History
Frostbite is a completely preventable injury that can occur with or without hypothermia. Below –10°C, any tissue that feels numb for more than a few minutes may become frostbitten. Progressive symptoms of frostbitten areas are as follows:
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Coldness
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Stinging, burning, and throbbing
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Numbness followed by complete loss of sensation (This history of anesthesia suggests a frostbite injury.)
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Loss of fine muscle dexterity (ie, clumsiness of fingers)
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Loss of large muscle dexterity (ie, difficulty ambulating)
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Severe joint pain
Numbness over the affected area is the initial symptom of frostbite. After rewarming, severe throbbing and hyperemia begin and may last for weeks. Many patients complain of paresthesias. Long-term symptoms include cold sensitivity, sensory loss, and hyperhidrosis.
Physical Examination
The initial appearance of frostbite does not accurately predict the eventual extent and depth of tissue damage. Signs and symptoms vary according to severity of the frostbite injury. The hands, feet, ears, and nose are the most commonly affected (see images below).
Frostbite of the foot. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
Frostbite of the ear. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
Physical examination in patients with superficial frostbite reveals the presence of soft, palpable skin. If a thumbprint can be left in the skin, the patient usually has more viable underlying tissue. Individuals with deeper frostbite effects present with skin that is hard to the touch.
Other signs may include the following:
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Excessive sweating
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Joint pain
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Pallor or blue discoloration
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Hyperemia
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Skin necrosis
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Gangrene
Degrees of frostbite injury
Four classic stages of frostbite injury have been defined: first degree, second degree, third degree, and fourth degree. This staging system has limited clinical usefulness, however, because it has not been shown to have a direct correlation with survival or tissue loss.
First-degree frostbite has the following characteristics:
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Nonsensate, central, white plaque surrounded by a ring of hyperemia
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Epidermal involvement
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Mild edema
Sequelae over the next few weeks include desquamation, transient swelling and erythema, and cold sensitivity.
Second-degree frostbite has the following characteristics:
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Full-thickness skin freezing
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Clear blister formation with surrounding erythema
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Hard outer skin but resilient tissue underneath
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Substantial edema
Blisters contain high amounts of thromboxane and prostaglandins. They contract and dry within 2-3 weeks, forming a dark eschar that sloughs off in 4 weeks, leaving poorly keratinized skin that is easily traumatized. Sequelae include paresthesias, hyperhidrosis, and persistent or transient cold sensitivity.
Third-degree frostbite has the following characteristics:
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Subdermal plexus freezing
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Hemorrhagic blister formation
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Blue-gray discoloration of the skin
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Deep burning pain on rewarming, lasting 5 weeks
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Thick gangrenous eschar formation within 2 weeks
Sequelae include tropic ulceration, severe cold sensitivity, and growth plate injury.
Fourth-degree frostbite has the following characteristics:
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Involvement of muscle, bone, and tendons
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Frozen, hard, and avascular skin and tissue underneath
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Mottled tissue, with nonblanching cyanotic skin that eventually becomes dry, black, and mummified
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Relatively little pain experienced on rewarming
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Minimal-to-mild postthaw edema
Demarcation between living and nonviable tissue takes 1 month. Spontaneous amputation takes another month after demarcation.
Superficial versus deep frostbite injury
Some experts have moved to a simpler classification of the severity of frostbite injury, in which frostbite is described as either superficial (ie, first- and second-degree injury) or deep (ie, third- and fourth-degree injury). This approach yields a better correlation between severity of injury and final outcome.
Superficial injury is characterized as follows:
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Only skin and subcutaneous tissues are involved
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Subcutaneous tissue is pliable
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Superficial injury precedes deep injury
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The lesion has a white mottled appearance with minimal capillary refill, becoming hyperemic and edematous with rewarming
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Initial numbness gives way to burning and stinging with rewarming
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Blisters, if present, are usually clear
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Neurovascular dysfunction is usually reversible
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Tissue loss is minimal to nonexistent
Deep injury is characterized as follows:
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Skin, subcutaneous levels, muscles, tendons, and bone are all involved
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The dermis does not roll over bony prominences
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Tissue remains mottled and pulseless after rewarming
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Loss of sensation persists after rewarming
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Increased loss of flexibility occurs with deeper tissue injury
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Blister formation is infrequent; when present, blisters tend to be hemorrhagic
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Tissue loss is common
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A high risk of infection is present because of devitalized tissue and loss of skin barrier
Postrewarming injury
Rewarming edema appears within 3 hours and lasts 1 week. Large clear blebs appear within 6-24 hours with superficial injuries. Small hemorrhagic blebs appear after 24 hours with deep injuries.
Eschar forms in 9-15 days and is described as a shrunken black carapace shell covering the wound. If the frostbite is superficial, new skin appears beneath the carapace. With deep injury, the area self-amputates. Mummification results in an apparent line of demarcation in 3-6 weeks.
Complications
The degree of long-term disability is related to the severity of frostbite injury. An increased risk of frostbite with lesser exposures and poor cold tolerance in the previously injured extremity are commonplace. Permanent sensory loss is also common.
Wound infection, which is observed in 30% of patients, may be caused by Staphylococcus aureus, beta-hemolytic streptococci, gram-negative bacilli, or anaerobes and may present with the following:
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Increased pain, swelling, redness, and fever
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Red streaks extending from area
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Pus discharge
Other complications may include the following:
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Tetanus
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Tissue loss and gangrene
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Bacteremia
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Lymphedema
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Fascial compartment syndrome [36]
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Irreversible growth plate injury (ie, destruction, fragmentation, or fusion of epiphyses) leading to growth deformities and postinjury arthritis [37]
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Premature closure of growth plates, the extent of which is related to the severity of the frostbite
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Premature closure in the digits, more frequently occurring in a distal-to-proximal direction
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Complex regional pain syndrome
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Altered thermal perception at the injury site, especially cold sensitivity
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Hyperesthesia
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Hyperhidrosis
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Squamous cell carcinoma development at the frostbitten area
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Hyperglycemia
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Acidosis
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Refractory dysrhythmias
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Death, in very rare cases
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Frostbite of the foot. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
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Frostbite of the ear. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
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Frostbite of the hand.
