Figure 321

Solute clearance in hemofiltration. Hemofiltration achieves solute clearance by convection (or the solvent drag effect) through the membrane. In contrast to diffusive hemodialysis, fluid flux is a prerequisite for the removal of solutes during hemofiltration, whereas the concentration gradient is not. For small solutes (eg, urea) that traverse the membrane unimpeded, concentrations in the blood compartment (Cb) and ultrafiltrate compartment (Cuf) are equivalent. For some molecules of middle molecular weight whose movement across the membrane is partially restricted, Cuf is lower than is Cb (ie, the sieving coefficient, defined as Cuf/Cb, is less than 1.0).

Ultrafiltrate-

-Postdilution

Blood

- Predilution

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