Insertion of a (plastic) tube through the nose or mouth into the TRACHEA. The tube often has a cuff at its lower end which, when inflated, provides an airtight seal. This allows an anaesthetist to supply oxygen or anaesthetic gases to the lungs with the knowledge of exactly how much the patient is receiving. Endotracheal intubation is necessary to undertake artificial ventilation of a patient (see ANAESTHESIA).