Abstract: A convertible endotracheal tube apparatus includes an outer lumen member, an inner lumen member, an outer lumen cuff, and an inner lumen cuff. The outer lumen member has a round tubular cross-section and is adapted to provide a first fluid path between a first external fluid source and both a left and a right lung of a patient. The inner lumen member has a semi-round tubular cross-section, is located at least partially within the round tubular cross-section of the outer lumen member, and is adapted to selectively provide a second fluid path between a second external fluid source and a chosen one of the left and right lungs. The outer lumen cuff encircles a portion of the outer lumen member and selectively provides a single lumen operation mode. The inner lumen cuff encircles a portion of the inner lumen member and selectively provides a double lumen operation mode.