One of the most commonly used non-invasive methods is nasal continuous positive airway pressure (nCPAP). Although high frequency ventilation (HFV) has been applied in many neonatal intensive care units, nasal high frequency oscillatory ventilation (nHFOV) is a relatively new non-invasive modality. The application of nasal high-frequency ventilation with the strategy of lung recruitment will combine benefits of improving gas exchange and decreasing lung injury together with avoiding complication of invasive ventilation.

Premature infants with respiratory distress syndrome (RDS) usually require respiratory support . Due to the complications of intubation and mechanical ventilation, in the last decade, attempts have been made to use non-invasive methods in the management of these patients . Over the past few decades, nasal ventilation has been used to control and improve respiratory failure in infants with RDS . nCPAP is a relatively simple and effective therapy in the early management of RDS in newborns . nCPAP is the application of positive pressure to the airways of spontaneously breathing neonates throughout the respiratory cycle . However, some neonates with this therapeutic approach also develop respiratory failure and need mechanical ventilatory support. According to some investigations, 43%-80% of infants with moderate to severe respiratory failure who are initially treated with nCPAP need mechanical ventilation .

In recent years, the beneficial effects of high-frequency ventilators (HFV) have been shown in the management of RDS as well as the use of this mode as the initial mode of support or as a rescue treatment after failure of conventional mechanical ventilation. In high-frequency ventilation, a low tidal volume with a higher frequency than that of physiological respiration is produced. This technique is very effective in eliminating carbon dioxide (CO2). Adequate recruitment of lung volume in this mechanical mode has the main role of protecting and preserving lung architecture as well as potentiating surfactant therapy.

The nHFOV is a non-invasive ventilation mode that applies an oscillatory pressure waveform to the airways using a nasal interface. nHFOV is effective and superior to nasal intermittent positive pressure ventilation in terms of lung CO2 elimination. This mode has been shown to facilitate CO2 elimination, but little is known about its use in neonates. There is increasing evidence of beneficial effects of nHFOV in reducing the duration of ventilator support compared with the effects of nCPAP in RDS. We intended to explore the benefits of nHFOV vs nCPAP in preterm neonates.

Inclusion Criteria:

• Gestational age: 30-34 weeks (determined by date of last menstrual period or ultrasound) and confirmed by Ballard score.
• Recruited immediately after birth Up to 24 hours of age.
• Appropriate weight for the gestational age.
• Spontaneous breathing and clinical signs and symptoms of respiratory distress syndrome (grunting, cyanosis, intercostal and subcostal retractions) or RDS Silverman Score > 5.

Exclusion Criteria:

• Major congenital abnormalities, congenital heart disease and diaphragmatic hernia.
• A need for intubation and mandatory ventilation during resuscitation or on the first day of life.
• Perinatal asphyxia (Umbilical cord pH < 7.16, and umbilical cord bicarbonate < 12 mEq/L)
• Pulmonary hemorrhage and severe intraventricular hemorrhage (IVH) on admission.

data can be shared upon accepted reasons