Frostbite

Frostbite is tissue freezing injury from exposure to temperatures below minus 0.55 degrees C, resulting in ice crystal formation, cell dehydration, and microvascular thrombosis. It affects fingers, toes, ears, nose and cheeks. At altitude, in the Mount Kenya and Kilimanjaro climbing environments, and with cold or wet clothing, wind chill, alcohol, smoking, malnutrition, peripheral vascular disease, diabetes and homelessness, risk is highest. Contact with liquid nitrogen, dry ice and compressed refrigerant gases causes similar injury.

Injury occurs in two phases: direct cellular injury from freezing, and reperfusion injury with inflammatory mediators (thromboxane A2, prostaglandin F2-alpha) causing vasoconstriction, platelet aggregation, and thrombosis after rewarming.

Depth is classified after rewarming: first degree (hyperaemia and oedema without blisters), second degree (clear blisters), third degree (haemorrhagic blisters), and fourth degree (full thickness necrosis of muscle and bone).

Eventual amputation rates are about 20 to 40 percent in hospitalised patients; most tissue demarcation takes 4 to 12 weeks.

• Initial: cold, numb, white or waxy, hard and insensate skin; clumsiness.
• After rewarming: burning pain, throbbing pain, hyperaemia, oedema, blisters (clear in superficial injury, haemorrhagic in deep injury), and sensory loss.
• Late: mummified black eschar, mottled cyanosis, demarcation, dry gangrene, cold intolerance, hyperhidrosis, chronic pain, and nail deformity.
• Associated: hypothermia (core temperature below 35 degrees C), dehydration, rhabdomyolysis, compartment syndrome, and trauma.
• Complications: infection, osteomyelitis, tetanus, joint stiffness, epiphyseal damage in children.
• Red flags: haemorrhagic blisters, absent pulses or Doppler signals, dusky skin proximal to the toe, compartment signs, core temperature under 35 degrees C.

• Clinical diagnosis: exposure history, anaesthetic cold, pale or waxy skin.
• Core temperature measurement; treat hypothermia first.
• Staging by blister and perfusion pattern after rewarming (initial grading is unreliable).
• Imaging for perfusion: technetium-99m triple phase bone scan at 48 hours (predicts demarcation line), CT or conventional angiography, or magnetic resonance angiography to detect vessel occlusion before thrombolysis; Doppler ultrasound of digital arteries.
• Laboratory: full blood count, electrolytes, creatine kinase (rhabdomyolysis), urea and creatinine, lactate, glucose, coagulation.
• X-rays for bone injury or trauma; MRI for deep tissue viability later.
• Exclude non-freezing cold injury (immersion foot), chilblains, vasculitis, Raynaud phenomenon, thromboangiitis obliterans (Buerger disease), and embolic disease.

• Pre-hospital: remove wet clothing, rings and constricting items, protect the area from re-freezing, and avoid rubbing or walking on frozen feet if evacuation is available. Do not thaw if there is a risk of re-freezing, because refreezing after thawing causes much worse injury.
• Treat hypothermia first: warm to a core temperature of 35 degrees C or above, give warm intravenous fluids (normal saline 20 mL/kg at 40 degrees C).
• Rapid rewarming: immerse the affected part in circulating water at 37 to 39 degrees C (checked by thermometer), with a mild antiseptic (chlorhexidine 0.05 percent) in the bath, for 15 to 30 minutes until the skin is pliable and flushed; do not use dry heat; give analgesia before and during.
• Analgesia: ibuprofen 12 mg/kg per day orally in 2 divided doses (adult 400 mg twice daily) as an antithromboxane agent (maximum 2400 mg per day) for 7 days or until healing starts; add paracetamol 1 g every 6 hours and opioids (morphine 0.05 to 0.1 mg/kg intravenously every 4 hours) for severe pain.
• Aspirin 75 to 150 mg orally once daily may be added when ibuprofen cannot be given; do not combine both for long.
• Topical: aloe vera gel 3 times daily on the affected skin (thromboxane inhibitor), applied after every dressing change; clear blisters debrided; haemorrhagic blisters left intact to avoid desiccation and infection; protective, non-adherent, loose dressings; elevate the limb; daily whirlpool at 37 degrees C for 20 minutes.
• Thrombolysis within 24 hours of rewarming, for third and fourth degree injuries with absent perfusion on angiography or bone scan: alteplase intra arterial 0.5 to 1 mg per hour via catheter with heparin 500 units per hour for 6 to 24 hours (maximum 24 hours), with repeat angiography; or intravenous alteplase 0.15 mg/kg bolus (maximum 15 mg) followed by 0.15 mg/kg per hour for 6 hours with heparin infusion. Contraindications are active bleeding, recent surgery or stroke, trauma, and tissue freezing after rewarming. Monitor fibrinogen and haemoglobin.
• Iloprost 0.5 to 2 nanograms/kg per minute intravenously for 6 hours daily for 5 to 8 days (adjusted to tolerance, may cause headache, flushing, hypotension), where thrombolysis is not possible.
• Tetanus toxoid 0.5 mL intramuscularly if not immunised in the last 5 years, with tetanus immunoglobulin 250 units intramuscularly in unimmunised patients.
• Antibiotics only for signs of infection: flucloxacillin 500 mg orally every 6 hours for 7 days or benzylpenicillin 1.2 g intravenously every 6 hours with flucloxacillin for severe infection.
• Surgery: delay amputation for 60 to 90 days until mummification and demarcation are complete, unless there is wet gangrene, sepsis or compartment syndrome (fasciotomy). Early surgery uses bone scan and MRI to determine viability.
• Rehabilitation: physiotherapy and occupational therapy starting early; sympathectomy or botulinum toxin 100 units for persistent vasospasm.
• Follow up: weekly wound review until demarcated, then monthly; review for cold sensitivity, neuropathic pain (gabapentin 300 mg orally nightly titrated to 300 mg three times daily), arthritis, and nail disorders; counsel on re-exposure risk.
• Prevention: layered insulated clothing, dry gloves and socks, avoid alcohol, smoking, and tight boots at altitude, and acclimatisation.