Abstract: The invention relates to an apparatus for measuring the parameters of respiratory gases comprising a respiratory tube, ultrasonic sensors and pre-amplifier electronic circuitry arranged in a separate housing. In order to prevent dangerous cross infections between patients following repeated utilization of the such measuring apparatus the ultrasonic sensors are permanently integrated in the respiratory tube so that they constitute a single part therewith and in that at least the respiratory tube together with the integrated ultrasonic sensors is designed in the form of an interchangeable part for use once only.