1. health and fitness
2. disease

4/30/12
Volumetric Capnography:
Clinical Utility of VCO2 during Mechanical
Ventilation of Pediatric and Neonatal Patients
Robert Campbell, RRT FAARC
National Ventilation Technical Specialist
Philips Healthcare
Objectives
• 
• 
• 
• 
• 
Define VCO2
Describe how VCO2 measured
Describe the difference between EtCO2 & PaCO2
Explain the relationship between VCO2 & PaCO2
Understand the clinical application of VCO2 for ventilator
management in the Pediatric and Neonatal environment
What is VCO2???
•  VCO2 is the volume of carbon dioxide
eliminated or excreted through the lungs
•  VCO2 reflects changes in both ventilation
and perfusion
•  In steady state, reflects CO2 production
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Why Monitor VCO2???
•  Validates need for ABGs
•  Identifies immediate changes in Ventilation and
Perfusion (V/Q matching)
•  Allows optimization of MV parameters
•  Trended data may expedite weaning
•  VD/VT measurements can determine the severity
of insult and prognosis
Ventilation- Perfusion Relationships
Relationship between ventilated alveoli and blood
flow in the pulmonary capillaries
CO2 O2
Shunt perfusion
Alveoli perfused
but not ventilated
Normal
Ventilation and
perfusion is matched
Deadspace Ventilation
Alveoli ventilated but not
perfused
What Have We
Traditionally Used
To Monitor Our
Patients?
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Respiratory Parameters
•  ABG – Arterial Blood Gas
–  Gold standard
–  Measures ventilation and oxygenation
•  Pulse oximetry measures oxygenation
•  Capnography measures ETCO2
Non-Invasive CO2
•  Detector/Indicator
•  Capnometry
•  Capnography
Advanced Monitoring
Capabilities
•  EtCO2
•  Capnogram
•  Respiratory
Rate
•  CO2 Elimination
•  Deadspace
•  Alveolar
Ventilation
•  Physiologic VD/VT
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Volumetric CO2
Leap Frog Technology
Single Breath CO2
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Volumetric Capnography Measures
the Volume of Exhaled CO2
ETCO2 is a Measure of the partial
pressure exerted in a gas
Volumetric CO2
EtCO2 = 32 mmHg
Vt = 600 ml
VCO2 = 50 ml/min
.
EtCO2 = 32 mmHg
Vt = 800 ml
VCO2 = 200 ml/min
EtCO2 = 32 mmHg
Vt = 1000 ml
VCO2 = 300 ml/min
.
.
Important Parameters
– 
Phys VD / VT
PaCO2 - PeCO2
PaCO2
– 
Alveolar
Ventilation
– 
Min. Vol. CO2
(VCO2)
=
Y+Z
X+Y+Z
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ETCO2/PaCO2 Gradient
•  What Does This Gradient tell us?
Capnography
Arterial - End Tidal CO2 Gradient
In healthy lungs the normal PaCO2 to
ETCO2 gradient is 2-4 mmHg
In diseased lungs, the gradient will
increase due to ventilation/perfusion
mismatch
Gradient as a tool
•  Why?
–  Lets clinicians know when patient status
improves
  PaCO2/ETCO2 gradient narrows
–  Aids in determining what caused a drop in
ETCO2
  If ventilation hasnt changed a sudden and
large drop in ETCO2 usually indicates a
change in perfusion
– Requires an ABG to differentiate
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Dead Space Ventilation
ETCO2 = 33 mmHg
PaCO2 = 53 mmHg
53
53
0
0
0
53
0
0
0
0
Alveoli that do not
take part in gas
exchange will still
have no CO2 –
Therefore they will
dilute the CO2 from the
alveoli that were
perfused
The result is a widened ETCO2 to PaCO2 Gradient
VD/VT
•  Ratio of Total Deadspace (VD and VDphys) to Tidal
Volume (VT)
•  Total Deadspace = Airway + Alveolar Deadspace
•  Normal = 0.25 to 0.30
•  Estimates the Overall (In)efficiency of the
Cardiorespiratory System
Why measure Vd/Vt?
•  Pulmonary dead space is ventilation that is
wasted as it does not participate in gas
exchange.
•  Increase in Vd represents impaired ability to
excrete CO2
•  Increased dead-space fraction is a feature of
the early phase of the ARDS
•  Elevated values of Vd/Vt are associated with an
increased risk of death*
*New England Journal of Medicine 2002;346: 1281-6
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Outcomes
•  Deadspace fraction
•  Elevated in early ARDS:
0.58 ± 0.09
•  Higher in patients who
died (0.63±0.10 vs.
0.54±0.10)
•  For every 0.5 , odds of
death by 45%
MValv
•  Alveolar ventilation per minute
•  Amount of VT that reaches the
alveoli and is available for gas
exchange (effective ventilation)
Why Measure MValv ?
  To provide the most effective CO2 Removal
  To manage alveolar ventilation and not Vte as measured by
the ventilator
Evaluate ventilator settings
500 ml delivered VT – 150 ml airway deadspace = 345 ml
Why is this important?
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Evaluate ventilator settings
Knowing how much of the delivered VT is available for
gas exchange is important – if the patient is fighting the
vent and restless, the issue may be alveolar VT
Ineffective Ventilation
Monitoring CO2 elimination
•  CO2 elimination provides continuous feedback
regarding ventilation and perfusion
–  Relationship between PaCO2 and CO2
elimination is either stable or inverse
–  Instant feedback when making ventilator
setting changes:
  Did perfusion change?
  Did ventilation change?
  With PaCO2 from an ABG, you can
answer the question, did Vd/Vt change?
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VCO2/MValv Relationship
VCO2/MValv Relationship
VCO2/MValv Relationship
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Duke university medical center
•  Extubation Study
–  Demonstrated that VD/
VT ratio measurements
successfully predicted
extubation outcomes
–  Elevated VD/VT,
warning of patient risk
for respiratory difficulty
100
4
90
33
80
70
80
60
50
96
40
67
30
20
20
10
0
<0.50
0.51-0.64
% Success
>0.64
% Failure
Independent Effect of Etiology of Failure and Time to Reintubation on Outcome for Patients Failing Extubation
S. Epstein & R Ciubotaru, AJRCCM, Vol. 158, N°2, August 1998, 489-493
Successful Weaning Trial
  Shows in spontaneous alveolar
ventilation & corresponding decrease
in ventilator support.
  VCO2 suggests metabolic
activity due to additional task of
breathing by the patient.
  Delivered mechanical tidal volume
has not changed & spontaneous tidal
volume is increasing (SIMV rate ).
  Shows PATIENT RESPONSE to
the trial allowing for better
management of the weaning process.
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Unsuccessful Weaning
Trial
  SIMV and patient started to
take over ventilation.
  But patient shows signs of fatigue
at early stage ( VCO2 followed by
in spontaneous tidal volume).
  Leads to in PaCO2 & EtCO2.
  Return to mechanical ventilation.
  Assists clinicians in determining
PATIENT RESPONSE.
  When used effectively, these
utilities may help reduce costly
ventilator days.
Spont Breathing Trials-SBT
Successful SBT
.
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Unsuccessful SBT
  Initially, patient had a small amount of
ventilatory support, but then was placed
on a T-piece. The entire task of breathing
was placed on the patient.
  Within minutes trends showed that the
patient was unable to support the required
level of ventilation (VCO2 decreasing
since total Alveolar Ventilation is
decreasing).
  Spontaneous Tidal Volume trend also
shows inadequate ventilation.
  Removal of mechanical support,
increased Vd/Vt, reducing ventilatory
efficiency and the patients ability to
remove CO2. This resulted in a pattern of
rapid shallow breaths requiring the patient
to be placed back on full mechanical
support.
Stable Ventilation with
Decreasing VCO2 Showing
a Change in Perfusion
  Monitoring trends allows for
detection of sudden and rapid in
VCO2, without change in Alveolar
Minute Volume or Tidal Volumes.
  Drop in VCO2 suggests change in
blood flow to the lungs.
  VCO2 may be due to in
C.O. or blood loss.
  VCO2 may be due to in
C.O. or malignant hyperthermia.
  Coupled with Alveolar Ventilation
and Deadspace measurements, this
allows for quick patient assessment.
Optimization of PEEP
•  To Minimize Lung Injury:
–  Provide enough PEEP to recruit the
recruitable alveoli, but not apply too much
PEEP to over distend the healthier regions
–  Avoid a PEEP/Vt/P combination that doesnt
unnecessarily over distend lung regions at
end inspiration (overall PIP)
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How Much Peep is Enough?
ALuRT
Observe for stable
baseline
•  PEEP is at 10 cm
H2O in this
example
ALuRT
Step 1
•  PEEP is from 10 cm
H2O to 12 cm H2O for
5-15 minutes. No change
in Vtalv and VCO2 (CO2
elimination) indicates no
alveolar recruitment
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ALuRT
Step 2
•  PEEP is to 14 cm H2O
for
5-15 minutes and Vtalv
and CO2 elimination begin
to increase indicating
alveolar recruitment.
ALuRT
Step 3
•  PEEP is increased to
16 cm H2O and VTalv
and CO2 elimination
continue to rise.
ALuRT
Step 4
•  At a PEEP of 18 cm
H2O we see no
increase in Vtalv and
VCO2 drops indicating
worsening V/Q from
decreased pulmonary
perfusion.
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ALuRT
Step 5
•  When PEEP is to 16
cm H2O, CO2 elimination
back to baseline
meaning optimal
recruitment pressures
and pulmonary
perfusion (V/Q).
Store plot prior to first PEEP increase
Single breath CO2 waveform
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Drop in Perfusion
Recruitment Maneuver
Before recruitment
After recruitment
ALuRT provides continuous monitoring
to detect derecruitment of alveoli
•
Alveolar ventilation and VCO2 will decrease if the
lung de-recruits
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Using VTalv and VCO2 to recruit alveoli
•  Clinical Course
–  PEEP increased by 2 cm
H2O every 10 minutes
–  Observed Vtalv/VCO2/SpO2
•  Red arrows show PEEP 
•  No deterioration in VCO2
  V/Q stable
•  VTalv starts to  at 16 cm H2O,
alveoli are being recruited
•  SpO2 responds at 20 cm H2O
Pt in Bronchospasm
Patient with Asthma –
Improvement Following Aerosol
Therapy
CO2
Day 1
Day 5
Exhaled Volume
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Bedside Applications
Monitoring the
Patients Response to
Ventilator
Management
Ventilation Management
Optimize Vt Setting
•  Use Vdaw and Vdalv to assure adequate VT
VCO2
•  Use Single Breath Curve to assess phase III
Vd/Vt
MValv
Ventilation Management
Optimize PEEP
VCO2
Vd/Vt
MValv
•  Use Vtalv, VCO2, and trend to determine lung
recruitment and optimal PEEP
•  Use Single Breath Curve for immediate
feedback
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Ventilation Management
Optimize Weaning
VCO2
Vd/Vt
•  Use MValv and VCO2 to trend weaning
tolerance
•  Early detection of fatigue and failure
MValv •  Enhanced titration of adequate support and
confirmation of resting state
Ventilation Management
Surfactant Replacement
VCO2
•  Use MValv, VCO2, and single breath curve to
manage ventilation during surfactant
replacement therapy
Vd/Vt
MValv •  Detect open and available lung units
•  Enhanced titration of adequate settings as
lung compliance and volume change
Ventilation Management
Inhaled Nitric Oxide
VCO2
•  Use MValv, VCO2, and single breath curve to
manage ventilation during Inhaled Nitric
Oxide therapy
Vd/Vt
MValv •  Especially useful during weaning of INO
•  Confirm maintenance of lung recruitment and
adequate PEEP
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Weaning Criteria
Guide Weaning Process
Vd/Vt is a single variable that defines total
cardiorespiratory system efficiency and can predict
successful extubation
“A Vd/Vt ratio less than 0.50 reliably predicts successful
extubation whereas a Vd/Vt ratio greater than 0.65
correlates with extubation failure.
Dead Space to Tidal Volume Ratio (Vd/Vt) Predicts Successful Extubation in Infants and Children –
Christopher Hubble MD, Mike Gentile RRT, Donna Tripp RRT, Damian Craig MS, Jon Meliones
MD, FCCM, Ira Cheifetz MD – Critical Care Medicine, Vol. 28, N°6 – June 2000
VCO2:
Useful adjunct for monitoring
during Mechanical Ventilation
Questions ?
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