Functional residual capacity and passive compliance measurements after antenatal steroid therapy in preterm infants

Studies in preterm animal models have shown that antenatal corticosteroids enhance lung maturation by improving a variety of physiologic variables, in cluding lung volumes. Changes in lung volume of preterm infants treated wit h a full course of antenatal steroids have not been investigated. We hypoth esized that a full course of antenatal steroids would significantly increas e functional residual capacity (FRC) in treated vs, untreated preterm infan ts. The objective of our study was to compare FRC and respiratory mechanics in steroid treated vs. untreated preterm infants. FRC and passive respirat ory mechanics were prospectively studied within 36 hr of life in 20 infants (25-34 weeks of gestation) who had received a full course of antenatal ste roids and in 20 matched untreated preterm infants. FRC was measured with th e nitrogen washout method, and respiratory mechanics with the single-breath occlusion technique. Preterm infants who received steroids (n = 20; mean birth weight = 1,230 g; gestational age = 28.8 weeks) had a significantly higher FRC (29.5 vs. 19. 3 mL/kg; P < 0.001) than un treated infants (n = 20; birth weight = 1,202 g ; gestational age = 28.5 weeks). Passive respiratory system compliance was also increased in treated vs. untreated infants (P < 0.05). In conclusion, FRC and passive respiratory system compliance were significa ntly improved in preterm infants (25-34 weeks gestation) treated with a ful l course of antenatal steroids, compared to matched untreated infants. Alth ough this study was not randomized, it confirms that antenatal steroids hav e important effects on pulmonary function that may contribute to a decrease d risk of respiratory distress syndrome in treated preterm infants. (C) 200 1 Wiley-Liss, Inc.