Determining the Depth of Endotracheal Tube Insertion

1. Airway length from the medial incisor to carina is divided into four segments ; the length from medial incisor to mouth angle, mouth angle to epiglottis, epiglottis to vocal cords and vocal cords to carina.
2. Determining the mean length of each segments with the direct laryngoscope, videolaryngoscope and fiberoptic bronchoscope at the time of endotracheal intubation.
3. Making a new formula to determine the proper individualized depth of intubation on the basis of the length of segments
4. Virtual experiment : comparing the new formula with conventional method of determining the depth of endotracheal intubation

Inclusion Criteria:

• Patients who are scheduled to take general anesthesia with endotracheal intubation

Exclusion Criteria:

• Patients undergoing general anesthesia with face mask ventilation or laryngeal mask airway