What term describes the reading that shows the level of CO2 inhaled and exhaled at any moment?

• A. Pulse oximetry trace
• B. Electrocardiogram
• C. Capnographic waveform
• D. Spirometry loop

Answer: (C)

Capnography provides a real-time readout of carbon dioxide during breathing, displayed as a capnographic waveform. It shows how CO2 levels rise during expiration and fall with inhalation, giving an instantaneous view of ventilation at every moment. The most clinically useful value is end-tidal CO2—the CO2 at the end of expiration—which approximates alveolar CO2 and indicates how well the patient is ventilating. The waveform pattern helps detect apnea, hypoventilation, airway obstruction, or disconnections. By comparison, a pulse oximetry trace measures oxygen saturation, not CO2; an electrocardiogram shows heart rhythm; and a spirometry loop tracks airflow and lung volumes rather than airway CO2 concentration.