Maximal flow rates and sieving coefficients in different plasmafilters: effects of increased membrane surfaces and...

In Europe, capillary membrane filters are the favored method for plasmapheresis and detoxification systems including a plasma separation unit. Using capillary membrane filters clearance depends on the filtration rate and the sieving coefficient (Qs) for the plasma substrates. We investigated whether the increase of the effective membrane surface of plasmafilters enables higher clearance rates than a small plasmafilter. Heparinized porcine blood (5 I.U./l) of healthy pigs was used for an in vitro circuit. Filter types used were from GAMBRO: n = 5 PF1000N (effective membrane surface: 0.15 m(2)), n = 4 PF2000N (0.35) and from ASAHI: n = 4 PLASMAFLO OP-05W (L) (0.5). Spontaneous hemolysis was chosen to indicate the individual threshold limit for maximal flow rates. Sieving coefficient was determined for ten parameters at lowest and highest blood flow (Qb) and filtration rates (Qf). PF1000N enabled maximal flow rates as high as PF2000N and PLASMAFLO (Qb/Qf in ml/min: 200/40). Qs for most substrates were similar between the filter types and the flow rates. Compared to PLASMAFLO, the filter type with the largest membrane surface, the PF1000N provided significantly better Qs for triglycerides and albumin and a trend for a better elimination of cholesterol, GGT, and LDH. The sieving properties of the PF2000N ranged between PF1000N and PLASMAFLO. Under standardized in vitro conditions, the larger plasmafilters tested did not improve the overall performance of the plasmapheresis procedure. Thus, enlargement of the membrane surface such as provided by two commercially available and clinically well-established plasmafilters could not be proven to enable higher clearance rates.