Transcutaneous oxygen tension in patients with calciphylaxis

Calciphylaxis Is a severe complication of chronic renal failure, confined a lmost exclusively to patients on dialysis therapy. Histological characteris tics of calciphylaxis include small-vessel calcifications of skin, subcutan eous tissue, and visceral organs. These vascular changes promote tissue isc hemia that often results in tissue necrosis. In this study, we investigated the extent of skin ischemia in patients with calciphylaxis by means of tra nscutaneous oxygen tension (TCPo2) measurement, a noninvasive test that acc urately assesses skin oxygenation. TCPo2 levels were measured in 21 patient s with calciphylaxis and 21 age- and sex-matched patients without evidence of calciphylaxis (controls). TCPo2 levels were measured bilaterally at the chest, anterior abdomen, and upper thigh while patients breathed room air a nd after a 30-minute exposure to 100% fraction of inspired oxygen (FIo(2))C ompared with controls, patients with calciphylaxis showed significantly low er TCPo2 levels at each body region. In both controls and patients with cal ciphylaxis, lower TCPo2 levels correlated with increased weight and use of hemodialysis. No correlation with serum parathyroid hormone (PTH), serum ca lcium, or serum phosphorus values was present, although 39% of the patients with calciphylaxis had markedly elevated PTH values (sixfold greater than normal; >300 pg/dL). Low TCPo2 levels in patients with calciphylaxis were d ocumented in body regions with and without skin lesions. In patients with c alciphylaxis, extremely low TCPo2 values (less than or equal to 30 mm Hg wh ile patients breathed room air) were present in 62% of the body regions wit h skin lesions and 26% of the body regions without lesions. Room-air TCPo2 levels less than or equal to 30 mm Hg were present in only 0.8% of the body regions of control patients. TCPo2 levels obtained while patients breathed 100% FIo(2) remained lower in patients with calciphylaxis than in controls . In conclusion, TCPo2 levels are abnormally low in patients with calciphyl axis, indicating that severe and diffuse skin ischemia exists, even at area s free of skin lesions. Low TCPo2 values did not substantially increase wit h 100% FIo(2) in many patients with calciphylaxis, suggesting a fixed insuf ficiency of the skin vessels. This study shows that TCPo2 measurements may allow rapid and noninvasive screening for skin ischemia before the developm ent of skin lesions in patients with calciphylaxis. (C) 2001 by the Nationa l Kidney Foundation, Inc.