An airway adapter comprising a flow channel configured to carry a respiratory gas, and a body comprising a surface at least partially coated with a luminophore that is excited by received radiation, wherein the luminophore emits luminescent radiation indicative of oxygen concentration of the respiratory gas when the luminophore is in contact with the respiratory gas, wherein the body comprises a transparent radiation path surrounded by the surface, the body being configured to guide at least one of the received radiation and the luminescent radiation emitted by the luminophore.
