Capnography confirms endotracheal tube placement by detecting CO2 in:

• A. The bloodstream
• B. The stomach
• C. The esophagus
• D. Exhaled air from the lungs

Answer: (D)

Capnography hinges on detecting carbon dioxide in the gas you exhale. When the endotracheal tube sits in the trachea and ventilation delivers air to the lungs, CO2-rich gas from the alveoli is expelled through the tube, producing a recognizable CO2 waveform. That waveform confirms the tube is in the airway. If the tube were misplaced into the esophagus or stomach, there wouldn’t be alveolar gas exiting through the tube, so little to no CO2 signal would appear. CO2 in the bloodstream isn’t read directly by capnography, since the monitor measures gas in the airway, not dissolved CO2 in blood. So the source detected by capnography to confirm placement is exhaled air from the lungs.