METHODS: Seventy patients were randomly divided into 2 groups . All patients were of American Society of Anesthesiologists (ASA) physical status of I-III, aged more than 65 years old and between 45 and 100 kg in weight. The induction Cet was targeted respectively at 1 and 2 ug/ml. Upon reaching the modified observer's assessment of alertness/sedation(MOAA/S) score 0-3, the Cet was increased or reduced during the procedures and the Ce level was set for the maintenance of sedation. Induction time, diagnostic procedures as well as the occurrence of adverse events such as apnea , hypotension or hypertension, heart rate, oxygen saturation (SpO2) ,any cardiac event, cough score, frequency of adjustments of drug doses were recorded.