The primary aim of this work is to evaluate the role of high frequency oscillatory ventilation (HFOV) in recruitment of lung in preterm newborns 32 to 37 weeks gestational age with moderate to severe respiratory distress. The secondary aim is to evaluate the role of chest ultrasound in monitoring of lung recruitment in comparison to routine chest x ray in those babies. Also cardiac hemodynamics will be assesed using functional echocardiography.

Inclusion Criteria:

• Infants will be enrolled if they are 32 to 37 weeks of gestational age, have respiratory distress (RD) in the first 24 h of life, intubated and have invasive respiratory support using HFOV. Signs of RD are tachypnea (respiratory rate > 60/min), grunting, nasal flaring, chest retraction, and need of oxygen supplementation or other respiratory support.

Exclusion Criteria:

1. Known major congenital anomalies including congenital heart diseases.
2. Fetal hydrops.
3. Babies with congenital heart diseases