ETCO2 (End Tidal CO2) is the partial pressure or maximal concentration of carbon dioxide (CO2) at the end of an exhaled breath, which is expressed as a percentage of CO2 or mmHg. The normal values are 5% to 6% CO2, which is equivalent to 35-45 mmHg. CO2 reflects cardiac output (CO) and pulmonary blood flow as the gas is transported by the venous system to the right side of the heart and then pumped to the lungs by the right ventricles.

End tidal CO2 (EtCO2) machine is designed to measure the exchange of carbon dioxide using a 50 ml per minute side stream method to provide highly accurate readings.