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 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 a gas diverter adapted for diverting at least a portion of the treatment gas and 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 &# 39 ; s mouth and functional for supplying a treatment gas and sampling gas exhaled by the patient .