Inclusion Criteria:  Preterm newborns between 26+0 and 36+6 weeks of gestation stratified in two groups: VLBWI 26-31+6and LBWI 32-36+6. Respiratory distress syndrome requiring surfactant therapy  Exclusion Criteria:  Need for emergency intubation in the delivery room Major congenital malformations (such as cardiopathies) Chromosomic abnormalities Fetal Hydrops Hypercapnia: CO2 > 65 mmHg Pneumothorax Hemodynamic compromise