ELBW infants receive inadvertent sodium load above the recommended intake.

To determine total sodium load, including inadvertent load, during the first 2 postnatal weeks, and its influence on serum sodium, morbidity, and mortality in extremely low birth weight (ELBW, birth weight <1000 g) infants and to calculate sodium replacement models. Retrospective data analysis on ELBW infants with a gestational age <28 + 0/7 weeks. Ninety patients with a median birth weight of 718 g and a median gestational age of 24 + 6/7 weeks were included. Median sodium intake during the first 2 postnatal weeks was 10.2 mmol/kg/day, which was significantly higher than recommended (2–5 mmol/kg/day). Sodium intake did not affect the risk for hypernatremia. Each mmol of sodium intake during the first postnatal week was associated with an increased risk of bronchopulmonary dysplasia (45%) and higher-grade intraventricular hemorrhage (31%), during the second postnatal week for necrotizing enterocolitis (19%), and during both postnatal weeks of mortality (13%). Calculations of two sodium replacement models resulted in a decrease in sodium intake during the first postnatal week of 3.2 and 4.0 mmol/kg/day, respectively. Sodium load during the first 2 postnatal weeks of ELBW infants was significantly higher than recommended owing to inadvertent sodium intake and was associated with a higher risk of subsequent morbidity and mortality, although the study design does not allow conclusions on causality. Replacement of 0.9% saline with alternative carrier solutions might reduce sodium intake.