Capnography in the PACU:
Theory and Clinical Applications
of end tidal C02 Monitoring
Perianesthesia Nurses Association of British
Columbia
Cathy Hanley, RN, BSN
November 6, 2010
Objectives





Review of physiology, ventilation vs oxygenation
Identify normal and abnormal etC02 values and
waveforms and appropriate clinical interventions
Discuss current applications of capnography in
the PACU and beyond
Discuss current standards and recommendations
Review of capnography case studies
Brief History of Capnography

Used in anesthesia
since the 1970s
 Canadian
Anesthesiologists’
Society requires it in
the OR
 New recommendations
and standards
expanding utilization
Capnography outside of the OR
Capnography = Solutions for all Intubated and
Non-Intubated patients
 Capnography can be used in all areas of the
hospital

PACU
ICU
OR
EP/
Cath
MedSurg
Pain
Mgmt
Peds
.
MRI
GI
Overview of Capnography

Capnography is the non-invasive, continuous
measurement of CO2 concentration at the airway

Capnography provides three important parameters:
• Respiratory rate detected
from the actual airflow
• Numeric etCO2 value
• Normal range 35-45 mmHg
• Waveform tracing for every
breath
Obtaining an Accurate Respiratory Rate
Manual Counting
Impedance (ECG Leads)
etCO2
• Measures:
• Chest or air movement
• Measures:
• Attempt to breathe
• Chest movement
• Measures:
• Actual exhaled breath at
airway
• Based on observation or
auscultation that may be
restricted by patient
movement, draping or
technique
• Based on measuring
respiratory effort or any
other sufficient movement
of the chest
• Hypoventilation and No
Breath detected
immediately!
• Most accurate RR, even
when you are not in the
room!
Respiratory Cycle =
Oxygenation and Ventilation
Oxygenation
• The process of
getting O2 into
the body
Two separate
physiologic processes
• The process of
eliminating CO2
from the body
Ventilation
• Measures etCO2
• Reflects
ventilation
• Hypoventilation
& apnea
detected
immediately
Pulse Oximetry
Capnography
Important Measurements
http://www.covidien.com
• Measures SpO2
• Reflects
oxygenation
• Values lag with
hypoventilation
& apnea,
several to many
minutes
The Relationship between PaCO2 and
etCO2


etCO2 normal range is
35 - 45 mmHg
Under normal
ventilation and
perfusion conditions,
the PaCO2 & etCO2 will
be very close
–
2 – 5 mmHg with
normal physiology
Ideally, every alveolus is involved in air exchange (ventilation) and has
blood flowing past it (perfusion), but in reality, ventilation and perfusion are
never fully matched, even in the normal lung
Ventilation-Perfusion Mismatch

There is inappropriate matching
of ventilation and perfusion
when:
–
“Dead space” is
being ventilated with
no perfusion
•
–
Since no gas exchange
occurs, air coming out is the
same as air going in (no CO2)
Unventilated areas of
lung are being
perfused (“Shunt”)
•
Effect on etCO2 may be small
but oxygenation may
decrease greatly
Dead Space Ventilation

Physiologic
–

Mechanical
–

conducting airways and
unperfused alveoli
breathing circuits
Disease states leading
to this include:
–
–
–
–
Severe hypotension
Pulmonary embolism
Emphysema
Bronchopulmonary
dysplasia
Ventilation-perfusion mismatch

Bronchial intubation

Increased secretions

Mucus plugging

Bronchospasm

Atelectasis
Summary - EtCO2 vs. PaCO2

End tidal CO2 (EtCO2) = noninvasive measurement of
CO2 at the end of expiration

EtCO2 allows trending of PaCO2 - a clinical estimate
of the PaCO2, when ventilation and perfusion are
appropriately matched

Wide gradient is diagnostic of a ventilation-perfusion
mismatch

EtCO2 monitoring allows for a breath by breath
assessment of ventilation.
Why use etC02 in the PACU ?

Accurately monitors effective ventilation, giving
a true airway respiratory rate
•
Early warning of :
 Hypoventilation
 Apnea
 Obstruction
Provides easy and accurate airway monitoring
for intubated or non-intubated patients
–
Promotes better ventilation assessment
resulting in timely interventions
–
Titrate sedation and pain medication
Why use etC02 in the PACU?
Indicator of Malignant Hyperthermia
 Use with patient with history of respiratory compromise,
such as asthma or COPD to monitor trend and need for
breathing treatments and response to treatment
 Endotracheal tube placement
 Monitoring during weaning
 Decrease frequency of arterial blood gases
 Use with non-invasive ventilation (NIV)

Case Study: Microstream
Capnography in the PACU:
Submitted by: Larry
Myers RRT
Cottonwood Hospital
Murray, Utah

Profile

A 31-year-old female s/p abdominal
hysterectomy 6 months prior to
admission is admitted with right
lower quadrant pain. The patient
underwent a bilateral salpingooophorectomy and lysis of
adhesions on this admission. On
post-op day one she became
hypotensive and had a substantial
decrease in her hematocrit. The
patient was returned to the OR for
an exploratory laparotomy.
Case Study in PACU
Clinical Situation:
When the patient was returned to the PACU, she was extubated
and became acutely hypoxic on a non-rebreather mask. The
patient was in profound distress, drowsy, lethargic, but arousable
and able to converse with c/o severe abdominal and chest pain.
Sp02: 82%
pH: 7.22
PaC02: 64.9mmHg
HCO3: 25.5mEq/L
Pa02: 53mmHg
Sa02: 81%
RR: 40bpm
HR: 130bpm
BP: 107/48
Clinical Situation
At this point anesthesia was preparing to reintubate. A
suggestion was made to use etC02 with an oral/nasal
cannula and place the patient on a high flow 02 delivery
system with an Fi02 of 1.0 and monitor the patient closely.
The patient was rushed to the Radiology Department for a
CT angiogram where a pulmonary embolus was ruled out.
Initial values:
etC02: 62mmHg
Sp02: High 80’s
Over the next 2 hours, etC02 fell to 44mmHg and Sp02
increased to 98%.
Discussion
The continuous monitoring of EtCO2 and SpO2 when
measured in concert but evaluated independently allowed
this patient to be safely observed and avoid reintubation
and mechanical ventilation. It is also interesting to note,
retrospectively, an expensive procedure to rule out PE may
have been avoided with a better understanding of the
relationship between arterial and end-tidal CO2. The
probability of a PE in this case was low with a measured
EtCO2 of 62 mmHg and a correlating PaCO2 of 64.9 mmHg.
One would expect a wider gradient in the presence of
significant dead space ventilation.
PACU, Post-op PCA, Med/Surg Floors
Post operative patients on Patient Controlled Analgesia (PCA)
- often starts in PACU
 Bariatric Patients/Obstructive Sleep Apnea(OSA) high risk
patients
 Awareness building regarding the need for monitoring
ventilation/breathing on general floors

–
–

Patient sentinel events/deaths
Recent professional statements (APSF, ISMP)
Great need for more education on Oxygenation vs.
Ventilation for nurses in non-acute areas
Compelling Recent Research
“During analgesia and anesthesia,
cases of respiratory depression were
28 times as likely to be detected if
they were monitored by capnography
as those that were not”
University of Alabama – Birmingham, Waugh, Epps, Khodneva - meta-analysis presented at the
Society of Technology in Anesthesia International Congress, January, 2008
Capnography monitoring in patients
receiving patient controlled analgesia
(PCA)
Patient safety with Patient
Controlled Analgesia (PCA)


Patient Controlled Analgesia (PCA) aids patients in
balancing effective pain control with sedation
The risk of patient harm due to medication errors with
PCA pumps is 3.5-times the risk of harm to a patient from
any other type of medication administration error

2004 more deaths with PCA than with all other IV
infusions combined

Due to oversedation and respiratory depression with PCA
delivery
Sullivan M, Phillips MS, Schneider P. Patient-controlled analgesia pumps. USP
Quality Review 2004;81:1-3. Available on the web at: http://www.usp.org/
pdf/patientSafety/qr812004-09-01.pdf.
PCA Issues List

PCA by proxy

Drug product mix-ups

Device design flaws

Inadequate patient/family education

Practice issues including pump
misprogramming

Inadequate monitoring
ISMP Medication Safety Newsletter, July 10, 2003 Vol 8, no.14
Currently, no monitoring during PCA
therapy at most hospitals
Post operative surgical units where there is no centralized
monitoring
 Large units making proximity to patient impossible
 Vital signs are typically every 4 hours
 Sometimes spot checking with pulse oximetry
 Nurse to patient ratio can be 1:6 – 1:10

How Ventilation Deteriorates
when Administering Opioids
Opioids Depress the
Brain’s signals to the
Respiratory Muscles
CO2 Production
CO2 Removal
Case scenario

16 yr-old Billy falls off his skateboard and sustains
a left femur fracture. He is now post-op from ORIF
and is in the PACU extubated. He rates his pain at
a 10 on 0-10 scale and has been given multiple
doses of IV Morphine and is now on a PCA pump
for pain.
Case scenario

Later that evening on the med-surg floor, after
hours of poor pain control, Billy falls asleep

Afraid Billy will soon wake up and again be in
severe pain, Billy’s mother repeatedly presses his
morphine PCA button while he is asleep

He subsequently stops breathing and is
resuscitated, but suffers hypoxic brain injury
Obstructive Sleep Apnea
Sleep apnea is the most widely known sleep disorder
besides insomnia
 Believed to be under-reported
 18-40 million people have sleep apnea

–
–
Effects 2% of middle-aged females
Effects 4% of middle-aged males
More common in men
 It is estimated that nearly 80% of men and 93% of
women with moderate to severe sleep apnea are
Practice Guidelines for the Perioperative Management of Patients with Obstructive
undiagnosed
Sleep Apnea, Anesthesiology 2006; 104:1081–93

Sleep Diagnosis and Therapy ♦ Vol 3 No 5 September-October 2008
Mechanism of OSA…a vicious pattern
Muscles of
the pharynx
relax
during deep
sleep
Stimulates
and arouses
patient to
ventilate
Survival
Mechanism
Acidosis
activates
respiratory
centers in
the CNS
Airway
obstruction
Hypoxemia
&
Hypercarbia
A more vicious pattern…with sedation
Muscles of
the pharynx
relax
during deep
sleep
Does not
ventilate
Acidosis
activates
respiratory
centers in
the CNS
Opiates & sedatives
inhibit arousal
mechanisms
Airway
obstruction
Hypoxemia
&
Hypercarbia
Respiratory Arrest
Without Intervention
PCA Case Scenario #2




60 year old female with morbid
obesity and history of intractable low
back pain
X-rays demonstrated severe bone-onbone changes in both knee and hip
areas
Placed on PCA continuous infusion
with PCA demand dose
Placed on continuous SpO2 and EtCO2
monitoring
PCA Case Scenario #2 cont.



Soon after starting PCA, patient desaturated
to SpO2 = 85%
Patient placed on 60% O2 aerosol mask and
EtCO2 monitoring discontinued
PCA continuous discontinued, PCA demand
dose continued
PCA Case Study #2 cont.




Following morning, patient appeared
very lethargic and difficult to arouse
SpO2 in high 90s
EtCO2 monitor reapplied on patient
with readings of 74 mmHg* indicating
elevated CO2 level
Patient was transferred to ICU with
diagnosis of obstructive sleep apnea
complicated by obesity and PCA
Normal Waveform
Anatomy of a Waveform
D
A-B: Baseline = no CO2 in breath, end of inhalation
B-C: Rapid rise in CO2
C-D: Alveolar plateau
D:
End point of exhalation (EtCO2)
D-E: Inhalation
Abnormal waveforms – No Breath
loss of waveform
Sudden loss of waveform and
EtCO2 to zero or near zero /
no respiration detected
–
Possible causes
•
Intubated:
Kinked or dislodged
ETT
 Total airway obstruction
•
 Complete disconnect from ventilator
 Non-intubated:
 Apnea
 Dislodged Capnoline
Abnormal waveforms
Loss of alveolar plateau
Absent alveolar plateau
indicates incomplete alveolar
emptying or loss of airway
integrity
–
Possible causes
 Intubated:
 Partial airway obstruction caused by
secretions
 Leak in the airway system
 Bronchospasm
 Endotracheal tube in the hypopharynx
 Non-intubated:
 Head and neck position
 secretions
Classic Hypoventilation
Classic Hyperventilation
Abnormal waveforms decreased etCO2
Gradual decrease in etCO2 with
normal waveform indicates a
decreasing CO2 production, or
decreasing systemic or
pulmonary perfusion
 Hypothermia (decrease in metabolism)
 Hyperventilation
 Hypovolemia
 Decreasing cardiac output
Capnography in Obstructive
Lung Disease
–
–
–
Waveform shape detects
presence of
bronchospasm
etCO2 trends assess
disease severity (e.g.,
asthma, emphysema)
etCO2 trends gauge
response to treatment
(e.g., asthma,
emphysema
Abnormal waveforms – rebreathing
intubated and non-intubated
Rise in baseline CO2 indicates
rebreathing of CO2
 Intubated patient
–
Addition of mechanical dead space
to ventilator circuit
–
Technical errors in CO2 analyzer
 Non-intubated patient
Poor head & neck alignment
Draping at the airway
Insufficient flow to O2 mask
Shallow breathing that does not clear anatomical dead space
Abnormal Waveforms – What to do





Assess patient
Check sample line
position – reposition or
check ET tube position
Check head/neck
alignment, and open
airway, suction if
needed
Instruct patient to take
a deep breath
If patient is not
breathing and not
Movers and Shakers / Clinical Compass
‘The monitoring used in the PACU
should be appropriate to the patient’s
condition and a full range of monitoring
devices should be available’.
Canadian Anesthesiologists’ Society, R. Merchant, et al
Revised edition 2010
Institute for Safe Medication Practices (ISMP)

“Do not rely on pulse oximetry readings alone to
detect opiate toxicity. Use capnography to detect
respiratory changes caused by opiates, especially for
patients who are at high risk (e.g., patients with
sleep apnea, obese patients).”
–
Establish guidelines for appropriate monitoring of patients
who are receiving opiates, including frequent assessment
of the quality of respirations (not just respiratory rate) and
specific signs of oversedation.
ISMP Medication Safety Alert, February 22, 2007,Vol.
12, Issue 4
ASA (American Society of Anesthesiologists)

Practice guidelines for the perioperative management of
patients with obstructive sleep apnea
CO2 monitoring should be used during moderate or deep sedation for
patients with OSA. If moderate sedation is used, ventilation should be
continuously monitored by capnography or another automated
method if feasible because of the increased risk of undetected airway
obstruction in these patients.
 Postoperative Management:
OSA patients should be monitored for a median of 3 hours longer
than the non-OSA counterparts before discharge. Monitoring of OSA
patients should continue for a median of 7 hours after the last
episode of airway obstruction or hypoxemia.

Practice guidelines for the perioperative management of patients with obstructive sleep apnea: a report by the
American Society of Anesthesiologists Task Force on Perioperative Management of Patients with Obstructive Sleep
Apnea. Anesthesiology 2006 May;104(5):1081-93
Conclusion

Capnography for sedation/analgesia/postoperative
monitoring:
–
–
–
–
–
Accurately monitors RR
Monitors adequate ventilation
Monitors hypoventilation due to over-sedation more
effectively than pulse oximetry
Earliest indicator of apnea and obstruction
Adds additional level of safety providing caregiver with
objective information to make accurate assessments
and timely interventions
Be Prepared. Be Proactive
Continuing Capnography Education

Oridion Knowledge Center:
www.capnographyeducation.com

Three capnography courses available:
A Guide to Capnography during Procedural Sedation
– A Guide to Capnography in the Management of the
Critically Ill
– A Guide to Monitoring etCO2 during Opioid Delivery
–