End-tidal carbon dioxide (ETCO₂) determines the carbon dioxide (CO₂) concentration in exhaled gas to provide information about a patient’s pulmonary, cardiac, and metabolic status. Such information aids patient management and helps prevent clinical compromise.

In ETCO₂ monitoring, a photodetector measures the amount of infrared light absorbed by airway gas during inspiration and expiration. (Light absorption increases along with the CO₂ concentration.) A monitor converts these data to a CO₂ value and a corresponding waveform, or capnogram, if capnography is used. (See How ETCO₂ monitoring works.) The sensor is positioned at one of two sites in the monitoring setup. With a mainstream monitor, it’s positioned directly at the patient’s airway with an airway adapter, between the endotracheal (ET) tube and the breathing circuit tubing. With a sidestream monitor, the airway adapter is positioned at the airway (regardless of whether or not the patient is intubated) to allow aspiration of gas from the patient’s airway back to the sensor, which lies either within or close to the monitor.

Some CO₂ detection devices provide semiquantitative indications of CO₂ concentrations, supplying an approximate range rather than a specific value for ETCO₂. Other devices simply indicate whether CO₂ is present during exhalation. (See Analyzing CO₂ levels, page 270.)

The 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care recommend ETCO₂ monitoring in combination with clinical assessment to confirm initial ET tube placement in the patient in cardiac arrest when continuous quantitative waveform capnography isn’t available.¹

ETCO₂ monitoring has become standard during anesthesia administration, such as in patients who are undergoing moderate sedation. It may also be used in those receiving epidural or patient-controlled analgesia for pain control. The ETCO₂ measurements can alert the nurse to hypoventilation from oversedation.²

When ETCO₂ is detected during cardiac arrest, it’s a good indicator that the ET tube is properly placed in the trachea. However, such conditions as pulmonary embolus, pulmonary edema, status asthmaticus, or gastric content contamination of the ETCO₂ detector may produce false results. Therefore, if CO₂ isn’t detected, a second method should be used to confirm ET tube placement, such as direct visualization or use of an esophageal detector device.¹