Hemodialysis vs Hemodiafiltration

Dialysis typically involves extracorporal cleansing with dialysate.

In this procedure, blood and dialysate are separated by semi permeable porous membrane through which water, and solutes pass, limited by the water, permeability characteristics and pore widths of the membrane.

Molecules and ions of a given molecular cut off,almost to the size of albumin may transmit through the pores.

Solute is removed by means of concentration gradient-driven diffusion from blood to dialysate, but also conductively by means of solvent drag, in which solvent is dissolved in plasma water traverses the dialysis membrane, driven by the hydraulic pressure of flowing blood and dialysate as pumped through the system.

Ultrafiltration refers to the bulk movement of water across the membrane.

During conductive ultrafiltration, larger size solutes are removed much more effectively than by diffusion.

Such ultrafiltration is the presumed benefit of high flux versus low flux hemodialysis.

Hemodiafiltration ultra filters, have a much larger volume per session such that an idealized substitution fluid must be provided to replace lost uremic plasma water.

This substitution fluid is derived from fresh dialysate, which is sterilized by the filter within the system and infused into the blood as it returns to the body.

In Hemodiafiltration high extracorporal blood flow rate of 23 L or greater per session is important.

Of four  a randomized controlled trials evaluating hemodiafiltration offering survival benefits as compared with hemodialysis, three were inconclusive, whereas the fourth showed a survival benefit for hemodiafiltration.

In the CONVINCE trial the incidence of death from any cause was lower among patients with kidney failure who underwent hemodiafiltration in among those who underwent high flux hemodialysis at a median follow up with 30 months (17.3 versus 21.9%).

As compared with highflux hemodialysis, hemodiafiltration at a high convective volume seems more effective and slows deterioration and improves survival as kidney replacement therapy.

There is a greater removal of larger molecular weight substances, with high convective hemodiafiltration, than  with high flux hemodialysis.

Hemodiafiltration has beneficial effects on vascular biology, inflammation, and intradialytic hemodynamics.

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