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Capnography: Is it helpful?. Has been called the 15 second triage tool The newest vital sign? Value lies in very simple application Advanced use requires in depth understanding of ventilation and perfusion. Key Uses of Capnography.

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capnography is it helpful
Capnography: Is it helpful?
  • Has been called the 15 second triage tool
  • The newest vital sign?
  • Value lies in very simple application
    • Advanced use requires in depth understanding of ventilation and perfusion
key uses of capnography
Key Uses of Capnography
  • If PetCO2 increases, ventilation is threatened and airway protection may be needed
  • If PetCO2 suddenly falls to zero, airway is lost, breathing may have stopped or sensor is malpositioned
    • Included is determining tube placement by detection of CO2 (ET and NG)
  • If PetCO2 suddenly falls (without a change in Ve), the loss of cardiac output is likely
Methods for Measuring Exhaled CO2 – ColorimetricLimited due to lack of waveform and easy to interpret numeric value

Purple – PetCO2% - < .5%

Tan – PetCO2% .5-2%

Yellow – PetCO2% - > 2%

Normal PetCO2 >4%

methods for measuring exhaled co2 capnography
Methods for Measuring Exhaled CO2 - Capnography

Bedside monitor mainstream capnogram

Hand held side stream capnogram

capnography reflects co2 as it is being exhaled from the lungs
Capnography reflects CO2 as it is being exhaled from the lungs


  • At the end of exhalation, called the end tidal CO2 or PetCO2 for pressure of CO2 at end tidal breathing, the exhaled CO2 is reflecting alveolar CO2. Normally, the PetCO2 value of 1-5 mm Hg below the arterial (or alveolar) CO2 level.




identifying adequate co2 emptying pattern
Identifying Adequate CO2 Emptying Pattern

Incomplete exhaled

CO2 pattern

Adequate plateau

Phase indicating good

Alveolar emptying

clinical application 1 detecting tube placement endotracheal and esophageal tubes
Clinical Application #1 Detecting Tube placement – Endotracheal and Esophageal tubes
  • Capnography detects carbon dioxide from lungs
  • Endotracheal tubes placed in the esophagus do not produce capnography waveform
  • Nasogastric tubes placed in trachea will produce a capnogram
clinical application detecting airway loss and ventilator disconnection
Clinical Application #Detecting airway loss and ventilator disconnection
  • Current Alarms to Identify Patient Disconnection from the Ventilator are Very Accurate. However, they are ventilator monitors, not patient monitors
  • The capnogram is the fastest, most reliable method to identify if a patient has lost the airway or is disconnected from the mechanical ventilator
  • When a patient loses the airway or is disconnected from the ventilator, the capnogram immediately goes flat.

Case study - A 21 year old female is being transported for a CT scan. During transport, she extubates herself. The CRNA who is present immediately reintubates. While waiting for the CT to be started, he extubates himself again. The CRNA is not present. The nurse attempts to reintubate by waiting for inspiration and then sliding the tube back in. She hears breath sounds and she is trying to get the CRNA or physician to help. However, the question is, is the endotracheal tube in the correct location?

literature supporting capnography in endotracheal tube placement
Literature supporting Capnography in Endotracheal Tube Placement
  • American Heart Association. Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2000;102 (8 suppl) :I86–I89.
  • American Society of Anesthesiologists. Standards for Basic Anesthetic Monitoring. Approved by House of Delegates, October 1986, amended 2005.
  • Hogg K, Teece S. Colourimetric CO2 detector compared with capnography for confirming ET tube placement. Emerg Med J 2003;20:265–6.
  • MacLeod BA, Heller MB, Gerard J, et al. Verification of endotracheal tube placement with colorimetric end-tidal CO2 detection. Ann Emerg Med 1991;20:267–70.
  • Recommendations for Standards of Monitoring During Anaesthesia and Recovery. 3rd edition, December 2000. The Association of Anaesthetists of Great Britain and Ireland.
  • 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;3:248–50.
  • Position statement number 1. Confirmation of endotracheal tube placement with end tidal CO2 detection. Emerg Med J 2001;18329
  • Repetto JE, Donohue PA-C PK, Baker SF, Kelly L, Nogee LM. Use of capnography in the delivery room for assessment of endotracheal tube placement. J Perinatol. 2001 Jul-Aug;21(5):284-7.
  • Silvestri S, Ralls GA, Krauss B, Thundiyil J, Rothrock SG, Senn A, Carter E, Falk J. 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 May;45(5):497-503.
  • Singh S, Allen WD Jr, Venkataraman ST, Bhende MS. Utility of a novel quantitative handheld microstream capnometer during transport of critically ill children. Am J Emerg Med. 2006 May;24(3):302-7.
  • Verification of endotracheal tube placement: policy statement. American College of Emergency Physicians.,4923,0.html
use in placing ng tubes
Use in Placing NG Tubes
  • When placing Nasogastric tubes, capnography can help identify if the NG tube is in the esophagus versus the lungs
  • Clinical applications also include placement of large diameter tubes prior to gastric lavage during treatment of an overdose patient
  • Obvious benefit is to avoid instillation of substances intended for the stomach (e.g. tube feeding, charcoal) in the lungs
  • May avoid a x-ray for tube placement
detecting esophageal intubations
Detecting Esophageal Intubations
  • Capnography detects carbon dioxide from lungs
  • Endotracheal tubes placed in the esophagus do not produce capnography waveform
  • Slide the nasogastric tube in about 20 cm and pause momentarily. If no CO2 is detected, the tube is in the esophagus.
  • Correct detection of tube placement is immediate
51 yr female requires ng placement after difficult attempt co2 analyzed
51 yr female requires NG placement. After difficult attempt, CO2 analyzed.
  • Should you instill the tube feeding or reposition the NG?
ng placement research
NG placement research
  • Ackerman MH, Mick DJ. Technologic approaches to determining proper placement of enteral feeding tubes. AACN Adv Crit Care. 2006 Jul-Sep;17(3):246-9.
  • Araujo-Preza CE, Melhado ME, Gutierrez FJ, Maniatis T, Castellano MA. Use of capnometry to verify feeding tube placement. Crit Care Med. 2002 Oct;30(10):2255-9.
    • Colorimetric device
    • There were no false positives or negatives; the technique was 100% specific. One placement out of the 53 was found to be in the trachea.
    • To verify the sensitivity, 20 placements were made directly into the trachea through an endotracheal tube. In all 20 cases, carbon dioxide was detected.
      • No false negatives occurred, indicating 100% sensitivity.
  • D'Souza CR, Kilam SA, D'Souza U, Janzen EP, Sipos RA. Can J Surg. 1994 Oct; 37(5): 404-8.
  • Ellett ML, Woodruff KA, Stewart DL. The use of carbon dioxide monitoring to determine orogastric tube placement in premature infants: a pilot study. Gastroenterol Nurs2007 Nov-Dec;30(6):414-7
  • Burns SM, Carpenter R, Blevins C, Bragg S, Marshall M, Browne L, Perkins M, Bagby R, Blackstone K, Truwit JD. Detection of inadvertent airway intubation during gastric tube insertion: Capnography versus a colorimetric carbon dioxide detector. Am J Crit Care. 2006 Mar;15(2):188-95.

Clinical Application #2 Assessing adequacy of ventilation

If PetCO2 increases, ventilation is threatened and airway protection is neededCapnography is more valuable than oximetry in assessing ventilation

ventilation assessment
Ventilation Assessment
  • The main reason for a PetCO2 value to increase is reduced alveolar ventilation
    • Obtaining a blood gas can confirm this possibility
  • During sedation, weaning from ventilation or managing reactive airway patients, the PetCO2 is the first indication of danger
    • If the PetCO2 increases by 10 mm Hg, airway protection should be implemented
    • If sedation or analgesia is being administered, stop the infusion until the PetCO2 returns to near baseline
      • Monitoring patient simultaneously for comfort and awareness
limited role of pulse oximetry in assessing ventilation
Limited Role of Pulse Oximetry in Assessing Ventilation
  • Normal SaO2 determined by PaO2
  • If patient hypoventilates, PaCO2 increases and will drive PaO2 downward in direct proportion to PaCO2 increase
    • If PaCO2 increases by 10, PaO2 will decrease by 10
    • If PaO2 is 90, will decrease to 80 mm Hg
      • SaO2 will decrease from 98 to 97.
  • Oximeter is not sensitive to rises in PaCO2
  • When oxygen therapy is added or increased, rise in PaCO2 is completely obscured

Case 4

A 44 yr old male admitted to MICU with unknown fever, SOB, hypoxemia. pH 7.34, PaCO2 38, PaO2 44, SpO2 .78. He is intubated, IMV 12/44. Extubates himself, is reintubated. Sedation is increased. RR decreases to 12. .What is the effect of sedation on ventilation?



capnography and mac
Capnography and MAC
  • Anderson JL, Junkins E, Pribble C, Guenther E. Capnography and depth of sedation during propofol sedation in children. Ann Emerg Med. 2007 Jan;49(1):9-13.
  • 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 May;13(5):500-4.
  • Deitch K, Chudnofsky CR, Dominici P. The utility of supplemental oxygen during emergency department procedural sedation and analgesia with midazolam and fentanyl: a randomized, controlled trial. Ann Emerg Med. 2007 Jan;49(1):1-8.
  • Fu ES, Downs JB, Schweiger JW, Miguel RV, Smith RA. Supplemental oxygen impairs detection of hypoventilation by pulse oximetry. Chest. 2004 Nov;126(5):1552
  • 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 Jun;13(3):189-93.
  • Lightdale JR, Goldmann DA, Feldman HA, Newburg AR, DiNardo JA, Fox VL. Microstream capnography improves patient monitoring during moderate sedation: a randomized, controlled trial. Pediatrics 2006 Jun;117(6):e1170-8.
  • Melloni C. Anesthesia and sedation outside the operating room: how to prevent risk and maintain good quality. Curr Opin Anaesthesiol. 2007 Dec;20(6):513-9.
  • Miner JR, Heegaard W, Plummer D. End-tidal carbon dioxide monitoring during procedural sedation. Acad Emerg Med. 2002 Apr;9(4):275-80.
  • Pino RM. The nature of anesthesia and procedural sedation outside of the operating room. Curr Opin Anaesthesiol. 2007 Aug;20(4):347-51.
  • Soto RG, Fu ES, Vila H Jr, Miguel RV. Capnography accurately detects apnea during monitored anesthesia care. Anesth Analg. 2004 Aug;99(2):379-82.
  • Tobias JD. End-tidal carbon dioxide monitoring during sedation with a combination of midazolam and ketamine for children undergoing painful, invasive procedures. Pediatr Emerg Care. 1999 Jun;15(3):173-5.
  • Vargo JJ, Zuccaro G Jr, Dumot JA, Conwell DL, Morrow JB, Shay SS. Automated graphic assessment (capnography) of respiratory activity is superior to pulse oximetry and visual assessment for the detection of early respiratory depression during therapeutic upper endoscopy. Gastrointest Endosc. 2002 Jun;55(7):826-31.
  • Webb RK, van der Walt JH, Runciman WB, Williamson JA, Cockings J, Russell WJ, Helps S. The Australian Incident Monitoring Study. Which monitor? An analysis of 2000 incident reports. Anaesth Intensive Care 529-42(5):, 1993 Oct;21
illustration of the formation of deadspace in the lungs


Ventilation &


Illustration of the Formation of Deadspace in the Lungs

Reduced blood flow decreases alveolar CO2 - this decrease

is detected in the exhaled

breath by capnography

capnography and deadspace
Capnography and Deadspace
  • Normally, the end portion of the capnography wave (end tidal PCO2 or PetCO2) is slightly lower than the arterial PCO2 level
  • The normal PaCO2 -PetCO2 gradient is 1-5 mm Hg.
  • The primary reason for the gradient to widen is an increase in physiologic deadspace (such as occurs with a change in perfusion)
  • Sudden change in PetCO2 and the PaCO2-PetCO2 gradient is usually due to sudden drop in pulmonary blood flow
cpr blood flow and outcomes
Ahrens et al – AJCC 2001

Weil et al 1999 - CCM

Levine, Wayne, Miller - NEJM - 1997

Asplin & White 1995 - Ann Emer Med

Domsky et al -1995 - CCM

Idris et al 1994 - Ann Emer Med

White & Asplin 1994 - Ann Emer Med

Ward et al 1993 - Ann Emer Med

Angelos et al 1992 - Resuscitation

Isserles & Breen 1991- A&A

Callaham & Barton 1990 - CCM

Gazmuri et al 1989 - CCM

Garnett et al 1987 - JAMA

Weil et al 1985 - CCM

Baraka AS, Aouad MT, Jalbout MI, Kaddoum RN, Khatib MF, Haroun-Bizri ST. End-tidal CO2 for prediction of cardiac output following weaning from cardiopulmonary bypass. J Extra Corpor Technol. 2004 Sep; 36(3) :255-7.

Deakin CD, Sado DM, Coats TJ, Davies G. Prehospital end-tidal carbon dioxide concentration and outcome in major trauma. J Trauma 2004 Jul;57(1):65-8.

Grmec S, Krizmaric M, Mally S, Kozelj A, Spindler M, Lesnik B. Utstein style analysis of out-of-hospital cardiac arrest--bystander CPR and end expired carbon dioxide. Resuscitation 2007; Mar;72(3):404-14.

Gazmuri RJ, Kube E. Capnography during cardiac resuscitation: a clue on mechanisms and a guide to interventions. Crit Care. 2003;7(6):411-412. Epub 2003 Oct 06.

Kline JA, Arunachlam M. Preliminary study of the capnogram waveform area to screen for pulmonary embolism. Ann Emerg Med. 1998 Sep;32(3 Pt 1):289-96.

Kunkov S, Pinedo V, Silver EJ, Crain EF. Predicting the need for hospitalization in acute childhood asthma using end-tidal capnography. Pediatr Emerg Care. 2005 Sep;21(9):574-7.

Mallick A, Venkatanath D, Elliot SC, Hollins T, Nanda Kumar CG. A prospective randomised controlled trial of capnography vs. bronchoscopy for Blue Rhino percutaneous tracheostomy. Anaesthesia. 2003 Sep;58(9):864-8.

Pernat A, Weil MH, Sun S, Tang W. Stroke volumes and end-tidal carbon dioxide generated by precordial compression during ventricular fibrillation. Crit Care Med. 2003 Jun;31(6):1819-23

Sanchez O, Wermert D, Faisy C, Revel MP, Diehl JL, Sors H, Meyer G. Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with an abnormal D-dimer test result. J Thromb Haemost. 2006 Jul;4(7):1517-22.

Sehra R, Underwood K, Checchia P. End tidal CO2 is a quantitative measure of cardiac arrest. Pacing Clin Electrophysiol 2003 Jan;26(1 Pt 2):515-7

CPR, Blood Flow and Outcomes
petco2 levels during cardiac arrest
PetCO2 levels during cardiac arrest
  • PetCO2 values should rise to > 10mm Hg during successful resuscitation efforts
  • Prolonged PetCO2 levels < 10 have been shown to correlate with low cardiac outputs and poor survival
    • Levine RL, Wayne MA, Miller CC. End tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. New England Journal of Medicine 1997;337:301-6.

Case #1 - A 66 yr old female is brought into the ER, CPR is in progress. She was found “down” in her house by her husband. Paramedics have been doing CPR for > 20 minutes. Her capnography wave shows a value of 6 mm Hg. How would you assess the adequacy of the resuscitation effort?






capnography wave

showing a value of

about 6


A 73 yr old male following a CABG and valve replacement complains of acute shortness of breath at 0630. He has the following information present:0600 0630 BP 112/68 122/76P – 92 110IMV 10/14 IMV 10/22SpO2 .97 SpO2 .95PaCO2 – 32 PaCO2 - 29PetCO2 - 28 PetCO2 - 7 (see waveform below)Is this possibly an anxious reaction due to postoperative fear or has some physiologic problem, like a PE occurred?




  • The severe drop in PetCO2 from 28 to 7 makes it unlikely this is anxiety. This is more likely a pulmonary embolism. The widened PaCO2-PetCO2 gradient clearly indicates a worsened deadspace.
  • If this was due solely to anxiety, the PaCO2 level would be about 12 (based on the PetCO2 of 7), a value unlikely to be achieved by the present respiratory rate.
  • An immediate workup for a PE is necessary in this patient.

1) Which of the following are indicators of sudden loss of blood flow

    • Rise of PetCO2 from 40 to <10 mm Hg within 2 minutes
    • Rise of PaCO2 > 10 mm Hg in 1 minute
    • Decrease in PaO2 of 10 mm Hg within 30 seconds
  • a, b
  • a, c
  • b, c
  • a, b, c

2) Which of the following indicate an increased deadspace

    • PaCO2 41, PetCO2 49
    • PaCO2 32, PetCO2 28
    • PaCO2 45, PetCO2 39
    • PaCO2 39, PetCO2 21

3) Which of the following are consistent with a sudden loss of cardiac output?

    • PetCO2 decrease from 30 to 10 mm Hg
    • Increase in PetCO2 from 30 to 40 mm Hg
    • PetCO2 of 30 with a Ve of 10 LPM
    • PetCO2 of 50 with a Ve of 4.1 LPM

4) If the PaCO2 is 40 and the PetCO2 is 35, what does that reveal about deadspace?

  • a. it is normal
  • b. it is high
  • c. deadspace is low
  • d. not able to tell from this information

5) If the PetCO2 suddenly falls from 35 to 20 without a change in Ve, what has likely happened?

    • the patient is likely becoming anxious
    • the patient is likely experiencing the need for an increased Ve
    • pulmonary blood flow has increased
    • cardiac output has likely decreased

6) If a capnogram suddenly goes flat on a patient on mechanical ventilation, what has likely happened?

    • The patient has likely developed a pneumothorax
    • A MI is likely occurring
    • The patient has potentially become disconnected from the ventilator
    • The patient is experiencing an severe anxiety reaction