Sedation can range from moderate to deep sedation, including General anesthesia.Intravenous sedation could depress the respiration, increase the risk of upper airway obstruction by relaxation of respiratory muscles, hypoxia and aspiration. Hypoxemia further increases periprocedural myocardial infarction,arrythmias and cerebral hypoxia.Usually, patients with complex co-morbidities:Obstructive sleep apnea syndrome, obesity, hypertension, DM, cardiac disorders, advanced age, high ASA physical status have increased risk of hypoxemia. Therefore, supplemental oxygen is provided to all patients undergoing ERCP using standard nasal cannula that can provide maximum up to 6L/min but the Fio2 is not more than 40% . The presence of the Endoscope precludes the use of face mask for delivering higher concentrations of oxygen. High flownasal oxygen is a new approach that provides heated and moist oxygen at a much higher gas flow rate (up to 70L/min), Fio2 up to 100%, provides flow dependent positive airway pressure to increase end expiratory lung volume, thus decreasing the work of breathing.

                     The HFNC is also used in perioperative setups including preoxygenation, airway management, awake intubation. However, use of HFNC has not been extensively studied in complex gastrointestinal procedures like ERCP.Thus, this study is intended to compare effect of high flow nasal cannula versus low flow nasal cannula on oxygenation in patients undergoing endoscopic retrograde cholangiopancreatography under sedation.