Table 2.

Comparison of studies examining ultrafiltration rate and mortality

Study	Population	Pre-KRT Fluid Status	KRT Modality	Exposure	Outcome/Results	Notable Features
Murugan et al. (2018)53,a	Retrospective cohort Single-center Medical and surgical ICU Jul 2000–Oct 2008 Pittsburgh, USA N=1075 AKI only	Fluid overload ≥5% body weight on admission	Intermittent HD and CKRT - CVVHDF - CVVHD - CVVH - SCUF	UF intensity - Low (≤20 ml/kg per day) - Moderate (20–25 ml/kg per day) - High (>25 ml/kg per day) Subgroup CKRT only - Low (<0.5 ml/kg per hour) - Moderate (0.1–1.0 ml/kg per hour) - High (>1.0 ml/kg per hour)	High-intensity UF (versus low-intensity) associated with improved 1-yr survival No difference between moderate- versus low-intensity groups Secondary outcomes - Hospital LOS - In-hospital mortality - Kidney recovery	Sensitivity analyses - Explored alternative UF thresholds - Propensity score matching - Quantitative bias analysis Demographic differences - Liver disease more in low-intensity group - Lower BP in low-intensity group - Higher vasopressor dose in low-intensity group - Higher KDIGO stage in high-intensity group
Tehranian et al. (2019)54,a	Retrospective cohort Single-center Medical and surgical ICU Dec 2006–Nov 2015 N=1398 Minnesota, USA AKI only	No criteria Subset analysis of fluid overload ≥10% body weight on admission	CKRT (CVVH)	UF intensity - Low (<35 ml/kg per day) - High (≥35 ml/kg per day)	High-intensity UF (versus low-intensity) associated with improved 30-d survival Secondary outcomes - Hospital LOS - In-hospital mortality - MAKE90 - Kidney recovery - 90-d mortality	Sensitivity analyses - Explored alternative UF thresholds - Subgroup analyses Demographic differences - More early hypotension in low-intensity group - More mechanical ventilation in high-intensity group
Murugan et al. (2019)55,b	Secondary analysis (RENAL trial) Multicenter Dec 2005–Nov 2008 Australia/New Zealand N=1434 AKI only	No criteria	CKRT (CVVHDF)	UF rate - Low (<1.01 ml/kg per hour) - Moderate (1.01–1.75 ml/kg per hour) - High (>1.75 ml/kg per hour)	High UF rate (versus low UF rate) associated with higher 90-d mortality Lowest mortality in the moderate UF rate group Higher complications in high UF rate group (not significant after adjustment for clearance and duration of CKRT)	Sensitivity analyses - Explored alternative UF thresholds - Propensity score matching - Varied time intervals - Subgroup analyses Demographic differences - Longer ICU length of stay prior to randomization in high UF rate group - More mechanical ventilation in high UF rate group - More CKRT initiation for severe organ edema due to kidney disease in high UF rate group
Naorungroj et al. (2021)56,b	Retrospective cohort Single-center Medical and surgical ICU 2016–2018 Australia N=347 AKI and chronic kidney failure	No criteria	CRKT - CVVHDF - CVVH	UF rate (in first 48 h) - Low (<1.01 ml/kg per hour) - Moderate (1.01–1.75 ml/kg per hour) - High (>1.75 ml/kg per hour)	High UF rate (versus low UF rate) associated with higher 28-d mortality	Sensitivity analyses - Subgroup analyses - Varied time of mortality assessment Demographic differences - Higher vasopressor use in low UF rate group - Longer duration of KRT in high UF rate group

This table provides a summary of the studies examining ultrafiltration and mortality in a critical care setting, with comparisons of study population, inclusion criteria, KRT modality, definition of net UF groups, outcomes, and other notable features. Note that while the studies refer to a net UF to account for the administration of intravenous fluids needed to complete KRT (in the case of these studies, this consisted of replacement fluid during hemofiltration) to avoid confusion, all fluid removal achieved using KRT is referred to simply as UF. ICU, intensive care unit; HD, hemodialysis; CKRT, continuous KRT; CVVHDF, continuous venovenous hemodiafiltration; CVVHD, continuous venovenous hemodialysis; CVVH, continuous venovenous hemofiltration; SCUF, slow continuous ultrafiltration; UF, ultrafiltration; LOS, length of stay; KDIGO, Kidney Disease Improving Global Outcomes; RENAL, Randomized Evaluation of Normal versus Augmented Level (RENAL) Replacement Therapy Study.

^aThe two studies that found an association between higher ultrafiltration rate and lower mortality.

^bThe two studies that found an association between higher ultrafiltration rate and higher mortality.