Frostbite

Frostbite - local injury to skin and subcutaneous tissue resulting from cold exposure.

"Cold induced injuries are almost exclusively a result of human's inability to properly protect themselves from the environment"

For those living in cold weather regions or spend time skiing, climbing, snowboarding, snowshoeing, ice fishing etc. cold exposure injuries become a serious but very preventable problem. With common sense, some basic information and understanding of human physiologic response to cold, and some warm clothes, the risk of frostbite injury should be minimal.

Frostbite was first reported in medical literature in 1805, and largely documented by Napoleon's physicians during the 1812 Russian campaign. It is estimated that Napoleon entered Russia with 250,000 troops, and retreated after six months of winter campaign with 350 effective men. From World War I to the Korean War about 1 million cases of frostbite were documented, and the media is abound with accounts of high altitude climbers around the world getting black noses or fingers from the cold.

Why are we at risk for these types of skin damage from cold? Humans are tropical dwellers with minimal hair and a neutral environmental temperature of 82F when naked and at rest. If the temperature drops to 70F a humans metabolic rate must double to maintain core body temperature. The arctic fox by comparison maintains equilibrium with an environmental temperature of -40F, and by doubling metabolic rate could survive -184F. So, we need to protect the skin with clothing, oil, or some covering when exposed to cold.

Factors leading to frostbite are type of contact with cold, duration of exposure, and degree of cooling of the skin. Frostbite is related to heat loss, not degree of coldness, and is dependent on wetness and wind-chill (large heat loss conditions) rather than absolute ambient temperature. Decreased local circulation is important in the development of frostbite

Avoid tight fitting clothes (poor circulation), wet clothes (good thermal conductors), and excessive skin washing - dirty skin cools less fast than dry, clean skin. Remember that 80% of body heat is lost through the head and neck. Cigarette smoking has been associated with increased risk for frostbite as it constrict blood flow to skin, and other vascular diseases such as atherosclerosis are risk factors. Prior cold injury or frostbite is another risk factor. And there are no data on sex or age as risk factors.

Skin is our protective layer that gets damaged with frostbite. 1-2mm thick two layers the epidermis (outside, and the dermis (deep). The skin has a complex blood supply that is regulated by the nervous system. In normal conditions, 80% of the blood to the arms or legs is in the skin and muscle. If the body is exposed to heat, the blood vessels dilate and more blood flows. If exposed to cold, vasoconstriction occurs and less blood flows. Under 50F the body has a reflex that alternates the constriction with 5-10 min of dilation to take heat to the skin and muscle. This response may be accentuated in people with a lot of cold exposure.

Frostbite occurs in four stages:

1. Prefreeze phase - cooling with loss of skin sensation at about 50F
2. Freeze-thaw phase - actual ice crystal formation in skin tissue - skin temperature about 24F
3. Slow Blood Flow phase - the blood vessels constrict or spasm and blood may sit still and coagulate
4. No Blood flow phase - the blood has clotted or been redirected to internal organs and the skin gets minimal to no blood and gangrene develops.

Many physiologic and metabolic factors are implicated when the above processes occur including prostoglandins, oxygen free radicals, small blood clots, and direct freeze damage.

1st degree frostbite - redness, numbness

2nd degree - white/yellow plaque, blisters, redness, swelling

3rd degree - deeper blood blisters (now into the deep layer of skin)

4th degree - mummification, no blood flow, with muscle/bone involvement.

Mild Frostbite

• No tissue loss
• Symptoms resolve 1month
• Burning sensation for 2-3 weeks
• Throbbing pain for 2-3 days
• Large clear blisters to ends of fingers
• Normal skin color

Severe Frostbite

• Tissue loss
• Symptoms resolve 6months or more
• Electric shock sensation for 6 weeks
• Small dark blisters No swelling
• Blue color that persists with pressure

Treatment

• Rapid rewarming with water at 104-108F for 15-30min
• Debride blisters if clear
• Tetanus booster
• Pain medication
• Elevate affected parts
• Apply aloe vera to skin
• Don't perform vigorous massage
• Most cases will be admitted to the hospital

Reference: Wilderness Medicine, Auerbach, P., ed., Mosbey-Year Book, 1995, pp 129-142