End-tidal carbon dioxide (EtCO2) is the partial pressure of carbon dioxide in the air exhaled during expiration. Through capnometry or capnography, the absorption of carbon dioxide at a specific wavelength (4.26 micrometers) is measured using infrared radiation. The normal ETCO2 value in expiration is 30-45 mmHg. Values between 25-30 mmHg should suggest hyperventilation, and an ETCO2 over 45 mmHg should suggest hypoventilation.
