Biocompatibility of hemodialysis membranes: evaluation in an ovine model

We studied the cardiopulmonary, hematologic, and inflammatory response to hemodialysis with seven different membranes in sheep. We also compared acetate dialysate with bicarbonate dialysate and evaluated the role of thromboxane in mediating these responses to dialysis with Cuprophan membranes (Baxter Healthcare Corp., Renal Division, Deerfield, Ill.) in sheep. The data generated in these studies indicate that dialyzer membranes can be divided into three major categories, defined by propensity to activate complement. High complement activators such as Cuprophan (low surface-area CF-1511 and high surface-area ST-25 dialyzers) produced dramatic neutropenia and hypoxemia and significant (p < 0.01) increases in the plasma concentration of thromboxane and in mean pulmonary artery blood pressure. The magnitude of these effects appeared to be surface area related. The low-flux Fresenius F-6 polysulfone membrane (Fresenius USA Inc., Concord, Calif.) also resulted in the generation of significant levels of C3a. In contrast, low complement activators such as polyacrylonitrile (AN-69; Gambro Hospal, Inc., Lakewood, Colo.) and cellulose triacetate (CT-110G; Baxter) produced little or no neutropenia, small transient increases in thromboxane, and no rise in mean pulmonary artery pressure. Dialyzers with intermediate complement-activating potential such as cellulose acetate (CA-110; Baxter) and Hemophan (HT-100; Baxter) produced small to moderate degrees of neutropenia and small increases in thromboxane and mean pulmonary artery pressure. Treatment of sheep with sodium ibuprofen before dialysis with Cuprophan CF-1511 membranes prevented the initial increases in mean pulmonary arterial pressure and thromboxane generation and the decrease in arterial oxygen tension, but did not affect the degree of complement activation or neutropenia. In sheep undergoing Cuprophan dialysis, bicarbonate dialysate did not prevent the increase in circulating complement and the associated neutropenia otherwise seen during the early portions of dialysis with acetate dialysate. Bicarbonate dialysate did, however, reduce (not prevent) the initial increases in thromboxane and mean pulmonary arterial pressure, and the magnitude of the hypoxemia seen with the use of acetate dialysate. The results of these experiments therefore indicate that (1) reactions in sheep correlate well with data collected in human beings and the model can be an effective means for comparing novel dialysis membranes and pharmacologic interventions during dialysis and (2) although complement appears to be the transducer of the hematologic and immunologic response, thromboxane appears to be the final effector of the cardiovascular responses to hemodialysis with Cuprophan membranes.