Predictors of Acute Kidney Injury in Very Low Birth Weight Infants

Background: Acute kidney injury (AKI) is a significant cause of morbidity and mortality in critically ill neonates with an incidence of 18-40%. Despite recent efforts to define and classify AKI in this group of patients, prediction of AKI onset in very-low-birth-weight (VLBW) infants remains unexplained. Through this study we aim to understand the implications of early fluctuations in weight, fluid administration, and urine output on renal function in the first two weeks of life. We hypothesize that VLBW infants who experience greater weight loss, higher urine output, and greater fluctuations in daily fluid administration are at a higher risk for development of early AKI. We additionally intend to examine the role of certain maternal and postnatal factors on development of AKI.

Methods: This is a retrospective case-control of VLBW infants (birth weight <1500gm) admitted to a level III Neonatal Intensive Care Unit (NICU) during a one-year period from 2019-2020. AKI was defined using the modified Kidney Disease: Improving Global Outcomes Definition (KDIGO). Risk factors were compared using R-software among infants with and without AKI using uni- and multivariate analyses.

Results: • Forty-five VLBW infants had complete data available and were included in our analysis.
• The incidence of AKI in our cohort was 20% (9/45) based on KDIGO definition criteria.
• Infants of lower birth weight were more likely to develop AKI (681gm vs 1157gm, p<0.001). However, impact of further postnatal weight loss and time to recovery to birth weight failed to have significant correlations with AKI.
• Infants with AKI were also noted to have high urine output (>4 ml/kg/hour).
• Hypernatremia (>150 mEq/L) in the first week of life was not associated with development of AKI.
• No maternal factors included in the study had significant correlations with postnatal development of AKI.
• Postnatal interventions such as intubation at birth, need for prolonged umbilical artery catheter (UAC), surfactant, dopamine, indomethacin, and packed red blood cells (PRBC) were initially associated with AKI, highlighting the overall morbidity. However, on adjusting for BW they did not remain statistically significant.
• Infants with AKI had higher day-day variation in fluid administration prior to onset and were at a higher risk for subsequent development of hyponatremia ( <135 mEq/L) following AKI.

Conclusion: Although lower birth weight was the single largest predictor of AKI among VLBW infants, high urine output and greater fluctuations in fluid intake were observed in infants who developed AKI. Also, infants with AKI subsequently were at higher risk of developing hyponatremia. These findings emphasize the need for recognizing infants at risk for AKI and practice caution in fluid administration. Targeted randomized studies in the future could help in developing recommendations for kidney friendly fluid management in VLBW infants to prevent AKI and manage sequalae.