An endoscopic mouthguard comprising a bite block comprising a generally annular body adapted to be inserted into the mouth of a patient so as to maintain the upper and lower teeth of the patient in a spaced apart relationship and define an endoscopic passage for introduction of an endoscope into the oral cavity of the patient. The bite block includes a gas delivery passage for delivery of a gas to the oral cavity of the patient, and a gas distribution manifold detachably engaged with the bite block. The gas distribution manifold comprises at least one inlet port for receiving gas from a gas supply, at least one nasal outlet port in fluid communication with the inlet port and adapted so as to direct gas to or toward the nasal passages of the patient; and an oral outlet port in fluid communication with the inlet port. The oral inlet port is configured such that when the gas distribution manifold is engaged with the bite block it is in fluid communication with the gas delivery passage, and when the gas distribution manifold is disengaged from the bite block and the bite block is removed from the mouth of the patient, the oral outlet port is adapted to direct gas over or toward the mouth of the patient.