There is variability in the practical prescription for CRRT and minimal evidence to inform basic settings such as blood flow rate (BFR). Blood flow is important for solute control and may also have an association with circuit clotting and premature CRRT failure.

The purpose of this pilot study was to collect data and assess the feasibility for a larger randomised controlled trial (RCT) investigating the impact of BFR on circuit life in patients treated with CRRT.

A prospective RCT conducted over one year in a tertiary ICU in Melbourne. Adult patients with acute kidney injury requiring CRRT were randomised to a BFR of either 150 mls/min or 250 mls/min. Circuit and patient data were collected until the circuit was clotted according to a standardised definition, or ceased electively for other reasons. Duration data are presented as median (inter-quartile range) and differences were examined using Mann–Whitney U, p < 0.05 was considered significant.

One hundred patients were randomised with 96 completing the study (150 mls/min–49; 250 mls/min–47). Groups were well matched for baseline characteristics with the exception that patients in the 150 mls/min group were slightly heavier (83.5 vs. 75.8 kg, p = 0.039).

The primary outcome measure of filter life for the first circuit prior to failing or clotting was not different (150 mls/min: 9.1 [5.5, 26] hrs vs. 10 [4.2, 17] hrs; p = 0.367). Kaplan Meier survival for the first circuit also did not differ between groups (p = 0.45).

BFR was not associated with any effect on circuit life. A power calculation from these results indicate a sample size of 465 patients would be required to assess the impact of BFR on circuit life more definitively. The methodology used in this study would be valuable in the preparation of a larger RCT.