Inclusion Criteria:  patients undergoing elective ERCP with deep sedation will be enrolled age 18 - 70 years old obesity (BMI 30-35 kg/m2) American Society of Anaesthesiologists' physical status classification of 1 to 3 Anticipated duration of the procedure is > 15 minutes.  Exclusion Criteria:  • BMI >35 kg/m2  Simple procedures of < 15 minutes duration. untreated or unstable cardiac conditions Nasal or oral disease resulting in difficulty of either nasal breathing or mouth breathing. Acute or chronic respiratory disorders as asthma and chronic obstructive pulmonary disease. Pregnant patients and patients having procedures with planned endotracheal intubation Expected difficult intubation patients.