Sodium Supplementation and Growth in Very Low Birth Weight Infants

Overview

Adequate growth during the neonatal period is critical for optimal long term outcomes. Despite maximal calorie intake, sixty percent of very low birth weight infants still fail to thrive suggesting that factors other than total calorie intake are important in ensuring consistent weight gain. Several reports have indicated a positive sodium balance is critical in ensuring good weight gain in very low birth weight infants, however these infants are susceptible to low serum sodium concentrations. Urine sodium values are sometimes used to diagnosis of hyponatremia or negative sodium balance after the first two weeks of life, but there is no evidence for this practice in preterm neonates. Our central hypothesis is that early supplementation with sodium will ensure positive sodium balance in very low birth weight infants and will result in optimal weight gain and enhanced long term outcomes. Secondarily we hypothesize that low sodium concentrations in the urine will not correlate with low serum sodium values.

This is a randomized, blinded, placebo-controlled trial in infants born at less than 32 weeks gestation, who are admitted to the Newborn Intensive Care Unit at University of Cincinnati Medical Center, Cincinnati, Ohio. Infants are randomized to receive either 4 meq/kg/day supplemental sodium or an equal amount of sterile water on days of life 7-35. Institutional data from 2008 revealed that a sample size of 56 infants completing the study will detect a 15% difference in the primary outcome of weight gain with 80% power and an alpha error of 0.05. Allowing that 33% drop-out rate (infants may be transferred to another hospital, expire, or be discharged prior to day of life 35), we choose to randomize 75 infants. Calorie intake, serum sodium, weight gain, urine sodium were monitored weekly till 35 days of life or discharge. Infants were assessed for common morbidities associated with prematurity including bronchopulmonary dysplasia, systemic hypertension, late-onset sepsis, necrotizing enterocolitis and retinopathy of prematurity.