History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include cold exposure, previous frostbite, and vascular insufficiency.

cold or numbness of affected extremity

The most common early symptoms of the affected extremity.

pain during rewarming

76% of patients report extreme pain during rewarming phase.[1]

purplish skin discoloration

Many patients have purplish discoloration that resembles cyanosis or early ecchymosis.

white or yellowish, waxy skin discolouration

A white or yellowish waxy discolouration in the area of injury is seen with first-degree injury. [Figure caption and citation for the preceding image starts]: Grade II frostbite injury of the footLloyd EL, BMJ 1994; 309:531-534 [Citation ends].com.bmj.content.model.Caption@778ab00

superficial skin vesiculation

The classic sign of a second-degree injury, with clear or milky fluid in blisters, surrounded by erythema and oedema.

deep purple blisters

Indicates third- or fourth-degree injury.

The purple colour is caused by blood-containing fluid in the blister, indicating injury into the reticular dermis and beyond the dermal vascular plexus.[Figure caption and citation for the preceding image starts]: Grade IV frostbite injury inappropriately thawed using boiling waterLloyd EL, BMJ 1994; 309:531-534 [Citation ends].com.bmj.content.model.Caption@55a1da5e

uncommon

tissue necrosis and mummification (dry gangrene)

This occurs at a later stage (10 to 14 days) and indicates fourth-degree injury.

Affected tissue appears black and necrotic.

Mummified tissue appears black and shrivelled due to extreme dehydration. [Figure caption and citation for the preceding image starts]: Grade IV frostbite injury inappropriately thawed using boiling waterLloyd EL, BMJ 1994; 309:531-534 [Citation ends].com.bmj.content.model.Caption@6170bc8c

Other diagnostic factors

common

erythema

Usually occurs in the presence of other skin changes.

More commonly associated with chilblains if other skin changes are absent.

uncommon

joint dislocation

Associated with weight-bearing on frostbitten feet or concurrent trauma.

fractures

Associated with weight-bearing on frostbitten feet or concurrent trauma.

Risk factors

strong

cold exposure

Frostbite requires exposure of tissue to freezing cold temperatures.[1][9]​​[17][18][19]​​

Repeated cold exposure and extended stays in cold environments do not seem to alter the risk of cold injuries.[20]

previous frostbite

Injured tissue has prolonged reduction in tolerance to cold. It is therefore thought to be more susceptible to injury if cold exposure is repeated.[1]

vascular insufficiency

Decreases the microcirculation that supports tissue warmth, and exacerbates the vascular component of the injury.[1][9]

weak

high altitude

Increases the susceptibility to cold injuries.[1][21]

hypoxia

Reduces reasoning powers and leads to a tendency towards laziness, carelessness, indecision, and lack of normal insight and judgement.[1]

alcohol

Worsens judgement and delays recognition of extreme circumstances.[1][22] Alcohol consumption also leads to heat loss through peripheral vasodilation.[14]

tobacco

Reduces normal peripheral circulation, increasing susceptibility to injury.[1]

dehydration

Decreases tissue perfusion.

extremity trauma

Alters normal physiology and normal tissue perfusion.

constrictive clothing or equipment

Interferes with distal tissue perfusion.

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