[Association between early net ultrafiltration rate and outcomes in patients with cardiac surgery-associated acute kidney injury receiving continuous renal replacement therapy].

To evaluate the association between early net ultrafiltration (NUF) rate and risk of death in patients with cardiac surgery-associated acute kidney injury (CSA-AKI) requiring continuous renal replacement therapy (CRRT). Adult patients who received CRRT for more than 24 hours due to CSA-AKI in the First Affiliated Hospital of Nanjing Medical University from January 2016 to December 2021 were prospectively included. The NUF rate during the first 48 hours of CRRT was taken as a classified variable (low rate:<1.70 ml·kg·h; moderate rate: 1.70-2.47 ml·kg·h; high rate:>2.47 ml·kg·h). The association between 90-day mortality and NUF rates was analyzed by Cox regression and mediation analyses. A total of 262 patients were enrolled (171 males and 91 females), with the median (, ) age of 64 (54, 71) years and median (, ) NUF rate of 2.03 (1.58, 2.62) ml·kg·h. The 90-day mortality was 60.3% (158/262). Compared with the moderate NUF rate, patients with the low NUF rate (adjusted =1.52, 95%: 1.01-2.27, =0.043) and high NUF rate (adjusted =1.54, 95%: 1.02-2.33, =0.039) had a significantly higher risk of 90-day death. In mediation analysis, compared with the moderate NUF rate, the putative effect of the high NUF rate on 90-day mortality was direct [adjusted average direct effects (ADE)=1.12, 95%: 1.04-1.21,=0.004] and not mediated by effects of the NUF rate on fluid balance [adjusted average causal mediation effects (ACME)=1.00, 95%:0.98-1.01, =0.502]. The putative effect of the low NUF rate on mortality was not direct (adjusted ADE=0.93, 95%:0.81-1.05, =0.274), but was mediated by its effect on fluid balance (adjusted ACME=0.93, 95%:0.87-0.98, =0.018). Compared with NUF rates between 1.70-2.47 ml·kg·h within the first 48 hour of CRRT, NUF rates>2.47 and<1.70 ml·kg·h were associated with higher mortality in CSA-AKI patients receiving CRRT.