The Wilderness Medical Society (WMS) convened an expert panel to develop a set of evidence-based guidelines for prevention and treatment of frostbite to guide clinicians and first responders and disseminate knowledge about best practices in this area of clinical care. Summarized here are the main pre-hospital prophylactic and therapeutic modalities and recommendations about their role in injury management.
Classification of Frostbite
Frostnip is superficial nonfreezing cold injury associated with intense vasoconstriction on exposed skin, usually cheeks, ears, or nose. Ice crystals, appearing as frost, form on the skin surface. Frostnip is distinct from and may precede frostbite. With frostnip, ice crystals do not form within the tissue and tissue loss does not occur. Numbness and pallor resolves quickly after warming the skin with appropriate clothing, direct contact, breathing with cupped hands over the nose, or gaining shelter. No long-term damage occurs. Frostnip signals conditions favorable for frostbite; appropriate action should be undertaken immediately to prevent injury.
Frostbite has historically been divided into 4 tiers or “degrees” of injury following the classification scheme for thermal burn injury. These classifications are based on acute physical findings and advanced imaging after rewarming. The classifications can be difficult to assess in the field before rewarming because the still-frozen tissue is hard, pale, and anesthetic. An alternate 2-tiered classification more appropriate for field use (after rewarming but before imaging) is suggested following the 4-tier classification below.
First-degree frostbite causes numbness and erythema. A white or yellow, firm, and slightly raised plaque develops in the area of injury. No gross tissue infarction occurs; there may be slight epidermal sloughing. Mild edema is common.
Second-degree frostbite injury causes superficial skin vesiculation; a clear or milky fluid is present in the blisters surrounded by erythema and edema.
Third-degree frostbite causes deeper hemorrhagic blisters, indicating that the injury has extended into the reticular dermis and beneath the dermal vascular plexus.
Fourth-degree frostbite extends completely through the dermis and involves the comparatively avascular subcutaneous tissues, with necrosis extending into muscle and bone.
For field classification, after spontaneous or formal rewarming but before imaging, we favor the following 2 tier classification scheme:
- Superficial — no or minimal anticipated tissue loss, corresponding to first- and second-degree injury
- Deep — anticipated tissue loss, corresponding to 3rd- and 4th-degree injury
Severity of frostbite may vary within a single extremity.
The adage that “prevention is better than treatment” is especially true for frostbite, which is typically preventable and often not improved by treatment. Underlying medical problems may increase the risk of frostbite, so prevention must address both environmental and health-related aspects. Frostbite injury occurs when tissue heat loss exceeds the ability of local tissue perfusion to prevent freezing of soft tissues (blood flow delivers heat). One must both ensure adequate perfusion and minimize heat loss to prevent frostbite. The adventurer should recognize cold-induced “numbness” as a warning that frostbite injury may be imminent if protective and/or avoidance measures are not taken to decrease tissue cooling. Subsequent loss of sensation does not mean the situation has improved, rather receptors and nerves are not conducting pain/cold signals because they are nearing the freezing point.
MAINTAINING PERIPHERAL PERFUSION
Preventive measures to ensure local tissue perfusion include:
- Maintaining adequate core temperature and body hydration
- Minimizing effects of known diseases, medications, and substances (e.g., including awareness and symptoms of alcohol and drug use) that might decrease perfusion
- Covering all skin and the scalp to insulate from the cold
- Minimizing blood flow restriction, such as occurs with constrictive clothing, footwear, or immobility
- Ensuring adequate nutrition
- Using supplemental oxygen in severely hypoxic conditions (e.g., >7500 meters/24600 feet in altitude)
Exercise is a specific method to maintain peripheral perfusion. Exercise enhances the level and frequency of cold-induced peripheral vasodilation. However, using exercise to increase warmth can lead to exhaustion with subsequent profound systemic heat loss should exhaustion occur. Recognizing this caveat, exercise and its associated elevation in core and peripheral temperatures can be protective in preventing frostbite.
PROTECTION FROM COLD
Measures should be taken to minimize exposure of tissue to cold. These measures include the following:
- Avoiding environmental conditions that predispose to frostbite, specifically below
–15°C/5°F, even with low wind speeds
- Protecting skin from moisture, wind, and cold
- Avoiding perspiration or wet extremities
- Avoiding perspiration or wet extremities
- Increasing insulation and skin protection (e.g., by adding clothing layers, changing from gloves to mitts, etc.)
- Ensuring beneficial behavioral responses to changing environmental conditions (e.g., not being under the influence of illicit drugs, alcohol, or extreme hypoxemia)
- Using chemical hand and foot warmers and electric foot warmers to maintain peripheral warmth (note: warmers should be close to body temperature before being activated, and must not be placed directly against skin or constrict flow if used within a boot)
- Regularly checking oneself and the group for extremity numbness or pain, and warming the digits and/or extremities as soon as possible if there is concern that frostbite may be developing
- Recognizing frostnip or superficial frostbite before it becomes more serious
- Minimizing duration of cold exposure. Emollients do not protect against—and might even increase—risk of frostbite. The time that a digit or extremity can remain numb before developing frostbite is unknown; thus, digits or extremities with paresthesias should be warmed as soon as possible. An extremity at risk for frostbite (e.g., numb, poor dexterity, pale color) should be warmed with adjacent body heat from the patient or a companion, using the axilla or abdomen.
Field Treatment and Secondary Prevention
If a body part is frozen in the field, the frozen tissue should be protected from further damage. Remove jewelry or other constrictive extraneous material from the body part. Do not rub or apply ice or snow to the affected area.
REFREEZING INJURYA decision must be made whether or not to thaw the tissue. If environmental conditions are such that thawed tissue could refreeze, it is safer to keep the affected part frozen until a thawed state can be maintained. One must absolutely avoid refreezing if field-thawing occurs.
SPONTANEOUS OR PASSIVE THAWING
Most frostbite thaws spontaneously and should be allowed to do so if rapid rewarming (described below) cannot be readily achieved. Do not purposefully keep tissue below freezing temperatures because this will increase the duration that the tissue is frozen and might result in more proximal freezing and greater morbidity. If environmental and situational conditions allow for spontaneous or slow thawing, tissue should be allowed to thaw.
Strategies for two scenarios are presented:
- Scenario 1: The frozen part has the potential for refreezing and is not actively thawed
- Scenario 2: The frozen part is thawed and kept warm without refreezing until evacuation is completed
THERAPEUTIC OPTIONS FOR BOTH SCENARIOS
Many of these guidelines parallel the state of Alaska cold injuries guidelines. Therapeutic options include:
Vascular stasis can result from frostbite injury. Appropriate hydration and avoiding hypovolemia are important for frostbite recovery. Oral fluids may be given if the patient is alert, capable of purposeful swallowing, and is not vomiting. If the patient is nauseated or vomiting or has an altered mental status, IV normal saline should be given to maintain normal urine output. Intravenous fluids should optimally be warmed (minimally to 37°C/98.6°F but preferably to 40-42°C/104-108°F with a method that has been proven to be effective in the present environmental conditions) before infusion and be infused in small (e.g., 250 ml), rapid boluses because slow infusion will results in fluid cooling and even freezing as it passes through the tubing. Fluid administration should be optimized to prevent clinical dehydration.
Ibuprofen should be started in the field at a dose of 12 mg·kg-1 per day divided twice daily (minimum to inhibit harmful prostaglandins) to a maximum of 2400 mg/d divided 4 times daily if the patient is experiencing pain.
SPECIFIC RECOMMENDATIONS—SCENARIO 1 (no active thawing)
Therapeutic options for frostbite in Scenario 1 include:
Bulky, clean, and dry gauze or sterile cotton dressings should be applied to the frozen part and between the toes and fingers
Ambulation and protection
If at all possible, a frozen extremity should not be used for walking, climbing, or other maneuvers until definitive care is reached. If using the frozen extremity for mobility is considered, a risk-benefit analysis must consider the potential for further trauma and possible poorer outcome. Although reasonable to walk on a foot with frostbitten toes for evacuation purposes, it is inadvisable to walk on an entirely frostbitten foot because of the potential for resulting morbidity. If using a frozen extremity for locomotion or evacuation is unavoidable, the extremity should be padded, splinted, and kept as immobile as possible to minimize additional trauma.
SPECIFIC RECOMMENDATIONS—SCENARIO 2 (thawing and continued warming)
Therapeutic options for frostbite in Scenario 2 include:
Rapid field rewarming of frostbite
Field rewarming by immersing the affected extremity in a warm water bath can and should be performed if the proper resources are available and definitive care is more than 2 hours distant. Other heat sources (e.g., fire, space heater, oven, heated rocks, etc.) should be avoided because of the risk of thermal burn injury. Rapid rewarming by water bath has been shown to result in better outcomes than slow rewarming. Field rewarming should only be undertaken if the frozen part can be kept thawed and warm until the victim arrives at definitive care. Water should be heated to 37°C to 39°C (98.6° to 102.2°F) using a thermometer to maintain this range. If a thermometer is not available, a safe water temperature can be determined by placing a caregiver’s uninjured hand in the water for at least 30 seconds to confirm that the water temperature is tolerable and will not cause burn injury. Circulation of water around the frozen tissue will help maintain correct temperature. Because the water may cool quickly after the rewarming process is started, the water should be continuously and carefully warmed to the target temperature. If the frozen part is being rewarmed in a pot, care must be taken that the frozen part does not press against the bottom or sides, to prevent damage to the skin. Rewarming is complete when the involved part takes on a red or purple appearance and becomes soft and pliable to the touch. This is usually accomplished in approximately 30 minutes but is variable depending on the extent and depth of injury. The affected tissues should then be allowed to air dry or be gently dried with blotting technique (not rubbing) to minimize further damage. Under appropriate circumstances, this method of field rewarming is the first definitive step in frostbite treatment.
During rewarming, pain medication (e.g., NSAIDs or an opiate analgesic) should be given to control symptoms as dictated by individual patient situation.
Spontaneous or passive thawing
According to the foregoing guidelines, rapid rewarming is strongly recommended. If field rewarming is not possible, spontaneous or slow thawing should be allowed. Slow rewarming is accomplished by moving to a warmer location (e.g., tent or hut) and warming with adjacent body heat from the patient or a caregiver as previously described.
Debridement of blisters
Debridement of blisters should not be routinely performed in the field. If a clear, fluid-filled blister is tense and at high risk for rupture during evacuation, blister aspiration and application of a dry gauze dressing should be performed in the field to minimize infection risk. Hemorrhagic bullae should not be aspirated or debrided in the field.
Topical aloe vera
Topical aloe vera should be applied to thawed tissue before applying dressings.
Bulky, dry gauze dressings should be applied to the thawed parts for protection and wound care. Substantial edema should be anticipated, so circumferential dressings should be wrapped loosely to allow for swelling without placing pressure on the underlying tissue.
Ambulation and protection
After the rewarming process, swelling should be anticipated. If passive thawing has occurred, boots (or inner boots) may need to be worn continuously to compress swelling. Boots that were removed for active rewarming may not be able to be re-donned if tissue swelling has occurred during the warming process. The panel’s clinical experience supports the concept that a recently thawed extremity should ideally not be used for walking, climbing, or other maneuvers, and should be protected to prevent further trauma.
Elevation of extremity
If possible, the thawed extremity should be elevated above the level of the heart, which might decrease formation of dependent edema.
Recovery of thawed tissue partly depends on the level of tissue oxygenation in the postfreezing period. Oxygen may be delivered by face mask or nasal cannula if the patient is hypoxic (oxygen saturation < 88%) or the patient is at high altitude above 4000 meters/13000 feet).
For a summary of the suggested approach to the field treatment of frostbite, see Table 1.
Table 1. Summary of field treatment of frostbite (42 hours from definitive care)
- Treat hypothermia or serious trauma
- Remove jewelry or other extraneous material from the body part
- Rapidly rewarm in water heated and maintained between 37° and 39°C (98.6° to 102.2°F) until area becomes soft and pliable to the touch (approximately 30 minutes). Allow spontaneous or passive thawing if rapid rewarming is not possible
- Ibuprofen (12 mg/kg per day divided twice daily) if available
- Pain medication (e.g., opiate) as needed
- Air dry (i.e., do not rub at any point)
- Protect from refreezing and direct trauma
- Apply topical aloe vera cream or gel if available
- Dry, bulky dressings
- Elevate the affected body part if possible
- Systemic hydration
- Avoid ambulation on thawed lower extremity (unless only distal toes are affected)
Patients with superficial frostbite can usually be managed as outpatients or with brief inpatient stays followed by wound care instructions. Initially, deep frostbite should be managed in an inpatient setting. Complete demarcation of tissue necrosis may take 1 to 3 months.
McIntosh SE, Freer L, Grissom CK, Auerbach PS, Rodway GW, Cochran A, et al. Wilderness Medical Society clinical practice guidelines for the prevention and treatment of frostbite: 2019 update. Wilderness Environ Med. 2019;30(4S):S19–32.