Pathophysiology
Clinical meaning
Frostbite occurs when tissue temperature drops below 0°C (32°F), causing ice crystal formation within cells and extracellular spaces. Intracellular ice crystals mechanically disrupt cell membranes and organelles causing immediate cell death. Extracellular ice formation draws water from cells via osmotic gradient, causing cellular dehydration and electrolyte concentration. Upon rewarming, reperfusion injury occurs as inflammatory mediators, reactive oxygen species, and thromboxane A2 cause endothelial damage, thrombosis, and progressive tissue ischemia. Frostbite severity classification: superficial (frostnip/first degree with numbness and erythema), partial thickness (second degree with clear blisters), full thickness (third degree with hemorrhagic blisters and dermal death), and deep (fourth degree extending to muscle, tendon, and bone). Rapid rewarming in 37-39°C water is the cornerstone of treatment, as slow rewarming causes more tissue damage. Tissue demarcation takes weeks to months, and amputation decisions should be delayed.