Transcutaneous oxygen tension in patients with calciphylaxis

Calciphylaxis is a severe complication of chronic renal failure, confined almost exclusively to patients on dialysis therapy. Histological characteristics of calciphylaxis include small-vessel calcifications of skin, subcutaneous tissue, and visceral organs. These vascular changes promote tissue ischemia that often results in tissue necrosis. In this study, we investigated the extent of skin ischemia in patients with calciphylaxis by means of transcutaneous oxygen tension (TCPo2) measurement, a noninvasive test that accurately assesses skin oxygenation. TCPo2 levels were measured in 21 patients 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 and after a 30-minute exposure to 100% fraction of inspired oxygen (Fio2). Compared with controls, patients with calciphylaxis showed significantly lower TCPo2 levels at each body region. In both controls and patients with calciphylaxis, lower TCPo2 levels correlated with increased weight and use of hemodialysis. No correlation with serum parathyroid hormone (PTH), serum calcium, 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 documented in body regions with and without skin lesions. In patients with calciphylaxis, extremely low TCPo2 values (≤30 mm Hg while patients breathed room air) were present in 62% of the body regions with skin lesions and 26% of the body regions without lesions. Room-air TCPo2 levels ≤30 mm Hg were present in only 0.8% of the body regions of control patients. TCPo2 levels obtained while patients breathed 100% Fio2 remained lower in patients with calciphylaxis than in controls. In conclusion, TCPo2 levels are abnormally low in patients with calciphylaxis, indicating that severe and diffuse skin ischemia exists, even at areas free of skin lesions. Low TCPo2 values did not substantially increase with 100% Fio2 in many patients with calciphylaxis, suggesting a fixed insufficiency of the skin vessels. This study shows that TCPo2 measurements may allow rapid and noninvasive screening for skin ischemia before the development of skin lesions in patients with calciphylaxis.