The Changing Landscape of Sodium Needs in the Preterm Neonate for Optimizing Growth and Development

Sodium (Na) is essential not only for maintaining extracellular fluid homeostasis as the dominant extracellular cation, but also for supporting the rapid tissue growth characteristic of the neonatal period. Despite its importance, the precise sodium requirements of preterm infants remain insufficiently defined. The immature renal tubules of preterm neonates lead to significant renal sodium losses, making negative sodium balance a common feature in this population. This issue has become increasingly relevant as survival rates improve among extremely preterm infants, while most available data are derived from studies involving more mature preterm or even full-term neonates. Fractional excretion of sodium (FENa) shows a clear inverse correlation with both gestational age and postnatal age, highlighting the developmental limitations in sodium retention among the youngest and most vulnerable infants. Current guidelines on sodium supplementation aim to promote optimal growth and neurodevelopment but vary across organizations. For instance, the most recent ESPGHAN recommendations suggest higher sodium intakes, in the range of 3-8 mEq/kg/day, whereas the American Academy of Pediatrics (AAP) provides more conservative guidance. These discrepancies underscore ongoing uncertainty in determining optimal sodium provision. This narrative review examines both classic and contemporary data on sodium needs in preterm neonates, with the goal of clarifying existing evidence and offering practical insights for clinical care. It also emphasizes unresolved questions and the need for well-designed studies that address the unique physiology of extremely preterm infants. A deeper understanding of sodium metabolism in this population is crucial for improving outcomes and guiding evidence-based supplementation strategies.