Interaction of β2-microglobulin mechanisms of convection, diffusion and adsorption in on-line hemodiafiltration

The in vivo contribution of diffusion, convection ad adsorption to beta(2)-microglobulin (beta(2)-m) elimination by hemodiafiltration (HDF) was investigated. 11 patients (8M/3W), with a mean age of 59 +/- 10 years and weighing 62.7 +/- 8.7 kg were studied. A 1.89 m(2) polysulphone membrane was used in 180 min postdilution HDF. Samples at blood inlet (bi), blood autlet (bo), dialysate outlet (do) and ultrafiltrate (uf) were taken to determine beta(2)-m concentrations at 30 and 150 min. Rates of flow (Q, ml(min) prescribed were: infusion, Q(inf) = 103.6 +/- 12.3, Q(uf) = 14.6 +/- 4.0 y Q(b) = 465 +/- 5.0. Effective Q(bi) was automatically measured by the machine and Q(do) = 800 + Q(uf). The removed beta(2)-m mass (M, mg/min) was obtained by multiplying rates of flow (Q, L/min) by beta(2)-m concentrations (mg/L) at each sampling point. From mass balance, we calculated the mass of beta(2)-m removed (mg/min) by adsorption 0.23 +/- 0.2, by convection 0.7 +/- 0.3 and by diffusion 1.0 +/- 0.4, at 30 min. At 150 min, the beta(2)-m mass removed was -0.06 +/- 0.1 by adsorption 0.4 +/- 0.1 by convection and 0.3 +/- 0.1 by diffusion. In HDF, these beta(2)-m eliminating mechanisms play a variable role throughout the session. The more significant conclusion is that diffusion of beta(2)-m with a synthetic "open" membrane is an important method of removing beta(2)-m, comparable to convection over the whole procedure. That result explain the relative efficacy of beta(2)-m clearance by HDF convection, and also explain why isolated diffusion is an efficient mechanism for beta(2)-m removal by high-flux hemodialysis.