The sample size estimation was estimated from the cue that the average propofol doses required for maintenance of anaesthesia (4.7+ 1.6 mg/kg/hr) when using manual propofol and remifentanil target controlled infusion18 with a 90% power employed to detect a 30% decrease of propofol dosage among the patients who will receive dexmedetomidine in addition to base anesthetic propofol; with a bilateral α risk value of 0.05, the investigators would require 66 patients for the study. To cover up for unanticipated losses the investigators would need additional 20% patients. Thus the investigators would require 80-patients for the study