Inclusion Criteria:  Gestational age (GA) of less than 30 weeks or birth weight less than 1500g Clinical diagnose of RDS and Oxygenation index(OI=(FiO2×Paw)×100/PaO2) more than 2 Age less than 2 hours  Exclusion Criteria:  Intubated for resuscitation or for other reasons at birth  Major congenital malformations or known complex congenital heart disease No parental consent