An endotracheal tube, which is used to secure the airway and allow ventilation of the lungs during general anesthesia, is inserted into the trachea either through the nose or mouth. In children, different formulae exist to determine the approximate size of the tube according to age, and how far it should be advanced into the airway. Once a tracheal tube is inserted, its position is routinely checked to make sure both lungs are ventilated. To prevent displacement, the tube is taped to the lip, chin or at the nose. However, head movement could cause alteration of the tube position, and risk selective endobronchial intubation or inadvertent extubation. Knowledge of how the different tracheal tubes move with head position can help determine the best tube selection to reduce the risk of accidental tube advancement or removal, in cases where certain head positions are required for surgical access.