frostbite

see also:

• hypothermia

• frostbite is necrosis of skin (usually extremities) resulting from a combination of cold-induced vasoconstriction and the low skin temperature itself and usually occurs when skin temperature falls below below −2°C.
• mild superficial frostbite of fingers or toes is relatively common in Winter areas when temperatures drop below 10deg C, particularly in those who have poor peripheral circulation such as peripheral vascular disease (PVD or PAD) or Raynaud's disease.
• severe frost bite and frostbite involving the exposed face can occur when effective air temperature after taking into account wind chill factor, falls below - 20deg C
• frostbite has far-reaching consequences in terms of functional morbidity and for some may be career-ending, particularly if their work involves cold environments
• non-freezing cold exposure to skin may cause:
  • chilblains
  • trench foot

• risk of frostbite is related to:
  • duration and degree of low temperature exposure
  • circulation issues eg. Raynaud's, smoking, diabetes, constrictive clothing, hypotension, anaemia, etc
  • susceptibility to cold stress and capacity for heat production with resultant general vasoconstriction:
    • lack of body fat reserves
    • female gender twice as likely to develop peripheral cold injury (typically have lower finger temperatures)
    • black races have 2-4x risk compared to Causasians
    • older age
    • high surface area (thus heat losses are much greater if limbs get wet)
    • fatigue and exhaustion
    • sleep deprivation
    • alcohol increases heat losses due to cutaneous vasodilatation
    • level of activity (exercise in air will usually allow sufficient heat production to maintain core temperature)
      • exercise in water will not as heat loss is about 25 times higher in water than air
    • hunger
    • dehydration (cold induces diuresis which may exacerbate pre-existing dehydration)
    • general hypothermia from inadequate or compromised clothing
• rate at which flesh gets cold depends upon:
  • ambient temperature
  • wind chill factor
  • evaporative heat loss from wet skin including from sweating, sleeping with boots on, snow falling into boots, as well as high humidity, rain, etc
  • exposed skin
  • loss of effectiveness of insulating clothing (eg. wet)
  • direct contact with certain materials
    • cold metals especially aluminium (2-3 x faster cooling than steel which is 3-4x faster than stone) are particularly a risk
• dressing for the cold :
  • Keep clothing Clean - dirt compromises insulation
  • Avoid Overheating - sweat is a major risk
  • Wear clothing loose and in Layers - another sweat mitigation strategy
  • Keep it Dry
  • take a spare pair of gloves, etc in case they get wet

Windchill Temperature = 0.045*(5.2735*SQROOT(W) + 10.45 - 0.2778*W)*(T - 33.0)+33

WCF = 1.1626*(5.2735*SQROOT(W) + 10.45 - 0.2778*W)*(33.0 - T)

where: ET = equivalent temperature (degrees Celsius) WCF = wind chill factor (Watts per square metre) W = wind speed (Km/hr) T = air temperature (degrees Celsius)

Wind chill and risk of frostbite to exposed facial skin in properly dressed persons who have normal vasculature (ie. no peripheral vascular disease or Raynaud's disease) ¹⁾:

• there are 3 zones:
  • Zone of coagulation
    • the most distal and often the most severely injured.
    • the injury is irreversible
    • the affected area initially becomes pale and then cyanotic
    • the rewarming phase results in marked cellular injury characterized by vasoconstriction and microthrombosis
    • over some hours after re-warming, the area will blister within 4-24hrs and turn black however the depth of gangrene may not be able to be assessed for several weeks
    • during rewarming, oedema may start to appear within 3-5 hours and may last 7 days.
    • presence of eschar will be obvious at 10-15 days and mummification with a line of demarcation may develop in 3-8 weeks.
  • Zone of stasis
    • the middle zone where the injury can be moderate to severe but it reversible.
  • Zone of intense hyperaemia
    • the proximal zone, which is the least injured.
• Grading of severity:
  • Grade 1: no cyanosis on the extremity; no blisters; no risk of amputation or sequelae predicted
  • Grade 2: cyanosis on distal phalanx only; clear blisters; amputation to soft tissue and sequelae of fingernail/toenail sequelae predicted
  • Grade 3: cyanosis on intermediate and proximal phalanges; haemorrhagic blisters; amputation to the bone of the digit and functional sequelae predicted
  • Grade 4: cyanosis over carpal/tarsal bones; haemorrhagic blisters; amputation to limb and functional sequelae predicted.
• even without necrosis, frostbite may result in long terms effects:
  • loss of ability of affected blood vessels to dilate or constrict
  • hypersensitivity to cold
  • causalgia / phantom pain
  • hyperhidrosis
  • coldness
  • stiff joints
  • epiphyseal damage in children may affect bone growth
  • muscle atrophy
  • loss of nails
  • cracked skin

• protect from further injury by covering exposed areas, dry areas and remove from wind chill and avoid vigourous rubbing
• see also hypothermia if there is co-existent hypothermia
• analgesics for pain control - non-steroidal anti-inflammatory drugs (NSAIDs), opiates and opioids
• rapid rewarming of affected areas as long as no further freezing is expected
  • thaw-refreezing may worsen injuries
  • much less tissue loss compared to slow rewarming
  • immerse in water at 103° and 107.5° F. (40° to 42° C.) although 39°C water with chlorhexidine and isopropyl alcohol is used in the Canadian protocol²⁾
    • higher temperatures risk further injury to the tissue
    • lower temperatures will not produce maximum benefit
  • re-examine for sensation frequently
• aspirin 250mg o each day
• general burn care to prevent infection or dehydration
• elevate affected part
• application of aloe vera protective ointment and porous low-adherent wound dressings
• avoid alcohol intake or smoking
• tetanus prophylaxis
• Mx of blisters remains controversial although many aspirate or debride clear blisters³⁾
• avoid early surgery unless evidence of compartment syndrome or sepsis
  • amputation is generally delayed up to 6-8weeks when the degree of necrosis can be better assessed.
• for grade 2 to 4 injuries
• early referral to a plastic surgeon or a burns or hands centre (eg. in Melbourne, StV's Hand Team or the Alfred Hospital)
• consider Iloprost 2ng/kg/min iv for 6 hours each day for 8 days appeared to markedly reduce rate of digital amputation from 60% to 0% (they also used buflomedil 400mg over 1 hour iv each day) ⁴⁾
  • has less risk and can be used for grades 2 to 4 frostbite within 48 hours of rewarming⁵⁾
  • unfortunately, IV Iloprost is not available in some countries
• or, if iloprost not available, those with full-thickness injuries and evidence of ischemia and no restoration of tissue perfusion after rewarming may be candidates for intra-arterial thrombolysis with IV heparin initiated within 24hrs of re-warming
  • Doppler US and angiography are usually performed first to prove the presence of a thrombosed digital artery and there are no C/I to thrombolysis
  • tPA with heparin may reduce the need for digital amputation⁶⁾ HOWEVER, the efficacy of tPA in reducing amputation rates cannot currently be established ⁷⁾
  • one study suggested that although there was no definite reduction in amputation rates, there appeared to be an additional 26.8% salvage loss with each hour of delay to thrombolysis from re-warming ⁸⁾
  • if considered, rt-PA should only be used for grade 4 frostbite where amputation is inevitable, and within 24 hours of rewarming⁹⁾
  • Helsinki frostbite management protocol introduced in 2013 includes r-TPA and possibly Iloprost¹⁰⁾
• see also:
  • Yukon Hospital Iloprost and alteplase protocol for Mx of deep frostbite (pdf)
  • Extreme Physiology & Medicine 2014 Frostbite: a practical approach to hospital management