Surfactant Replacement Therapy

Despite medical and technological advances, respiratory distress syndrome (RDS) remains a major cause of morbidity and mortality in premature infants. Thirty years have passed since Avery and Mead demonstrated that infants dying of RDS were deficient in pulmonary surfactant. In those three decades, advances in our understanding of the composition, function, and metabolism of pulmonary surfactant have finally led to clinical trials of surfactant replacement therapy in thousands of premature infants. This article reviews the current status of surfactant replacement therapy. BACKGROUND Pulmonary surfactant is essential for normal lung function. Surfactant forms a film at the alveolar surface, which prevents the lung from collapsing at the end of expiration. Surfactant may have other functions as well, including the prevention of pulmonary edema, the prevention of infection, and the prevention of lung injury from toxic substances, such as oxygen (Table 1) CHEMICAL MAKEUP The chemical makeup of pulmonary surfactant has been well defined (Table 2). Lipids are the major component, comprising up to 80% to 90% of surfactant by weight. The majority of the lipids in pulmonary surfactant are highly polar phospholipids, predominantly phosphatidylcholine. Three proteins associated with surfactant have been these surfactant proteins may play a critical role in surfactant function by improving the adsorption of surfactant at the alveolar surface and by aiding in surfactant re-uptake and metabolism.