Impact of Early Sodium Supplementation on Hyponatremia and Growth in Premature Infants

Background: We tested the hypothesis that sodium supplementation in early preterm infants prevents late-onset hyponatremia and improves growth without increasing common morbidities during birth hospitalization. Materials and Methods: This was a randomized, masked controlled trial of 4 mEq/kg/d of sodium (intervention) versus sterile water (placebo) from days-of-life 7 to 35 in infants born at <32 weeks corrected gestational age. The primary outcome was weight gain in the first 6 weeks of life. Secondary outcomes included weekly serum sodium concentrations, growth in body length and head circumference, and complications of prematurity during birth hospitalization. Results: Fifty-three infants with an average corrected gestational age of 28.5 ± 2.4 weeks were randomized. Infants receiving the intervention had fewer (P = .012) reports of serum sodium concentrations <135 mmol/L and greater velocity of weight gain during the study period, mean (SD) 26.9 (3.1) vs 22.9 (4.7) g/kg/day, P = .012. At 6 weeks of age, infants <28 weeks’ gestation who received sodium supplementation had greater percentage weight change from birth, mean (SD) 193% (22%) vs 173% (10%), P = .041, and maintained fetal reference birth percentile for body weight more often (P = .002) compared with infants receiving placebo. Growth in length and head circumference was not significantly different between study arms. No increase in common prematurity-related morbidities was detected in infants who received supplemental sodium chloride. Conclusion: Sodium supplementation of enteral feedings in very premature infants averts hyponatremia and enhances weight gain.