Impact of Ultrafiltration Rate Among Adults with AKI Treated with Continuous Renal Replacement Therapy (CRRT)

Background: Observational data supports the view that fluid removal with dialysis in critical illness confers survival benefit. The optimal fluid removal rate is unknown with some suggesting that ultrafiltration rate (UFR) greater than 1.75 mL/kg/hr may be harmful. Methods: We conducted a single-center retrospective cohort study among adult AKI patients admitted to the intensive care unit (ICU) at University of Chicago treated with CRRT from April 1, 2016 to March 31, 2020. We collected information regarding patient demographics, severity of illness, daily fluid balance (all intakes minus outputs, inclusive of RRT), RRT ultrafiltration, and outcomes (length of stay, dialysis dependence, and mortality). We calculated UFR restricted to the first 72 hours of dialysis treatment as net ultrafiltrate (mL) per hour treatment duration adjusted for patient’s baseline body weight. Results: 742 patients had low UFR (≤1.01 mL/kg/hr), 269 had moderate UFR (between 1.01 and 1.75 mL/kg/hr), and 167 had high UFR (≥1.75 mL/kg/hr). Those with low UFR were older, had higher baseline body weight, and had less positive fluid balance in the 72 hours prior to starting dialysis. Severity of illness (SOFA) and burden of co-morbidities were not significantly different across UFR groups. Those with low UFR had a median cumulative fluid balance of 2.38 L over 72 hours, lower likelihood to remain dependent on dialysis at 90-days, and highest 90-day mortality (Table 1). In an adjusted Cox proportional hazards model, low UFR was associated with an increased risk of 90-day mortality (HR 1.88, 95% CI 1.10-3.21 p=0.02) whereas high UFR was not significantly associated with 90-day mortality (HR 0.66, 95% CI 0.31-1.42, p=0.29). Conclusions: Low UFR is associated with increased 90-day mortality while high UFR was not associated with 90-day mortality. Future studies should investigate the ideal UFR to improve patient outcomes. Funding: Commercial Support - Fresenius Medical Care - Outcomes By 72 Hour Net Ultrafiltration Rate Low NUF <1.01 ml/kg/hr Moderate NUF 1.01-1.75 ml/kg/hr High NUF >1.75 ml/kg/hr p-value N 742 269 167 72H Fluid Balance (L), med (IQR) 2.38 (-0.02, 5.97) -0.62 (-3.33, 2.37) -3.25 (-5.38, -0.35) <0.001 72H UFR (mL/kg/hr), med (IQR) 0.39 (0.07, 0.71) 1.29 (1.14, 1.47) 2.27 (1.93, 2.76) <0.001 ICU Days, med (IQR) 8 (3, 19) 12 (6, 24) 13 (5, 25) <0.001 Hospital Days, med (IQR) 14 (5, 27) 19 (9,33) 19 (9, 31) <0.001 RRT at Day 90 (%) Survivors, N=403 31 (14.3) 13 (12.1) 16 (20.3) 0.016 90-Day Mortality (%) 525 (70.8) 162 (60.2) 88 (52.7) <0.001