Testing surfactant treatment responses: a comparison of two models

We have compared treatment responses of two surfactants in two animal models of respiratory distress syndrome. Preterm rabbits at 27 days gestation and premature lambs at 126 days gestation were treated with natural sheep surfactant Survanta (Ross Laboratories), or no surfactant and then were ventilated with the same ventilation style to achieve tidal volumes of 8 ml/kg. Dynamic compliances at 15 min were higher for control and surfactant-treated rabbits than for preterm lambs. Sheep surfactant and Survanta increased compliances in rabbits, but only sheep-surfactant-treated lambs had compliances higher than controls at 15 min of age. Maximal lung volumes (milliliters per kilogram) of the rabbits (after 15 min ventilation) were about twice those of the lambs (after 4 h of ventilation). Lung volumes of sheep-surfactant-treated rabbits were larger than for Survanta-treated rabbits, but no differences in lung volume were evident between the surfactant-treated lambs. The two models for testing surfactants do not give the same results when directly compared.