Sodium Patterns and Their Variables in a Cohort of ELBW Infants in the First 10 Days of Life

Background: Sodium regulation is critical in extremely low-birth-weight (ELBW, <1000 g) infants. In a recent systematic review, a sodium pattern over postnatal age and its variables (care factors, fluid regimens, and maturational factors) has been summarized. However, this systematic review also illustrated the shortages and limitations of reported cohorts, and the need to report on additional datasets. This study therefore aims to describe the postnatal sodium patterns and their variables in a cohort of ELBW neonates in the first 10 days of postnatal life. Methods: Data on 1704 serum sodium observations in the first 10 days of life from 211 ELBW infants hospitalized in a single neonatal intensive care unit were available to explore associations between serum sodium and perinatal variables. Multivariate linear models with sodium as a response variable and postnatal day as a factor were hereby applied. Baseline and treatment characteristics were included as variables, applying an unstructured covariance matrix to account for the longitudinal data. Results: Gestational age, birth weight, and length showed variable correlations with serum sodium concentrations over postnatal age. Interestingly, the analysis of sodium patterns in this ELBW cohort also revealed significant associations between prenatal betamethasone use, delivery mode, ibuprofen, or the use of inotropes and the postnatal serum sodium concentrations patterns. Multivariate analyses confirmed that gestational age and birth weight independently impacted sodium concentration patterns, and that ibuprofen use remained a significant variable after adjusting for these variables. Conclusions: Gestational age and birth weight complexities emphasize the need for nuanced understanding and standardized methodologies. Sodium patterns in the current ELBW cohort provide support for previously published sodium reference patterns in this population. New variables associated with sodium levels include ibuprofen administration and the use of inotropic agents.