BACKGROUND:RDS is usually defined by the presence of acute respiratory distress with disturbed gas exchange in a preterm infant with a typical clinical course or x-ray.The main risk factor for RDS,by far,is prematurity.The central feature of RDS is surfactant deficiency due to lung immaturity,commonly due to prematurity.Surfactant replacement therapy reduces mortality and several aspects of morbidity in babies with RDS.