Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate, Inc. and/or its affiliates. All Rights Reserved.

Carbon dioxide monitoring (capnography)

Baruch Krauss, MD, EdM, FAAP
Jay L Falk, MD
Section Editors
Susan B Torrey, MD
Deputy Editor
Jonathan Grayzel, MD, FAAEM


The term capnography refers to the noninvasive measurement of the partial pressure of carbon dioxide (CO2) in exhaled breath expressed as the CO2 concentration over time. The relationship of CO2 concentration to time is graphically represented by the CO2 waveform, or capnogram (figure 1). Changes in the shape of the capnogram are diagnostic of disease conditions, while changes in end-tidal CO2 (EtCO2), the maximum CO2 concentration at the end of each tidal breath, can be used to assess disease severity and response to treatment. Capnography is also the most reliable indicator that an endotracheal tube is placed in the trachea after intubation.

Oxygenation and ventilation are distinct physiologic functions that must be assessed in both intubated and spontaneously breathing patients. Pulse oximetry provides instantaneous feedback about oxygenation. Capnography provides instantaneous information about ventilation (how effectively CO2 is being eliminated by the pulmonary system), perfusion (how effectively CO2 is being transported through the vascular system), and metabolism (how effectively CO2 is being produced by cellular metabolism).

Capnography became a routine part of anesthesia practice in Europe in the 1970s and in the United States in the 1980s. It is now part of the standard of care for all patients receiving general anesthesia and is an emerging standard of care in emergency medical services, emergency medicine, and intensive care.

This topic review will discuss the basic physiology and interpretation of capnography and its use in the emergency department.


Carbon dioxide (CO2) monitors measure gas concentration, or partial pressure, using one of two configurations: mainstream or sidestream. Mainstream devices measure respiratory gas (in this case CO2) directly from the airway, with the sensor located on the airway adapter at the hub of the endotracheal tube (ETT). Sidestream devices measure respiratory gas via nasal or nasal-oral cannula by aspirating a small sample from the exhaled breath through the cannula tubing to a sensor located inside the monitor (picture 1).

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:

Subscribers log in here

Literature review current through: Sep 2017. | This topic last updated: Oct 13, 2016.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
  1. Friesen RH, Alswang M. End-tidal PCO2 monitoring via nasal cannulae in pediatric patients: accuracy and sources of error. J Clin Monit 1996; 12:155.
  2. Gravenstein N. Capnometry in infants should not be done at lower sampling flow rates. J Clin Monit 1989; 5:63.
  3. Sasse FJ. Can we trust end-tidal carbon dioxide measurements in infants? J Clin Monit 1985; 1:147.
  4. Yamanaka MK, Sue DY. Comparison of arterial-end-tidal PCO2 difference and dead space/tidal volume ratio in respiratory failure. Chest 1987; 92:832.
  5. Hardman JG, Aitkenhead AR. Estimating alveolar dead space from the arterial to end-tidal CO(2) gradient: a modeling analysis. Anesth Analg 2003; 97:1846.
  6. Stewart RD, Paris PM, Winter PM, et al. Field endotracheal intubation by paramedical personnel. Success rates and complications. Chest 1984; 85:341.
  7. Shea SR, MacDonald JR, Gruzinski G. Prehospital endotracheal tube airway or esophageal gastric tube airway: a critical comparison. Ann Emerg Med 1985; 14:102.
  8. Pointer JE. Clinical characteristics of paramedics' performance of endotracheal intubation. J Emerg Med 1988; 6:505.
  9. Jenkins WA, Verdile VP, Paris PM. The syringe aspiration technique to verify endotracheal tube position. Am J Emerg Med 1994; 12:413.
  10. Bozeman WP, Hexter D, Liang HK, Kelen GD. Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation. Ann Emerg Med 1996; 27:595.
  11. Sayre MR, Sakles JC, Mistler AF, et al. Field trial of endotracheal intubation by basic EMTs. Ann Emerg Med 1998; 31:228.
  12. Eckstein M, Chan L, Schneir A, Palmer R. Effect of prehospital advanced life support on outcomes of major trauma patients. J Trauma 2000; 48:643.
  13. Wang HE, Sweeney TA, O'Connor RE, Rubinstein H. Failed prehospital intubations: an analysis of emergency department courses and outcomes. Prehosp Emerg Care 2001; 5:134.
  14. Katz SH, Falk JL. Misplaced endotracheal tubes by paramedics in an urban emergency medical services system. Ann Emerg Med 2001; 37:32.
  15. Gausche M, Lewis RJ, Stratton SJ, et al. Effect of out-of-hospital pediatric endotracheal intubation on survival and neurological outcome: a controlled clinical trial. JAMA 2000; 283:783.
  16. Jones JH, Murphy MP, Dickson RL, et al. Emergency physician-verified out-of-hospital intubation: miss rates by paramedics. Acad Emerg Med 2004; 11:707.
  17. Jemmett ME, Kendal KM, Fourre MW, Burton JH. Unrecognized misplacement of endotracheal tubes in a mixed urban to rural emergency medical services setting. Acad Emerg Med 2003; 10:961.
  18. Silvestri S, Ralls GA, Krauss B, et al. The effectiveness of out-of-hospital use of continuous end-tidal carbon dioxide monitoring on the rate of unrecognized misplaced intubation within a regional emergency medical services system. Ann Emerg Med 2005; 45:497.
  19. Goldberg JS, Rawle PR, Zehnder JL, Sladen RN. Colorimetric end-tidal carbon dioxide monitoring for tracheal intubation. Anesth Analg 1990; 70:191.
  20. Knapp S, Kofler J, Stoiser B, et al. The assessment of four different methods to verify tracheal tube placement in the critical care setting. Anesth Analg 1999; 88:766.
  21. Ornato JP, Shipley JB, Racht EM, et al. Multicenter study of a portable, hand-size, colorimetric end-tidal carbon dioxide detection device. Ann Emerg Med 1992; 21:518.
  22. MacLeod BA, Heller MB, Gerard J, et al. Verification of endotracheal tube placement with colorimetric end-tidal CO2 detection. Ann Emerg Med 1991; 20:267.
  23. Vukmir RB, Heller MB, Stein KL. Confirmation of endotracheal tube placement: a miniaturized infrared qualitative CO2 detector. Ann Emerg Med 1991; 20:726.
  24. Grmec S, Mally S. Prehospital determination of tracheal tube placement in severe head injury. Emerg Med J 2004; 21:518.
  25. Kelly JJ, Eynon CA, Kaplan JL, et al. Use of tube condensation as an indicator of endotracheal tube placement. Ann Emerg Med 1998; 31:575.
  26. Pollard BJ, Junius F. Accidental intubation of the oesophagus. Anaesth Intensive Care 1980; 8:183.
  27. Birmingham PK, Cheney FW, Ward RJ. Esophageal intubation: a review of detection techniques. Anesth Analg 1986; 65:886.
  28. Bhende MS, Thompson AE. Evaluation of an end-tidal CO2 detector during pediatric cardiopulmonary resuscitation. Pediatrics 1995; 95:395.
  29. Sayah AJ, Peacock WF, Overton DT. End-tidal CO2 measurement in the detection of esophageal intubation during cardiac arrest. Ann Emerg Med 1990; 19:857.
  30. Silvestri S, Krauss B, Ralls G, et al. Emergency department capnographic confirmation of prehospital endotracheal intubation in cardiac arrest patients - A preliminary report. Ann Emerg Med 2005; 46:6.
  31. Grmec S. Comparison of three different methods to confirm tracheal tube placement in emergency intubation. Intensive Care Med 2002; 28:701.
  32. Reid C, Lewis A, Habig K, et al. Sustained life-like waveform capnography after human cadaveric tracheal intubation. Emerg Med J 2015; 32:232.
  33. Cook TM, Nolan JP. Use of capnography to confirm correct tracheal intubation during cardiac arrest. Anaesthesia 2011; 66:1183.
  34. American Society of Anesthesiologists. Basic Standards for Preanesthesia Care 1999. American Society of Anesthesiologists: Standards for basic anesthetic monitoring. http://www.asahq.org/publicationsAndServices/standards/32.html (Accessed on April 16, 2006).
  35. O'Connor RE, Swor RA. Verification of endotracheal tube placement following intubation. National Association of EMS Physicians Standards and Clinical Practice Committee. Prehosp Emerg Care 1999; 3:248.
  36. American College of Emergency Physicians Policy Statement. Verification of Endotracheal Tube Placement. http://www.acep.org/webportal/PracticeResources/PolicyStatements/pracmgt/VerificationofEndotrachealTubePlacement.htm (Accessed on April 16, 2006).
  37. Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010; 122:S729.
  38. Falk JL, Rackow EC, Weil MH. End-tidal carbon dioxide concentration during cardiopulmonary resuscitation. N Engl J Med 1988; 318:607.
  39. Garnett AR, Ornato JP, Gonzalez ER, Johnson EB. End-tidal carbon dioxide monitoring during cardiopulmonary resuscitation. JAMA 1987; 257:512.
  40. Sheak KR, Wiebe DJ, Leary M, et al. Quantitative relationship between end-tidal carbon dioxide and CPR quality during both in-hospital and out-of-hospital cardiac arrest. Resuscitation 2015; 89:149.
  41. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, Part 7. 1: Adjuncts for airway control and ventilation. Circulation 2005; 112(suppl IV):IV.
  42. Davis DP, Sell RE, Wilkes N, et al. Electrical and mechanical recovery of cardiac function following out-of-hospital cardiac arrest. Resuscitation 2013; 84:25.
  43. Sanders AB, Kern KB, Otto CW, et al. End-tidal carbon dioxide monitoring during cardiopulmonary resuscitation. A prognostic indicator for survival. JAMA 1989; 262:1347.
  44. Levine RL, Wayne MA, Miller CC. End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. N Engl J Med 1997; 337:301.
  45. Wayne MA, Levine RL, Miller CC. Use of end-tidal carbon dioxide to predict outcome in prehospital cardiac arrest. Ann Emerg Med 1995; 25:762.
  46. Grmec S, Klemen P. Does the end-tidal carbon dioxide (EtCO2) concentration have prognostic value during out-of-hospital cardiac arrest? Eur J Emerg Med 2001; 8:263.
  47. Sanders AB, Ewy GA, Bragg S, et al. Expired PCO2 as a prognostic indicator of successful resuscitation from cardiac arrest. Ann Emerg Med 1985; 14:948.
  48. Asplin BR, White RD. Prognostic value of end-tidal carbon dioxide pressures during out-of-hospital cardiac arrest. Ann Emerg Med 1995; 25:756.
  49. Bhende MS, Karasic DG, Karasic RB. End-tidal carbon dioxide changes during cardiopulmonary resuscitation after experimental asphyxial cardiac arrest. Am J Emerg Med 1996; 14:349.
  50. Berg RA, Henry C, Otto CW, et al. Initial end-tidal CO2 is markedly elevated during cardiopulmonary resuscitation after asphyxial cardiac arrest. Pediatr Emerg Care 1996; 12:245.
  51. Grmec S, Lah K, Tusek-Bunc K. Difference in end-tidal CO2 between asphyxia cardiac arrest and ventricular fibrillation/pulseless ventricular tachycardia cardiac arrest in the prehospital setting. Crit Care 2003; 7:R139.
  52. Brain Trauma Foundation. Management and prognosis of severe traumatic brain injury guidelines. http://www2.braintrauma.org/guidelines/downloads/btf_guidelines_management.pdf (Accessed on April 29, 2006).
  53. Davis DP, Dunford JV, Ochs M, et al. The use of quantitative end-tidal capnometry to avoid inadvertent severe hyperventilation in patients with head injury after paramedic rapid sequence intubation. J Trauma 2004; 56:808.
  54. Helm M, Schuster R, Hauke J, Lampl L. Tight control of prehospital ventilation by capnography in major trauma victims. Br J Anaesth 2003; 90:327.
  55. Deakin CD, Sado DM, Coats TJ, Davies G. Prehospital end-tidal carbon dioxide concentration and outcome in major trauma. J Trauma 2004; 57:65.
  56. Miller RD. Miller's Anesthesia, 6th, Elsevier Churchill Livingstone, New York 2005.
  57. Swedlow, DB. Capnometry and capnography: The anesthesia disaster early warning system. Seminars in Anesthesia 1986; 3:194.
  58. Weil MH, Bisera J, Trevino RP, Rackow EC. Cardiac output and end-tidal carbon dioxide. Crit Care Med 1985; 13:907.
  59. Krauss B. Capnography as a rapid assessment and triage tool for chemical terrorism. Pediatr Emerg Care 2005; 21:493.
  60. Mieloszyk RJ, Verghese GC, Deitch K, et al. Automated quantitative analysis of capnogram shape for COPD-normal and COPD-CHF classification. IEEE Trans Biomed Eng 2014; 61:2882.
  61. Krauss B, Hess DR. Capnography for procedural sedation and analgesia in the emergency department. Ann Emerg Med 2007; 50:172.
  62. Hart LS, Berns SD, Houck CS, Boenning DA. The value of end-tidal CO2 monitoring when comparing three methods of conscious sedation for children undergoing painful procedures in the emergency department. Pediatr Emerg Care 1997; 13:189.
  63. Miner JR, Heegaard W, Plummer D. End-tidal carbon dioxide monitoring during procedural sedation. Acad Emerg Med 2002; 9:275.
  64. Burton JH, Harrah JD, Germann CA, Dillon DC. Does end-tidal carbon dioxide monitoring detect respiratory events prior to current sedation monitoring practices? Acad Emerg Med 2006; 13:500.
  65. Lightdale JR, Goldmann DA, Feldman HA, et al. Microstream capnography improves patient monitoring during moderate sedation: a randomized, controlled trial. Pediatrics 2006; 117:e1170.
  66. Krauss BS, Andolfatto G, Krauss BA, et al. Characteristics of and Predictors for Apnea and Clinical Interventions During Procedural Sedation. Ann Emerg Med 2016; 68:564.
  67. Deitch K, Miner J, Chudnofsky CR, et al. Does end tidal CO2 monitoring during emergency department procedural sedation and analgesia with propofol decrease the incidence of hypoxic events? A randomized, controlled trial. Ann Emerg Med 2010; 55:258.
  68. Qadeer MA, Vargo JJ, Dumot JA, et al. Capnographic monitoring of respiratory activity improves safety of sedation for endoscopic cholangiopancreatography and ultrasonography. Gastroenterology 2009; 136:1568.
  69. Friedrich-Rust M, Welte M, Welte C, et al. Capnographic monitoring of propofol-based sedation during colonoscopy. Endoscopy 2014; 46:236.
  70. Beitz A, Riphaus A, Meining A, et al. Capnographic monitoring reduces the incidence of arterial oxygen desaturation and hypoxemia during propofol sedation for colonoscopy: a randomized, controlled study (ColoCap Study). Am J Gastroenterol 2012; 107:1205.
  71. Conway A, Douglas C, Sutherland JR. A systematic review of capnography for sedation. Anaesthesia 2016; 71:450.
  72. Fearon DM, Steele DW. End-tidal carbon dioxide predicts the presence and severity of acidosis in children with diabetes. Acad Emerg Med 2002; 9:1373.
  73. Garcia E, Abramo TJ, Okada P, et al. Capnometry for noninvasive continuous monitoring of metabolic status in pediatric diabetic ketoacidosis. Crit Care Med 2003; 31:2539.
  74. Nagler J, Wright RO, Krauss B. End-tidal carbon dioxide as a measure of acidosis among children with gastroenteritis. Pediatrics 2006; 118:260.
  75. Kartal M, Eray O, Rinnert S, et al. ETCO₂: a predictive tool for excluding metabolic disturbances in nonintubated patients. Am J Emerg Med 2011; 29:65.
  76. Solmeinpur H, et al. Predictive Value of Capnography for Diagnosis in Patients with Suspected Diabetic Ketoacidosis in the Emergency Department. West J Emerg Med 2013; (www.escholarship.org/uc/item/5qz744fv).
  77. Hunter CL, Silvestri S, Dean M, et al. End-tidal carbon dioxide is associated with mortality and lactate in patients with suspected sepsis. Am J Emerg Med 2013; 31:64.
  78. Hunter CL, Silvestri S, Ralls G, et al. A prehospital screening tool utilizing end-tidal carbon dioxide predicts sepsis and severe sepsis. Am J Emerg Med 2016; 34:813.