Effect of intra-amniotic administration of Exosurf in preterm rabbit fetuses

Currently, treatment of respiratory distress syndrome (RDS) of the preterm newborn incorporates exogenous surfactant administration. Because fetuses make breathing motions, we proposed that intra-amniotic administration of an exogenous surfactant, Exosurf, to the preterm rabbit fetus results in uptake of Exosurf into the lungs and improves pulmonary mechanical properties compared with post-delivery treated and untreated litter mates.

Ten preterm rabbit fetuses were used in a labeling study. A mixture of iron dextran and Exosurf was given in utero, and the minimum dose required to assure delivery of the mixture into the distal airways was 5 mL. In a lung function study, 30 rabbit pups received either 5 mL Exosurf in utero, 0.2 mL Exosurf post-delivery, or no treatment. Pressure-volume curves, opening pressures, and lung volumes at 50 cm H2O were compared among the three groups.

Those rabbit pups receiving Exosurf either in utero or after delivery had significantly better pressure-volume relationships (P less than .001) and lower opening pressures (P less than .005) than the rabbit pups with no treatment. There were no differences between the animals treated intra-amniotically and post-delivery.

Intrauterine administration of exogenous surfactant results in uptake of the surfactant solution into the lungs and alters the pulmonary characteristics of the preterm rabbit pup. Potential adverse effects of this means of surfactant administration must be evaluated further. Intrauterine surfactant delivery may provide an additional means of RDS prophylaxis in the antepartum period.