Abstract: Abstract Objective:To investgat whether supplemental fentanyl 50μg decreased the effective concentration for 50% of the attempts to secure laryngeal mask insertion of propofol using a target controlled infusion technology. Method: eighty-four elective patients were divided into 2 groups by ages and then randomly assigned to four groups (n = 21 for each group) and given saline (control) or fentanyl 50μg. Propofol target concentration was determined and EC50 was calculated by a modification of Dixon's up-and-down method. Complication occurrence of circulation and respiration system and awareness were record during the insertion. Results: The EC50 of normal group without tentanyl was 4.03土0.21μg.ml-1，normal plus fentanyl 3.07土0.23μg.ml-1，and in geriatric group3.76土0.42μg.ml-1，geriatric plus fentanyl2.35土0.22μg.ml-1。The accurrence of circulation depression were comparable in four group,and no awareness happened in all patients, but in group geriatric plus fentanyl the accurence of respiration depression is more than the other groups. Conclusion: A fentanyl dose of 50μg is suffcient to decrease EC50 of propofol TCI to secure laryngeal mask insertion in normal and geriatric patients with minimum cardiovescular depression. Key words: fentanyl, geriatric, median effective concentration , propofol, laryngeal mask

Key words: fentanyl, geriatric, median effective concentration, propofol, laryngeal mask