Flexible bronchoscopy (FB) sedation requires keeping sedative level in a narrow window to prevent over or under sedation. Sedative drug titration according to subjective adjustment by individual physician may cause unsteady drug concentration. Target controlled infusion (TCI) has been provided a precise pharmacokinetic control of propofol, direct control the effect side, (eg. Brain) concentration (Ce), and been applied in surgical anesthesia and variable procedure sedation. We designed this pilot study to evaluate the optimal regimen of TCI in FB sedation.