Capnography is used to monitor which parameter, and what is the normal end-tidal CO2 range?

• A. Capnography monitors expired CO2; normal ETCO2 is approximately 35–45 mmHg.
• B. Capnography measures inspired CO2; ETCO2 80–100 mmHg.
• C. Capnography assesses respiratory rate only; ETCO2 15–25 mmHg.
• D. Capnography monitors humidity; ETCO2 0–5 mmHg.

Answer: (A)

Capnography measures the CO2 present in the air the patient exhales, focusing on the end of expiration. This end-tidal CO2 value reflects how effectively the lungs are ventilating the patient and gives a quick read on alveolar CO2 levels. The normal end-tidal CO2 range in a healthy adult is about 35–45 mmHg. This measurement is about expired CO2, not inspired CO2 (which is near zero in room air), and it isn’t a humidity measurement. While the waveform can hint at rate and breathing pattern, the key parameter it provides is CO2 concentration at the end of expiration, which is why 35–45 mmHg is considered normal.