Timing of Surfactant Administration Determines Its Physiologic Response in a Rabbit Model of Airway Lavage

Surfactant response depends on timing of surfactant administration in infants with respiratory distress syndrome (RDS). We performed lung function studies in an animal model to describe the underlying differences in response related to gas exchange, lung volume and lung mechanics comparing early and late surfactant administration protocols. Young New Zealand rabbits were made surfactant deficient by repeated airway lavage with warm saline until the a/A O 2 ratio decreased to ≤0.12. A natural ovine surfactant was administered at 1 h (early intervention) or at 3 h (late intervention) after the last lavage. Functional residual capacity (FRC), a/A O 2 ratio, effective breath fraction (EBF = V A /V T ), ventilation efficiency index (VEI), dynamic compliance (C rs ), nitrogen clearing index (NCI) and specific (volumic) compliance (sC rs = C rs /FRC) were followed for 2 h after surfactant administration. FRC, a/A O 2 ratio, VEI, C rs and sC rs were all significantly different between the two intervention groups in favor of the surfactant administration protocol at 1 h after lavage. EBF and NCI were not affected by timing of surfactant administration. We conclude that early surfactant administration elicits a superior response related to gas exchange, lung volume and lung mechanics in this animal model. These findings are in line with the more pronounced surfactant effects in the clinical setting when premature infants with RDS are treated using early intervention protocols.