In very preterm infants with severe respiratory distress syndrome(RDS), invasive ventilation(IV) , besides nasal continuous positive airway pressure (NCPAP) and early/selective pulmonary surfactant administration, is one key cornerstone to reduce neonatal mortality. However, IV is related to increased risks of bronchopulmonary dysplasia (BPD) and abnormal developmental outcomes in the survival.Weaning from IV is therefore a key procedure to reducing these risks above, and if extubation does not success, repeated intubation and/or prolonged duration of IV will result in increased medical burden and intubation-associated complications and death. How to minimize the need for endotracheal ventilation and subsequent complications constitutes a challenge for neonatologists.

Early weaning from invasive ventilation and avoiding re-intubation remains a focus. Nowadays, early use of noninvasive respiratory support strategies has been suggested to be the most effective pathway to reduce those risks. NCPAP is a widely used way of noninvasive ventilation strategies in preterm infants. However, there is only 60% success rate in avoiding intubation. Supplying with the combined advantages of HFOV and NCPAP with high CO2 removal, no need for synchronisation, less volume/barotraumas, non-invasion and increased functional residual capacity, nasal high frequency oscillation ventilation (NHFOV) is considered as a strengthened version of NCPAP. Thus, NHFOV may be more effective as post-extubation respiratory support to avoid re-intubation and subsequent complications/sequelae comparing with NCPAP in preterm infants. To date, NHFOV was used increasingly in neonatal intensive care unit (NICU) around the world due to its convenient operation and no consideration of synchronisation, and several small studies have reported the beneficial effects of NHFOV in preterm infants. However, there were rare randomized controlled studies compared NHFOV with NCPAP as post-extubation respiratory support strategies in preterm infants.

The purpose of the present study was to compare NHFOV with NCPAP as post-extubation respiratory support on the need for endotracheal ventilation and subsequent complications in preterm infants.

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.