Which of the following statements about pulmonary surfactant are true?

a. Endogenous surfactant deficiency is the key physiologic problem in preterm infants with the infant respiratory distress syndrome

c. Exogenous surfactant replacement has been shown to reduce mortality in preterm infants with the infant respiratory distress syndrome

The pulmonary surfactant complex lowers surface tension, stabilizing the alveolus even at low lung volumes. It is a complex material secreted by Type II alveolar epithelial cells. It is composed of 80 to 90 percent phospholipid (primarily phosphatidylcholine) and unique surfactant-associated proteins (10 percent). Surfactant proteins appear to play a critical role in the organization of the phospholipid molecules, and modify the surface-active properties of the lipids. Phospholipid synthesis and the expression of surfactant proteins increase with advancing gestational age. Amniotic fluid surfactant concentrations have been used for many years to predict pulmonary maturity. Surfactant deficiency is the primary factor in the pathophysiology of the neonatal respiratory distress syndrome. The use of exogenous surfactant replacement therapy is currently under investigation for the treatment of neonatal respiratory distress and has been shown to reduce mortality in a variety of specific circumstances involving preterm infants. Several commercially available preparations are available and are undergoing clinical investigation.