Fig. 1. Diffusion (A ) and convection (B ) solute transport principles. Hemodialysis (C ) and hemofiltration (D ) extracorporeal circuits. For the hemodialysis circuit, the green bag represents the dialysate and the yellow bag the used dialysate. For the hemofiltration circuit, the yellow bag represents the ultrafiltrate and the purple bag the postdilution replacement fluid.