A dual-purpose device inserted into a patient's mouth to maintain oral patency during an endoscopic procedure primarily to protect the endoscope, introduced via the mouth, from the patient's natural tendency to bite down on the instrument, and that simultaneously supports an oxygen (O2) line to provide the patient with an uninterrupted flow of O2 during and after endoscopy. The device also protects the tongue and teeth of the patient during endoscopy and may include a gas sample line that enables monitoring of the expired carbon dioxide (CO2) during the procedure. This is a single-use device.