For oral fiberoptic intubation, the preliminary insertion depth of the fiberoptic bronchoscope should be important because the excessive insertion depth or too shallow depth might be the reason why the clinicians cannot perform oral fiberoptic intubation completely.~The purpose of the study is to find out the optimal preliminary insertion depth of the fiberoptic bronchoscope for visualization of glottic opening in oral fiberoptic intubation.~The investigators will enroll the subjects of the present study after obtaining the written consent.~After enrollment, the investigators will measure some anatomical distance, such as patient height.~After induction of anesthesia and muscle relaxation for tracheal intubation, An investigator who has experiences of numerous fiberoptic intubation will measure the optimal preliminary insertion depth of the fiberoptic bronchoscope from the philtrum, the upper lip, or the incisors for oral fiberoptic intubation, with the aid of assistants. Then, tracheal intubation with a laryngoscope as a routine manner of our institute.~The investigators will calculate the mean value of the optimal depth and find out an formula for that from our data.
For oral fiberoptic intubation, the preliminary insertion depth of the fiberoptic bronchoscope should be important because the excessive insertion depth or too shallow depth might be the reason why the clinicians cannot perform oral fiberoptic intubation completely.~The purpose of the study is to find out the optimal preliminary insertion depth of the fiberoptic bronchoscope for visualization of glottic opening in oral fiberoptic intubation.