Hyaline membrane surfactant prophylaxis in the preterm baboon: A comparison of postpartum versus in utero therapy

Objective: Intra-amniotic administration of surfactant (IAS) in the preterm baboon 24 h before delivery reduces the clinical and pathological aspects of hyaline membrane disease (HMD) when compared to saline controls. The purpose of this study is to describe clinical, radiographical, and pathological endpoints of HMD in the preterm baboon treated with a single intratracheal dose of surfactant (ITS) for comparison with those of IAS and intra-amniotic saline-treated control groups. Methods: Five preterm baboons received control intra-amniotic saline injections before delivery and ITS (4 ml/kg Survanta, Ross Laboratories, Cincinnati, Ohio) following delivery. An additional saline-treated baboon was delivered but not given surfactant. Fetuses were delivered at 137-139 days' gestation, maintained for 24 h using standard neonatal intensive care techniques and assessed for study endpoints. These data were compared to those from our previous report to assess differences between intratracheal and intra-amniotic administration of surfactant and controls. Results: Compared to saline controls, ITS- and IAS-treated animals had significantly better clinical courses, as documented by PaO₂/PAO₂ (p < 0.05), FiO₂ (p < 0.01), and PaCO₂ (p < 0.05). Saline controls had significantly more evidence of HMD than intra-amniotic and intratracheal surfactant-treated animals in blindly scored radiographs (p < 0.03). Using a panel-of-standards method blindly to score pathological findings in the fixed left lung, those treated with intra-amniotic and intratracheal surfactant had significantly more inflation (p < 0.05) than saline-treated animals. ITS- and IAS-treated animals had no differences in study endpoints. Animals receiving intratracheal surfactant tended to have residual inflation in the central and medial aspects of each lobe, in contrast to intra-amniotic surfactant-treated animals which had a more even distribution of inflation. Conclusion: Intratracheal surfactant treatment improves the clinical, radiographical and pathological aspects of respiratory distress in the preterm baboon, but does not prevent hyaline membrane disease in this established model. Variations in distribution of inflation between intratracheal and intra-amniotic surfactant-treated animals suggest differences in pulmonary distribution of surfactant that depend on the route of administration.