AS enhance lung function in the scenario of preterm delivery. Gravidas who remain undelivered after initial therapy with betamethasone (BMZ) (two 12mg doses), are often repetitively dosed at 7 day intervals until delivery. The efficacy of repetitive dosing (REP) with AS is unknown. To evaluate the effect of REP dosing on lung volume and pulmonary mechanics, we measured FRC and Crs within the first 24 hours of life in preterm infants 25 to 34 weeks of gestation. 24 infants (mean BW=1686g, GA 31.0 wks, 54% male, 8% treated with surfactant(S)) received REP AS (2 or more courses of BMZ with delivery within 14 days of the last dose). 31 infants (mean BW=1602g, GA=30.7 wks, 32% male, 6% treated with S) received a single course (SC) of AS (2 doses BMZ with the first at least 24 hours prior to delivery and the last within 7 days of delivery). 24 control infants (mean BW=1596g, GA=30.9 wks, 50% male, 54% treated with S) received no AS. FRC was measured with the nitrogen washout technique within 24 hours of age, and prior to surfactant therapy if required. A minimum of two measurements were performed with the neonate supine and quiet. Only consistent tracings initiated at end expiration and without evidence of a leak were accepted. A study was acceptable if the measurements had a coefficient of variation less than 10%. Crs was measured using the single breath occlusion technique (SensorMedics 2600). FRC and Crs are shown as mean±SEM. REP AS and SC AS, when given in a timely manner, significantly increase FRC and Crs in preterm infants when compared to controls. We speculate that the comparable increase in FRC and Crs after REP AS vs SC AS may be secondary to the continued induction of biochemical effects that would have dissipated 7 to 14 days after initial dosing.Table

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