Phase IV: the initiation of inspiration, which should be a nearly vertical drop to a baseline. If prolonged or bleeding into the expiratory phase, consider a leak in the expiratory portion of the circuit, such as an ETT tube cuff leak.2
Phase 0: the inspiratory segment
Another important part of the capnogram is the alpha angle. This is the angle of transition between Phase II and Phase III. The combination of a prolonged phase II and steeper phase III leads to a more obtuse alpha angle and will have a “shark-fin” appearance to the capnogram. This suggests an obstructive process, such as asthma or COPD (Figure 2).1,2,6
Standard Uses
Intubation
Capnography, along with visualizing ETT placement through the vocal cords, is the standard of care for confirming correct placement during intubation.4,10,11 Alternative signs of endotracheal intubation, such as chest wall movement, auscultation, condensation of water vapor in the tube lumen, or pulse oximetry, are less accurate.12
While not ideal, correct ETT placement can be confirmed qualitatively using a colorimetric device.13 Upon correct placement, the resultant exhalation of CO2 will change the paper color from purple to yellow (indicating EtCO2 values > 15 mm Hg).2,4 Without this color change, tube placement should be verified to rule out esophageal intubation. Unfortunately, qualitative capnography has false positives and negatives that limit its utility in the ED, and this method should be avoided if quantitative capnography is available.