Association between Net Ultrafiltration Rate and Renal Recovery among Critically Ill Adults with Acute Kidney Injury Receiving Continuous Renal Replacement Therapy: An Observational Cohort Study
<b><i>Introduction:</i></b> Higher net ultrafiltration (UF<sub>NET</sub>) rates are associated with mortality among critically ill patients with acute kidney injury (AKI) and treated with continuous renal replacement therapy (CRRT). <b><i>Objective:</i></b> The aim of the study was to discover whether UF<sub>NET</sub> rates are associated with renal recovery and independence from renal replacement therapy (RRT). <b><i>Methods:</i></b> Retrospective cohort study using data from the Randomized Evaluation of Normal versus Augmented Level of Renal Replacement Therapy trial that enrolled 1,433 critically ill patients with AKI and treated with CRRT between December 2005 and November 2008 across 35 intensive care units in Australia and New Zealand. We examined the association between UF<sub>NET</sub> rate and time to independence from RRT by day 90 using competing risk regression after accounting for mortality. The UF<sub>NET</sub> rate was defined as the volume of fluid removed per hour adjusted for patient body weight. <b><i>Results and Conclusions:</i></b> Median age was 67.3 (interquartile range [IQR], 57–76.3) years, 64.4% were male, median Acute Physiology and Chronic Health Evaluation-III score was 100 (IQR, 84–118), and 634 (44.2%) died by day 90. Kidney recovery occurred in 755 patients (52.7%). Using tertiles of UF<sub>NET</sub> rates, 3 groups were defined: high, >1.75; middle, 1.01–1.75; and low, <1.01 mL/kg/h. Proportion of patients alive and independent of RRT among the groups were 47.8 versus 57.2 versus 53.0%; <i>p</i> = 0.01. Using competing risk regression, higher UF<sub>NET</sub> rate tertile compared with middle (cause-specific hazard ratio [csHR], 0.79, 95% CI, 0.66–0.95; subdistribution hazard ratio [sHR], 0.80, 95% CI, 0.67–0.97) and lower (csHR, 0.69, 95% CI, 0.56–0.85; sHR, 0.78, 95% CI 0.64–0.95) tertiles were associated with a longer time to independence from RRT. Every 1.0 mL/kg/h increase in rate was associated with a lower probability of kidney recovery (csHR, 0.81, 95% CI, 0.74–0.89; and sHR, 0.87, 95% CI, 0.80–0.95). Using the joint model, longitudinal increases in UF<sub>NET</sub> rates were also associated with a lower renal recovery (β = −0.29, <i>p</i> < 0.001). UF<sub>NET</sub> rates >1.75 mL/kg/h compared with rates 1.01–1.75 and <1.01 mL/kg/h were associated with a longer duration of dependence on RRT. Randomized clinical trials are required to confirm this UF<sub>NET</sub> rate-outcome relationship.