Evaluation of urea and creatinine change during continuous renal replacement therapy: effect of blood flow rate.

Objective: To determine if faster blood flow rate (BFR) has an effect on solute maintenance in continuous renal replacement therapy. Design: Prospective randomised controlled trial. Setting: 24-bed, single centre, tertiary level intensive care unit. Participants: Critically ill adults requiring continuous renal replacement therapy (CRRT). Interventions: Patients were randomised to receive one of two BFRs: 150 mUmin or 250 mUmin. Main outcome measures: Changes in urea and creatinine concentrations (percentage change from baseline) and delivered treatment for each 12-hour period were used to assess solute maintenance. Results: 100 patients were randomised, with 96 completing the study (49 patients, 150 mUmin; 47 patients, 250 mL/min). There were a total of 854 12-hour periods (421 periods, 150 mUmin; 433 periods, 250 mL/min). Mean hours of treatment per 12 hours was 6.3 hours (standard deviation [SD], 3.7) in the 150 mUmin group, and 6.7 hours (SD, 3.9) in the 250 mUmin group (P = 0.6). There was no difference between the two BFR groups for change in mean urea concentration (150 mUmin group, -0.06%; SD, 0.015; v 250 mL/min group, -0.07%; SD, 0.01; P = 0.42) or change in mean creatinine concentration (150 mUmin, -0.05%; SD, 0.01; v 250 mL/min, -0.08%; SD, 0.01; P = 0.18). Independent variables associated with a reduced percentage change in mean serum urea and creatinine concentrations were low haemoglobin levels (-0.01 %; SD, 0.005; P = 0.002; and 0.01 %; SD, 0.005; P = 0.006, respectively) and less hours treated (-0.023%; SD, 0.001; P = 0.000; and -0.02%; SD, 0.002; P = 0.001, respectively). No effect for bodyweight was found. Conclusions: Faster BFR did not affect solute control in patients receiving CRRT; however, differences in urea and creatinine concentrations were influenced by serum haemoglobin and hours of treatment.