Radiocontrast removal by dialysis membranes

To examine the effect of membrane characteristics on radiocontrast mass transfer, we studied in vitro clearances with cuprophane and polyacrylonitrile (PAN) dialyzers and with polysulfone hemofilter. A perfusate of saline at 37 degrees C, with 7.5 mmol/l (45 mg/dl) of urea and either Renografin (molecular weight 723) or Hexabrix (1405), was pumped through the blood path of dialyzers at 200 ml/min for 5 min. Each radiocontrast agent (RCA) and dialyzer was tested at 0, 150, and 250 or 300 mm Hg transmembrane pressure. In experiments with the use of hemofilter, clearances were tested at the perfusate flow of 50, 100 and 150 ml/min. RCAs were measured by fluorescent excitation analysis of iodine. Mean urea clearance was 16% higher in PAN than in cuprophane dialyzers. Clearance of RCAs was 1.5-3 times higher in PAN than cuprophane dialysers. With the latter, increases in transmembrane pressure resulted in a small amount of ultrafiltration (UF) and little increment in RCA clearance. With the former, increases in transmembrane pressure resulted in massive UF and remarkable increases in RCA clearance. Renografin clearance generally exceeded that of Hexabrix, which we attributed to Renografin's lower molecular weight. With the hemofilter, sieving coefficients were approximately 0.8 for each RCA. Yet, because of the lack of diffusive transport and a small surface area even at the highest perfusate flow rates, RCA clearance by the hemofilter was 20-50% less than that of cuprophane dialyzers. We conclude that PAN dialyzers are more efficient for RCA removal than cuprophane dialyzers or polysulfone hemofilters.