Frostbite (cold injury) refers to tissue damage caused by prolonged exposure of the body or local areas to low temperatures. This includes injuries caused by temperatures below the freezing point, known as freezing cold injury, and injuries caused by temperatures above freezing but accompanied by moisture, known as non-freezing cold injury.
Non-Freezing Cold Injury
Continuous exposure or immersion of the body or local areas in temperatures between 10°C and the freezing point for 24–48 hours can result in non-freezing injuries. In a cold and damp environment, blood vessels constrict and spasm, causing blood flow stasis, cellular hypoxia, and metabolic disturbances, eventually leading to cellular degeneration and necrosis. Rewarming can exacerbate injury due to ischemia-reperfusion.
Non-freezing cold injuries include chilblains, trench foot, and immersion foot (or hand). Exposed and peripheral areas such as the hands, feet, and ears are common sites for chilblains. Trench foot originated in wartime, caused by prolonged standing in cold, wet trenches. Immersion foot (or hand) is common among fishermen, sailors, rice field workers, and construction workers. Affected areas may feel stiff and numb due to cold exposure; rewarming may cause burning, itching, pain, redness, swelling, purplish-red spots or nodules, and sometimes blisters. If erosion or ulcers develop, they may become chronic. Severe cases of trench foot or immersion foot may lead to occlusive vascular disease and related pathological changes.
Prolonged exposure to cold, damp environments should be avoided. Workers should use appropriate protective equipment. Rubbing, moving limbs and the body, and applying antifreeze creams may help reduce the severity of frostbite. Chilblain ointments can be applied to non-ulcerated chilblains. For eroded wounds, topical antibiotic ointments or wet dressings can be used. For trench foot or immersion foot (or hand), elevating the affected limb, keeping it dry, and avoiding pressure is beneficial. In more severe cases, medications that improve circulation and promote tissue repair may be considered.
Freezing Cold Injury
Freezing cold injury refers to tissue freezing, ischemia, and inflammatory damage caused by prolonged exposure of the body or local areas to temperatures below freezing or brief exposure to extremely low temperatures. It includes both local and systemic freezing cold injuries (frozen body).
The injury mechanisms include three main aspects:
- Direct cold injury: Sub-freezing temperatures cause severe vasoconstriction, leading to metabolic disturbances. Prolonged or extreme cold exposure allows cold to penetrate cells, causing extracellular and intracellular ice crystal formation, resulting in irreversible cellular damage.
- Post-rewarming injury: Rewarming causes vasodilation, congestion, and exudation, with possible thrombosis. Ischemia-reperfusion injury further contributes to cell death.
- Inflammatory response: Tissue and cell damage triggers the release of inflammatory mediators and cytokines, exacerbating the injury.
Systemic freezing cold injury, also known as frozen body, occurs when the body is exposed to cold for prolonged periods, resulting in significant heat loss, reduced metabolism, and an inability to maintain body temperature, ultimately leading to coma and full-body freezing. It often occurs during sudden temperature drops or snowstorms, especially when individuals are lightly clothed, hungry, fatigued, lost, or intoxicated. Initially, the body responds with increased metabolism, shivering, elevated heart rate, increased blood pressure, and faster breathing, along with peripheral vasoconstriction to reduce heat loss. If exposure continues and heat loss exceeds heat production, body temperature begins to fall. Below 30°C, shivering stops, metabolism slows, and blood pressure, pulse, and breathing rates decline. Below 25°C, coma and rigidity ensue, which can result in death if not promptly treated.
Local freezing cold injury is classified into four degrees based on depth of injury:
- First-degree frostbite: Involves the epidermis. Skin appears blue or purple with local swelling, itching, and tingling. Typically heals within 5–10 days without scarring.
- Second-degree frostbite: Involves the dermis. Presents with bruising, marked redness and swelling, blisters (sometimes blood-filled), pain with decreased sensation. Scabs form gradually; healing usually occurs within 2–3 weeks without significant scarring if no infection occurs.
- Third-degree frostbite: Involves the full thickness of the skin and possibly some subcutaneous tissue. Initially resembles second-degree frostbite, but blisters contain blood, and skin gradually turns black and necrotic. Surrounding tissue may be red, swollen, and painful, with loss of sensation. Necrotic tissue may dry into eschar, healing slowly with scarring or requiring skin grafts if infection is absent.
- Fourth-degree frostbite: Extends to muscle, bone, and other deep tissues. Initially similar to third-degree frostbite, but swelling may exceed the visibly frostbitten area. Affected tissues turn black and dry (dry gangrene), though wet gangrene and expanded necrosis may occur if infection or vascular disease develops.
Treatment Principles for Frostbite
The primary goal is to remove the person from the cold environment and frozen objects to halt injury and initiate early, rapid rewarming.
Emergency Care and Rewarming
Affected limbs should be immersed in water at 38–42°C, or the whole body bathed, achieving local rewarming within 20 minutes and full-body rewarming within 30 minutes. The target is to restore peripheral skin temperature to approximately 36°C.
Systemic Treatment
Shock Prevention and Respiratory Support
Fluids and vasopressors may be needed to treat shock. Arrhythmias, cerebral edema, and renal failure require appropriate management. Airway patency, oxygen therapy, respiratory stimulants, and mechanical ventilation (if necessary) should be used while monitoring for lung infections.
Circulatory Support and Anticoagulation
Medications such as dextran 40, tolazoline, thromboxane inhibitors, and herbal medicines that improve circulation and dissolve blood stasis may help alleviate vasospasm, narrowing, and thrombosis.
Nutritional Support
High-protein, high-calorie diets with multivitamin supplementation can support recovery.
Antibiotics and Tetanus Antitoxin
These are used as needed.
For first-degree frostbite, the wound should be kept clean and dry and typically heals spontaneously. Second-degree frostbite requires rewarming and disinfection. If the wound remains dry, a soft dry dressing may be applied. For larger blisters, fluid can be aspirated, followed by the application of frostbite ointment or antibiotic ointment to prevent infection, then covered with sterile gauze. Infected wounds should undergo early debridement and drainage, with antibiotic ointments and frostbite ointments applied.
Third- and fourth-degree frostbite generally requires an exposed treatment approach to keep wounds dry and clean. Once necrotic tissue margins become clear, necrotic tissue can be removed and skin grafting performed as needed. In cases of wet gangrene, amputation is often required.