A Randomized Comparative Crossover Study to Assess the Affect on Circuit Life of Varying Pre-Dilution Volume Associated with CVVH and CVVHDF

Abstract

Objective To determine if circuit life is influenced by a higher pre-dilution volume used in CVVH when compared with a lower pre-dilution volume approach in CVVHDF. Design A comparative crossover study. Cases were randomized to receive either CVVH or CVVHDF followed by the alternative treatment. Subjects All patients ≥ 18 yrs of age who required CRRT while in ICU were eligible to participate, but excluded if coagulopathic, thrombocytopenic or unable to receive heparin. Based on an intention-to-treat, 45 patients were randomized to receive either CVVH or CVVHDF followed by the alternative treatment. Setting: A 24-bed, tertiary, medical and surgical adult intensive care unit (ICU). Intervention Blood flow rate, vascular access device and insertion site, hemofilter, anticoagulation and machine hardware were standardized. An ultrafiltrate dose of 35 ml/ kg/h delivered pre-filter was used for CVVH. A fixed pre-dilution volume of 600 mls/h with a dialysate dose of 1 L was used for CVVHDF. Results Thirty-one patients received CVVH or CVVHDF out of 45 participants followed by the alternative technique. There was a significant increase in circuit life in favor of CVVHDF (median=16 h 5 min, range=40 h 23 min) compared with CVVH (median=6 h 35 min, range=30 h 45 min). A Mann-Whitney U test was performed to compare circuit life between the two different CRRT modes (Z=-3.478, p<0.001). Measurements of circuit life on the 93 circuits which survived to clotting (50 CVVH and 43 CVVHDF) were log transformed prior to under taking a standard multiple regression analysis. None of the independent variables - activated prothrombin time (aPTT), platelet count, heparin dose, patient hematocrit or urea - had a coefficient partial correlation >0.09 (coefficient of the determination=0.117) or a linear relationship which could be associated with circuit life (p=0.228). Conclusion Pre-diluted CVVHDF appeared to have a longer circuit life when compared to high volume pre-diluted CVVH. The choice of CRRT mode may be an important independent determinant of circuit life.