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

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.