From December 2011 to March 2013 , 107 preterm infants with RDS who received intubation-pulmonary surfactant ( PS ) - extubation in our NICU were randomly divided ( by means of random number table ) into three groups based on the primary mode of ventilation : nasal continuous positive airway pressure [ NCPAP , n = 39 , male/female ratio was 27/12 , mean gestational age ( GA ) was ( 32.0 2.1 ) weeks , mean birth weight ( BW ) was ( 1752 457 ) g ] , bi-level positive airway pressure [ BiPAP , n = 35 , male/female ratio was 25/10 , GA was ( 31.4 2.0 ) weeks , BW was ( 1530 318 ) g ] , and synchronized bi-level positive airway pressure [ SBiPAP , n = 33 , male/female rate was 25/8 , GA was ( 31.5 2.2 ) weeks , BW was ( 1622 447 ) g ] .