Evidence of fetal pulmonary aspiration of intra-amniotic administered surfactant in animal experiment

Introduction: The instillation of surfactant into the airways of patients with respiratory distress syndrome (RDS), especially in the neonatal period, is a proven therapy. The preventive therapy of RDS through intra-amniotic injection of surfactant has been reported recently. It has not been conclusively shown, however, that the surfactant administered in this way actually reaches the fetal pulmonary airways. Objective: To study the distribution in fetal organs of a natural surfactant labeled with technetium-99m and injected through amniocentesis into the amniotic sac of guinea pigs in the last third of pregnancy. Methods: After stimulating fetal respiratory movements with aminophylline 0.3 ml of an aqueous suspension containing 0.75 mg of phospholipids of a natural bovine surfactant labeled with technetium-99m, together with 0.1 ml of the biological dye carmine indigo, were injected into the amniotic sac. One hour later fetuses were delivered by cesarean section. In those that were dye-stained, dosimetric and gammagraphic tests were applied to trachea, lungs, esophagus, stomach, heart, liver, kidneys and placenta. Results: Significant radio isotopic activity was found in both lungs of six treated fetuses, with a dose capture of between 1.0% and 5.3% of total dose. The level of activity in the stomachs was similar to that in the lungs (0.9% to 3.0% dose capture), whereas activity in other organs was negligible except in two placentae. No radio isotopic activity was found in non-injected control fetuses. Conclusions: In the present animal model natural surfactant injected intra-amniotically is aspirated into the lungs within one hour.