What Capnography Measures
Capnography measures the concentration of exhaled carbon dioxide (ETCO2) and displays it as a numeric value and a waveform. A normal ETCO2 is roughly 35 to 45 mmHg. It reflects ventilation, perfusion, and metabolism, which makes it more informative than pulse oximetry alone.
Reading the Waveform
A normal waveform has a rectangular shape. A shark-fin shape suggests bronchospasm, as in asthma or COPD. A flat line may mean the tube is misplaced, the patient is apneic, or the device is disconnected. A sudden drop in ETCO2 during CPR can indicate loss of pulse or poor compressions.
Use During Resuscitation
Waveform capnography is the most reliable way to confirm and monitor advanced airway placement. During CPR, an ETCO2 below 10 mmHg after 20 minutes suggests a poor prognosis, while a sudden rise may indicate return of spontaneous circulation. Know these ideas for the exam even if your scope limits direct use.