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

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 >or= 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.