Preceding risks and mortality outcomes of different neonatal acute kidney injury in preterm infants

Background: The aim of the study was to examine preceding risks and mortality outcomes of oliguric and non-oliguric acute kidney injury (AKI) in very preterm infants. Methods: Infants born ≤30 weeks’ gestation were included. AKI was diagnosed based on neonatal Kidney Disease: Improving Global Outcomes criteria and was classified as oliguric and non-oliguric according to the urine-output criteria. We used modified Poisson and Cox proportional-hazards models for statistical comparisons. Results: Of 865 enrolled infants (gestational age 27.2 ± 2.2 weeks and birth weight 983 ± 288 gm), 204 (23.6%) developed AKI. Before AKI, the oliguric AKI group had significantly higher prevalence of small-for-gestational age (p = 0.008), lower 5-min Apgar score (p = 0.009) and acidosis (p = 0.009) on admission, and hypotension (p = 0.008) and sepsis (p = 0.001) during admission than the non-oliguric AKI group. Oliguric (adjusted risk ratio 3.58, 95% CI 2.33–5.51; adjusted hazard ratio 4.93, 95% CI 3.14–7.72) instead of non-oliguric AKI had significantly higher mortality risks than no AKI. Oliguric AKI showed significantly higher mortality risks than non-oliguric AKI, irrespective of serum creatinine and severity of AKI. Conclusions: Categorizing AKI as oliguric and non-oliguric was crucial because of the distinct preceding risks and mortality outcomes of these two types of AKI in very preterm neonates. Impact: The differences of the underlying risks and prognosis between oliguric and non-oliguric AKI in very preterm infants remain unclear.We found that oliguric AKI, but not non-oliguric AKI, carries higher mortality risks than infants without AKI. Oliguric AKI possessed higher mortality risks than non-oliguric AKI, irrespective of concomitant serum creatinine elevation and severe AKI.Oliguric AKI is more associated with prenatal small-for-the-gestational age and perinatal and postnatal adverse events, while non-oliguric AKI is associated with nephrotoxins exposures.Our finding highlighted the importance of oliguric AKI and is helpful in developing future protocol in neonatal critical care.