What does capnography measure in prehospital patients?

• A. Oxygen saturation
• B. End-tidal CO2, reflecting ventilation status and perfusion
• C. Blood pressure
• D. Arterial pH

Answer: (B)

Capnography measures end-tidal CO2, the CO2 concentration at the end of expiration. This value, along with the waveform, reflects how well ventilation is delivering air to the lungs and how well blood is transporting CO2 to those lungs, making it a real-time indicator of both ventilation status and perfusion in prehospital patients. It’s the best choice because it directly monitors CO2 elimination and circulation, unlike oxygen saturation (which measures oxygenation), blood pressure (perfusion but not ventilation), or arterial pH (a lab value). In practice, end-tidal CO2 helps confirm airway placement, track ventilation during care, and detect changes in perfusion or resuscitation effectiveness.