Ninety patients with ASA 1-2 requiring painless colonoscopy for colonic polyps resection were randomized to receive DEX 0.3 micro ; g/kg ( group D , n = 45 ) followed by propofol 1 mg/kg or propofol 2 mg/kg ( group C , n = 45 ) , and according to the body activity and operation time , additional doses of propofol ( 0.2-0 .5 mg/kg ) were given .