Which monitoring modality provides the earliest indication of respiratory compromise before oxygen desaturation occurs?

• A. Capnography (end-tidal CO2) tracing
• B. Pulse oximetry
• C. Electrocardiography
• D. Airway ultrasound assessment

Answer: (A)

Ventilation status is detected in real time by capnography, which measures end-tidal CO2 and provides a continuous waveform. When a patient under sedation begins to hypoventilate or develop an airway obstruction, ventilation changes show up within seconds on the capnography tracing. A sudden loss of waveform or a notable change in end-tidal CO2 is an early warning that ventilation is failing, often before oxygen levels fall. Oxygen saturation can remain normal for a period because of oxygen reserves and supplemental oxygen, so pulse oximetry may lag behind true ventilatory problems. ECG monitors electrical activity of the heart and doesn’t reflect ventilation, and airway ultrasound isn’t a continuous monitor of breathing status. For this reason, capnography offers the earliest indication of respiratory compromise before desaturation occurs.