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Kidney Week

Abstract: PO0254

The Temporal Relationship Between Ultrafiltration and Mortality in Continuous Renal Replacement Therapy

Session Information

Category: Acute Kidney Injury

  • 102 AKI: Clinical, Outcomes, and Trials

Authors

  • Hocker, Nathaniel, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Pickthorn, Sean, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Mann, Lewis, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Venkatasubramanian, Ravinandan, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Sambharia, Meenakshi, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Nizar, Jonathan, The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
  • Griffin, Benjamin R., The University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States
Background

In acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT), studies suggest that higher ultrafiltration rate (to a point) is associated with reduced mortality, but fluid gain is associated with increased mortality. However, the impact of the timing of net ultrafiltration rate (NUF) on mortality is unknown. Here we evaluated whether the relationship between NUF and mortality is mediated by temporal factors.

Methods

Adults requiring CRRT at the University of Iowa from 2019-2020 were included. Patients were excluded if they survived less than 48 hours on CRRT. Cumulative fluid volume was collected at CRRT initiation and at 24, 48, and 72 hours after initiation. NUF was calculated for each day on therapy by taking the difference in cumulative volume between timepoints and dividing by patient weight. The primary outcome was in-hospital mortality. Covariates were age, gender, BMI, illness severity, CRRT days, volume at CRRT initiation, and comorbidities.

Results

A total of 200 patients met inclusion criteria. Neither NUF from CRRT initiation to 24 hours, nor NUF from 48 to 72 hours, differed significantly between survivors and non-survivors. Strikingly, however, NUF from 24 to 48 hours was strongly statistically associated (Table 1), and remained independently associated after adjustments for covariates.

Conclusion

A temporal relationship was observed between NUF and in-hospital mortality in AKI-CRRT patients. NUF from 24-48 hours was a strong predictor of mortality, but outside of this interval no association was observed. Modern fluid resuscitation strategies emphasize the importance of timing and of appropriate de-resuscitation. A similar paradigm may be advisable in CRRT, but further studies are needed.

Table 1. Net ultrafiltration rate by day in survivors and non-survivors
In-hospital Mortality NUF*: Initiation to 24 HoursNUF*: 24 to 48 HoursNUF*: 48 to 72 Hours
Survivors (N=85)Median, mL/kg/day5.414.26.5
Interquartile Range, mL/kg/day-10.3 to 17.7-0.1 to 27.1-1.0 to 22.8
Non-Survivors (N=115)Median, mL/kg/day-0.32.41.7
Interquartile Range, mL/kg/day-20.1 to 14.2-17.3 to 14.8-7.4 to 16.7
Total (N=200)Median, mL/kg/day1.36.64.7
Interquartile Range, mL/kg/day-13.4 to 16.1-9.6 to 19.3-5.6 to 19.6
P-value .28.001.56

* By convention, positive NUF means greater fluid loss, and negative NUF mean an overall fluid gain; NUF - net ultrafiltration