Diagrammatic representation of key distances related to endotracheal tube positioning. Malpositioning of the endotracheal tube can be suspected from the depth of insertion. In the average adult, the 18-24 cm mark will show at the incisors when the tip of the tube is midway between the vocal cords and the carina.
Redrawn from Stone, DJ, Bogdonoff, DL, Anesth Analg 1992; 74:276.