree (frostnip)
  • Partial-skin freezing
  • Stinging and burning, followed by throbbing
  • Numbness, erythema, swelling, dysesthesia, desquamation (days later)
  • Minimal pain with rewarming
  • Prognosis excellent
• Second degree
  • Full-thickness skin freezing
  • Numbness followed by aching and throbbing
  • Substantial edema over 4-6 hours
  • Skin blisters form w/in 6-24 hours
    • Desquamate and form hard black eschars over several days
  • Mild to Moderate pain with rewarming
  • Prognosis is good
• Third degree
  • Tissue loss involving entire thickness of skin
  • Extremity feels like a "block of wood" followed by burning, throbbing, shooting pains
  • Hemorrhagic blisters form and are associated with skin necrosis and blue-gray discoloration
  • Severe pain with rewarming
  • Prognosis is often poor
• Fourth degree
  • Extension into subcutaneous tissues, muscle, bone, and tendon; little edema
  • Deep, aching joint pain
  • Skin is mottled w/ nonblanching cyanosis and formation of deep, dry, black eschar
  • Painless during rewarming
  • Prognosis is extremely poor

Differential Diagnosis

Cold injuries

• Generalized
  • Accidental hypothermia
  • Therapeutic hypothermia
• Freezing
  • Frostbite
• Non-freezing
  • Trench foot
  • Chilblains (Pernio)
  • Cold panniculitis
  • Cold urticaria
  • Polar thigh

Diagnosis

• Usually clinical

Treatment

• Thawing
  • Do NOT attempt until the risk of refreezing is eliminated
    • Refreezing will cause even more severe damage
  • Rapid rewarming is the core of therapy and should be initiated as soon as possible
    • Extremities
      • Place in water w/ temperature of 40-42C (104-107.6)
      • Leave in for 20-30min, when the extremity should become pliable and erythematous
    • Face
      • Apply moistened compresses soaked in warm water
• Analgesia
  • Provide parenteral opiates
• Local wound care
  • Apply topical aloe vera cream q6hr (interrupts arachidonic acid cascade)
  • Affected digits should be separated w/ cotton and wrapped w/ sterile, dry gauze
  • Elevate involved extremities
  • Blister removal is controversial
    • Consider drainage of nonhemorrhagic bullae that interfere w/ movement
    • Never debride hemorrhagic bullae
• Systemic care
  • Ibuprofen may be helpful in interrupting arachidonic cascade
  • Prophylactic treatment is controversial; Pen G 500K untis IV q6hr may be beneficial
  • Intra-arterial tPA reduces digit amputation rate
• Tetanus
  • Reported complication of frostbite; provide prophylaxis
• Surgery
  • May be required if wet gangrene or infection occurs
  • Usually not performed until full demarcation occurs (3-4wk)

Disposition

• Patients with superficial local frostbite may be discharged home if social circumstances allow

Complications

• 65% of patients with frostbite experience sequelae from their injuries
  • Hypersensitivity to cold, pain, ongoing numbness
  • Arthritis, bone deformities, scars, and skin and nail dystrophia

See Also

• Cold injuries