Target-Controlled Infusion (TCI) of Propofol has been proved to be a safe agent for conscious sedation in flexible bronchoscopy (FB) due to its fast onset of action and rapid recovery time. By virtue of an aging population, the number of bronchoscopy performed will likely increase in the elderly patients , however, the target setting of "effect-site"concentration (Cet) of propofol is still unclear among this population.