A SLE5000 infant ventilator was used as the high-frequency ventilator.HFOV setting were as follows: initial frequency was set between 11 and 15Hz; pressure amplitude of oscillation was initially adjusted to provide adequate chest wall movement and was subsequently titrated to maintain the PaCO2 between 40 and 55 mmHg.Extubation was considered when the patient's condition was stable for 12-24h, while adequate oxygenation could be maintained with an FIO2 <0.3 and respiratory rate <25/min.

A Servo-i-Maquet will be used as the conventional mechanical ventilator. CV settings were: exhaled tidal volumes set at 5-6 mL/kg, initial peak inspiratory pressure (PIP) of 15-25 cmH2O; positive expiratory end pressure (PEEP) set to 4-6 cmH2O; inspiratory times of 0.25-0.40s; rates set to <60/min. The weaning process was initiated when the following parameters were achieved: PIP <18 cmH2O, PEEP <4 cmH2O, and FIO2 <0.4. Extubation was considered when the patient's condition was stable for 12-24h, while adequate oxygenation could be maintained with an FIO2 <0.3 and respiratory rate <25/min. All infants extubated onto nasal continuous positive airway pressure (Infant Flow, Electro Medical Equipment) and then weaned to a nasal cannula, and then to room air.

Ventilation strategies for both groups were to emphasize lung recruitment and avoid atelectasis and over distention. The optimum lung volume was determined as expansion to 8 to 9.5 ribs for most infants, and 7 to 8 ribs for infants with air leak. HFOV setting were as follows: initial frequency was set between 11 and 15Hz; pressure amplitude of oscillation was initially adjusted to provide adequate chest wall movement and was subsequently titrated to maintain the PaCO2 between 40 and 55 mmHg; The initial mean airway pressure (MAP) was set at 8-10 cmH2O. MAP and FIO2 were set to maintain arterial oxygen saturation between 88 to 95%, an arterial pH of at least 7.25. Extubation was considered when MAP was ≤7 cmH2O and the pressure amplitude of oscillation reach 10 to 15 cmH2O.

To count the number of patients with bronchopulmonary dysplasia at 36 weeks of postmenstrual age.

To calculate how many days of the newborn baby with mechanical ventilation either HFOV or CV at 36 weeks postmenstrual age.