Fluids in bags for hemodiafiltration

The objective of hemodiafiltration (HDF) is to increase the convective transport of solutes poorly removed by diffusion, and therefore ultrafiltration (UF) beyond the desired weight loss is prescribed. The excess UF is compensated for by infusion of a physiological solution which should be sterile and nonpyrogenic. This replacement solution can be provided either in bags containing commercially prepared infusion solution, i.e. so-called classic HDF, or by an integrated stepwise filtration of the dialysis fluid, i.e. so-called online HDF. In both cases the composition of the replacement solution should mirror that of plasma water. When the fluid is provided in bags, practical handling is a limiting factor, and the amount of convection that can be delivered is most often restricted to 10-12 l/session. Results from clinical studies show that the degree of convective transport obtained in classic HDF corresponds to what can be achieved in contemporary high-flux dialysis, where uncontrolled UF and backfiltration take place inside the dialyzer. Classic HDF with replacement fluid in bags offers the possibility of delivering an HDF treatment with controlled convective dose and fluid quality, albeit with a limited amount of convection.