Capnography:
The Window Into Your
Patient
Talk Code 682
Mike McEvoy, PhD, RN, CCRN, REMT-P
Senior Staff RN – Cardiothoracic Surgical ICUs – Albany Medical Ctr
EMS Coordinator – Saratoga County, New York
EMS Editor – Fire Engineering Magazine
EMS Director – New York State Association of Fire Chiefs
mikemcevoy.com
SpO2 versus EtCO2
Physiology
Oxygen  lungs  alveoli  blood
Oxygen
breath
CO2
muscles + organs
lungs
Oxygen
CO2
energy
blood
CO2
cells
Oxygen
+
Glucose
Contrasting Pulse Ox
with Capnography
Pulse oximetry measure
oxygen going OUT
from the heart
Capnography
measures
what is coming BACK
from the periphery
Two Different Concepts
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
What is Capnography?
• “Capnos” = Greek for smoke
– From the “fire of life”  metabolism
– CO2 is the waste product of metabolism
• Carbon Dioxide is a compound molecule
– 2 oxygen + 1 carbon
– Odorless; heavier than atmospheric air
– Green plants scavenge excess CO2
– 0.03% concentration in room air
– Resting adults produce
2.5 mg/kg/min
Capnography Basics
Carbon Dioxide (CO2)
– Produced by all living cells
– Diffused into the bloodstream
– Transported to the lungs
– Perfused into the alveoli
– Exhaled through the airway
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Measuring Exhaled CO2
Colorimetric
Capnometry
Capnography
Waveform Capnography
• Available for spontaneously breathing and
for intubated patients
Capnography
is the window
INTO the patient
Normal Capnography Waveform
45
0
• Normal range is 35-45 mmHg
• Height = total CO2
• Length = time/rate
Capnogram Phases
C
A
B
D
End-tidal
E
Inhale
Capnogram Phases
C
A
B
D
End-tidal
E
Exhale (dead space)
Capnogram Phases
C
A
B
D
End-tidal
E
Exhale (rapid rise)
Capnogram Phases
C
A
B
D
End-tidal
E
Exhale (plateau)
Capnogram Phases
C
A
B
D
End-tidal
E
End of the wave of exhalation
How Capnography Can Help
• Airway
• Breathing
• Circulation
What Happened?
The endotracheal tube became dislodged!
Apnea
Airway Obstruction
Displaced airway (esophageal)
Airway or vent disconnection
Vent malfunction
Cardiac Arrest
What about the Pulse Ox?
Sp02
98
Normal:
Esophageal tube:
Breathing
Capnography Waveforms
45
Normal
0
45
Hyperventilation
0
45
0
Hypoventilation
Rebreathing
Possible causes:
 Faulty expiratory valve
 Inadequate inspiratory flow
 Breath stacking (wrong mode, undersedated)
 Malfunction of CO2 absorber system
What’s the SHAPE?
The Shark Fin
Possible causes:
 Partially kinked or occluded artificial airway
 Presence of foreign body in the airway
 Obstruction in expiratory limb of vent circuit
 Bronchospasm
Bronchospasm (asthma)
Mild
Moderate
Marked bronchospasm
Airway:
Leaking tube cuff
“Curare Cleft”
Appears when NMBAs begin to wear off
Depth of cleft inversely proportional to
degree of blockade
Circulation
The lungs and the heart
are inextricably
tied together
CO2 clearance reflects perfusion
In other words: CO2
production is largely
dependent on
oxygen
consumption!
Cardiac Arrest
• Little O2 delivery or consumption
• Little CO2 production or venous
return
…Little Need to Ventilate!
1. Use EtCO2 as guide to avoid
overventilation during
resuscitation:
< 20: slooooow down
> 40: increase breaths
2. Increased CO2 may = ROSC
Decision to Call the Code
• 120 prehospital patients in nontraumatic
cardiac arrest
• EtCO2 had 90% sensitivity in
predicting ROSC
• Maximal level of <10mmHg during the first
20 minutes after intubation was never
associated with ROSC
Source: Canitneau J. P. 1996. End-tidal carbon dioxide during cardiopulmonary resuscitation in
humans presenting mostly with asystole, Critical Care Medicine 24: 791-796
What about other shock states?
“These data suggest that
respiratory rate alone cannot
be used to predict
measured capnography levels.”
R. Fowler, P. Pepe
September, 2007
Wide a-A gradient:
EtCO2 = 11
PaCO2 = 28
Something is blocking
gas exchange:
• Pulmonary embolism
• PNA, ALI or ARDS
• Shunting
• Low CO state
• Very low HCO3
Test: your patient is seizing
Thank You !
Talk Code: 682