Effects of prenatal steroids on water and sodium homeostasis in extremely low birth weight neonates.

OBJECTIVE: We sought to determine if prenatal steroid (PNS) treatment affects water and sodium (Na) balance in extremely low birth weight infants (<1000 g).

METHODS: PNS treatment enhances lung maturation in preterm infants and induces maturation of renal tubular function and adenylate cyclase activity in animals. We compared water and Na homeostasis for the first week of life in those infants whose mothers received steroids before delivery (PNS: n = 16) to those who did not (nonsteroid group [NSG]: n = 14). The data were collected prospectively, but PNS treatment was not given in a randomized manner. Fluids were initiated at 100 to 125 mL/kg/d and adjusted every 8 to 12 hours to allow a daily weight loss of </=4% of birth weight and to maintain normal serum electrolytes. Weight, serum and urine electrolytes, and urine output were frequently measured and fluid intake was adjusted by increasing the amount of free water to achieve these goals.

RESULTS: When using our fluid management protocol, the percent weight loss in both groups was equivalent during each of the 7 days (15% PNS vs 17% NSG maximum loss) as well as the cumulative urine output at 1 week of age (663 mL/kg/wk PNS vs 681 mL/kg/wk NSG). PNS infants had a higher urine output on the first 2 days of life and a lower daily fluid intake for the first week. PNS infants also had significantly less insensible water loss for each of the first 4 days of life. The PNS group had a significantly lower mean peak serum Na of 138 +/- 1 mmol/L vs 144 +/- 2 mmol/L and none had a peak serum Na >150 mmol/L compared with 36% of the NSG infants. PNS infants had a higher cumulative Na excretion at day 2 of life (10 +/- 2 mmol/kg vs 6 +/- 1 mmol/kg) but a less negative cumulative Na balance at 1 week (-10 mmol/kg vs -14 mmol/kg).

CONCLUSION: PNS treatment was associated with lower estimated insensible water loss, a decreased incidence of hypernatremia, and an earlier diuresis and natriuresis in extremely low birth weight neonates. We speculate that PNS effects these changes through enhancement of epithelial cell maturation improving skin barrier function. PNS treatment may also enhance lung Na, K-ATPase activity leading to an earlier postnatal reabsorption of fetal lung fluid increasing extracellular volume expansion to help prevent hypernatremia.