Outcome of interest Primary outcomes were to determine the predictors of difficult bag mask ventilation. The difficult bag mask ventilation was defined as the occurrence at least 2 following events which were requiring application of CPAP with opening airway maneuvers, requiring oropharyngeal airway or nasopharyngeal airway, requiring 2- person bag mask ventilation, unable to perform bag mask ventilation or presence of desaturation (SpO2 < 95%).