 Preterm infants will be recruited consecutively from NICU of Mansoura University Childrens Hospital. They will be randomized in two groups; one group will start on nasal CPAP Fisher Paykel Healthcare, Auckland, New Z ealand Pressure 5 cmH2O for 60 minutes and then will be switched to HHHFNC Fisher Paykel Healthcare, Auckland, New Z ealand flow of 4 lm for another 60 minutes. The other group will start on HHHFNC and then switched to nasal CPAP. 