Figure 328

Pressure inside the blood compartment (dark colored arrow) and the dialysate compartment (light colored arrow) with a fixed net zero ultrafiltration rate. The pressure gradually decreases in the blood compartment as blood travels from the inlet toward the outlet. Beyond a certain point along the dialyzer length (x, where the two pressure lines intersect), the pressure in the dialysate compartment exceeds that in the blood compartment, forcing fluid to move from the dialysate to the blood compartment. This movement of fluid in the direction opposite to that of the designed ultrafiltration is called backfiltration. Backfiltration may carry with it contaminants (eg, endotoxins) from the dialysate. Increasing the net ultrafiltration rate shifts the pressure intersection point to the right and diminishes backfiltration.

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