Impact of acute kidney injury and dysnatremia on length of stay in infants after cardiac surgery

BACKGROUND: Acute kidney injury (AKI) and dysnatremia following pediatric cardiac surgery are common conditions associated with worse outcomes. While the multifactorial etiology of AKI is well-known, the role of concomitant dysnatremia is limited. This study aims to describe the occurrence of AKI, its association with the length of stay in the intensive care unit (ICU-LOS), and the impact of dysnatremia in the context of AKI. METHODS: Retrospective study comprising 228 congenital heart procedures in 213 infants at Rigshospitalet, Copenhagen, Denmark, from 2017 to 2019. AKI development was evaluated separately in neonates and infants > 1 month and its impact on ICU-LOS. Risk factors for AKI were analyzed across age groups using the univariate and multivariate logistic regression analysis. RESULTS: AKI occurred in 61% of neonates and 62% of infants. Severity was comparable across age groups, except for KDIGO-stage 3, where seven out of eight children treated with peritoneal dialysis were neonates. Urine output was well-preserved despite AKI development, but children with AKI required more than double the furosemide dose. In multivariate analysis, prolonged cardiopulmonary bypass (CPB) duration, higher furosemide doses, and hypernatremia were independently associated with AKI. AKI was only associated with prolonged ICU-LOS in infants, while hyponatremia was associated with prolonged ICU-LOS in all individuals with AKI. CONCLUSIONS: AKI occurs frequently in neonates and infants after congenital heart surgery but is only associated with prolonged ICU-LOS in infants. The co-occurrence of AKI and hyponatremia leads to longer ICU-LOS in both neonates and infants. Independent predictors of AKI were prolonged CPB duration, hypernatremia, and reduced furosemide sensitivity.