Protein-membrane interactions during hemodialysis: Effects on solute transport

Although several previous studies have shown that plasma protein adsorption can reduce solute clearance during hemodialysis, there is currently no quantitative understanding of the factors that govern the extent of these protein-membrane interactions. In this study, quantitative data were obtained for the clearance of urea, vitamin B₁₂, and polydisperse dextrans using polyacrylonitrile (AN69) and cellulose triacetate dialyzers before and after exposure to human plasma in a simulated dialysis session. Contact with plasma had little effect on clearance of urea and vitamin B₁₂, but caused more than an order of magnitude reduction in clearance for solutes with molecular weights >10,000. These data were analyzed using a two layer model in which contact with plasma was assumed to cause a thin protein layer to form on the surface of the membrane. The protein layer had an effective pore size of ≈12 angstroms, and was ≈1 μm thick, as determined by a hydrodynamic analysis of the clearance data, and from independent estimates based on changes in fiber bundle volume and ultrafiltration coefficient. The thickness of the protein layer increased with increasing dialysis time, ranging from 0.25 μm after 40 min to 0.86 μm after 180 min. These results provide important insights into the effects of contact with plasma on solute clearance during hemodialysis.