The procedure will be started once the patients feel that they are relaxed. Vital signs including NIBP, SpO2, HR, RR, and OAA/S will be monitored throughout the sedation and procedure process every 5 minutes. If the patient becomes totally unresponsive or any adverse event occurs, the procedure will be stopped. If the SpO2 falls to below 90% for more than 10 seconds, the endoscope will be removed and the patient's vital signs observed, and O2 administered as required by the attending anesthesiologist until the patient becomes responsive again. Once the patient starts responding to command, the procedure will continue. Duration of unresponsiveness would be recorded. The time of start of procedure and duration of procedure and the frequencies of interruption due to patient events will be noted. The PCS propofol and alfentanil will be terminated and disconnected from the patient when the endoscopist indicates that the operative procedure is completed, and the dose consumption recorded. The endoscopist will determine the operating conditions by evaluating the ease of insertion and the patient's lack of motion and ability to obey commands, using NRSsatisfactionendoscopist.