Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.
In 2010, the American Society of Anesthesiologists (ASA) expanded its Standards for Basic Anesthetic Monitoring to require continuous monitoring of exhaled CO₂, oxygenation, circulation, and body temperature during moderate and deep sedation unless monitoring is prevented or invalidated by the patient, procedure, or equipment (Weaver et al., 2011). Along with several other guidelines, modern standards continue to require continual assessment of ventilation during anesthesia and distinguish monitoring according to the anesthetic technique (American Society of Anesthesiologists, 2025). Intraoperative CO2 monitoring provides precise information about patient oxygenation status, making it highly beneficial for patient safety, as reflected by its inclusion in professional guidelines.
Capnography, the measurement of CO₂, continuously measures information about ventilation and airway integrity (Deasy et al., 2024). It displays the level of CO₂ in exhaled breath and quantifies both an end-tidal CO₂ (EtCO₂) value and a waveform representing ventilation throughout the respiratory cycle (Maskay et al., 2023). Unlike pulse oximetry, which measures peripheral blood oxygenation, capnography provides immediate information about whether a patient is effectively moving air in and out of the lungs (Deasy et al., 2024). This distinction makes CO₂ monitoring particularly valuable for detecting apnea, airway obstruction, equipment failure, or inadequate ventilation before significant oxygen desaturation develops (Deasy et al., 2024).
Although waveform capnography is not as precise as imaging verification is when confirming tracheal intubation, it provides more information than a simple numerical EtCO₂ value (Klein et al., 2021). Capnography can also provide early evidence of airway obstruction, bronchospasm, rebreathing, apnea, or changes in pulmonary blood flow (Klein et al., 2021). The Association of Anaesthetists recommends that a flat capnogram following attempted tracheal intubation be considered evidence of esophageal intubation until this possibility has been excluded (Klein et al., 2021).
During general anesthesia, ventilation should be evaluated using clinical observations, such as chest excursion, observation of the reservoir breathing bag, and auscultation of breath sounds, in combination with continuous EtCO₂ monitoring (American Society of Anesthesiologists, 2025). When an endotracheal tube or supraglottic airway is inserted, correct airway placement should be confirmed through clinical assessment and detection of exhaled CO₂ (American Society of Anesthesiologists, 2025).
Guidelines also require that continual quantitative end-tidal CO2 monitoring be performed through capnography, capnometry, or mass spectrometry during the intraoperative period, from the time of endotracheal tube or supraglottic airway placement until extubation, airway device removal, or initiation of transfer to a postoperative care location (American Society of Anesthesiologists, 2025). When capnography or capnometry is used, the EtCO₂ alarm must be audible to the anesthesiologist or anesthesia care team (American Society of Anesthesiologists, 2025). If ventilation is controlled by a mechanical ventilator, the ASA requires continuous use of an additional alarmed device capable of detecting disconnection of components of the breathing system (“Practice Guidelines for Moderate Procedural Sedation,” 2018).
There is no universal guideline requiring every anesthetized patient to maintain an EtCO₂ of exactly 35–45 mm Hg. Instead, values should be interpreted according to the patient’s physiology, ventilation strategy, and surgical circumstances (American Society of Anesthesiologists, 2025). More important than an isolated number may be an unexpected change in the EtCO₂ trend or waveform.
CO₂ monitoring should also extend beyond the intraoperative period when appropriate. The Association of Anaesthetists recommends uninterrupted capnography during induction, airway insertion, anesthesia maintenance, emergence, and transfer when an artificial airway remains in place (Klein et al., 2021). Monitoring should continue until the airway is removed and the patient has recovered an appropriate response to verbal communication (Klein et al., 2021). These recommendations apply regardless of whether anesthesia occurs in a traditional operating room or a non-operating-room anesthesia location.
Intraoperative CO₂ monitoring provides anesthesia professionals with continuous insight into airway integrity and ventilation, allowing respiratory compromise to be recognized and treated earlier, and its value is reflected in practice guidelines. Alongside pulse oximetry, clinical observation, and appropriate alarms, it supports careful management of ventilation and oxygenation.
References
American Society of Anesthesiologists Committee on Practice Parameters. (2025). Standards for basic anesthetic monitoring. https://www.asahq.org/standards-and-practice-parameters/standards-for-basic-anesthetic-monitoring
Deasy, A., & O’Sullivan, E. P. (2024). Capnography: A fundamental in safe airway management. International Anesthesiology Clinics, 62(4), 29–36. https://doi.org/10.1097/AIA.0000000000000453
Klein, A. A., Meek, T., Allcock, E., Cook, T. M., Mincher, N., Morris, C., Nimmo, A. F., Pandit, J. J., Pawa, A., Rodney, G., Sheraton, T., & Young, P. (2021). Recommendations for standards of monitoring during anaesthesia and recovery 2021. Anaesthesia, 76(9), 1212–1223. https://doi.org/10.1111/anae.15501
Maskay, S. S., Shrestha, N., Bastola, P., Pradhan, B., & Shrestha, A. (2024). Ultrasonography imaging versus waveform capnography in detecting endotracheal tube placement during intubation at a tertiary hospital. Journal of Medical Ultrasound, 32(1), 70–75. https://doi.org/10.4103/jmu.jmu_98_22
Practice guidelines for moderate procedural sedation and analgesia 2018: A report by the American Society of Anesthesiologists Task Force on Moderate Procedural Sedation and Analgesia, the American Association of Oral and Maxillofacial Surgeons, American College of Radiology, American Dental Association, American Society of Dentist Anesthesiologists, and Society of Interventional Radiology. (2018). Anesthesiology, 128(3), 437–479. https://doi.org/10.1097/ALN.0000000000002043
Weaver, J. (2011). The latest ASA mandate: CO₂ monitoring for moderate and deep sedation. Anesthesia Progress, 58(3), 111–112. https://doi.org/10.2344/0003-3006-58.3.111
