Cold Injury - non-freezing cold injury, frost-nip and frost-bite

Cold Injury

Cold injuries run the gamut of both temperature ( freezing/non-freezing) and severity (chilblains - trench foot – frost nip – frostbite). All can be painful and debilitating and all require effective treatment to preserve tissue, relieve pain and restore or maintain mobility.

Non-freezing cold injury

• chilblains

• trench foot / immersion foot

Freezing cold injury

• frost-nip (superficial frost-bite)
• frost-bite

 Non-freezing cold injury

 Chilblains

Trench foot

‘Trench foot’ or ‘immersion foot’ is the most common non-freezing cold injury, and is typically experienced after prolonged exposure to a wet and cold environment (sweating inside waterproof boots can create conditions for trench foot to occur).  Trench foot frequently occurs in temperatures as mild as +5˚C to -5˚C.  The patient often experiences impaired sensation in the affected foot.   Affected feet will appear pale and cold (not frozen) to begin with and will then progress to being swollen and red.  Failure to recognise trench foot risks serious infection.

 Treatment for non-freezing cold injuries is the provision of shelter, gentle drying and slow re-warming.  The affected part should be elevated and movement encouraged.  As with frostbite, recovery from non-freezing cold injuries can be painful, and appropriate analgesia may be required.

Freezing Cold Injury

Pathophysiology

Frostbite is the freezing of soft tissue, typically at temperatures below -5°C. However, tissue can freeze at temperatures as mild as -0.5˚C.

Usually is is the extremities that freeze because these are more often exposed and/or wet, have a larger surface area to volume ratio and have their circulation reduced as the body tries to reduce heat loss.

As the person starts to cool, a normal physiological response is the shutting down of circulation to the periphery which thus cools further (there may be some preservation of circulation by vasodilation as part of the 'hunting' response which occurs in cycles of 5-10 minutes); later circulation stops,  the extremity continues to cool and then starts to freeze.

Initially ice crystals form in the extracellular fluid (the fluid surrounding the cells), this results in water being drawn out of the cells (because of changes in oncotic pressure), further cooling leads to damage to the cell membrane (the outside of cells) and electrolyte (chemical) imbalance inside and outside the cells. This results in the tissues being damaged, The severity of the damage depends on a number of factors, see below.

Classification of Frostbite

 There have been various classifications suggested for frostbite.  The following is simple and is graded in a similar manner to burns:

• superficial (a.k.a. frost-nip)
• partial thickness of skin
• deep - full thickness of skin and variable levels below, can include muscle and bone
  

The degree of frostbite injury reflects the duration, extent and severity of exposure to the cold. Predisposing factors include: pre-existing injury or illness, fatigue, decreased local tissue perfusion, constrictive clothing, some medications (such as beta-blockers), alcohol, high altitude and, significantly, previous occurrence of cold injury.

 Superficial frostbite (frost-nip) is suggested  by sharp pain progressing to numbness with red skin at first, then turning cold and white. The skin remains soft and can move freely. Ears, noses and cheeks are regular sites. This should be treated by applying body heat for 30 minutes. There are no long-term problems following recovery.

 Partial thickness frostbite is indicated by skin turning red then white, becoming cold and numb, and developing a waxy appearance. Blisters often occur following thawing.

 Deep frostbite occurs when the deep tissues are frozen – muscles, tendons and even bones may be affected. The skin will appear whitish-yellow, be hard and numb, and not pliable. The injury may be painless initially.

Management of frost-bite

Rewarming involves the application of gentle warmth or immersion in water no warmer     than 40˚C (recheck the temperature because the water will cool quickly)
 

• Re-warming is usually extremely painful - ibuprofen, paracetamol (acetaminophen) may help but opioid analgesics (eg. morphine or fentanyl) may be required
• It is important not to rub the affected part, and to protect any blisters that may form
• If there is a likelihood of re-freezing (inability to keep the extremity warm) then do not thaw/rewarm the affected part
• Rewarming in water no warmer than 40˚C should continue twice a day for 30 minutes on an ongoing basis if possible
• Ibuprofen helps with pain but also affects prostaglandin synthesis which can help with the excessive coagulation (clotting) that occurs
• If the person needs to walk, it may be best to leave a deeply frozen foot frozen so that mobilisation is possible
• In severe deep frostbite, treatment with thrombolysis ('clot busters') may be helpful if it can be accessed within 24 hours
• If socks or gloves are frozen to the limb, treat the injury with them still on
• Following thawing, multiple fluid-filled and haemorrhagic blisters may form; these should be protected with sterile, non-adherent dressings
• It is important to note, however, that even with very severe frostbite and an appearance that a body part may not survive, recovery is often much better than the initial appearance may suggest
• The administration of broad-spectrum antibiotics should be considered to help prevent infection

Prevention of Cold Injury

Cold injury, both freezing and non-freezing, can be avoided by avoiding exposure to the cold and wet.  In environments where we are at risk of cold injury we should be aware of the hazards and and pay close attention to prevention.

Three key concepts:

1. Stay dry

• protection from the environment
• minimise sweating
• waterproof gloves and footwear

2. Keep the core warm

• good clothing, layer systems, hat - layer up immediately if immobilised
• eat well and stay hydrated
• shelter from the wind/rain
• use of heat packs if immobile

3. Keep the extremities warm

• gloves, hand warmers
• footwear - not so tight as not to restrict circulation, toe warmers, down booties
• face masks

Useful, and light/small additions to your pack for cold environments are spare over-gloves, chemical hand/toe warmers and down booties.  These are particularly useful if injured and immobilised when often our standard protective gear and boots are not enough to insulate us.

The use of oxygen at high altitude will help keep the tissues oxygenated.

Avoiding alcohol and smoking are essential.

Recommended Further Reading

Managing Frostbite – Hallam, Cubison, Dheansa and Imray. BMJ Vol 341, 27 Nov 10.

Wilderness Medicine – Auerbach. 5^th Edition, 2007. Pt 2, Chaps 7 and 8.

Field Guide to Wilderness Medicine – Auerbach, Donner and Weiss. 3^rd Edition, 2008. Chap 4.

Oxford Handbook of Expedition and Wilderness Medicine – Johnson, Anderson, Dallimore, Winser and Warrell. 1^st Edition, 2008. Chap 19.