Insertion of a rubber or plastic tube through the nose or mouth into the TRACHEA. The tube often has a cu? at its lower end which, when in?ated, 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 arti?cial ventilation of a patient (see ANAESTHESIA).