Radiocontrast Removal by Dialysis Membranes

Abstract

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 °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 trans-membrane 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.

Influence of Dialysis Procedure, Membrane Surface and Membrane Material on Iopromide Elimination in Patients with Reduced Kidney Function

“…In contrast to prior findings [7], both groups with haemofiltration showed elimination rates and plasma clearance values comparable to haemodialysis membranes. If haemodialysis is not possible, haemofiltration can therefore be regarded as an adequate procedure for contrast medium elimination.…”

“…This has been described before in an early in vitro study [7][. Even so plasma clearance was not significantly higher and reduction in iodine concentration during the dialysis period is equal, the highest urinary iodine concentrations can be found in patients with Cuprophan membranes.…”

“…Since most low-osmolar contrast media are middlesized molecules, the main factors influencing haemodialysis are: blood flow, membrane surface area, molecular size, transmembrane pressure and dialysis time [4,7,9]. Indeed, an increase in surface area was followed by a small but insignificant increase in clearance values of polysulfone membranes.…”

“…A comparison of the results published in the litera ture, however, shows a large variation in the haemodialy-sis procedures performed, membrane materials and surface areas used. As a consequence, the clearance rates of contrast media found in different studies ranged from 70 to 108 ml/min and even 160 ml/min in one in vitro study [4,6,7].The latter in vitro study stated a 1.5-3 times higher clearance rate for polyacrylonitrile in comparison to Cuprophan dialyzers.…”

Preventing Complications of Radiographic Contrast Media: Is There a Role for Dialysis?

“…The blood flow in each of these studies was a modest 200 ml/min. Even though the molecular weights of these molecules put them in the ‘‘middle molecule’’ category in which blood flow rate does not play an important role in clearance, these molecules are still relatively small and clearance has been shown to be enhanced with increases in the rate of blood flow (10). As contrast is limited to the extracellular space, the volume of distribution is relatively small.…”