 Initial nHFOV settings are: MAP: 8cmH2O, Frequency:10 MHz, Amplitude:35 cmH2O will be adjusted to achieve adequate chest wall vibration, I:E1:1 and FiO2: adjusted to keep preductal sPO2 between 90-95. Initial nCPAP settings are: PEEP:6 cmH2O and FiO2: adjusted to keep preductal sPO2 between 90-95. Failure of the primary mode is defined as FiO2 requirement of 60, capillary blood gas obtained at the 4th hour of therapy showing pH7.20 or pCO265 cmH2O. When nCPAP or nHFOV failure occurs, nasal intermittent positive pressure ventilation nIPPV will be applied as a rescue therapy with the following settings: Frequency:30min, PIP:18 cmH2O, PEEP:6 cmH2O, inspiration time:0.50 sec., inspiratory flow:10 Lmin, FiO2:adjusted to keep preductal sPO2 between 90-95. If the rescue mode fails, the infant will be intubated and conventional mechanical ventilation will be initiated. 