Frostbite is a cold weather injury that freezes the water in the cells of skin and deep tissues. As the water in a cell freezes, the structures within the cell become dehydrated. As a result, the cell dies. As freezing of tissue penetrates deeper, increased tissue damage is sustained. Frozen tissue becomes nonviable and will die resulting a localized wound. The tissue affected by frostbite may or may not regenerate in time.
Almost half of the cases of cold weather injuries treated in hospital emergency rooms affect the feet. Cold weather injuries of the feet can be broken down into two basic categories; damp/cold and dry/cold. Damp/cold is a much more common foot injury. Damp/cold injuries go by many names including frostnip, immersion foot, trench foot, chilblains and pernio, and may occur at temperature above 32 F. Dry/cold injuries, what we usually call frostbite, require a much colder environment to cause damage to the foot.
The reason water is such an important part of cold weather injuries is that water carries a higher specific heat than air. A higher specific heat means that water can absorb much more heat, far more than air. As a result, damp/cold injuries are a much more common and problematic injury. Most damp/cold injuries occur at or just above the freezing point.
There's a number of ways that the body looses heat. Heat can be lost by conduction. Water is a great conductor of heat. Heat is also lost by windy conditions (convection) and contacting a cooler surface (radiation) such as standing on snow or a cold concrete floor.
Our bodies are made of cells that are 75-85% water. With cold weather injuries, as the water in these cells begins to freeze, the result is interruption of normal cell function and rupture of the cell by expansion of the frozen water crystal. Some authors refer to this process as dehydration of the cell. Ultimately, blood flow is arrested and even shunted away from the threatened area. The following is a comparison of dry and damp cold weather injuries;
Damp Cold Injuries (immersion foot)
- Tissue damage usually deep (nerves, arteries subcutaneous tissue)
- Damaged cells may not heal and cause chronic pain, edema and blotchy discoloration of the skin
- Superficial wounds (gangrene) and infections are uncommon
Dry Cold Injuries (frostbite)
- Typically more superficial (2-3mm) tissue damage (skin, nails, superficial subcutaneous tissues)
- Tissue damage more severe and more obvious
- Damaged cells will heal over time
- Local wound care is necessary following the injury
- Infection is common
There are four degrees of frostbite -
First degree frostbite - Frostnip (seen in image to the right) is the term used to describe superficial or first degree frostbite. Frostnip can be confused with superfical skin infections and athlete's foot in that the it presents with superficial crusting of the skin of the toes and fingers. Frostnip responds well to superficial wound care and rarely results in permanent neurological symptoms of the toes and fingers.
Second degree frostbite - Soft tissue damage associated with second degree frostbite is still superficial and specific to the skin and nails. Blistering becomes worse and is often black. Wounds are managed with topical wound care and light debridement. Permanent insensativity to cold is common.
Third degree Frostbite - Superficial and deep tissues are affected in third degree frostbite. Normal tissue structure will likely return following third degree frostbite with no significant tissue loss. Permanent neurological loss and chronic pain and temperature sensativity is found upon healing.
Fourth degree frostbite - Deeps tissue loss with permanent loss of tissue due to the depth of the injury. Digital loss or limb loss is common. Pemanent neurological deficit and intolerance to cold will be found.
Causes and contributing factors
There are a number of factors that can contribute to cold weather injuries. These factors include alcohol, hunger, anemia and cardiovascular disease. Each of these conditions make you more susceptible to heat loss and cold weather injury.
The differential diagnosis for frost bite includes;
Treatment of cold exposure and thermal injuries consists of gradual warming. Be sure to warm the feet slowly with luke warm water at a temperature no higher than 104-106° F. Re-warming does not take long and can often be completed in less than 30 minutes. In severe cases, care of soft tissue gangrene and infection should be managed by your doctor. Wound care may include antibiotics, anticoagulants or other medications to reverse platelet aggregation and decrease blood viscosity. Hyperbaric oxygen and sympathetic nerve blocks are also employed to aid in wound healing. Pain management is also essential. Most surgeons will defer treatment of frostbite for several months to offer mother nature a chance to heal the majority of the injury.
There is no accepted treatment for the long term neurological pain following damp/cold tissue injuries. Patients do respond to treatment parameters similar to treating peripheral neuropathy. Treatment includes the pharmaceutical agents Neurontin or Lyrica. Nutritional products including Alpha Lipoic Acid and B complex vitamins may be helpful. Topical pain medication can also help to desensitize the foot and relieve persistent pain.
Button up, it's cold out there. And don't forget your hat.
When to contact your doctor
Cases of frostbite should be evaluated by your podiatrist, orthopedist or primary care doctor.
References are pending.
Author(s) and date
Competing Interests - None
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Cite this article as: Oster, Jeffrey. Frostbite http://www.myfootshop.com/article/frostbite
Most recent article update: December 23, 2015.
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