A system is configured to determine one or more breathing parameters of a subject, such as one or both of end-tidal carbon dioxide concentration and/or breath rate. The system is configured to make a plurality of preliminary determinations of an individual breathing parameter according to a plurality of different algorithms. A final determination of the breathing parameter is obtained by selecting one of the preliminary determinations based on therapy parameters, gas parameters, and/or other parameters that impact the accuracy and/or precision of the different algorithms.
