2. Objectives
• List three indications for capnography.
• Differentiate between mainstream and
sidestream capnography.
• Given a time-based capnogram, identify
and distinguish between the phases.
• Given a time-based capnogram, interpret
any abnormality present.
• Given a volume-based capnogram, identify
and distinguish between the phases.
• Given a volume-based capnogram, state
the significance of each phase.
3. Objectives
• Given a volume-based capnogram,
interpret any abnormality present.
• List two instances where volume-based
capnography can lead to improved patient
management.
• State the formula used for the calculation of
non-invasive cardiac output via the CO2
Partial-Rebreathing method.
• Describe the set-up used to measure
cardiac output via the CO2 Partial-
Rebreathing method.
• List two additional uses for capnography.
4. Physiology of Carbon Dioxide
METABOLISM PERFUSION VENTILATION
ALL THREE ARE IMPORTANT!
10. Phases of the Time Capnogram
• Phase I: Inspiration
• No CO2 detected (hopefully)
• Phase II: Appearance of CO2 in the
system.
• Mixed alveolar and deadspace gas.
• Phase III: Plateau
• Constant emptying of alveolar gas.
• Presence of CO2 through the end of the
breath.
• Phase IV: Washout of CO2 from
subsequent inspiration.
11. Abnormal Waveforms
Sudden loss of PETCO2 to zero or near zero
indicates immediate danger because no
respiration is detected.
•Esophageal intubation
•Complete airway disconnect from ventilator
•Complete ventilator malfunction
•Totally obstructed/kinked endotracheal tube
12. Abnormal Waveforms
Exponential decrease in PETCO2 reflects a
catastrophic event in the patient’s
cardiopulmonary system.
•Sudden Hypotension/massive blood loss
•Circulatory arrest with continued ventilation
•Pulmonary embolism
•Cardiopulmonary Bypass
13. Abnormal Waveforms
Gradual decrease in PETCO2 indicates a
decreasing CO2 production, or decreasing
systemic or pulmonary perfusion.
•Hypothermia
•Sedation
•Hyperventilation
•Hypovolemia
•Decreasing Cardiac Output
20. Checklist for Interpreting a Volume-
Based Capnogram
• Phase I – Deadspace Gas
• Rebreathing? (1)
• Deadspace seem right?
• Phase II – Transitional Phase
• Transition from upper to lower airways.
• Should be steep. (3)
• Represents changes in perfusion.
• Phase III – Alveolar Gas Exchange
• Changes in gas distribution.
• Increased slope = mal-distribution of gas delivery. (5)
• End of Phase III is the PETCO2. (6)
• Area under the curve represents the volume of expired CO2
(VCO2).
• Exhaled volume (8)
25. Phase 2 assessment
If ↓ in phase 2
– Assure stable minute ventilation
• Assess PEEP level
• ↑ intrathoracic pressure may cause ↓ venous return
• Assess hemodynamic status
• Is minute ventilation stable?
• Volume resuscitation or vasopressors may be indicated
27. ↓ Phase 2
• When minute ventilation is stable,
indicative of a ↓ in perfusion.
28. Phase 3 assessment
If ↑ or absent phase 3 mal-distribution of
gas at alveolar level exists
• Assess for appropriate PEEP level
• Inadequate PEEP may be present
• Bronchospasm
• Bronchodilator tx my be indicated
• Structure damage at alveolar level may be
present
• Pnuemothorax?
32. Effective Tidal Volume
• The volume of gas between the end of
Phase I and the end of Phase III.
• Phase I represents the volume of gas
being delivered from the ventilator
which doesn’t participate in gas
exchange.
• Monitoring of the effective tidal volume can
indicate on a breath-by-breath basis when
PaCO2 changes will be occurring before they
actually rise.
33. Area X = Vol CO2
Allows determination of VCO2 in one min. (200 mL/min.)
Exhaled
Volume
% CO2
Volume CO2
(Area X)
34. VCO2
• VCO2 represents the volume of CO2
eliminated.
• This is usually the same as what is produced.
• CO2 balance is dependent on four factors:
• Production
• Transportation (cell to blood & blood to lungs)
• Storage (conversion to CO2 containing substances in the
muscle, fat and bone)
• Elimination
• Monitoring VAand VCO2 allows for evaluation of a
successful weaning process.
35. Waveform Regions
Z = anatomic VD; Y = VD Alveolar
% CO2
VD VALV
%CO2 in Arterial Blood
Z
X
Y
Exhaled Tidal Volume
36. Sum of VDanat (Z) and VDalv (Y) is
Physiologic VD
X
Y
Z
PaCO2 - PeCO2
PaCO2
Y + Z
X + Y + Z
=• Phys VD / VT
• Alveolar
Ventilation
• Min. Vol. CO2
( VCO2 )
37. Uses of Volumetric Capnography
• Assess work of breathing during
weaning trial.
39. Using Vtalv and VCO2 to Recruit
Alveoli in a Postoperative
CABG Patient Suffering from
Hypoxemia
HOSAM M ATEF
40. Using Vtalv and VCO2 to Recruit
Alveoli
• Patient Profile
• 72 yo male, post-op CABG, MV
• Clinical Challenge
• Developed a low SpO2 within 2 hours of
arrival into the ICU
• FIO2 and PEEP increased, no acceptable
change in PaO2 and SpO2
• Clinical Intervention
• Lung recruitment
41. •Clinical Course
•PEEP increased by 2 cm
H2O every 10 minutes
•Observed Vtalv, VCO2 and
SpO2
•Monitoring Data
•Red arrows show PEEP
increases
•No deterioration in VCO2,
oV/Q stable
•Vtalv starts to increase at
16 cm H2O, alveoli are being
recruited
•SpO2 responded at 20
cm H2O
Using Vtalv and VCO2 to Recruit
Alveoli
42. • Summary
• Vtalv is an ideal parameter to show
alveolar recruitment
• VCO2 indicates V/Q status during the
procedure
• SpO2 did not show improvement until
best PEEP
• Vtalv combined with VCO2 were best to
indicate increased PEEP levels were
working
Using Vtalv and VCO2 to Recruit
Alveoli
43. Uses of Volumetric Capnography
• Optimal PEEP
• Overdistension leads to increased
Vdanat and reduced perfusion.
• Increased Vdanatcan be assessed by an
increase in Phase I volume.
• Reduced perfusion can be assessed by a
decrease in Phase II slope combined with
a decrease in VCO2.
45. VCO2 to Determine Optimal PEEP
• Patient Profile
• 25 yo male, motorcycle accident
• Head injury, rib fractures
• Pentobarbital induced coma
• Clinical Challenge
• Developed acute lung injury
• Low PaO2, SpO2
46. • Clinical Intervention
• Maximize lung recruitment
• Determine optimal PEEP
• Without aversely affecting intracranial
pressures
• Clinical Course
• Monitor VCO2 and VA
• Increase PEEP in 2 cm H2O increments
VCO2 to Determine Optimal PEEP
47. •Results
•PEEP increased
from 14 to 20
•Each step increased
VA, VCO2 initially
decreased but
recovered
•At PEEP of 22, VA
did not increase,
VCO2 did not recover
•PEEP reduced to 20,
VCO2 recovered
22 cmH20 Optimal
PEEP
VCO2 to Determine Optimal PEEP
48. • Determining Optimal PEEP
• VA
Showed sharp rises after initial PEEP settings
A result of alveolar recruitment
• VCO2
Initial decrease after PEEP increase,
recovered quickly
Confirmed that pulmonary perfusion was not
compromised
VCO2 to Determine Optimal PEEP
50. Which graph represents ARDS?
•Graphs show
PECO2 vs. Volume
(hatched line).
•VAE represents
the “alveolar
ejection volume”
(true alveolar gas
mixing volume).
51. Uses of Volumetric Capnography
• Pulmonary Embolism
• 650,000 cases/year in US
• 50,000 to 200,000 die.
• Most deaths occur within first hour.
• Prompt therapy can reduce mortality from 30% to 2.5 to
10%.
• 70% of deaths from PE identified by autopsy were not
identified before death.
• Methods of PE detection
• Evaluation of Vd/Vt
• PaCO2-PETCO2 gradient with maximum exhalation.
• Late deadspace fraction (Fdlate)
52.
53. Uses of Volumetric Capnography
•Non-Invasive Cardiac Output
•Fick Principle (1870)
OR
22
2
OvCCaO
OV
QC
−
=
•
22
2
CaCOCOvC
COV
QC
−
=
•
57. Other uses for Capnography
• During Apnea Testing in Brain-dead patients.
• Eur J Anaesthesia Oct 2007, 24(10):868-75
• Evaluating DKA in children.
• No patients with a PETCO2 >30 had DKA.
• J Paeditr Child Health Oct 2007, 43(10):677-680
• Vd/Vt ratio and ARDS Mortality
• Elevated Vd/Vt early in the course of ARDS was
correlated with increased mortality.
• Chest Sep 2007, 132(3): 836-842
• PCA Administration
• “Continuous respiratory monitoring is optimal for
the safe administration of PCA, because any RD
event can progress to respiratory arrest if
undetected.”
• Anesth Analg Aug 2007, 105(2):412-8
Hinweis der Redaktion
Summarize the phases
…the slope of phase II is eliminated and a clear separation of deadspace is established.
Area under the SBCO2 curve IS the volume of CO2 in a single breath. Sum all the Co2 volumes in a minute and you get the same results as a Douglas Bag collection
If we add a horizontal line representing %CO2 in arterial blood, 4 distinct regions of the curve are established:
1 – Area X represents the actual amount of CO2 exhaled in the breath.
2 – Area Y represents the amount of CO2 that was NOT eliminated because we have some alveolar deadspace
3 – Area Z represents the amount of CO2 that was NOT eliminated because we have a certain anatomic structure
4 – Area X, Y and Z in total represent the maximum volume of CO2 possible to exhale in a single breath IF we have no airway deadspace AND no alveolar deadspace (or shunt). This would represent the perfect situation.
The relationship between the areas (with the added Arterial Blood line) gives us some very important parameters for analysis.
Three very important ventilation assessment parameters emerge and mimic the action of the douglas bag…
The ratios of the areas created in the SBCO2 curve are the same as the relationship seen in the Enghoff modified Bohr equation.
Keep in mind here that the elimination of CO2 volume (VCO2) is necessary to balance CO2 produced in the metabolism process. Alveolar ventilation details how much ventilation is required to eliminate the CO2 volume that is presented to the alveoli by perfusion.
P R O F I L E
This is a 72-year-old male patient, status post open heart surgery for four vessel CABG. The patient was taken to the Open Heart Cardiac Surgery Intensive Care Unit post procedure.
Ventilator settings:
SIMV 12, DP 22 cmH2O, IT 1.1 seconds, FIO2 40%, PEEP 5 cmH2O, PS 5 cmH2O. The ventilator settings were based on protocol
and the anesthesia settings.
Clinical problem:
The patient developed a low SpO2 within two hours of arrival into the ICU. FIO2 was increased to 60%, PEEP increased to 10 cmH2O, DP increased to 28 cmH2O. A subsequent blood gas revealed a PaO2 of 61 mmHg. The patient’s compliance was 41 cmH2O/mL.
Clinical intervention:
The Health Care Team (HCT) decided to utilize the NICO2 monitor to optimize PEEP and maximize lung recruitment.
Advanced Lung Recruitment Technology (ALuRT)
CLINICAL COURSE
Patient was set up on the NICO2 monitor and baseline Vtalv, VCO2, and SpO2 was measured. PEEP was increased by 2 cmH2O every 10 minutes to observe increases in Vtalv and SpO2. If the lung overdistends, VCO2 will drop significantly (greater than 20%). At a PEEP level of 14 cmH2O, Vtalv, VCO2, and SpO2 did not change significantly. PEEP was increased by 2 cmH2O up to 20 cmH2O. Within 15 minutes, Vtalv, VCO2 and SpO2 increased. Subsequent PaO2 increased to 151 mmHg. Compliance increased to 81 cmH2O/ml. The DP and IT was decreased to maintain the same minute ventilation. FIO2 was decreased to 40%. Over the next 24-36 hours, the patient’s PEEP was weaned utilizing the Vtalv parameter.
DISCUSSION
Most patients undergoing heart/lung bypass have adequate lung re-expansion from aggressive manual bagging by the clinician in the operating
room prior to transfer to the ICU. If the procedure is not adequate, the patient can suffer from alveolar collapse and poor ventilation in the hours after the surgery. Using NICO2 to monitor Vtalv, VCO2, and SpO2 served two purposes:
1) increase the PEEP while monitoring for over distension
2) continuous monitoring of Vtalv to demonstrate the alveolar recruitment moment.
In this case, the lung was never “over distended” at anytime, no cardiac compromise was noted.
The reduction in DP, IT, and FIO2 facilitated a minimal support ventilation strategy.
Additional note:
Notice as the PEEP levels increased there was no deterioration in VCO2 indicating that V/Q was maintained. Vtalv was most sensitive to showing that alveoli were being recruited. SpO2 lagged until optimal PEEP was achieved.
Another example is in this increasing PEEP model…phase II shifts right due to expanding airways (increasing PEEP stints the airways open more). Notice that slope of phase II decreases as well. This is a result of lower CO2 concentration occurring at a identical volume point (in a less/more PEEP setting).
This demonstrates the need to manage alveolar volume in changing PEEP conditions…you must compensate for the loss of gas exchange volume
P R O F I L E
A 25-year-old male motorcycle operator struck a tree head-on. He sustained a massive head injury requiring ventriculostomy and eventually a pentobarbital-induced coma to control intracranial pressures. Patient rapidly
developed acute lung injury due to multiple rib fractures and bilateral lung contusions. Ventilator settings were PCV-AC, RR of 14 breaths/minute, DP of 25 cmH2O, FIO2 80%, PEEP 14 cmH2O. The patient’s arterial PO2 was 78 mmHg.
In light of the patient’s lung injury, the Health Care Team sought to maximize lung recruitment and determine the
patient’s optimal PEEP without adversely affecting intracranial pressures.
C L I N I CA L C O U R S E
A baseline VCO2 trend was gathered. The NICO® Monitor was utilized to trend •VCO2 while PEEP was increased in 2 cmH2O increments. VCO2 was monitored for approximately five to seven minutes after each increase in PEEP. A decrease in VCO2 occurred immediately when PEEP was increased to 16 cmH2O. Over the next two minutes, sharp rises in MValv occurred and the VCO2 returned to baseline.
An increase in PEEP to 18 cmH2O resulted in a decrease in VCO2 and no change in MValv. Over the next two minutes, sharp rises in MValv occurred and the VCO2 returned to baseline. The trial continued until the PEEP level reached 22 cmH2O. At this point, VCO2 decreased by over 40 ml/min and did not rise. PEEP was decreased to 20 cmH2O and VCO2 increased. The subsequent blood gas resulted in an arterial PO2 of 120 mmHg. The FIO2 was decreased over the next hour to 50%. The NICO Monitor was utilized over the next 24 to 48 hours to assist in weaning PEEP.
The NICO Monitor was instrumental in determining optimal PEEP. The sharp rises in MValv and VCO2 after the initial two PEEP changes were a result of lung recruitment. Once the patient was receiving 22 cmH2O of PEEP, the alveoli were over-distended and pulmonary capillaries were compressed preventing adequate CO2 diffusion across
the alveolar-capillary membrane. Determining optimal PEEP and fully recruiting the alveoli dramatically reduced
the FIO2 requirement.