Nasal High Frequency Oscillation Ventilation(NHFOV) for Respiratory Distress Syndrome

Inclusion Criteria: * The gestational age was less than 37 weeks; * These neonates were diagnosed with RDS and supported by invasive ventilation with synchronized intermittent mandatory ventilation (SIMV. The diagnosis of RDS was based on clinical manifestations and chest X-ray findings. The clinical signs and symptoms of RDS were respiratory distress, tachypnea, nasal flaring, groan, and cyanosis after birth. The typical X-ray picture of RDS showed a grain shadow, air bronchogram or white lung; * The neonates were ready to be extubated for the first time and subsequent noninvasive ventilation. Exclusion Criteria: * parents' decision not to participate; * major congenital anomalies; * died or left the NICU within 24 hour. Eligibility criteria for extubation: Besides the improved symptoms, X-rays and sufficient spontaneous breathing efforts, the eligibility criteria for extubation were peak inspiratory pressure (PIP) of 15-20 cm H2O, positive end expiratory pressure (PEEP) of 4-6 cm H2O, respiratory rate of 15 to 30, FiO2 from 0.21 to 0.30, hematocrit more than 35%. and arterialized capillary blood gas analysis need to meet the following criteria: pH\>7.20, PaCO2\<=55 mmHg.