The depth of Endotracheal Tube refers to the distance from the front end of Endotracheal intubation to the alveolar. Generally, the depth of Endotracheal Tube for adult males is 22 to 24 cm, while the depth of Endotracheal Tube for adult females is 20 to 22 cm. If the Endotracheal Tube is inserted too deeply, it is easy to cause the Endotracheal Tube to be inserted into one lung to carry out one-lung ventilation, while the other lung will appear atelectasis, which will affect the rescue of the patient. Endotracheal Tube is a special Endotracheal Tube inserted into the trachea through the glottis. This technology can provide the best conditions for airway patency, ventilation and support, respiratory tract suction and aspiration prevention.