This disclosure describes novel systems and methods for monitoring volumetric CO2 during ventilation of a patient being ventilated by a medical ventilator. The disclosure describes more accurate, more cost effective, and/or less burdensome non-invasive methods and systems for calculating volumetric CO2 than previously utilized methods and systems. The disclosure describes estimating a flow rate in a breathing circuit to calculate a volumetric CO2. Further, the disclosure describes synchronizing the estimated flow rate with a measured CO2 to calculate a volumetric CO2. Additionally, the disclosure describes synchronizing a measured flow rate from within the breathing circuit with a measured CO2 to calculate a volumetric CO2.
