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Net Ultrafiltration Rate and Mortality in Critically Ill Patients: A Multicenter Cohort Study With Analysis of Fluid
Nadine C Monai1, Carmen A Pfortmueller1, Joerg C Schefold1
1Department of Intensive Care Medicine, University Hospital, University of Bern, Bern, Switzerland.
Critical Care Medicine
|August 12, 2026
Summary
Net ultrafiltration (NUF) rate does not directly impact mortality in critically ill patients on continuous renal replacement therapy (CRRT). Achieving a negative fluid balance is the key determinant of better outcomes, not the NUF rate itself.
Area of Science:
- Critical Care Medicine
- Nephrology
- Fluid Management
Background:
- Continuous renal replacement therapy (CRRT) is vital for fluid management in critically ill patients.
- Net ultrafiltration (NUF) rate is a parameter of CRRT, but its independent association with mortality is unclear.
- Fluid balance is a known predictor of outcomes in critical illness.
Purpose of the Study:
- To investigate the independent association between NUF rate and 28-day mortality in critically ill patients undergoing CRRT.
- To determine the role of fluid balance changes in mediating the relationship between NUF rate and mortality.
Main Methods:
- Multicenter retrospective observational study involving 973 adult critically ill patients from two European ICUs.
- CRRT data, including hourly NUF rates and fluid balance, were collected for at least 24 hours.
- Statistical analyses included multivariable regression, random forest modeling, and mediation analysis.
Main Results:
- No independent association was found between NUF rate and 28-day mortality after adjusting for fluid balance.
- Higher NUF rates were associated with improved survival, but this effect was mediated by achieving a more negative fluid balance.
- Positive fluid balance changes were significantly linked to adverse outcomes, including increased 28-day mortality.
Conclusions:
- NUF rate alone is not an independent predictor of mortality in CRRT patients.
- Fluid balance, specifically achieving negative balance, is the critical factor influencing outcomes.
- Clinicians should prioritize achieving patient-specific fluid balance targets using NUF, rather than focusing on NUF rate in isolation.
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