To investigate treatment, route and dose of prenatal corticosteroids on postnatal lung function, 39 pregnant ewes at 127d GA were randomized to 5 groups: 0.2 mg/kg (0.2E) or 0.5 mg/kg (0.5E) betamethasone based on maternal weight, 0.2 mg/kg (0.2F) or 0.5 mg/kg (0.5F) betamethasone based on estimated fetal weight given by fetal IM injection, or saline for controls. Preterm lambs were delivered 24 h later, treated with Survanta® and ventilated for 4 h.

Dynamic compliances, ventilatory efficiency indices and lung volumes at 35 cmH2O (V35) were higher for the 0.5M and 0.5F than for the other groups (Table). Betamethasone decreased alveolar protein. Large aggregate surfactant (LA) recovered by alveolar wash from all groups had minimum surface tensions below 1 dyne/cm at 0.05 mg lipid/ml. The low surface tensions were inhibited by addition of 1.2 mg/ml plasma (LA + plasma), and LA from the 0.5F and 0.5M was less sensitive to inhibition by plasma protein than the other groups.

Table 1
Full size table

Superior postnatal lung function after the higher betamethasone dose given by either route was associated with reduced protein leak and increased resistance to surfactant inhibition.