• Recognizing frostbite

Authors: Malcolm Davidson, Alex Poole, Caitlin Champion

Identifying Frostbite

Frostbite is a freezing injury to the skin that occurs in below zero temperatures. Suspect frostbite in a patient who presents with a history of exposure to temperature <10 degrees Celsius for several minutes to hours with inadequate protection (i.e. – exposed skin, thin/damp clothing, clothing not warm enough) and pain/tingling/loss of sensation in their digits or extremities. The skin may appear normal or pale and there may be a line of demarcation where the frostbite progressed to. Frostbite can be classified by both its depth and by grade, best applied after the skin has been rewarmed, as the tissue will appear different before and after rewarming. If skin looks and feels normal after rewarming to normal temperatures, frostbite is unlikely. The appearance of frostbite will also evolve over time with the most severe changes such as greyish skin or blisters taking 24-48h to appear. 

Appearance of frostbite with time:


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Before rewarming, still cold

Immediately after rewarming

24 hours after rewarming

48 hours after rewarming

72 hours after rewarming

10 days after rewarming

30 days after rewarming

5 months later

Grading Frostbite Injury

Many healthcare providers use the Cauchy grading scale, following rewarming, to assess severity and guide treatment. While this system is not prospectively validated, it appears to correlate well with findings on bone scan and amputation rates. It reflects the fact that as the cyanotic injury progresses proximally the risk of amputation increases. This system provides early prognostication for the risk of a functionally important amputation, and in our experience the Cauchy grading system is the easiest for clinicians to use to guide therapy. In the absence of advanced imaging (i.e. – bone scan, SPECT-CT), grading the case as the proximal extent of cyanosis or hemorrhagic blistering post rewarming is recommended.

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Source: Cauchy E, Davis CB, Pasquier M, Meyer EF, Hackett PH. A New Proposal for Management of Severe Frostbite in the Austere Environment. Wilderness Environ Med. 2016 Mar;27(1):92-9

Grading injuries based on the most proximal level of cyanosis or hemorrhagic blistering is demonstrated in this photo.

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Grading injuries based on the most proximal level of cyanosis or hemorrhagic blistering is demonstrated in this photo.

Thumb: The thumb is clearly a grade 2 with cyanosis involving only the distal phalanx.

Index and long finger: Both the index and long fingers have cyanotic changes abutting the middle phalanx, so a certainly a Grade 2 and arguably a Grade 3.

Ring finger: The ring finger is more convincingly a grade 3 with cyanosis and likely hemorrhagic blister into the middle phalanx.

Fifth finger: The fifth finger has unquestionably cyanosis and hemorrhagic blistering into the middle phalanx; clearly a grade 3 injury.

Overall, the above injury is best assessed and treated as a Grade 3 injury based on the most severe extent of injury.

NOTE: all the photos above were obtained with permission from patients at the Whitehorse General Hospital, Yukon, Canada. The photos obtained from other sources are indicated.