Predilution versus postdilution for continuous arteriovenous hemofiltration

When compared to the postdilution mode, the predilution mode has the following advantages and disadvantages:

A significant increase in net urea clearance when compared to the postdilution mode: This study, showing a net 18% increase, confirms the conclusions of our preliminary studies 15, 16. It allows for a more liberal use of suction-assist: The combination of predilution and suction-assist can yield a 60% increase in net urea clearance without the generation of prohibitively high hematocrits and protocrits. A potential increase in effective filter life by dilution of prefilter hematocrit, clotting factors, and platelet count. Disadvantages: Increased cost of replacement fluid: This is usually modest, approximately a 10 to 30% increase in total volume needed. With a total output of 20 L/day this would represent approximately 6 L. In the manner prepared (Table 4, Ref 6) this represents approximately $10 a day and must be contrasted with the potential for increased filter life, the replacement of which represents the major cost of CAVH therapy. Furthermore, and perhaps more important, is that this modest increase in replacement fluid costs yields a substantial increase in urea clearance, especially when used with suction-assist, thus eliminating the need for intermittent hemodialysis and the costs it incurs. The filtrate chemistries can no longer be used to monitor the patient's plasma values: Although the potential savings in blood drawing is real, experience with the postdilution mode suggests that filtrate values are rarely considered adequate by the attending medical staff.