Urine Output and Acute Kidney Injury in Neonates/Younger Children

Abstract

Introduction: Pediatric acute kidney injury (AKI) is associated with significant morbidity and mortality, yet a precise definition, especially concerning urine output (UO) thresholds, remains unproven. We evaluate UO thresholds for AKI in neonates and children aged 1-24 months with indwelling urinary catheters undergoing cardiac surgery. Methodology: A six-year prospective cohort study (2018-2023) after cardiac surgery was conducted at a reference center in Brazil. All patients had indwelling urinary catheters up to 48 hours after surgery and at least two serum creatinine (sCr) measurements, including one before surgery. The main objective of this study was to determine the optimal UO thresholds for AKI definition and staging in neonates and younger children compared with the currently used criteria—neonatal and adult Kidney Disease Improving Global Outcomes (KDIGO) definitions. The outcome was a composite of severe AKI (stage 3 AKI diagnosed by the sCr criterion only), kidney replacement therapy, or hospital mortality. Results: The study included 1,024 patients: 253 in the neonatal group and 772 in the younger children group. In both groups, the lowest UO at 24 hours as a continuous variable had good discriminatory capacity for the composite outcome (AUC-ROC 0.75 [95% CI 0.70–0.81] and 0.74 [95% CI 0.68–0.79]). In neonates, the best thresholds were 3.0, 2.0 and 1.0 mL/kg/hour, and in younger children, the thresholds were 1.8, 1.0 and 0.5 mL/kg/hour. These values were used for modified AKI staging for each age group. In neonates, this modified criterion was associated with the best discriminatory capacity (AUC-ROC 0.74 [0.67-0.80] vs. 0.68 [0.61-0.75], P<0.05) and net reclassification improvement (NRI) in comparison with the neonatal KDIGO criteria. In younger children, the modified criteria had good discriminatory capacity but were comparable to the adult KDIGO criteria, and the NRI was near zero. Conclusion: Using indwelling catheters for UO measurements, our study reinforced that the current KDIGO criteria may require adjustments to better serve the neonate population. Additionally, using the UO criteria, we validated the adult KDIGO criteria in children aged 1-24 months.