Capnography is a reliable method for confirming proper endotracheal tube placement because:

• A. CO2 is present in the esophagus
• B. CO2 is not present in the esophagus
• C. CO2 is detected in the bloodstream
• D. Capnography measures airway pressure only

Answer: (B)

Capnography works because it detects carbon dioxide in the gas a patient exhales. When the endotracheal tube is correctly in the trachea, alveolar gas with CO2 is exhaled, producing a reliable CO2 waveform and a measurable end-tidal CO2 value. If the tube is in the esophagus, the exhaled gas has little to no alveolar CO2, so the capnogram is flat or shows no CO2 peak. In short, the presence of CO2 in exhaled gas confirms tracheal placement, while CO2 is not found in the esophageal expiratory gas. Capnography provides information about CO2 in the breath, not bloodstream CO2, and it offers more than just airway pressure measurement.