What is the noninvasive method used to measure the concentration of carbon dioxide in expired air?

The noninvasive method used to measure the concentration of carbon dioxide in expired air is capnography. This technique involves the use of a capnometer to measure the levels of carbon dioxide (CO2) at the end of an exhalation, providing important information about a patient's ventilation status. By analyzing the concentration of CO2 in the exhaled air, healthcare providers can assess respiratory function, identify potential respiratory distress, and monitor patients during sedation or general anesthesia.

Capnography is especially useful in critical care settings, as it helps in real-time monitoring of a patient's respiratory status, ensuring timely interventions if abnormalities are detected. This method is preferred for its noninvasive nature and its ability to quickly give feedback on the effectiveness of ventilation.

In contrast, spirometry is primarily used to measure lung volumes and flow rates during inhalation and exhalation, which aids in diagnosing and managing conditions like asthma and chronic obstructive pulmonary disease (COPD), but it does not directly measure carbon dioxide levels. Electrocardiography is focused on monitoring the electrical activity of the heart, while a peak flow meter measures the maximum speed of expiration without evaluating CO2 concentration. Thus, capnography stands out as the correct answer for measuring carbon dioxide in