Effects of high blood flow and high pre-dilution replacement fluid rates on small solute clearances in hemofiltration

In pre-dilution hemofiltration (HF), solute clearance is less than the HF rate. While the amount of this loss is predictable, it has not been validated in high-volume HF associated with high blood flow rates.

Using isovolemic pre-dilution HF, we studied small solute clearances using combinations of blood flow (Q(B); 150, 250, 350, 450 ml/min) and replacement fluid (RF) flow (Q(RF); 2, 4, 6 l/h) to determine clearance losses we entitled 'measured efficiency' (E(M)). E(M) was compared to predicted efficiency (E(P)) = (Q(B)/Q(B) + Q(RF)).

Pre-dilution produced E(M) values of 61-93%. Increases in Q(B) for any Q(RF) and decreases in Q(RF) for any Q(B) increased E(M) over a wide range of Q(B) and Q(RF). E(P) was equivalent to E(M).

In high-volume pre-dilution HF, E(P) can be used to determine E(M) across a broad range of Q(B) and Q(RF) values. Higher Q(RF) requires higher Q(B) to minimize the attenuating effects of pre-dilution on clearance.