Ultrafiltration rate in conventional hemodialysis: Where are the limits and what are the consequences?

Background: Ultrafiltration rate (UFR) has attracted attention as a modifiable aspect of volume management. Objective: The objective of this review is to summarize the evidence that links UFR to patient outcomes and discuss UFR cut-offs proposed, and discuss possible consequences of adapting UFR as a quality metric. Results: Higher UFRs has been associated with younger age, longer dialysis vintage, greater prevalence of comorbidities, higher Kt/V, lower weight, greater interdialytic weight gain, lower residual renal function, and shorter treatment times. Many of the characteristics associated with high UFRs have also been independently associated with poor patient outcomes. Four observational studies have assessed the association between UFR and patient mortality. All of them reported an association between higher UFR and greater patient mortality, though the studies differed in their definition of UFR, follow-up, and adjustment for confounding. Evidence for the association between higher UFR and potential mediations of the mortality association, such as interdialytic hypotension, cardiac remodeling, and cardiovascular events was less consistent. There was a graded association between higher UFRs and all-cause mortality; no definitive cut-off for acceptable UFR can be established based on the current evidence. Targeting UFR in isolation might result in volume expansion and worsening patient outcomes. Residual confounding likely contributed to the findings of the observational studies. No randomized controlled trials addressed the questions. Conclusion: Evidence supporting UFR limits is weak and confounded. Randomized controlled trials are needed before UFR can be used as a quality of care indicator.