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Multicenter Study
. 2023;52(6):532-540.
doi: 10.1159/000530146. Epub 2023 Apr 18.

Impact of Continuous Renal Replacement Therapy Initiation on Urine Output and Fluid Balance: A Multicenter Study

Kyle Christopher White  1   2 , Kevin B Laupland  3   4 , Emily See  5   6   7   8   9 , Ary Serpa-Neto  6   10   11 , Rinaldo Bellomo  6   7   9
Affiliations
Multicenter Study

Impact of Continuous Renal Replacement Therapy Initiation on Urine Output and Fluid Balance: A Multicenter Study

Kyle Christopher White et al. Blood Purif. 2023.

Abstract

Introduction: The effect of continuous renal replacement therapy (CRRT) on renal function is poorly understood. However, the initiation of CRRT may induce oliguria. We aimed to investigate the impact of CRRT commencement on urine output (UO).

Methods: This was a retrospective cohort study in two intensive care units. We included all patients who underwent CRRT and collected data on hourly UO and fluid balance before and after CRRT commencement. We performed an interrupted time series analysis using segmented regression to assess the relationship between CRRT commencement and UO.

Results: We studied 1,057 patients. Median age was 60.7 years (interquartile range [IQR], 48.3-70.6), and the median APACHE III was 95 (IQR, 76-115). Median time to CRRT was 17 h (IQR, 5-49). With start of CRRT, the absolute difference in mean hourly UO and mean hourly fluid balance was -27.0 mL/h (95% CI: -32.1 to -21.8; p value < 0.01) and - 129.3 mL/h (95% CI: -169.2 to -133.3), respectively. When controlling for pre-CRRT temporal trends and patient characteristics, there was a rapid post-initiation decrease in UO (-0.12 mL/kg/h; 95% CI: -0.17 to -0.08; p value < 0.01) and fluid balance (-78.1 mL/h; 95% CI: -87.9 to -68.3; p value < 0.01), which was sustained over the first 24 h of CRRT. Change in UO and fluid balance were only weakly correlated (r -0.29; 95% CI: -0.35 to -0.23; p value < 0.01).

Conclusion: Commencement of CRRT was associated with a significant decrease in UO that could not be explained by extracorporeal fluid removal.

Keywords: Acute kidney injury; Continuous renal replacement therapy; Critical care.

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Conflict of interest statement

The authors have no conflicts of interest to declare.

Figures

Fig. 1.
Fig. 1.
Cumulative UO and fluid balance over time. Top: cumulative UO over time in all patients. Circles are mean, and error bars, 95% confidence intervals. Bottom: cumulative fluid balance over time in all patients. Circles are mean, and error bars, 95% confidence intervals.
Fig. 2.
Fig. 2.
UO over time in all patients. Top: UO over time in all patients. Circles are mean, and error bars, 95% confidence intervals. Bottom: circles are the mean UO in each time point. Solid lines represent fitted lines from the segmented regression, and dashed line is the counterfactual outcome had the pre-CRRT trends continued.
Fig. 3.
Fig. 3.
Fluid balance over time in all patients. Top: fluid balance over time in all patients. Circles are mean, and error bars, 95% confidence intervals. Bottom: circles are the mean fluid balance in each time point. Solid lines represent fitted lines from the segmented regression, and the dashed line is the counterfactual outcome had the pre-CRRT trends continued.
Fig. 4.
Fig. 4.
XY plot of change in urine output versus change in fluid balance. Left: change in hourly UO from 0 h to 4 h on the Y axis compared to change in hourly fluid balance from 0 h to 4 h on the X axis. Right: change in hourly UO from 0 h to 24 h on the Y axis compared to change in hourly fluid balance from 0 h to 24 h on the X axis.
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