Inclusion Criteria:  Severe acute cholangitis of either sex Aged between 21-70 years Undergoing urgent therapeutic ERCP for severe cholangitis with American Society of Anaesthesiologist (ASA) Grade II - III.  Exclusion Criteria:  Patients who had ASA physical status Grade VI, Baseline SpO2 <90%, Patients who had difficulty in communication, Patients allergic to the studied medications, Morbidly obese patients, Patients with chronic obstructive pulmonary disease, Complicated airway, Pregnant patients.