In a capnogram during respiratory distress, when is the patient's ETCO2 level measured?

In a capnogram, the end-tidal carbon dioxide (ETCO2) level is assessed at the end of expiration when the alveolar gas is being exhaled. This is indicated at Point D on the waveform, which represents the plateau phase of exhalation. During this phase, carbon dioxide that has been removed from the bloodstream is being expelled through the lungs, allowing for the measurement of the maximum concentration of CO2 in the exhaled air.

The significance of this measurement lies in its ability to provide real-time feedback on the patient's ventilation status and overall respiratory function. By accurately determining the ETCO2 levels at this point, healthcare providers gain valuable insight into metabolic status and can assess whether adequate ventilatory effort is occurring, especially in scenarios of respiratory distress.

Points A, B, and C correlate with different phases of the respiratory cycle. Point A involves the onset of exhalation where low CO2 levels may be present, Point B reflects a transitional phase where CO2 levels begin to rise but not at their peak, and Point C represents the initial trough after inspiration, where expired air does not yet reflect the alveolar CO2. Therefore, these points do not provide an accurate representation of the ETCO2 measured at Point