Beneficial use of predilution in reducing the amount of anticoagulation and the occurrence of bleeding during CRRT in critically ill patients: a prospective randomized study

Abstract

Objectives Anticoagulation during CRRT is one of the major issues. We have to take into account three parameters: bleeding occurrence, filter life and filter efficiency. The purpose of the study was to assess prospectively the efficacy of the predilution technique in reducing the amount of anticoagulation during CRRT allowing to use it in critically ill patients at risk for bleeding. Design Prospective randomized study. Setting Fifteen bedded, adult polyvalent intensive care unit in a general hospital. Methods Twenty consecutive critically ill patients were randomized to have either a predilution set or a post-dilution one during CRRT using the prisma Hospal pump. Full circuit standard heparinisation was used to achieve an APTT twice baseline. The vascath site was restricted to the right internal jugular vein. The pump speed was kept at 100 ml/min. Filter efficiency was assessed by the haemopermeability index (HPI). The HPI represents the ultrafiltrate flow divided by the transmembrane pressure. The filter efficiency is lost when the HPI has dropped by 70%. Filter life was measured in hours until the circuit clotted off. Data were analysed using non parametric statistical methods. Entry criteria included normal prothrombine time (PT) and normal activated partial thromboplastin time (APTT). The platelet count had to be over 100×109/1. The study was restricted to the first filter of each patient. Results The two groups were well matched prior to the therapy for platelet count, haematocrit, oncotic pressure and total calcium measured in the serum. As shown by the table, the predilution allows a reduction in heparin without imparing the filter life. To try to understand the mechanism involved, we have also measured the haematocrit, the platelet count, the oncotic pressure and the total calcium in the circuit prior to the filter but after the dilution as shown by the following table. Conclusions The predilution technique is a good tool for clinicians in the setting of CRRT in critically ill patients at risk for bleeding. It allows the physician to reduce drastically the amount of heparin used without impairing the filter life and the filter efficiency. The mechanism involved seems to be the reduction of the oncotic pressure rather than other systems involving the calcium. Table Predilution Postdilution group n = 10 group n = 10 P value Median filter life in hours 38.5 39.3 >0.05 Median filter efficiency in hours 32.3 33.9 >0.05 Symptomatic bleeding 1 4 <0.01 (during the study period) Median amount of heparin 451 U/h 742 U/h <0.01 Predilution Postdilution group n = 10 group n = 10 P value Median haematocrit 25.1% 28.5% <0.05 Median platelet count 116 × 109/1 131 × 109/l <0.05 Median oncotic pressure 31.3 mmHg 37.2 mmHg <0.01 Total calcium 3.8 mEq/l 3.88 mEq/l >0.05