Urine Output (UO) and AKI Diagnosis in Neonates and Infants: A Prospective Study in Cardiac Surgery Patients with Indwelling Urinary Catheters

Background: AKI in neonates and younger infants is associated with significant mortality, yet a precise definition, especially concerning UO thresholds, remains elusive. This study aimed to evaluate UO thresholds for AKI in neonates and infants (1 month to 2 years old) with indwelling urinary catheters. Methods: Six-year prospective cohort study involving children aged 2 years or younger who were undergoing cardiac surgery. All patients had indwelling urinary catheters for accurate urine output measurements up to the second postoperative day and at least two sCr measurements—one before surgery. The main objective of this study was to determine the optimal UO thresholds for AKI definition and staging in neonates and infants compared with the currently used criteria—neonatal and KDIGO definitions. The outcome was a composite of severe AKI, KRT or hospital mortality. Results: The study included 1,024 patients: 253 in the neonatal group and 772 in the infant group. In both groups, the lowest UO at 24 h had good discriminatory capacity for the composite outcome. In neonates, the best thresholds (evaluated by ROC curves) were 3.0, 2.0 and 1.0 mL/kg/h, and in infants, the thresholds were 1.8, 1.0 and 0.5 mL/kg/h. These values were used for modified AKI staging for each age group. In neonates, this modified criterion was associated with the best discriminatory capacity (see figure left) and net reclassification improvement (NRI) - 17.3% in comparison with the neonatal KDIGO criteria. In infants, the modified criteria was comparable to the adult KDIGO criteria, and the NRI was near zero. sensitivity analysis according to diuretic use was performed with similar results. Conclusion: For the first time, 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 infants.