Surfactant supplementation in the preterm rabbit: effects of applied volume on compliance and survival.

Preterm rabbit neonates, delivered on the 27th day of gestation, were treated before the first breath with a tracheal instillation of ESA, a suspension of lipids extracted from pulmonary surfactant. Lung compliance development and neonatal survival were studied after treatment to determine the effect of suspension volume and concentration. Compliance development was not dependent on either delivery volume or suspension concentration, but rather on the quantity of phospholipids instilled. Indices of improved expansion and stability demonstrated a dose response relationship up to 1.1 mg phospholipid per g lung. Larger doses neither improved nor detracted from the response. The ability of the neonates to survive and adapt to an air breathing environment was influenced by the instillation volume. Viability was reduced when the treatment volume exceeded 16% of the functional residual capacity. Prophylactic surfactant supplementation therapy may be useful in preventing the development of neonatal respiratory distress syndrome. Surfactant extract may prove acceptable for both prophylaxis and treatment of established respiratory distress syndrome.