Postnatal lung function after fetal betamethasone retreatment in preterm lambs

Rapid (24 h), persistent (7 d) improvement in postnatal pulmonary function occurs in preterm sheep after a single fetal dose of betamethasone. Augmented pulmonary function is similar among animals studied 1 d, 4 d or 7 d after injection. To test the effect of retreatment, we determined compliance (Comp, ml/cm H2O·kg), ventilation efficiency index (VEI, an integrated measure of ventilation and pCO2) and total lung volume at 40 cm H2O (V40, ml/kg) in preterm (128 d gestation) lambs following 40 min of ventilation. Fetuses received an initial dose of betamethasone (0.5 mg/kg) followed 6-7 d later by either saline (Beta/Saline group) or a second dose of betamethasone (Beta/Beta). A third group of fetuses receiving only saline was included (Saline/Saline); all lambs were studied 24 h after retreatment. Group n VEI V40 Comp Saline/Saline 7 4.48 ± 0.58 * 19.4 ± 3.2 * 0.22 ± .02 * Beta/Beta 8 7.04 ± 1.18 39.9 ± 5.6 0.31 ± .02 Beta/Saline 7 6.86 ± 0.73 39.2 ± 4.8 0.31 ± .03 Data are reported as mean ± SEM. * differs from steroid-treated fetuses, p<0.05 Conclusions: While steroid exposure clearly improved postnatal lung function, no effect of retreatment was noted. Speculation: Strategies relying on repeated steroid exposure to improve preterm pulmonary outcome are ineffective.