Abstract: A gas measuring device (1000) for determining the concentration of a gas component in a breathing gas mixture includes a radiation source (1) with a illuminant (2) and a mirror arrangement (3) for emitting light radiation. A sample gas cuvette (5) is formed as a hollow body. A detector arrangement (15) with at least two bandpass filter elements (17, 18) and at least two detector elements (20, 21) receives the filtered light radiation. A control unit (42) is configured to detect signals from the detector elements (20, 21) and determine a concentration of a gas component in the breathing gas mixture. A light guide element (11) is provided in the form of a hollow body.