Hospital-acquired Hyponatremia in Children: Incidence and Association with Fluid and Sodium Supplementation

Hospital-acquired hyponatremia (HAH) is a common and preventable electrolyte disorder in hospitalized children, and its pathogenesis involves a complex interplay among fluid therapy, non-osmotic release of antidiuretic hormone, and underlying clinical conditions. This study aimed to determine the incidence of HAH at a tertiary pediatric center and to evaluate the relationship among intravenous fluid (IVF) composition, total fluid volume, and sodium supplementation. This prospective observational study included all pediatric inpatients admitted during a one-year period. Patients who were normonatremic on admission and received IVFs for at least 24 hours were monitored for the development of hyponatremia. At the time hyponatremia was detected, detailed clinical data, biochemical parameters [including urinary sodium and serum pro-B-type natriuretic peptide (proBNP) levels], total IVF intake, and oral/intravenous sodium supplementation were recorded, covering the previous 24 hours. The cohort was stratified into two age groups: younger than 100 days and older than 100 days. Among 8065 hospitalized children, 373 met the study criteria. The incidence of HAH was 4.6%. Hyponatremia occurred earlier in infants under 100 days of age (median 6 days) than in older patients (median 10.5 days), and moderate-to-severe hyponatremia was more frequent in the younger group. Urinary sodium excretion was elevated in most patients, particularly in those older than 100 days. Nearly half of infants who received only IVF developed moderate-to-severe hyponatremia, and 35.8% of these infants received sodium supplementation below physiological requirements. Serum sodium showed a positive correlation with age and inverse correlations with blood urea nitrogen, creatinine, and proBNP levels; no association was found between serum sodium and total IVF volume. In conclusion, HAH remains an important clinical problem, particularly in neonates, critically ill children, and oncology patients. Inadequate sodium supplementation—especially in young infants—appears to contribute to hyponatremia, even in the absence of fluid overload. These findings underscore the importance of individualized fluid prescriptions, routine electrolyte monitoring, and adherence to isotonic fluid strategies to prevent iatrogenic hyponatremia in hospitalized children.