Routine monitoring of ECG, pulse oximetry, non-invasive blood pressure will be established before induction of sedation. BIS three electrodes sensor will be applied over the patient's forehead using fronto-temporal montage for the monitoring of level of sedation . The baseline variables will be recorded and documented as well as continuous monitoring and documentation every 5 min for the first 30 min and every 10 min till the end of procedure. Supplemental oxygen will be administered with nasal prongs at 3 l.min-1. The total duration of the procedure, defined as the time taken from insertion of the endoscope to its removal, will also be documented.