What is a normal end-tidal carbon dioxide (ETCO2) level?

From the Guidelines

A normal end-tidal carbon dioxide (ETCO2) level typically ranges between 35-45 mmHg in healthy adults. This measurement represents the concentration of carbon dioxide at the end of exhalation and serves as an important indicator of ventilation adequacy and perfusion status. ETCO2 is slightly lower than arterial CO2 (PaCO2) by about 2-5 mmHg in healthy individuals [ 1 ]. During clinical monitoring, values consistently below 35 mmHg may indicate hyperventilation, while values above 45 mmHg often suggest hypoventilation.

Key Points to Consider

• ETCO2 monitoring is particularly valuable in anesthesia, critical care, and emergency medicine as it provides real-time feedback on respiratory status [ 1 ].
• Changes in ETCO2 can reflect important physiological shifts such as decreased cardiac output, pulmonary embolism, or respiratory depression.
• The measurement is typically obtained non-invasively through capnography, making it an accessible and reliable tool for continuous patient assessment.
• Maintaining normocapnia with end-tidal carbon dioxide between 35 and 45 mm Hg is recommended [ 1 ].

Clinical Implications

• ETCO2 levels can be used to guide ventilation and optimize respiratory care.
• Abnormal ETCO2 levels can indicate underlying respiratory or cardiovascular issues, prompting further investigation and intervention.
• ETCO2 monitoring can help identify patients at risk of complications, such as hyperventilation or hypoventilation, and allow for timely intervention.

From the Research

Normal End-Tidal Carbon Dioxide (ETCO2) Levels

• The normal end-tidal carbon dioxide (ETCO2) level is typically considered to be between 30-40 mmHg 2.
• However, the ideal intraoperative ETCO2 target is still unclear, and there is significant variability in practice patterns among anesthesiologists 2.
• A study of 317,445 adult patients who received general anesthesia found that the median ETCO2 was 33 [31.0-35.0] mmHg in 2008 and 35 [33.0-38.0] mmHg in 2016 2.

Factors Affecting ETCO2 Levels

• ETCO2 levels can be affected by various factors, including respiratory rate, tidal volume, and dead space 3.
• Controlled hypotensive anesthesia can lead to a decrease in ETCO2 levels, which may not reflect changes in arterial carbon dioxide levels 3.
• Anaphylaxis can cause a significant decrease in ETCO2 levels, with a median minimum ETCO2 value of 17 [12-23] mmHg 4.

Clinical Applications of ETCO2 Monitoring

• ETCO2 monitoring can be used to detect respiratory events prior to current sedation monitoring practices 5.
• Abnormal ETCO2 findings can indicate hypoventilation or apnea during procedural sedation and analgesia 5.
• ETCO2 monitoring may be useful in diagnosing anaphylaxis in patients with severe postinduction hypotension 4.