The normal arterial-to-end-tidal CO2 difference is which range?

The normal arterial-to-end-tidal CO2 difference is which range?

• A. 2-4 mmHg
• B. 4-6 mmHg
• C. 6-8 mmHg
• D. 8-10 mmHg

Answer: (B)

The main idea is that end-tidal CO2 closely reflects alveolar CO2, while arterial CO2 comes from the blood in the lungs. A small difference between these two values exists because some gas in the dead space doesn’t participate in gas exchange, causing a slight underestimation of arterial CO2 by the end-tidal measurement. In a healthy lung, this gradient is minimal, typically around a few millimeters of mercury. The normal arterial-to-end-tidal CO2 difference falls in about 4–6 mmHg, which best matches the typical range seen in practice. If this gradient becomes larger, it suggests ventilation-perfusion mismatch or other factors raising PaCO2 relative to ETCO2.

The main idea is that end-tidal CO2 closely reflects alveolar CO2, while arterial CO2 comes from the blood in the lungs. A small difference between these two values exists because some gas in the dead space doesn’t participate in gas exchange, causing a slight underestimation of arterial CO2 by the end-tidal measurement. In a healthy lung, this gradient is minimal, typically around a few millimeters of mercury. The normal arterial-to-end-tidal CO2 difference falls in about 4–6 mmHg, which best matches the typical range seen in practice. If this gradient becomes larger, it suggests ventilation-perfusion mismatch or other factors raising PaCO2 relative to ETCO2.