A medical apparatus that holds open a mouth of a patient. The apparatus contains a passage through which the patient can breathe by mouth. The apparatus contains a port to which an oxygen line is connected and which delivers oxygen to the passage for inhalation by the patient. The apparatus contains a sampling port which samples air in the passage and delivers sampled air to a monitoring device. The latter measures, for example, carbon dioxide content in the sampled gas, and issues a warning if carbon dioxide concentration is out-of-bounds. Phosphor material can be added to the apparatus, to make the apparatus glow in a darkened operating room, to allow technicians to easily find the patient's mouth and to insert tools, tubing, instruments and the like in the patient's mouth.