End-Tidal Capnography: Background, Indications, Technical Considerations (2024)


End-Tidal Capnography

  • Sections End-Tidal Capnography

  • Overview
    • Background
    • Indications
    • Technical Considerations
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  • Periprocedural Care
    • Patient Education and Consent
    • Equipment
    • Patient Preparation
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  • Technique
    • Approach Considerations
    • Monitoring of End-Tidal Carbon Dioxide
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  • Media Gallery
  • References



End-tidal capnographyrefers to the graphical measurement of the partial pressure of carbon dioxide (in mm Hg) during expiration (ie, end-tidal carbon dioxide [EtCO2, PetCO2]). First established in the 1930s, clinical use of EtCO2 measurement became accessible in the 1950s with the production and distribution of capnograph monitors. [1, 2]

With continuous technologic advancements, EtCO2 monitoring has become a key component in the advancement of patient safety within anesthesiology, and the American Society of Anesthesiologists (ASA) has endorsed end-tidal capnography as a standard of care for general anesthesia and moderate or deep procedural sedation. [3, 4]

Studies showed that during cardiac arrest, EtCO2values of greater than 10-20 mm Hg are associated with return of spontaneous circulation (ROSC). [5, 6, 7, 8] Accordingly, other specialties, including critical care and emergency medicine, [9] began to implement end-tidal capnography monitoring more frequently, though there remains room for greater uptake of this life-saving technology outside of the operating room. [10, 11, 12]

End-Tidal Capnography: Background, Indications, Technical Considerations (1)



Continuous waveform capnography, combined with clinical assessment, is "the most reliable method of confirming and monitoring correct placement of an endotracheal tube," according to the American Heart Association (AHA). [13] Capnography can also be used to ensure ventilation with supraglottic devices, as well as to confirm that a spontaneously ventilating patient is in fact breathing (eg, via face mask or nasal cannula sampling).

More generally, end-tidal capnography is used in the following settings:

  • General anesthesia

  • Procedural sedation, including sedation with monitored anesthesia care

  • Analysis of ventilation (eg, in the intensive care unit [ICU])

  • Cardiac arrest, toconfirm tracheal intubation and adequacy of chest compressions [6, 13]

Cardiopulmonary resuscitation

The balance between production, delivery, and elimination of CO2 can be monitored by means of end-tidal capnography. In the event of cardiopulmonary arrest, cardiac output drops to zero, and thus, no transport of CO2 from the tissues to the lungs can occur. End-tidal capnometry of an artificially ventilated patient would, after several washout breaths, show a flat EtCO2 capnogram with EtCO2equaling zero during the arrest. Once chest compressions are initiated, circulation of blood will again deliver CO2 to the lungs, and the EtCO2capnogram will rise and fall with each breath as CO2 is ventilated.

EtCO2 levels of 20 mm Hg or greater indicate adequate chest compressions during cardiopulmonary resuscitation (CPR), and failure to achieve a level of at least 10 mm Hg after 20 minutes of CPR may help in making the decision to terminate resuscitative efforts. [6, 14, 13]

Complication prevention

Continuous EtCO2monitoring can provide an early warning of impending hypoxemia. Several studies have demonstrated that respiratory depression is detected via end-tidal capnography 30-60 seconds before it is detected via oxygen saturation. [15, 16]

End-Tidal Capnography: Background, Indications, Technical Considerations (2)



Technical Considerations

Best practices

In anesthesia and procedural sedation, end-tidal capnography has become the standard of care. Class IA evidence has established the indications for use, with several randomized trials demonstrating reductions in episodic hypoxia during procedural sedation.

Reading the capnogram

Cellular metabolism produces carbon dioxide, while the lungs work to eliminate it from the body. The balance between production and elimination can be followed in the rise and fall of EtCO2 as displayed by the capnogram. More specifically, EtCO2waveforms provide clinicians with a tool for quick and reliable diagnoses of common pulmonary pathophysiology.

Generally, EtCO2is displayed as a waveform with partial pressure of CO2on the y-axis and time on the x-axis (see the images below).

Normal breathing.

View Media Gallery

The capnogram has four phases, as follows:

  • Phase I represents the end of inspiration, and early expiration of gas from dead space (circuit tubing, anatomic)

  • Phase II represents gas from late anatomic and alveolar dead space, upsloping as alveolar gas mixes in and raises the CO 2

  • Phase III (plateau) represents the partial pressure of carbon dioxide exchanged at the alveoli; the amplitude of the plateau is referred to as EtCO 2;phase III normally has a very slight upslope due to physiologic V/Q mismatch

  • Phase IV signifies the start of inspiration, and the capnogram reflects the transition at the sampler from alveolar air flow to fresh air flow, or “scrubbed” air, in a closed circuit [17]

Of note, the information captured by end-tidal capnography (partial pressure of CO2) is devoid of volumetric information. Therefore, capnography should be used with end-tidal volume measurements for a full assessment ofventilation parameters. (See the video below.)

Pathology and the capnogram

Causes of high EtCO2include the following:

  • Malignant hyperthermia

  • Shivering

  • Fever

  • Sepsis

  • Endocrine disease

  • Hypoventilation (see the video below)


View Media Gallery

Causes of low EtCO2include the following:

  • Hypothermia

  • Low cardiac output

  • Pulmonary embolism

  • Hyperventilation (eg, with metabolic acidosis; see the video below)


View Media Gallery

Other waveform findings include the following:

  • Curare clefts (see the image below) typically occur when a mechanically ventilated patient attempts to inspire (eg, when analgesia is inadequate); they may also represent surgeon manipulation of the chest or adbomen

  • A long, steeply upsloping phase III "plateau" is indicative of obstructive airway disease (eg, chronic obstructive pulmonary disease [COPD] or bronchospasm)

  • An elevated baseline during phases IV or I may indicate a failing CO 2 absorber

  • A less acute phase IV slope suggests a failing expiratory valve

  • Cardiogenic oscillations are seen with prolonged expiratory time

Curare cleft.

View Media Gallery

End-Tidal Capnography: Background, Indications, Technical Considerations (3)



  1. Westhorpe RN, Ball C. The history of capnography. Anaesth Intensive Care. 2010 Jul. 38 (4):611. [QxMD MEDLINE Link].

  2. Jaffe MB. Infrared measurement of carbon dioxide in the human breath: "breathe-through" devices from Tyndall to the present day. Anesth Analg. 2008 Sep. 107 (3):890-904. [QxMD MEDLINE Link].

  3. [Guideline] Committee on Standards and Practice Parameters. Standards for basic anesthetic monitoring. American Society of Anesthesiologists. Available at http://www.asahq.org/quality-and-practice-management/standards-guidelines-and-related-resources/standards-for-basic-anesthetic-monitoring. December 13, 2020; Accessed: January 3, 2023.

  4. [Guideline] 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. Anesthesiology. 2018 Mar. 128 (3):437-479. [QxMD MEDLINE Link]. [Full Text].

  5. Pearce AK, Davis DP, Minokadeh A, Sell RE. Initial end-tidal carbon dioxide as a prognostic indicator for inpatient PEA arrest. Resuscitation. 2015 Jul. 92:77-81. [QxMD MEDLINE Link].

  6. Paiva EF, Paxton JH, O'Neil BJ. The use of end-tidal carbon dioxide (ETCO2) measurement to guide management of cardiac arrest: A systematic review. Resuscitation. 2018 Feb. 123:1-7. [QxMD MEDLINE Link].

  7. Javaudin F, Her S, Le Bastard Q, De Carvalho H, Le Conte P, Baert V, et al. Maximum Value of End-Tidal Carbon Dioxide Concentrations during Resuscitation as an Indicator of Return of Spontaneous Circulation in out-of-Hospital Cardiac Arrest. Prehosp Emerg Care. 2019 Oct 31. 1-7. [QxMD MEDLINE Link].

  8. Poppe M, Stratil P, Clodi C, Schriefl C, Nürnberger A, Magnet I, et al. Initial end-tidal carbon dioxide as a predictive factor for return of spontaneous circulation in nonshockable out-of-hospital cardiac arrest patients: A retrospective observational study. Eur J Anaesthesiol. 2019 Jul. 36 (7):524-530. [QxMD MEDLINE Link].

  9. Mohr NM, Stoltze A, Ahmed A, Kiscaden E, Shane D. Using continuous quantitative capnography for emergency department procedural sedation: a systematic review and cost-effectiveness analysis. Intern Emerg Med. 2018 Jan. 13 (1):75-85. [QxMD MEDLINE Link].

  10. Long B, Koyfman A, Vivirito MA. Capnography in the Emergency Department: A Review of Uses, Waveforms, and Limitations. J Emerg Med. 2017 Dec. 53 (6):829-842. [QxMD MEDLINE Link].

  11. Whitaker DK, Benson JP. Capnography standards for outside the operating room. Curr Opin Anaesthesiol. 2016 Aug. 29 (4):485-92. [QxMD MEDLINE Link]. [Full Text].

  12. Ilko SA, Vakkalanka JP, Ahmed A, Evans DA, House HR, Mohr NM. End-tidal CO2 Monitoring is Available in Most Community Hospitals in a Rural State: A Health System Survey. West J Emerg Med. 2019 Mar. 20 (2):232-236. [QxMD MEDLINE Link]. [Full Text].

  13. [Guideline] Panchal AR, Bartos JA, Cabañas JG, Donnino MW, Drennan IR, Hirsch KG, et al. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020 Oct 20. 142 (16_suppl_2):S366-S468. [QxMD MEDLINE Link]. [Full Text].

  14. Einav S, Bromiker R, Weiniger CF, Matot I. Mathematical modeling for prediction of survival from resuscitation based on computerized continuous capnography: proof of concept. Acad Emerg Med. 2011 May. 18 (5):468-75. [QxMD MEDLINE Link].

  15. Anderson CT, Breen PH. Carbon dioxide kinetics and capnography during critical care. Crit Care. 2000. 4 (4):207-15. [QxMD MEDLINE Link]. [Full Text].

  16. Millane T, Greene S, Rotella JA, Leang YH. End-tidal capnography provides reliable ventilatory monitoring for non-intubated patients presenting after sedative overdose to the emergency department. Emerg Med Australas. 2020 Feb. 32 (1):164-165. [QxMD MEDLINE Link].

  17. Kaczka DW, Chitilian HV, Vidal Melo MF. Respiratory monitoring. Gropper MA, Cohen NH, Eriksson LI, Fleisher LA, Leslie K, Wiener-Kronish JP, eds. Miller's Anesthesia. 9th ed. Philadelphia: Elsevier; 2020. Vol 1: 1298-339.

  18. Hotta M, Hirata K, Nozaki M, Mochizuki N, Hirano S, Wada K. Availability of portable capnometers in children with tracheostomy. Pediatr Int. 2021 Jul. 63 (7):833-837. [QxMD MEDLINE Link].

  19. Hotta M, Hirata K, Nozaki M, Mochizuki N, Hirano S, Wada K. Feasibility of portable capnometer for mechanically ventilated preterm infants in the delivery room. Eur J Pediatr. 2022 Feb. 181 (2):629-636. [QxMD MEDLINE Link]. [Full Text].

  20. Jo T, Inomata M, Takada K, Yoshimura H, Tone M, Awano N, et al. Usefulness of Measurement of End-tidal CO2 Using a Portable Capnometer in Patients with Chronic Respiratory Failure Receiving Long-term Oxygen Therapy. Intern Med. 2020 Jul 15. 59 (14):1711-1720. [QxMD MEDLINE Link]. [Full Text].

Media Gallery

  • Normal breathing.

  • Normal mechanical ventilation.

  • Hyperventilation.

  • Hypoventilation.

  • Bronchospasm.

  • Exhausted carbon dioxide absorbant.

  • Esophageal intubation.

  • Capnogram breathing. Courtesy of Pedro Tanaka, MD.

  • Curare cleft.

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    End-Tidal Capnography: Background, Indications, Technical Considerations (4)

    End-Tidal Capnography: Background, Indications, Technical Considerations (5)

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    Contributor Information and Disclosures


    Robert Thomas Arrigo, MD, MS Resident Physician, Department of Anesthesiology, Stanford University School of Medicine

    Disclosure: Nothing to disclose.


    Arjun M Desai, MD Resident Physician, Department of Anesthesiology, Stanford University Hospital and Clinics

    Disclosure: Nothing to disclose.

    Pedro P Tanaka, MD, PhD, MACM Clinical Professor, Associate Program Director for Anesthesia Residency, Fellowship Director, Advanced Training in Medical Education, Department of Anesthesiology, Pain and Perioperative Medicine, Stanford University School of Medicine

    Pedro P Tanaka, MD, PhD, MACM is a member of the following medical societies: American Society of Anesthesiologists, Brazilian Society of Anesthesiology, California Society of Anesthesiologists, Latin American Society of Regional Anesthesia, Paranaense Society of Anesthesiology

    Disclosure: Nothing to disclose.

    Alex Macario, MD, MBA Professor of Anesthesia, Program Director, Anesthesia Residency, Professor (Courtesy), Department of Health Research and Policy, Stanford University School of Medicine

    Alex Macario, MD, MBA is a member of the following medical societies: American Medical Association, American Society of Anesthesiologists, California Medical Association, International Anesthesia Research Society

    Disclosure: Received consulting fee for: Merck.

    Chief Editor

    Zab Mosenifar, MD, FACP, FCCP Geri and Richard Brawerman Chair in Pulmonary and Critical Care Medicine, Professor and Executive Vice Chairman, Department of Medicine, Medical Director, Women's Guild Lung Institute, Cedars Sinai Medical Center, University of California, Los Angeles, David Geffen School of Medicine

    Zab Mosenifar, MD, FACP, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Federation for Medical Research, American Thoracic Society

    Disclosure: Nothing to disclose.

    Additional Contributors

    Christopher D Press, MD Resident Physician, Department of Anesthesiology, Stanford University School of Medicine

    Christopher D Press, MD is a member of the following medical societies: American Medical Association, American Society of Anesthesiologists

    Disclosure: Nothing to disclose.



    Special thanks to Cheri Touchard and the Tulane Center for Advanced Medical Simulation.


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    End-Tidal Capnography: Background, Indications, Technical Considerations (2024)


    What are the three indications for end tidal CO2 monitoring? ›

    The wider use of EtCO2 monitoring in different clinical areas reflects its importance as a monitoring tool that gives indication into three crucial aspects: the patient's airway patency, breathing adequacy and circulatory status.

    What does end tidal capnography measure? ›

    1Introduction. End-tidal carbon dioxide (ETCO2) is the level of carbon dioxide that is released at the end of an exhaled breath. ETCO2 levels reflect the adequacy with which carbon dioxide (CO2) is carried in the blood back to the lungs and exhaled.

    What is EtCO2 monitoring and clinical application answers? ›

    An end-tidal CO2 monitor also can help monitor a patient's respiratory status during different medical procedures. Respiratory decline can be detected earlier during sedation procedures with end-tidal CO2 monitoring. A patient may receive too much sedative or have a lower tolerance to the sedation medication.

    What level of EtCO2 would indicate a problem? ›

    Normal EtCO2 levels range from 30s and 40s, but this may vary based on the patient's underlying respiratory and metabolic status. 3. EtCO2 levels that rise from a normal baseline to or above 50 may indicate hypoventilation is occurring.

    Do you need an order for ETCO2 monitoring? ›

    A provider order is not needed for RNs or RTs to use ETCO2. DEFINITIONS: A. Capnography monitoring- Non invasive measurement of carbon dioxide ventilation through interpretation of a waveform produced for each respiration, which reveals respiratory rate, depth, efficiency of ventilation, and the presence of apnea.

    What does it mean if ETCO2 is high? ›

    Causes of increased ETCO2 include decreased CO2 elimination [7], which can be seen with inadequate ventilation and malfunction of anesthesia equipment [8]; increased production of CO2 from hypermetabolic states [9]; and iatrogenic causes such as CO2 insufflation.

    What does capnography tell you? ›

    Capnography measures ventilation through a metric known as end-tidal carbon dioxide (EtCO2). EtCO2 values are recorded in mm Hg (millimeters of mercury), a unit of pressure. The normal values for patients regardless of age, sex, race, or size range between 35-45 mm Hg, or about 5% CO2.

    What does it mean when ETCO2 is low? ›

    The amount of exhaled CO2 depends on the adequacy of circulation to the lungs, which provides clues about circulation to the rest of the body. Low ETCO2 with other signs of shock indicates poor systemic perfusion, which can be caused by hypovolemia, sepsis or dysrhythmias.

    Why is ETCO2 monitoring important? ›

    End-tidal carbon dioxide (ETco2) monitoring provides valuable information about CO2 production and clearance (ventilation). Also called capnometry or capnography, this noninvasive technique provides a breath-by-breath analysis and a continuous recording of ventilatory status.

    Which is the most likely to cause a gradual increase in ETCO2? ›

    Hypoventilation causes an increase in ETCO2.

    Is end-tidal CO2 monitoring standard of care? ›

    In anesthesia and procedural sedation, end-tidal capnography has become the standard of care.

    What is the normal range for ETCO2? ›

    End-tidal CO2 (EtCO2) monitoring is a noninvasive technique which measures the partial pressure or maximal concentration of carbon dioxide (CO2) at the end of an exhaled breath, which is expressed as a percentage of CO2 or mmHg. The normal values are 5% to 6% CO2, which is equivalent to 35-45 mmHg.

    How to correct high ETCO2? ›

    The simplest way to correct high ETCO2 is to simply ventilate (“bag”) the animal more frequently. Low ETCO2 levels are most commonly a result of hyperventilation or diluted exhaled carbon dioxide caused by high oxygen flow rates such as those used with non-rebreathing systems.

    What is the main determinant of ETCO2? ›

    Monitoring EtCO2 levels provides vital information to guide resuscitation efforts and optimize chest compressions during cardiac arrest and CPR. The primary determinant of a patient's EtCO2 reading is the effectiveness of chest compressions in generating blood flow to oxygenate tissues and produce carbon dioxide.

    Will respiratory failure result in ETCO2? ›

    In severe cases of respiratory distress, increased effort to breathe does not effectively eliminate CO2. This causes CO2 to accumulate in the lungs and more of it to be excreted with each breath (hypercapnea), which would cause the ETCO2 level to rise.

    Why do we monitor end-tidal CO2? ›

    ETCO2 monitors give continuous, real-time details about how a person is breathing. They analyze each breath you take. The devices can show if breathing becomes fast, slow, or shallow. They provide an early warning if you are starting to have trouble breathing.

    What is the main determinant of end-tidal carbon dioxide ACLS? ›

    Monitoring EtCO2 levels provides vital information to guide resuscitation efforts and optimize chest compressions during cardiac arrest and CPR. The primary determinant of a patient's EtCO2 reading is the effectiveness of chest compressions in generating blood flow to oxygenate tissues and produce carbon dioxide.

    What is the purpose of using end-tidal CO2 during a code? ›

    However, in ACLS and in a cardiac arrest, I'm using end-tidal not necessarily for the pulmonary or respiratory status but to look at the function of the pump, the function of the heart. It can also help determine the effectiveness of the chest compressions I'm doing if the heart fails.

    What is Phase 3 of capnography waveform? ›

    That would be phase III, also called the alveolar plateau. Phase III forms the top of the waveform rectangle. It should maintain a mostly constant pressure between 35-45 mm hg as your patient breathes out. The peak pressure at the very end of the plateau is your end-tidal carbon dioxide value.

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