Detecting end-tidal pressure of carbon dioxide (PetCO2) is becoming increasingly common in the emergency transport setting. Several CO2 detection devices are suitable for emergency transport, including colorimetry, capnometry, and capnography. Capnography is the only device that displays a waveform of CO2 levels throughout the respiratory cycle. Analysis of this waveform is key to avoiding therapeutic errors. End-tidal PCO2 is best used for verifying endotracheal and nasal gastric tube placement and assessing the effectiveness of CPR. The use of capnography as a means of guiding manual or mechanical ventilatory therapy is unreliable in unstable, critically ill, or injured patients.