How does surfactant really work?

Although administration of exogenous surfactant to the neonate with RDS often relieves hypoxia rapidly, it is events occurring some 18-48 h later that determine the ultimate clinical outcome, indicating a vital second stage to 'rescue'. It is proposed that, whereas a reduction in surface tension facilitates the initial penetration of the lungs by air, the second stage is provided by surface-active phospholipid (SAPL) slowly adsorbing (binding) to alveolar epithelium to displace water in the same way that surfactants are widely used industrially as 'de-watering' agents. In the normal newborn, this de-watering lining of SAPL is already in place, explaining the extremely rapid expulsion of fluid from the lungs at birth. The selection or formulation of a surfactant for rescue should thus take both stages into consideration.