The measurement of End-Tidal Carbon Dioxide (EtCO2) is standard practice in advanced life support for patients experiencing cardiac arrest. EtCO2 represents the carbon dioxide concentration in a patient’s exhaled breath at the end of their respiratory cycle. Monitoring this non-invasive value provides clinicians with a real-time assessment of how effectively cardiopulmonary resuscitation (CPR) is being performed. Measured in millimeters of mercury (mmHg), EtCO2 offers a direct window into the body’s circulatory function and helps guide immediate resuscitation efforts.
Understanding the Capnography Measurement
Capnography measures and displays the concentration of carbon dioxide in the exhaled air, typically shown as a number and a waveform. The EtCO2 value serves as a surrogate for cardiac output, reflecting the volume of blood the heart is pumping. During CPR, chest compressions artificially generate blood flow, pushing CO2 from the tissues to the lungs for exhalation. Effective compressions result in a measurable EtCO2 reading. If compressions are inadequate, blood flow and CO2 delivery drop significantly, causing the EtCO2 reading to fall, reflecting poor pulmonary perfusion.
Target EtCO2 Levels for Effective CPR
For effective CPR, the goal is to maintain the EtCO2 level above a minimum threshold. Resuscitation guidelines suggest targeting a reading of at least 10 mmHg during ongoing chest compressions. An EtCO2 value between 15 mmHg and 20 mmHg is considered ideal, indicating high-quality CPR and sufficient artificial blood flow. If the reading consistently falls below 10 mmHg, it signals inadequate compressions requiring immediate improvement, prompting the team to adjust depth or rate. Maintaining this minimum threshold is associated with an increased likelihood of achieving the return of spontaneous circulation (ROSC).
Using EtCO2 to Identify Return of Spontaneous Circulation
A primary application of capnography is identifying the return of spontaneous circulation (ROSC). When the heart begins to beat effectively, CO2-rich blood is suddenly pumped to the lungs. This physiological change causes an abrupt, sustained increase in the EtCO2 reading, often rising quickly from low CPR levels to a normal range (typically 35 mmHg to 45 mmHg or higher). This sudden surge is often the earliest sign that the heart has restarted, appearing before a palpable pulse can be felt. This definitive signal prompts the team to pause chest compressions and check for a pulse, allowing providers to transition rapidly to post-cardiac arrest care.