Capnography primarily provides information about which physiological parameter?

• A. CO2 in exhaled air
• B. Blood glucose
• C. Blood pressure
• D. Oxygen saturation

Answer: (A)

Capnography measures the amount of carbon dioxide in exhaled breath over time, focusing on the end-tidal CO2 that appears at the end of expiration. This directly reflects ventilation and alveolar CO2 elimination, so the waveform and EtCO2 value tell you how effectively a patient is ventilating. It’s particularly useful for detecting hypoventilation, apnea, airway obstruction, or disconnection in real time during sedation or anesthesia. While PaCO2 in blood is related, capnography provides a noninvasive estimate of ventilation through the CO2 in exhaled air, not measurements of glucose, blood pressure, or oxygen saturation, which are monitored by other methods.