Platelet Consumption and Filter Clotting Using Two Different Membrane Sizes during Continuous Venovenous Haemodiafiltration in the Intensive Care Unit

Background. The aim of this study was to investigate whether different haemofilter surface areas affect clotting and platelet consumption in critically ill patients undergoing continuous venovenous haemodiafiltration (CVVHDF). Methods. CVVHDF was performed in postdilution technique using a capillary haemofilter with two different membrane sizes, Ultraflux AV 1000S (n = 17, surface 1.8 m(2), volume 130 mL), and the smaller AV 600S (n = 16, surface 1.4 m(2), volume 100 mL), respectively. Anticoagulation was performed with heparin. Results. No significant differences were found when the two filters were compared. CVVHDF was performed for 33 (7-128) hours with the filter AV 1000S and 39 (7-97) hours with AV 600S (P = 0.68). Two (1-4) filters were utilised in both groups over this observation period (P = 0.94). Platelets dropped by 52,000 (0-212,000) in AV 1000S group and by 89,500 (0-258,000) in AV 600S group (P = 0.64). Haemoglobin decreased by 1.2 (0-2.8) g/dL in AV 1000S group and by 1.65 (0-3.9) g/dL in AV 600S group (P = 0.51), leading to the transfusion of 1 (0-4) unit of blood in 19 patients (10 patients with AV 1000S and 9 with AV 600S). Filter observation was abandoned due to death (12.1%), need for systemic anticoagulation (12.1%), repeated clotting (36.4%), and recovery of renal function (39.4%). Conclusion. Our study showed that a larger filter surface area did neither reduce the severity of thrombocytopenia and anaemia, nor decrease the frequency of clotting events.