Relation of haemofilter type to venous catheter resistance is crucial for filtration performance and haemocompatibility in CVVH--an in vitro study.

BACKGROUND Main factors for the overall performance of haemofilters (HF) are membrane features and filter durability without clogging/clotting of capillaries. However, the venous line resistance (Pv) is a powerful force for net filtrate flux resulting in haemoconcentration and thus is enhancing the phenomenon of membrane clogging. Therefore, we hypothesized that catheter type, as it is associated with Pv-levels, contributes to the extent in which filter longevity and filtration performance are restricted due to blocked hollow fibres. METHODS Heparinized porcine blood (5 IU/ml) was circulated in an in vitro system for haemofiltration (FH6S-filters were used, Ca. Gambro). Three different sizes of catheters for peripheral vein access (Vygonuele V, Ca. Vygon) were alternately inserted into the circuit for blood return from the filter to the reservoir. To produce Pv-levels lower than commonly induced by Shaldon catheters, a 14G-vygonuele was used. Pv-levels standard for 11-12 French catheters were provided by using a 16G-vygonuele. To produce Pv-levels common for low-French or tri-lumen catheters, a shortened 18G-vygonuele was used. The respective Pv-levels attained were compared with respect to the overall filtration performance (system pressures, haemocompatibility and sieving coefficients). RESULTS Catheters of 14 and 16G enabled transiently maximal blood flow (Qb)/filtration rates (Qf) of 300/60 ml/min and continuous filtration with Qb/Qf of 200/40 ml/min. The shortened 18G catheter reduced maximal flow rates down to Qb/Qf of 200/40 ml/min, and continuous flow rates down to Qb/Qf of 125/25 ml/min. At the end, median values for blocked hollow fibres were, 35% in the 14G-group, 40% in the 18G-group and 70% in the 16G-group. Haemocompatibility appeared to be higher in the 14G-group with respect to various parameters when compared with the other groups. CONCLUSIONS The flow resistance by the catheter chosen for haemofiltration clearly influenced the filtration performance. Thus, investigations focused on compatibility of catheter type as it related to Pv-levels with the particular method of renal replacement therapy that should be performed. This point could be crucial in reducing filter clogging and haemostasis during CVVH.