- Design
- Two-centre retrospective cohort with mediation analysis
- Population
- 973 critically ill adults on CRRT ≥24 hours (6,914 CRRT days)
- Primary outcome
- 28-day mortality
- Effect
- No independent association with NUF rate; positive fluid balance associated with higher mortality
This retrospective study from ICUs in Bern and Amsterdam analysed 973 critically ill adults receiving continuous renal replacement therapy for at least 24 hours, covering 6,914 days of treatment. Net ultrafiltration rate and daily fluid balance were calculated from hourly data.
After accounting for fluid balance, net ultrafiltration rate was not independently associated with 28-day mortality. Mediation analysis suggested that the apparent survival advantage of higher rates came through achieving a more negative fluid balance. A more positive daily fluid balance was linked to higher mortality.
Earlier observational work had raised concern that high ultrafiltration rates themselves were harmful. This analysis suggests the rate is a means, not an end: set a fluid balance goal for the patient and use ultrafiltration to reach it.
- Set a patient-specific daily fluid balance target on CRRT, and titrate net ultrafiltration to it.
- Positive fluid balance on CRRT was associated with higher mortality.
- Net ultrafiltration rate alone was not linked to death once fluid balance was considered.
- Watch haemodynamics closely when removing fluid; the target should match the patient's tolerance.
Why it matters
It challenges the idea that ultrafiltration rate is itself the danger, and points to fluid accumulation instead.
Don't overread it
Observational, two centres — it cannot prove that targeting negative balance improves survival.
The statistics, in plain English
Mediation analysis estimates how much of an association runs through another factor; here most of the link between ultrafiltration rate and survival ran through fluid balance.
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