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Frostbite

Frostbite is a freezing, cold thermal injury which occurs when tissues are exposed to temperatures below their freezing point (typically below -0.5°C but can occur up to 2°C with prolonged exposure).

It most commonly affects the extremities of the body - in particular, the head (especially nose, ears and cheeks), as well as the hands and feet.

Predisposing factors include extremes of age, altered mental status (e.g. intoxication) and underlying vascular disease. High risk groups include military personnel, winter sports enthusiasts and outdoor workers as well as the elderly and homeless.

Pathophysiology of Frostbite

Exposure to sub-freezing conditions results in the formation of ice crystals intracellularly and extracellularly. This causes cell damage and is accompanied by the release of inflammatory mediators from damaged tissue, contributing further to ischaemia.

However, frostbite does not arise from the freezing injury alone – the effects of thawing also initiate a ischaemic reperfusion injury and associated inflammatory response, causing further tissue damage.

Classification of frostbite

  • “Frostnip” is distinct from frostbite but may precede it. This is a superficial non-freezing cold injury associated with intense vasoconstriction on exposed skin (e.g. cheeks, ears, nose) and formation of ice crystals on the skin surface, but not within tissues.
  • Superficial frostbite involves only superficial skin structures and usually has no tissue loss. The skin is usually pale and numb with surrounding oedema and/or erythema which may progress to the formation of clear blisters.
  • Deep frostbite is usually associated with inevitable tissue loss. It is characterised by haemorrhagic blisters that indicate dermal involvement and may extend into deeper tissues like muscle and bone. The affected areas will appear mottled, deeply red or cyanotic – they may be numb initially but develop severe pain/burning on rewarming.

Clinical features

  • Frostbite is a clinical diagnosis.
  • Poor prognostic indicators include haemorrhagic blisters, persistent cyanosis, mottling, anaesthesia and reduced mobility after rewarming.
  • Look for underlying factors that may have contributed to cold exposure such as trauma, hypoglycaemia, underlying cardiac or neurological problems and intoxication.
  • Also look for injuries resulting from cold exposure, including hypothermia and compartment syndrome.
  • Devitalized tissue demarcates as the injury evolves over time (weeks to months) resulting in skin necrosis and dry black eschar.

Management

Prehospital
  • Try to move the patient wind into shelter and give warm fluids if available.
  • Remove wet clothing and replace with dry clothing if possible.
  • Try to avoid further trauma to the frostbitten area – do not walk on frostbitten feet unless absolutely necessary. Protect and immobilize frostbitten area during transport.
  • Field rewarming should only be attempted if there is no further risk of refreezing – tissue that thaws and then refreezes results in more extensive injuries.
  • Rubbing the limb or applying snow while it is still frozen may worsen the injury.
Resuscitation
  • Patients with more severe frostbite will often also have hypothermia.
  • Resuscitate as per usual guidelines, including rewarming and IV fluids for severe frostbite and hypothermia. Look for and exclude any other associated injuries.
Specific therapy
  • Remove jewellery from affected digits, as significant swelling can develop post thaw.
  • Initiate rewarming of the frostbitten part in a warm water bath (38°C) – this should be done until affected tissue becomes pink and soft to touch. Typically this takes around 30 minutes to 1 hour. Be careful to maintain water temperature around 38°C as the water temperature will drop with time.
  • Analgesia is important - many patients have significant pain during rewarming.
  • Oral NSAIDs should be given (unless contraindicated) and opiates if needed.
  • Examination of the frostbitten tissue after rewarming can predict depth of injury more accurately than before thawing.
  • Once rewarmed, areas of blistering or significant damage should have non-adherent dressings placed. Limbs should be splinted and elevated.
  • Prophylactic antibiotics are not routinely recommended unless signs of infection – if antibiotics are required, Pseudomonas should be covered in addition to usual skin organisms.
  • Check tetanus status.
  • Surgical consultation should be obtained – early debridement should be avoided. Nuclear medicine scans or MRI may be useful to predict tissue viability and support any decision to debride tissue early.
  • Other potential treatments for severe frostbite include intra-arterial thrombolysis, vasodilators and hyperbaric oxygen therapy. Expert advice should be obtained.

Further References and Resources

Patient Factsheets

  • NSW Health Environmental Health Factsheets - Frostbite

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