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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
• 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 – Colorimetric
Limited 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
Hand held side stream capnogram
Bedside monitor mainstream
capnogram
Capnography reflects CO2
as it is being exhaled from
the lungs
4
3
1
2
• 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
Incomplete exhaled
CO2 pattern
Adequate
plateau
Phase
indicating
good
Alveolar
emptying
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
7
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
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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. http://www.asahq.org/publicationsAndServices/standards/02.pdf#2
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. www.aagbi.org/guidelines.html
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 outof-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.
www.acep.org/1,4923,0.html
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
• 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
12
51 yr female requires NG
placement. After difficult
attempt, CO2 analyzed.
• Should you
instill the tube
feeding or
reposition the
NG?
NG placement research
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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.
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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.
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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 Nurs 2007
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 needed
Capnography is more valuable than
oximetry in assessing ventilation
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
• 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 Example of Limited Role
of Oximetry in Hypoventilation
PaO2
95
80
99
SpO2
.98
.96
.98
FIO2
RA
RA
.30
PetCO2
39
54
60
pH
7.38
7.25
7.23
Case 1
A 56 year old man admitted to the outpatient procedure area for a follow-up colonoscopy. The patient had a colonoscopy 3 years
earlier where a pre cancerous polyp was removed. During the last colonoscopy, the patient required above normal amounts of
sedation and had a prolonged post procedure recovery. During this procedure, the physician elects to use Propofol instead of
Midazolam due to it’s more rapid elimination and shorter recovery time. Since Propofol can suppress respiration as well, the
physician elects to use capnography to monitor the patient. The capnography is to be measured by a nasal cannula, sidestream
method. Twenty minutes into the procedure, you note the PetCO2 listed below. What would your actions be based on this
information?
Admission
72
12
132/72
100
37
5 minutes
into
procedure
76
10
128/70
100
42
20 minutes
into
procedure
73
10
134/78
100
48
Case 2
A 76 year old female is being weaned from mechanical ventilation. He has a
mainstream CO2 analyzer in his ventilator circuit. Fifteen minutes into the weaning
attempt, the following information is available. Based on this information, what would
you do?
P
RR
BP
SpO2
PetCO2
0730 (weaning 71
initiated)
15
130/86
98
35
0745
19
128/88
97
51
82
Case 3
A 73 year old man is on your unit with the diagnosis of CHF and COPD.
He has been improving and is expected to be discharged tomorrow. He is
on oxygen therapy at 4 LPM and is simultaneously be monitored by
capnography via the nasal cannula, sidestream method. At 0300, you
hear the CO2 alarm and go into investigate. He is difficult to arouse. The
following information is available to you. What would your actions be
based on this information?
0100
87
14
138/82
95
31
0200
79
10
134/84
97
33
0300
83
10
138/78
95
59
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?
Pulse
RR
NIBP
SpO2
PetCO2 Meds
Pre extubation
114
44
132/64
98
34
2 mg Midazolam,
50 mcg/Fentanyl
Extubated
102
38
138/60
97
33
5 mg bolus
Gtt to 4 mg Midazolam,
Gtt to 100 mcg/Fentanyl
Post reintubation
and sedation
76
12
128/88
99
47
47
33
Capnography and MAC
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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):27580.
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
Application #3
Capnography and
Assessment of Blood Flow
Use in Critical Care
24
Normal
Ventilation &
Perfusion
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
• 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
26
blood flow
CPR, Blood Flow and
Outcomes
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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
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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 endtidal 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 endtidal 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
PetCO2 levels during cardiac
arrest
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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
•
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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.
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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?
15
10
5
0
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
122/76
P – 92
110
IMV 10/14
IMV 10/22
SpO2 .97
SpO2 .95
PaCO2 – 32
PaCO2 - 29
PetCO2 - 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?
20
10
0
31
Answer
• The severe drop in PetCO2 from 28 to 7 makes it
unlikely this is anxiety. This is more likely a
pulmonary embolism. The widened PaCO2PetCO2 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.
32
Questions
1) Which of the following are indicators of sudden loss of blood flow
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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
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a, b
•
a, c
•
b, c
•
a, b, c
2) Which of the following indicate an increased deadspace
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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?
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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
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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?
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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?
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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