Capnography
Mike McEvoy, PhD, NRP, RN, CCRN
EMS Coordinator – Saratoga County, NY
EMS Editor – Fire Engineering magazine
Cardiac Surgical ICU RN & Chair Resuscitation
Committee – Albany Medical Center
Mike McEvoy: www.mikemcevoy.com
Outline:
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Carbon dioxide
Capnography – what, where, why?
Oxygenation
Ventilation
EtCO2 equipment
Waveforms
Uses
Cases
Carbon Dioxide = CO2
• 2 oxygen atoms + 1 carbon atom
• Trace gas on earth (0.036-0.039%)
• CO2 produced by:
– Coal combustion (hydrocarbons)
– Fermentation of beer
– Respiration of living organisms
• Plants: sunlight + CO2 + water  O2
Carbon Dioxide = CO2
• Human body produces 2.3 # per day
• Solid form = dry ice
• Gas = fire extinguishers, carbonated
drinks…
CO2 (Carbon Dioxide)
Greenhouse gas (heavier than air)
– Global warming
– Ocean acidification (carbonic acid)
Physiology of Metabolism
Oxygen  Lungs  alveoli  blood
Breath
CO2
Muscles + Organs
Lungs
Oxygen
CO2
Blood
Oxygen
ENERGY
CO2
Cells
Oxygen
+
Glucose
Carbon Dioxide
• Oxygen (O2) enters the body through
the lungs and is used to produce energy
• This process is called metabolism
• Carbon Dioxide (CO2) is the waste
product of metabolism
Typical Gas Percentages
Gas
Nitrogen (N2)
Oxygen (O2)
Carbon Dioxide (CO2)
Water (H2O)
Atmospheric Exhaled
78%
21%
0.04%
0.5%
74%
16%
4%
6%
Normal Exhaled CO2 = 35 – 45 mmHg
CO2 In the Blood
• CO2 is your drive to breathe
•  CO2 causes air hunger
• Goal is to maintain PaCO2 at 40
– Body adjusts respiratory rate & depth
• Oxygen does not
affect respirations
Question:
What would happen if you injected
CO2 into the blood?
Respiratory rate and depth would 
Question:
Why do swimmers who hyperventilate
loose consciousness underwater?
 CO2 eliminates the drive to breathe
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Colorimetric
Pros
• Accurate
• Cheap (~$10-15)
• Changes color
when CO2 present
• Work for 2+ hours
• Disposable
Cons
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Secretions
Not quantitative
Adds dead space
False positives
Hard to read at night
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Capnometry
Pros
Cons
• Numeric value + RR
• Portable
• Cheaper than
waveform
capnography
• No waveform
• Does not trend
• Bulky adapter/unit
PHASEIN
EMMA™ (Masimo)
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Capnography
Pros
Cons
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•
• Expensive
• Fragile
• Warm-up time
(some units)
• Secretions
• Temperature
sensitive (some)
Numeric value + RR
Waveform
Trending
Very accurate
Infrared Spectroscopy
• CO2 absorbs 4.26 µm wavelength
• Infrared light aimed at sample
• Infrared sensors detect absorption
and calculate CO2
Capnography Technologies
• Sidestream (1st generation)
– Sensor in remote location
– Samples gas from circuit (150-250 mL/min)
• Mainstream (2nd generation)
– Sensor in the airway
Capnography Technologies
• Microstream® (next generation)
– Sensor in remote location
– Samples only 50 mL/min from circuit
SpO2 versus EtCO2
Oxygenation and Ventilation
Oxygenation (Pulse Ox)
– O2 for metabolism
– SpO2 measures
% of O2 in RBCs
– Reflects changes in
oxygenation within
5 minutes
Ventilation (Capnography)
– CO2 from metabolism
– EtCO2 measures exhaled
CO2 at point of exit
– Reflects changes in
ventilation within
10 seconds
Physiology of Metabolism
Oxygen  Lungs  alveoli  blood
Breath
CO2
Muscles + Organs
Lungs
Oxygen
CO2
Blood
Oxygen
ENERGY
CO2
Cells
Oxygen
+
Glucos
e
Pulse Oximetry
Problems:
• Accuracy
• Motion & artifact
• Dyshemoglobins
• Perfusion
Pulse Oximetry
Pulse Oximetry
Model of Light Absorption At Measurement
Site Without Motion
AC Variable light absorption due
pulsatile volume of arterial blood
Absorption
DC Constant light absorption due to
non-pulsatile arterial blood.
DC Constant light absorption due to
venous blood.
Time
DC Constant light absorption due to
tissue, bone, ...
Model of Light Absorption At Measurement
Site With Motion
Absorption
AC Variable light absorption due
pulsatile volume of arterial blood
DC Constant light absorption due to
non-pulsatile arterial blood.
AC Variable light absorption due to
moving venous blood
Time
DC Constant light absorption due to
venous blood.
DC Constant light absorption due to
tissue, bone ...
Influence of Perfusion on Accuracy of
Conventional Pulse Oximetry During Motion
Good Perfusion (Conventional PO)
SpaO2=98
SpvO2=88
SpO2=93
Poor Perfusion (Conventional PO)
SpaO2=98
SpvO2=50
SpO2=74
Conventional Pulse Oximetry
Algorithm
R & IR
Digitized,
Filtered &
Normalized
R/IR
MEASUREMENT
T
CONFIDENCE
Post
Processor
% Saturation
3 options during motion or low perfusion:
1. Freeze last good value
2. Lengthen averaging cycle
3. Zero out
Next Generation Pulse
Oximetry
Next Generation Pulse
Oximetry
Masimo SET: Signal Extraction
Technology
R/IR
(Conventional Pulse
Oximetry)
MEASUREMENT
CONFIDENCE
MEASUREMENT
DSTTM
R & IR
Digitized,
Filtered &
Normalized
CONFIDENCE
MEASUREMENT
FSTTM
CONFIDENCE
Confidence
Based
Arbitrator
Post
Processor
% Saturation
DST
SET – 97%
MEASUREMENT
SST
TM
CONFIDENCE
0
Proprietary
Algorithm 4
MEASUREMENT
CONFIDENCE
SET “Parallel Engines”
50%
66% 97% 100%
SpO2%
Discrete Saturation Transform (DST)
SET separates the venous and arterial saturation values
(conventional oximetry averages the values to produce a reading)
Variable
Constant
Variable
Averaging inaccurate
0
50%
66%
86%
Constant
97% 100%
SpO2%
Conventional Pulse
Oximetry
0
50%
Separating - accurate
66%
86%
97% 100%
SpO2%
Measure Through
Motion Pulse Oximetry
Carbon Monoxide (CO)
Gas:
– Colorless
– Odorless
– Tasteless
– Nonirritating
Physical Properties:
– Vapor Density = 0.97
– LEL/UEL = 12.5 – 74%
– IDLH = 1200 ppm
Limitations of Pulse Oximetry
Conventional pulse oximetry can not distinguish
between COHb and O2Hb
From Conventional
Pulse Oximeter
SpCO-SpO2 Gap:
The fractional difference between
actual SaO2 and display of SpO2
(2 wavelength oximetry) in
presence of carboxyhemoglobin
From invasive COOximeter Blood
Sample
Barker SJ, Tremper KK. The Effect of Carbon Monoxide Inhalation on Pulse Oximetry and
Transcutaneous PO2. Anesthesiology 1987; 66:677-679
Pulse CO-oximetry
Pulse CO-oximetry
• Uses multiple wavelengths of light
• Differentiates CO from O2
Hgb Signatures: Physics of O2
Pathways
SpCO User Concerns
1. Multiple wavelengths of light (8+) =
Probe Placement:
– Probe fits the finger
– Centered over nail bed
2. Visible spectrum light =
Protect from ambient light
– Sunlight, strobes, etc.
Know Your Equipment
Back to CO2…
What does exhaled CO2 tell us?
1. Ventilation
2. Perfusion
3. Metabolism
Endotracheal Intubation
What Should Happen
Lungs (Good)
$tomach (Bad, Very Bad)
Anesthesia Litigation
Respiratory Damaging Events
60%
50%
40%
30%
20%
10%
0%
1970's
1980's
1990's
2000's
American Society for Anesthesiologists:
Closed Claims Project Database, 2010
Guidelines 2005
EtCO2 recommended
to confirm ET tube
placement
Intubated Patient
• Airway adapter plugs into LifePak®
• Be sure adapter is tightly attached
• If not seated, waveform may flatten
Capnography Information
Respiratory Rate
End Tidal Carbon Dioxide
Capnography Waveform
Capnography Waveforms
• The higher the waveform, the more
CO2
45
0
• Normal EtCO2 is 35 – 45 mmHg
(usually the same as arterial CO2)
Capnography Waveforms
• The length of the waveform
corresponds to respiratory rate
45
Hyperventilation
0
45
0
Hypoventilation
Capnography Waveform
Inspiration or manual
ventilation with a bagvalve-mask or ventilator
Capnography Waveform
Exhalation
Capnography Waveform
End-tidal
End-tidal (EtCO2)
is the end point of
expiration. This is
the point on the
waveform that
produces the
numeric CO2 value.
Capnogram Parts
Phase I
• Start of exhalation
• No CO2 (dead space)
Capnogram Parts
Phase II
• Exhalation continues
• Rapid rise in CO2
• Mixing dead space & alveolar gases
Capnogram Parts
Phase III
also called the
Alveolar Plateau
• End exhalation
• All alveolar gas
Capnogram Parts
• Rapid drop in CO2
• Start of inhalation
Phase IV
Capnogram Angles
 (beta angle)
 (alpha angle)
•  normal = 100 – 110°
• Airway obstruction will 
•  normal = 90°
• Rebreathing will 
Capnography Waveforms
Normal
45
0
Hyperventilation
45
0
Hypoventilation
45
0
Intubation
• You have intubated a 36 year old
motorcyclist laying in the roadway
• HR 128, RR 14 by BVM, SpO2 99%
• Esophageal intubation
• 6 breaths to evacuate gastric CO2
What about the Pulse Ox?
Sp02
98
SpO2 will not drop for several
minutes (5+ minutes)
Intubation
• You re-intubate the motorcyclist
• This is the capnography waveform:
• Is the tube in?
• Is the ventilation rate and depth
appropriate?
During Transport
• Enroute to the trauma center, you
observe this on the capnography:
• What happened?
• When is this most likely to occur?
• Tubes most commonly displace
during patient movement
Ventilator Transport
• You are moving a 23 yo GSW to
the head from a community ED to a
neurosurgical ICU
• He is intubated and sedated:
• EtCO2 = 35, RR = 24
• “Curare Cleft” = diaphragmatic
movement (breathing over drugs)
Ventilator Transport
• You don’t make any changes
• The patient appears to awaken:
• EtCO2 = 30, RR = 38
• “Curare Cleft” = diaphragmatic
movement (breathing over drugs)
• “Bucking” ventilation needs drug tx
Ventilator Transport
• You are moving a ventilated patient
• The patient appears short of breath
• Waveform does not return to zero
• Baseline gradually increasing
• This is called “rebreathing”
Ventilator Transport
• You’re cardiac arrest reversal is
unresponsive, on BVM ventilation
• BP 110/58, HR 90, RR 22, SpO2 97
• Is the patient ventilating? NOT WELL
• Causes: cuff leak, ETT displaced…
Cardiac Arrest
Carbon Dioxide (CO2) Production
Cardiac
Arrest
Oxygen
Circulation
Carbon Dioxide
Respiration
AHA Guidelines 2010
• Continuous quantitative waveform
capnography recommended for
intubated patients throughout periarrest period. In adults:
1. Confirm ETT placement
2. Monitor CPR quality
3. Detect ROSC with EtCO2 values
1. Confirm ET placement
• When is an advanced airway most
likely to become dislodged?
• During patient movement
2. Monitor the quality of CPR
• Try to maintain a
minimum EtCO2 of 10
mmHg
• Push
HARD (> 2” or 5 cm)
FAST (at least 100)
• Change rescuer
Every 2 minutes
CPR in progress:
• Compression depth
• Compression rate
• Compressor
• Extreme acidosis
• Futility
• Other?
High-Quality CPR =  CO2
3. EtCO2 to detect ROSC
(Return Of Spontaneous Circulation)
• 90 pre-hospital intubated arrest patients
• 16 survivors
• 13 survivors: rapid rise in exhaled CO2
was the earliest indicator of ROSC
• Before pulse or blood pressure were
palpable
Wayne MA, Levine RL, Miller CC. “Use of End-tidal Carbon
Dioxide to Predict Outcome in Prehospital Cardiac Arrest” .
Annals of Emergency Medicine. 1995; 25(6):762-767.
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(5):301-306.
3. EtCO2 to detect ROSC
Question: Would bicarbonate  EtCO2?
Answer: Yes
CPR – What Causes This?
• Notice the small “ripples” ?
• Compressions generate air
movement – this expels CO2
Spontaneously Breathing
Capnography helps assess:
– Accurate respiratory rate
– Airway patency (bronchospasm, air
trapping, obstruction)
– Shock states
– Response to treatment
Bronchospasm
• Asthma, COPD…
• Elevation of  angle, loss of alveolar
plateau (“shark-fin” appearance)
• Degree of angle = severity
Effects of Treatments
Air Trapping
• Emphysema is results in prolonged
expiration
• Increases  angle:
Unconscious
• 16 yo found unresponsive in high
school locker room – unknown hx
• Hypoventilation (? pharmaceutical)
• Use capnography on EVERY
patient you treat with narcotics!
Difficulty Breathing
• 14 yo asthmatic – severely SOB
• Hyperventilation
• No evidence of airway obstruction
or air trapping
Difficulty Breathing
• 81 yo with COPD and heart failure
• Acutely short of breath
• Capnogram favors pulmonary
edema (no evidence acute COPD
exacerbation)
Same Patient – Diff Breather
• 81 yo with COPD and heart failure
• Acutely short of breath
• Capnogram favors COPD
exacerbation
Chest Pain
• 51 yo with substernal chest pain
• No distress, STEMI work up
• “Cardiac oscillations” – cardiac
pressures being transmitted to
airway (ripple effect)
Perfusion and pH
• Cardiac arrest = no CO2
– Capnography reflects perfusion
–  cardiac output =  EtCO2
• CO2 is transported in the blood as
bicarbonate (HCO3)
– In severe acidosis,  HCO3 =  EtCO2
Post Cardiac Arrest Patient
• You have resuscitated a 47 yo pt.
found in v-fib on a city bus
• The patient is unresponsive,
ventilated by BVM; pulses are weak
• Suspect falling cardiac output!
17 yo pt. in DKA
• You are called to a physician office
to transport a patient in DKA
• The patient is alert and oriented;
blood sugar is reportedly 880
General Weakness Patient
• You are called to see a 75 yo heart
failure pt. with general weakness
• She is cool, BP 80/50, HR 128 afib
• What does the capnography say?
Cardiogenic Shock!
Rounded Waveforms
Be suspicious of rounded waveforms:
• These often imply low perfusion,
acidosis, sepsis, poisoning or other
metabolic derangements
Review
Label Inhalation & Exhalation
Inhalation
Expiration
Inhalation
Where is EtCO2 Measured?
End-tidal CO2
Normal EtCO2 is 35 – 45 mmHg
AHA Guidelines 2010
• What are the three reasons for use
of continuous quantitative waveform
capnography during cardiac arrest?
1. Confirm ETT placement
2. Monitor CPR quality
3. Detect ROSC with EtCO2 values
Goals During Cardiac Arrest
• Try to maintain a
minimum EtCO2 of ?
• 10 mmHg
• Push
HARD (> 2” or 5 cm)
FAST (at least 100)
• Change rescuer
Every 2 minutes
Review
• 14 yo patient, SOB, asthma hx
• Clutching her albuterol inhaler
• Slow upstroke = bronchospasm
Review
• 67 yo COPD patient, acute SOB
• SpO2 97%, HR 88, BP 138/86
• Normal waveform, hyperventilation
Review
• 74 yo ROSC post v-fib arrest,
unconscious, on ventilator, VSS
• Cleft (“curare cleft”) suggests noncompliance with vent
Review
• 45 yo auto-pedestrian, bilateral tibfib fractures, BP 120/60, HR 90,
RR 16, SpO2 97%, EtCO2 45
• Normal waveform
Review
• Elderly cancer pt., unresponsive at
home in bed
• Normal waveform – hypoventilation
• RR 4, EtCO2 75 (> than 70 in
without COPD = respiratory failure)
Review
• 60 yo COPD patient fever, chest
pain, denies SOB, using accessory
muscles to breathe
• Prolonged expiration (  angle);
air trapping – normal capnogram in
emphysema
Review
• 90 year old cardiac arrest,
immediately after endotracheal
intubation:
• Esophageal intubation
• 6 breaths to evacuate gastric CO2
Review
• 55 yo COPD patient with flu like s/s
• Cardiac oscillations – normal EtCO2
Review
• 18 yo GSW to chest
• Profound hypoperfusion – arrest
imminent
Questions?
Thanks for your attention!
Slides posted at:
www.mikemcevoy.com