EMed

Frostbite

Background

  • Frostbite is the damage sustained by tissues while subject to temperatures below their freezing point (typically -0.5°C)
  • Can include non-freezing cold injuries (tissues not frozen but prolonged cooling)
  • Severity of frostbite injury is proportional to the temperature, duration of exposure, and amount and depth of frozen tissue

Note

  • Prevention is key
  • Rewarm frostbite as soon as risk of refreezing is minimal
  • Consider thrombolysis (tPA) in severe injuries presenting within 24 hours of exposure
  • Delay surgery unless evidence of compartment synd or overwhelming sepsis

Predisposing factors

  • General: Unusually cold weather, prolonged exposure to cold, inadequate clothing, inadequate use of appropriate clothing, homelessness, smoking, dehydration, old age, ethnic origin, high altitude
  • Systemic disease: Peripheral vascular disease, diabetes, Raynaud’s disease, sepsis, previous cold injury
  • Psychiatric illness
  • Drugs: β blockers, sedatives, and neuroleptics
  • Trauma: Any immobilising injury, but especially head and spinal injuries and proximal limb trauma that compromises the distal circulation
  • Intoxication: Alcohol and illicit drug use

Pathology

Phases

  1. Pre-freeze phase
  2. Freeze-thaw phase
  3. Vascular stasis phase
  4. Late ischaemic phase
  • Direct and indirect effects of a freezing insult
  • Direct - intra- and inter-cellular ice crystals
  • Extracellular ice causes A) cellular dehydration and B) release of cytokines
  • As ice crystals melt - oedema
  • Local ischaemia (initially vasoconstriction then increased local blood viscosity then direct freezing)
  • Endothelial damage - microthrombi worsens ischaemia (but rewarming damages cells - prothrombotic)
  • Most severe damage with freeze, thaw, and freeze again

Assess

  • Note details how injury occurred, likely temperature, wind chill, and duration of exposure—factors
  • Pre-morbid state (NB peripheral vascular disease, smoking, diabetes, medications)
  • Ascertain if injury occurred < (suitable for thrombolysis) or > 24 hours ago and decide if mild or severe

Clinical

Features of Frostbite
Early features Late Features
Affected part feels cold ± painful White and waxy skin with distinct demarcation
Continued freezing produces paraesthesia / numbness Woody insensate tissues
Areas or blanching blending into areas of uninjured skin Progression to bruising and blister formation (usually on thawing)
Degrees of frostbite
Clinical appearance Mild frostbite injury Severe frostbite injury
1st degree 2nd degree 3rd degree 4th degree
Depth of tissue freezing Partial thickness skin freezing Full thickness skin freezing Freezing of the skin and subcutaneous tissue Freezing of the skin, subcutaneous tissue, muscle, tendon, and bone
Colour of tissues Erythematous or hyperaemic Erythematous Blue or black Initially deep red and mottled; eventually black and mummified
Blistering or necrosis None Blistering (clear fluid) haemorrhagic blistering an some tissue necrosis Profound necrosis
Oedema Minor Substantial Substantial Little or none
FrostBite Grdaes - Thank You BMJ Nov 2010

Fig 1 A typical frostbite affecting the hallux and third left toes showing the initial injury at presentation at base camp on Everest (A), at six weeks (B), and at 10 weeks (C). Note the delayed surgical amputation of the hallux after definitive demarcation and the recovery of the third digit after appropriate management

Pre-hospital phase?

  • Beware hypothermia, trauma, triggering "medical" condition
  • Hypothermia (12% of those with frostbite)
  • Trauma (one study - 19% of frostbite cases) - Confirm Hx and normal ABCDE [T°]

Thrombolysis

  • Useful if within 24 hours acute severe frostbite with anticipated tissue loss
  • Intra-arterial or intra-venous (intra-arterial tPA reduced digit loss from 41% to 10% in one study)
  • Risks are bleeding ± infection
  • Contraindications - usual plus underlying TRAUMA

Tips

  • Prevention is key
  • Treat any serious or life threatening conditions in the field
  • Do not rewarm frostbitten tissues if possibility of refreezing
  • Establish the likely severity of the injury
  • Rewarm mainly non-freezing cold injuries slowly
  • Rewarm mainly freezing cold injuries at 40-42°C for a minimum of 30 minutes in a whirlpool device or foot spa with Chlorhexidine solution
  • Leave blisters intact (elevated, protected, no weight bearing)
  • Tissue loss requires antibiotic an antitetanus cover
  • Consider thrombolysis
  • Early surgical debridement is rarely beneficial
  • Adjuncts:
    • Topical aloe vera (reduce vascular spasm)?
    • Iloprost and buflomedil are powerful vasodilators?
    • Hyperbaric O2
  • Beware chronic pain (? vasomotor dysfunction) which may respond to amitriptyline

Content by Dr IOS 26/11/2020 From BMJ Article . Last updated Dr IOS 21/06/21.