How are EtCO2 values commonly expressed?

• A. In mmHg
• B. In kPa
• C. In percent
• D. In atmospheres

Answer: (A)

EtCO2 is a partial pressure measurement of carbon dioxide in the air exhaled at the end of expiration. Because it reflects pressure, the value is expressed in a pressure unit, and the standard in medical practice is millimeters of mercury (mmHg). Typical healthy values fall in the 35–45 mmHg range, which helps clinicians estimate arterial CO2 and ventilation status. While some devices can show the value in other pressure units like kilopascals, mmHg remains the most common expression. Expressing EtCO2 as a percentage would describe concentration rather than pressure, and atmospheres aren’t used for routine monitoring.