Hyponatremia in the neonatal intensive care unit: incidence, risk factors and effect on mortality

The aim of this study was to evaluate the incidence of hyponatremia, risk factors, and its effect on mortality in neonates hospitalized in the neonatal intensive care unit (NICU). This retrospective study was conducted in the NICU of a university hospital in Türkiye over a seven-month period in 2016. All 527 infants admitted to the NICU during the study period were included in the study. Hyponatremia was defined as a serum sodium level < 135 mEq/L. Demographic data, clinical diagnoses, fluid therapy, diuretic use, and survival outcomes were analyzed. Multivariate logistic regression analysis was used to identify independent risk factors. The incidence of hyponatremia in the cohort was 21.2% (112/527). The incidence was higher in preterm (23.6%) and extremely low birth weight (ELBW) infants (61.1%). Hyponatremia was mild in the majority of cases (79.9%). The average gestational age and birth weight of hyponatremic infants were significantly lower than those of non-hyponatremic ones (p = 0.011 and p = 0.038, respectively). In logistic regression analysis, low gestational age was identified as an independent risk factor for hyponatremia (OR = 0.905, p = 0.031). Respiratory system disorders (55.4%) were the most common accompanying comorbidity. Diuretic use in 31.8% and administration of hypotonic fluids (1/5 normal saline) in 45.2% of babies were common associated factors. Mortality was significantly higher in hyponatremic babies when compared with non-hyponatremic ones (10.7% vs. 2.9%; p = 0.001). Hyponatremia is a common and serious condition in the NICU, associated with a significant increase in mortality; with low gestational age being a key independent risk factor. The frequent use of diuretics and hypotonic fluids highlights potential iatrogenic contributions. These findings suggest the need for careful serum sodium monitoring and a re-evaluation of fluid management protocols, especially for vulnerable ELBW preterm infants.