Maintenance Fluids for Late Preterm and Term Infants: Is it Time to Reconsider?

Abstract

Background: Late preterm and term infants represent the majority of neonatal intensive care unit admissions globally, yet their fluid management remains underexplored.

Methods: We conducted a retrospective medical record review of 174 infants 34 weeks' gestational age or older who received dextrose-containing fluids shortly after birth. These infants had 24-hour serum sodium measurements at our institution between April 2018 and April 2021. We used regression models to analyze the correlation among intravenous fluid (IVF) intake per kilogram, gestational age, fluid balance (FB), weight change, and sodium status, adjusting for clinical factors.

Results: At 24 hours, the average IVF intake was 57.2 mL/kg/d (SD 14.9). Of the infants, 130 (75%) had positive FB, 128 (74%) maintained or gained weight, 41 (24%) had sodium levels 132 mEq/L or less, and 68 (39%) had sodium 134 mEq/L or less. Positive FB was associated with weight gain and an increased likelihood of hyponatremia. Regression analysis showed a 0.07-mEq/L decrease in serum sodium (95% CI, -0.09 to -0.05; P < .001) for every milliliter per kilogram of positive FB and a 6% increase in the odds of sodium 132 mEq/L or less (95% CI, 1.03-1.08; P < .001). Term infants exhibited greater decreases in sodium levels than preterm infants. Infants who did not receive enteral feeds had more pronounced sodium decreases compared with those who were fed.

Conclusion: Positive FB was common and strongly associated with hyponatremia in infants receiving standard IVF rates. These effects were most significant in term and unfed infants. Current fluid strategies may overestimate needs, particularly for term infants not receiving enteral feeds.