The depth of tracheal intubation refers to the distance of the front end of the tracheal tube from the alveolar ridge, which is generally 1-2 cm deeper after the front end of the tracheal tube passes through the acoustic canal. The depth of tracheal intubation for adult males is about 22-24 cm, while that for adult females is about 20-22 cm. Too deep or too shallow tracheal intubation can have adverse effects on the patient. If the tracheal tube is inserted too deeply, the tracheal tube may reach the bronchus of one lobe of the lung, causing hypoxia or atelectasis; if it is inserted too shallowly, the tracheal tube will be easily detubated and cannot play the role of ventilation.