P2.I168: Urine Sodium and Weight Velocity in Preterm Infants

Background: Preterm infants are at high risk for sodium depletion due to inadequate sodium intake and excessive sodium losses and may explain, in part, the high prevalence of slow somatic growth in this population. In recognition of the high risk for sodium depletion, the American Academy of Pediatrics (AAP) and European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) recommend 3 – 5 meq/kg (69 – 115 mg/kg) of daily sodium intake for preterm infants and recognize that some infants may need up to 8 meq/kg (184 mg/kg) of dietary sodium each day. In response to this dilemma, recent clinical studies suggest that sodium supplementation may improve postnatal growth in preterm infants.
For preterm infants, sodium losses are primarily due to low nephron investment and associated dysmaturity of sodium reabsorption mechanisms leading to excessive losses into the urine. Urine sodium content has been suggested as a potential marker for sodium repletion and institution of a sodium repletion protocol based on gestational age-dependent urine sodium values appears to improve weight gain and head circumference. Although this approach is rationale, correlation studies between urine sodium content and somatic growth are lacking. Here, we measured urine sodium content in a cohort of preterm infants and examined correlations with weight gain during the first month of life and at 36 weeks postmenstrual age (PMA).

Methods: Spot urine sodium was measured in 224 preterm infants ( < 34 weeks postmenstrual age, PMA) between day of life (DOL) 7 and 28 and relationships between urine sodium content and weight velocity (grams/kilogram/day) at DOL 28 and 36 weeks PMA were assessed by multivariate analysis with subgroup comparisons by Student’s t-test and analysis of variance.

Results: In 224 preterm infants (199 ± 17 days, 56% male, 71% Black), urine sodium content did not associate with weight velocity at DOL 28 and 36 weeks PMA. Urine sodium content was weakly associated with gestational age at birth and Black preterm infants had higher urine sodium values when compared with “other” , but not white preterm infants. As seen in Figure 1, a weak statistically significant (p = 0.0257) downward trend for urine sodium content and advancing gestational age was observed and no variation on urine sodium content and day of life for urine sodium measurement was observed. A simple linear model failed to identify (p = 0.6) a relationship between urine sodium content and weight velocity at 28 days of life (Figure 2A). Similar relationships between urine sodium and weight velocity at 36 weeks PMA were examined and no statistically significant relationships were identified (Figure 2B, D, F).

Conclusion: Spot urine sodium during the first month of life does not associate with weight velocity at DOL 28 or 36 weeks PMA.