Inclusion Criteria:  BMI >30 kg/m2 Mallampati class III or IV Requiring general anesthesia  Exclusion Criteria:  Acute and chronic respiratory disorders, including Chronic obstructive pulmonary disease(COPD)and asthma American Society of Anesthesiologists (ASA)physical status classification ≥IV Emergency surgery Induction requiring rapid sequence for intubation Patients requiring awake intubation Pregnant women Untreated ischemic heart disease Contraindication for mask ventilation