Frostbite: first aid

Frostbite is damage to tissue caused by freezing. Initial manifestations may be deceptively benign. The skin may be white or blistered, numb, and rewarming causes severe pain. Frostbite may progress to gangrene. Treatment involves gradual rewarming in warm (40-42°C) water and local application. Self-amputation of severely damaged areas is possible. Surgical amputation is sometimes necessary, but the decision, often based on imaging studies, is usually delayed for several months after the injury.

Frostbite usually develops in extremely low temperatures, especially at altitude. The distal parts of the extremities and exposed areas of skin are most often affected.

Ice crystals form within the cells and intercellular spaces, essentially freezing the tissue and causing cell death. Adjacent, unfrozen areas of the body are at risk because they may become ischemic due to local vasoconstriction and thrombosis. During reperfusion, as the tissue warms, inflammatory cytokines (e.g., thromboxanes, prostaglandins) are released, further increasing tissue damage.

Symptoms of frostbite

The injured area is cold, hard, white, and numb, becoming mottled red, swollen, and painful on warming. Blisters form within 4 to 6 hours, but the full extent of the injury may take several days to become apparent. Blisters filled with clear plasma indicate superficial injury; proximally located blisters filled with blood indicate deep injury and probable tissue loss. Superficial lesions heal without residual tissue loss. Deep frostbite causes dry gangrene, with a hard black scab over healthy tissue; wet gangrene, with a gray, swollen, soft surface, is less common. Wet gangrene may become infected, which is unusual for dry gangrene. The depth of tissue necrosis depends on the duration and depth of freezing. Autoamputation of severely damaged tissue is possible. All degrees of frostbite can lead to symptoms of neuropathy in the late period: sensitivity to cold, sweating, impaired nail growth and numbness [symptoms resembling those of complex regional pain syndrome (see the relevant section), although any connection between these two pathological conditions has not been proven].

First aid for frostbite

In the field, frostbitten extremities should be rewarmed quickly by completely immersing the injured areas in warm (tolerable to the touch) water (<40.5 °C). Due to numbness, rewarming with an uncontrolled dry heat source (e.g., fire, heating pad) may cause burns. Rubbing may also damage the tissue and should be avoided. The longer the area remains frozen, the greater the eventual damage. However, thawing the feet is inadvisable if the patient must walk some distance before receiving help, since thawed tissues are particularly sensitive to injury during walking and will suffer less damage if frozen than if thawed. If thawing is unavoidable, the frozen area is carefully cleaned, dried, and protected with a sterile compress; patients are given analgesics and the rest of the body is warmed if possible.

In hospital, the limbs are rapidly warmed in large containers of circulating water at <40.5°C for 15 to 30 minutes. Defrosting is often stopped somewhat earlier than necessary because pain may be severe. Parenteral analgesics, including opioids, may be used. Patients are encouraged to perform gentle movements of the affected limb during rewarming. Large, clear blisters are left alone. Hemorrhagic blisters are also left unbroken to avoid secondary desiccation of the deep skin layers. Ruptured blisters are sanitized.

Anti-inflammatory measures may be effective (eg, topical aloe every 6 hours, ibuprofen 400 mg orally every 8 hours). The affected areas are left open to warm air, and the extremities are elevated to reduce swelling. Anticoagulants, low-molecular-weight dextrans, and intra-arterial vasodilators (eg, reserpine, galazolin) have not been clinically proven to be useful. Phenoxybenzamine (10-60 mg orally once daily), a long-acting alpha-blocker, may theoretically reduce vasospasm and improve blood flow.

Prevention of infection is of great importance. In case of wet gangrene, broad-spectrum antibiotics are prescribed. If there is no vaccination data, tetanus toxoid is administered.

Adequate nutrition is important to maintain metabolic heat production.

Imaging studies (such as nuclear scanning, MRI, microwave thermography, laser Doppler flowmetry, angiography) can help assess blood flow and tissue viability and thus guide treatment. MRI and especially magnetic resonance angiography (MRA) can define the demarcation zone before demarcation has developed clinically, allowing earlier definitive surgical debridement or amputation. However, whether early surgery improves long-term outcome is unclear. Surgery is usually delayed as long as possible because viable tissue often becomes exposed after the black eschar falls away. “Frosted in January, operate in July,” goes the old saying. Patients with severe frostbite should be advised that it may take several weeks for demarcation to develop and for the extent of necrotic tissue to be fully defined.

Whirlpool baths at 37°C 3 times daily with gentle drying, rest and time are the best long-term treatment. There are no absolutely effective treatments for the late effects of frostbite (such as numbness, sensitivity to cold), although chemical or surgical sympathectomy may be effective for the late symptoms of neuropathy.