Solute-removal enhancement caused by local convective flow in a hemodialyzer.

Filtration, namely, convective mass transport through a hemodialysis membrane, has recently been utilized in maintenance hemodialysis to enhance the removal of high-molecular-weight uremic toxins. However, it has been practically impossible to estimate the clearance of solutes from hemodialyzers operated at predetermined net filtration rates, even if the mass-transfer parameters of the membrane are obtainable. Here, we discuss the effect of convective flow on the solute-removal performance of a hemodialyzer. The velocity and concentration profiles in the hemodialyzer were formulated on the basis of transport phenomena and obtained using the finite element method with commercially available software. The concentration profile obtained under conditions whereby local convective flow occurred through the membrane and the net filtration rate was negligible was measurably different from that obtained under conditions of no local convective flow. The result was a large discrepancy in the clearances obtained, indicating that local convective flow through a high-performance membrane cannot be ignored when estimating the solute-removal performance of a hemodialyzer containing such membranes or in designing the membrane and hemodialyzer--even if the hemodialyzer is operated at a net filtration rate of zero. The enhancement of clearance due to filtration, which had been discussed qualitatively elsewhere, was also quantified in relation to net filtration rate.