More versus less intensive renal replacement therapy (RRT) for acute kidney injury is associated with greater reduction in urine output during the first week of therapy, according to a new study. More intensive RRT also is associated with an increased risk of a 50% or greater decline in daily urine output.

“These results suggest that lower urine output is a potential early adverse effect of more intensive RRT,” investigators led by Finnian R. McCausland, MD, of Brigham and Women’s Hospital in Boston, wrote.

The team studied 1124 critically ill patients requiring RRT initiation. The patients, who participated in the Acute Renal Failure Trial Network Study, were randomly assigned to more intensive RRT (hemodialysis [HD] or sustained low-efficiency dialysis 6 times per week or continuous venovenous hemodiafiltration [CVVHDF] at 35 mL/kg per hour) or less intensive RRT (HD or sustained low-efficiency dialysis 3 times per week or CVVHDF at 20 mL/kg per hour). The primary outcome was the rate of change in daily urine output in patients who survived from randomization up to and including day 7 (871 patients: 436 in the less intensive and 435 in the more intensive group).

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In unadjusted analyses, among patients who survived 7 or more days, mean urine output was, on average, 31.7 mL/day higher in the less intensive group than the more intensive group, Dr McCausland’s group reported online ahead of print in the Clinical Journal of the American Society of Nephrology. More intensive RRT was associated with 29% greater unadjusted risk of decline in daily urine output of 50% or more. In a model adjusting for baseline covariates such as sex, race, age, and numerous comorbid conditions, the mean urine output in the less intensive group was, on average, 36.3 mL/day higher compared with the more intensive group. In the same model, more intensive RRT was associated with a 37% increased risk of a 50% or greater decline in daily urine output.

“An important factor that may contribute to differences in urine output accord to RRT intensity could be the presence of more hemodynamic instability associated with greater intensity or frequency of dialytic therapy,” the researchers explained.

In an accompanying editorial, Christine K. Federspiel, MD, of the University of Copenhagen in Denmark and the University of California San Francisco (UCSF) and Kathleen D. Liu, MD, of UCSF, commented that the new study shows “yet another way in which more intensive RRT is not beneficial and may be harmful: through a decline in urine output. Although this analysis does not show an association with longer-term outcomes, including dialysis dependence at day 28 or 60, there certainly seems to be no benefit with more intensive dialysis.”

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