An oral cannula for placement within the oral cavity of a patient for delivery of a treatment gas and for collecting end-tidal carbon dioxide (EtCO2) includes a treatment gas delivery lumen including at least one aperture near a distal end of the treatment gas delivery lumen； an exhaled gas sampling lumen. The cannula also includes a cap having (i) a gas diverter adapted for diverting at least a portion of the treatment gas and (ii) an exhaled gas inlet including flutes and apertures there between that are in communication with the exhaled gas sampling lumen. The oral cannula is adapted for custom bending or has a bend such that the oral cannula is insertable and retainable in a patient's mouth and functional for supplying a treatment gas and sampling gas exhaled by the patient.
