Results from the freezing of tissue
It is a disease of morbidity, not mortality
Risk correlated with temperature and wind speed
Risk is <5% when ambient temperature (includes wind chill) is > –15°C (5°F)
Most often occurs at ambient temperature < –20°C (–4°F)
Wetness and humidity increase the risk (water has 25x thermal conductivity of air)
Can develop within 2-3sec when metal surfaces that are at or below –15°C (5°F) are touched
Most commonly affects distal part of extremities, face, nose, and ears
High-risk groups: outdoor workers, elderly, homeless, drug or alcohol abusers, psychiatric disease, high-altitude or cold-weather athletes, military personnel
"Hunter's response" - prolonged repeated exposure to cold is protective
Risk is <5% when ambient temperature (includes wind chill) is > –15°C (5°F)
Most often occurs at ambient temperature < –20°C (–4°F)
Freezing alone is usually not sufficient to cause tissue death
Thawing contributes markedly to the degree of injury
Endothelial damage, beginning at the point of thaw, is the critical event in<unk> 
Resulting damage results in swelling, platelet aggregation, vessel thrombosis
Thawing contributes markedly to the degree of injury
Endothelial damage, beginning at the point of thaw, is the critical event in<unk> 
Resulting damage results in swelling, platelet aggregation, vessel thrombosis
Resulting damage results in swelling, platelet aggregation, vessel thrombosis
Most severe and usually most distal
Damage is irreversible
Middle zone characterized by severe, but possibly reversible, cell damage
It is this zone for which treatment may have benefit
Least severe and usually most proximal
Generally recovers without treatment in <10d
Frostbite
Generalized
Le Fort fractures
Hypothermia
Shark bite
Freezing
Nasal fracture
Nailbed laceration