Improved oxygenation with exogenous surfactant administration in experimental meconium aspiration syndrome

Fifteen adult New Zealand white rabbits were used to determine if exogenous surfactant immediately improves oxygenation in experimental meconium aspiration syndrome (MAS). They were ventilated with 100% O2 before insufflating 3 mL/kg of 40% filtered meconium. Arterial blood gases, dynamic lung compliance (CLdyn) and resistance (RL) were monitored for 2 hours before and 1 hour after the intratracheal administration of calf lung surfactant extract or air placebo. The arterial/alveolar O2 tension ratio [P (a/A)O2] increased 133% within 1 hour of surfactant therapy but CLdyn did not change. The increase of RL was comparable in the surfactant and control groups after meconium instillation. A further increase of 44% in RL occurred after surfactant administration with no change in the controls. Qualitative histologic analysis confirmed the presence of alveolar meconium as well as inflammation and atelectasis. Persistently elevated RL suggested airway obstruction in both groups throughout the study. Most likely no increase in CLdyn occurred with surfactant administration or it could not be detected because it was measured only with ventilator-induced breaths and ventilator settings were held constant. In the face of airway obstruction CLdyn is an inadequate reflection of pulmonary elasticity. We conclude that exogenous surfactant therapy improves oxygenation in this model of MAS. Further studies are needed to understand the mechanism of this improvement.