Pre-Dilution vs. Post-Dilution during Continuous Veno-Venous Hemofiltration: Impact on Filter Life and Azotemic Control

Abstract

Background/Aims: To determine the impact of replacement fluid infusion site on filter life and azotemic control during continuous veno-venous hemofiltration (CVVH). Methods:Pre-dilution CVVH was conducted from February 2001 to December 2001 and then practice was changed to post-dilution (from January 2002 to July 2002). Filter life was prospectively observed and the following data obtained for each filter: starting date and time, ending date and time, heparin use, heparin dose and protamine use. Daily creatinine, urea, INR, APTT and platelet count were also collected. Results: Forty-eight patients were studied (33 in pre-dilution and 15 in post-dilution) for a total of 309 filters (202 in pre-dilution and 107 in post-dilution). The median filter life was significantly shorter in the post-dilution period (18.0 vs. 13.0 h, p = 0.021). Multivariate linear regression analysis showed that pre-dilution was a significant independent predictor of increased filter life (p = 0.029), together with platelet count (p = 0.0035) and heparin dose (p = 0.046). There was no significant improvement in daily creatinine and/or urea reduction in the post-dilution period (% Δ creatinine: 7.9 vs. 10.2%/day, p = 0.99, urea: 5.4 vs. 9.7%/ day, p = 0.78). Conclusions: Post-dilution was associated with reduced filter life without any beneficial effect on daily changes in urea and creatinine levels. Pre-dilution appears a preferable technical approach to CVVH.

Bubble Chamber Clotting during Continuous Renal Replacement Therapy: Vertical versus Horizontal Blood Flow Entry

“…to create a fluid and blood separation. Administration of substitution fluids as 100% pre-filter has been associated with an increase in ‘filter life’ during CRRT [13]; however, data for bubble trap clotting with 100% post-dilution is not reported. It could be concluded that if pre-filter fluid administration reduces clotting within the membrane, fluids administration into the chamber (100% post-dilution) might reduce clotting in the chamber.…”

Effects of High Blood Flow and High Pre-Dilution Replacement Fluid Rates on Small Solute Clearances in Hemofiltration

“…The pre-dilution modality for HF has been shown to extend filter life on average by 5 h [10,11]. Thus, pre-dilution may be desirable in certain instances because of the decreased or even lack of need for anticoagulation [1], the advantages of which should include avoidance of the costs of administration and monitoring, as well as decreased risk of side effects.…”

Continuous Renal Replacement Therapy and Anticoagulation:

“…17 Depending on the therapy chosen, fluids in CRRT are administered into the blood before the hemofilter (predilution continuous venovenous hemofiltration) or after the hemofilter (postdilution continuous venovenous hemofiltration) or infused into the outside compartment of the hemofilter as a dialysate. Infusion of fluids before the filter can cause dilution of the blood and thus reduce the hematocrit of blood entering the hemofilter, leading to less hemoconcentration.…”

“…Infusion of fluids before the filter can cause dilution of the blood and thus reduce the hematocrit of blood entering the hemofilter, leading to less hemoconcentration. 4,17 Infusion of these same fluids after the filter has no effect on the blood entering the hemofilter. 17 Dialysate fluid used in continuous venovenous hemofiltration dialysis does not come in contact with the blood and therefore has no effect on the blood viscosity.…”

“…4,17 Infusion of these same fluids after the filter has no effect on the blood entering the hemofilter. 17 Dialysate fluid used in continuous venovenous hemofiltration dialysis does not come in contact with the blood and therefore has no effect on the blood viscosity. So in patients in whom anticoagulation is not desirable, predilution continuous venovenous hemofiltration may prevent clotting.…”