They aren’t the same thing
Daniel Dunham
Capnometry
Displays the value (as a number) of the partial pressure
of CO2
Capnography
Waveform capnography shows (as a wave) the change in
CO2 over time
Both are valuable, and both measure CO2, but they
should be used for different things.
Why are we measuring end-tidal
CO2?
 CO2 is a byproduct of aerobic metabolism
 CO2 is carried by the blood to be excreted by the lungs
 Respiratory rate controls the amount of CO2 in the
blood
 End tidal CO2 can non-invasively reveal cardiac
output, patient response to ventilation, and ETT
placement confirmation and monitoring.
Capnometry
 In capnometry, the resultant value is directly
correlated to the blood CO2, HOWEVER, values may
not match
 EtCO2 is closest to PaCO2 in healthy patients, when
cardiac function is not reduced
 In patients with reduced cardiac output, EtCO2 and
PaCO2 can be very different – For example, a patient in
cardiac arrest (without chest compressions), EtCO2 will
be very low or zero, but PaCO2 will be very high.

This is because without cardiac output, blood will not be
flowing to bring CO2 to the lungs to allow them to exhale the
CO2.
Normal Values
 Normal values of PaCO2 are 35-45.
 Normal values of EtCO2 are approximately 35-45.
 The waveform of a healthy patient, will be a deep square,
with sharp, straight upstroke, plateau, and downslope.
(this waveform will be present in healthy patients whether
they are breathing spontaneously or being ventilated via
any adjunct)
Exhalation begins
CO2 does not increase immediately:
the first air exhaled does not
contain CO2 because of airway dead
space.
Exhalation continues
The flat plateau shows exhalation
Exhalation ends
Exhalation ends
No air movement, or inspiration
A value of zero indicates
inspiration or no air movement
During Intubation
 Following intubation, waveform capnography is much
more valuable than numerical capnometry.
 A square waveform does not occur unless air exchange is
occurring in the lungs
Esophageal Intubation
 This is what you can expect from an esophageal
intubation. CO2 may be returned initially (due to CO2
that is already in the stomach), but it will rapidly taper
off.
 A LOW CO2 READING IS CAUSE FOR CONCERN
PEA, Pulmonary Embolism
 Because EtCO2 is a function of cardiac output, if the
patient is still intubated, a decreasing CO2 can also
indicate low lung perfusion, could be a sign the patient
has become pulseless, or is developing a PE
 A LOW CO2 READING IS CAUSE FOR CONCERN
Shark Fin
 A “shark fin” wave form indicates bronchospasm (asthma/COPD). This
occurs because exhalation requires effort, and CO2 output increases as
resistance is overcome.
 The longer the slope lasts, the more effort is being put into exhalation,
and more “tired” the patient is becoming, and the more effort is
required in exhalation. Manage this patient aggressively, and be
prepared for respiratory failure.
 Both of these waveforms show bronchospasm, but one is “sicker” than
the other, which one?
Curare Cleft
 A Curare Cleft is a notch that can be found anywhere in a
waveform, with varying depths.
 It is the result of spontaneous respiration from the patient
 This can be due to inadequate sedation, neuromuscular
blockade wearing off, due to the patient resisting ventilations
(usually on a mechanical vent)
 Fix this by more sedation or neuromuscular blockade. BVM
ventilations (instead of ventilation by mechanical vent) can
also improve this.
Normal Values
 Normal values for capnometry are 35-45.
 Remember that capnometry is dependent on cardiac output and
the ability of CO2 to cross from blood to inspired air for
exhalation. Pulselessness, low metabolic rate (like hypothermia),
or interrupted metaboilc process (like occurs with cyanide
poisoning – when aerobic metabolism doesn’t occur, CO2 is not
being created) can also effect EtCO2.
 It’s also important to remember that while there is a direct
correlation between EtCO2 and PaCO2, they are not necessarily
the same (however, if you obtain a PaCO2 and EtCO2 at the same
time, it is ok to assume that the difference will remain the same
for a reasonable amount of time; e.g., EtCO2 is 32 and PaCO2 is
36, add 4 to your changing EtCO2 to approximate PaCO2 if you
make changes to how you are ventilating)
During CPR
 EtCO2 > 20 indicate chest compressions are being
performed well
 Values any higher than 20 indicate the patient may
have a spontaneous pulse (this will help you
differentiate PEA and hypotension, and help you
decide on continuing CPR or started a fluid bolus and
dopamine)
 Values less than 10 mean chest compressions are not
being performed well, ETT is displaced, or the
metabolic processes are no longer occurring (i.e., the
patient is dead)
For ventilation
 It is not uncommon to see values over 110 after intubating
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patients that had inadequate respirations for an extended
period of time.
Increasing ventilation rate results in a lower EtCO2
Goal is to maintain EtCO2 of 35-45 (hyperventilation to
maintain EtCO2 of 30 in head injuries is no longer
recommended)
It is rarely warranted to ventilate >24 or <8/minute
regardless of EtCO2; possible exceptions include DKA and
hypothermia
The biggest clinical benefit in EMS is to avoid
hyperventilation of intubated patients
COPD/CHF discrimination
 EtCO2 values will be higher in patients with acute
bronchoconstriction.
 Along with higher peak values, the baseline may
become elevated .
COPD/CHF discrimination
 EtCO2 can be used to determine whether
bronchoconstriction is present, even in patients with
inaudible lung sounds.
 A high EtCO2 in indicative of bronchoconstriction.
 A normal EtCO2 is non-diagnostic (it does not rule out
bronchoconstriction, or confirm pulmonary edema).
 If you’ve determined that a patient is either having a
exacerbation of COPD or CHF, but you’re not sure
which, EtCO2 can answer this question for you.
Continuous EtCO2 Monitoring
 EtCO2 is non-invasive and can be performed on any patient with any
symptoms, but is strongly encouraged for all patients with respiratory distress.
 Continuous EtCO2 monitoring is now expected (mandatory) for
all patients in which nebulized medication is administered (be
sure to document this in your report)
 When you administer nebulized medications, you are treating
bronchoconstriction, if you’re going to treat bronchoconstriction, you should
assess for bronchoconstriction (of course, this can be done with lung sounds,
but in a loud ambulance environment and many people will less than perfect
hearing, EtCO2 can be easier to assess – so do both!)
 EtCO2 changes are an excellent indicator of the effectiveness of
bronchodilators.
 As nebulizer is more effective, you will see EtCO2 return to normal levels, and
baseline return to zero.
 An elevated, unchanging EtCO2 indicates that bronchoconstriction is not
improving
 Capnography and capnometry can be very valuable tools if
you understand how they work and their limitations.
 In conjunction with SpO2, a normal EtCO2 range indicate a
patient is being ventilated very well.
 A square waveform on a capnograph is nearly irrefutable
and objective evidence that intubation was successful, and
that ventilations are being performed properly.
 EtCO2 can be used on spontaneously breathing patients,
ETT, King Tube, or LMA intubation, Trach or cric patients,
or any other adjunct that you attach a BVM to, and the
reference values do not change.