Capnography Self-Study Guide

PAtieNt MONitORiNG

PROCESS FOR RECEIVING CONTINUING EDUCATION CREDIT

To earn 1.0 contact hour for this activity, follow these directions:

1. Read the self-study guide.

2. Complete the post-test and check your answers against the answer key provided.

Refer back to content for clarification of any incorrect answers.

3. Complete the Evaluation/Registration Form at the back of this guide. Record the

answers to the post test.

4. Submit the completed form to:

Lisa Cifaldi

Smiths Medical PM, Inc.

Patient Monitoring and Ventilation

N7W22025 Johnson Drive

Waukesha, WI 53186

Or

Fax: 262-542-0718

5. You will be sent your certification of completion within six weeks. Records for

education activities will be maintained for five years.

*AARC members must include their member number for entry into CRCE record

This course will expire December 2008.

ACCREDITATION – RESPIRATORY

This program has been approved for 1 contact hour continuing Respiratory Care

Education (CRCE) credit by the American Association for Respiratory Care,

9425 N. MacArthur Blvd. Suite 100, Irving, TX 75063

Program approval refers only to this continuing education activity and does not

imply AARC endorsement of any commercial products.

COMMERCIAL SUPPORT

This continuing education activity is supported by Smiths Medical PM, Inc.

Table of Contents

Capnography A. Learning Objectives i B. Glossary 1 C Introduction to Capnography 2 D Carbon Dioxide Physiology 3 E. Measurement Techniques and Methods 4 F. Alveolar-Arterial Gradient 5 G. Pulse Oximetry or Capnography 6 H. Clinical Applications 6 I. Capnogram 9

Post Test 14 Evaluation 18

Learning Objectives Learning Objective

1. Define and describe ETCO2 2. Methods of measuring ETCO2

3. Describe various clinical applications of ETCO2 4. Describe relationship between exhaled and arterial ETCO2

5. Identify common waveforms

1

Glossary

a-ADCO2 - The arterial to end-tidal difference of CO2 concentration – the gradient

Capnography – Measurement with graphic as well as numeric display of carbon dioxide

Capnogram – A graphical waveform display of carbon dioxide concentration over time

Capnometry – Measurement with numeric display of carbon dioxide

CO2 – Carbon Dioxide, a byproduct of cellular metabolism that is exhaled during the respiratory

cycle

Dead Space – Areas within the respiratory system that do not participate in gas exchange. These

areas can be anatomical, alveolar, or mechanical

Dead Space Ventilation – Portions of the lung which normally partake in gas exchange, but because

of lack of perfusion, are no longer able to do so

End Tidal CO2 – Peak concentration of carbon dioxide occurring at the end of expiration

Hypotension – The presence of abnormally low blood pressure

Hypothermia – Abnormally low body temperature

Hypovolemia – Diminished volume of circulating blood in the body

PaCO2 – The partial pressure of CO2 in the blood

Shunt Perfusion – Areas of the lungs that are perfused but not ventilated which leads to an absence

of gas exchange

V:Q Mismatch – An imbalance between ventilation compared to perfusion as occurs with shunt

perfusion and dead space ventilation

Introduction

The measurement of end-tidal CO2 (ETCO2) currently is the optimal method of

continuously monitoring the adequacy of ventilation and circulation in adult through

infants. It measures expired carbon dioxide using infrared spectroscopy. ETCO2 can

be of value in the assessment of ventilation, metabolism, and of a patient’s circulation

status.

3

Carbon Dioxide Physiology

Carbon dioxide (CO2) is a waste product of normal cellular metabolism. CO2 leaves

the cells and is carried by the venous blood to the heart (circulation) and lungs

(respiration). Once CO2 reaches the lungs, it is eliminated in the process of exhalation.

In order for CO2 to be effectively eliminated from the body, there must be adequate

blood flow to the lungs, adequate gas exchange across the alveolar-capillary

membrane, and adequate ventilation of the lungs to “blow off” the CO2. Therefore,

changes in respired CO2 may reflect alterations in metabolism, circulation, respiration,

the airway or breathing system.

Metabolism, changes in ETCO2 can be a reliable indicator in metabolic changes.

• Metabolic conditions that may increase ETCO2: fever, sepsis, shivering

and convulsions

• Metabolic conditions that may decrease ETCO2: hypothermia, paralytics

and sedation

• Malignant hyperthermia is a hypermetabolic state with a massive increase in

CO2 production. The increase occurs early, before the rise in temperature. Early

detection of this syndrome is one of the most important reasons for routinely

monitoring CO2

Circulat ion, a decrease in ETCO2 is seen with a decrease in cardiac output if

ventilation remains constant. ETCO2 transport to the lungs is dependent on adequate

cardiovascular function; any factor that alters cardiovascular function can affect CO2

transport to the lungs

• ETCO2 can alert the clinicians to changes in cardiovascular function of the

patient with a “normal” respiratory status,

• Cardiac conditions that may decrease ETCO2: hypovolemia, hypotension

Respiratory, ETCO2 can be a guide for determining the ventilation requirement of a

patient

• Changes in respiratory function will affect the removal of CO2 from the lung

thus affecting the ETCO2

4

Measurement Techniques

Infrared Absorption (IR), is the most common technique in measuring ETCO2.

The principle is based on the fact that CO2 molecules absorb infrared light energy of

specific wavelengths, with the amount of energy absorbed being directly related to the

CO2 concentration. When an IR light beam is passed through a gas sample containing

CO2, the electronic signal from a photodetector can be obtained. This signal is then

compared to the energy of the IR source and calibrated to accurately reflect CO2

concentration in the sample. To calibrate, the photodetector’s response to a known

concentration of CO2 is stored in the monitor’s memory.

Measurement Methods

Mainstream vs. Sidestream Sampling – Mainstream and sidestream sampling

are the two basic configurations of CO2 monitoring. Each term refers to the position of

the actual measurement device (often referred to as “the IR bench”) relative to the

source of gas being sampled.

Mainstream method utilizes a sensor or infrared measuring device placed directly

in-line between the ventilator breathing circuit and the ET tube. Mainstream generally

provides a fast response time and the elimination for the need of water traps.

Sidestream method requires a gas sample to be aspirated from the patient’s airway

and transported to the senor inside a monitor by means of a pump. This type of system

can be used on non-intubated patients while utilizing a variety of sampling cannulas.

Colorimetr ic are disposable devices that provide a qualitative measurement of

ETCO2. It’s use is based on a chemical reaction of litmus paper rather than an actual

measurement. Depending on the device used, a color change of purple or blue indicates

low or absent CO2 concentration and yellow when there is a concentration of CO2.

This device is generally used for intubation purposes.

5

What is the Alveolar-Arterial

Gradient?

Observing the difference between arterial and exhaled carbon dioxide can also give

valuable data about the patient’s condition. The alveolar-arterial gradient is the

difference between the alveolar carbon dioxide level (ETCO2) and the arterial level.

• Normal PaCO2 is 35-45 mmHg.

• In adults with normal cardiorespiratory function (normal ventilation and

perfusion) the ETCO2 is 2-5mmHg lower than the PaCO2, this is generally

due to alveolar mixing

• In infants and small children the gradient is lower and closely reflects PaCO2

(< 3mmHg). This is due to better V/Q matching and hence a lower alveolar dead

space4

The gradient can vary from patient to patient and at times the ETCO2 may be higher

than the PaCO2.

• It healthy subjects with large tidal volumes and low frequency ventilation

• In pregnant women

Vent i lat ion-Perfusion Rela tionship (V/Q), ventilation in the alveoli must be

properly matched with blood perfusion in the pulmonary capillaries for adequate gas

exchange to occur. The ventilation-perfusion ratio (V/Q) describes the relationship

between airflow in the alveoli and blood flow in the pulmonary capillaries. If

ventilation is perfectly matched to perfusion, the V/Q is 1. Both ventilation and

perfusion are unevenly distributed throughout the normal lung the normal V/Q is 0.8

• Dead space venti lat ion occurs when the alveoli are ventilated but not

perfused. Clinical situations such as hypotension, hypovolemia, excessive

PEEP, pulmonary embolism, or cardiopulmonary arrest result in a decreased

ETCO2 and a widening of the gradient.

• Shunt perfusion occurs when the alveoli are perfused but not ventilated. This

can be due to pneumonia, mucous plugging, atelectasis. ETCO2 may decrease

slightly, but carbon dioxide is highly soluble and will diffuse out of the blood

into the available alveoli. Therefore, little effect on the gradient is seen. In this

case, the patient’s oxygenation status may suffer, and positive end-expiratory

pressure (PEEP) or continuous positive airway pressure will be indicated to re-

expand the atelectatic lung units.

6

Clinicians unfortunately think that the capnography device is not accurate when the

blood-gas CO2 differs from the ETCO2. This is generally due to physiology, rather than

accuracy. Although abnormal amounts of dead-space ventilation prevent the clinician

from estimating the arterial carbon dioxide when observing the ETCO2, there is value

in noting a widening or narrowing of the gradient. A narrowing gradient can indicate an

improvement in the patient’s status, while a widening gradient indicates a worsening of

the patient’s condition.

Pulse Oximetry or

Capnography?

Capnographs monitor ventilation whereas pulse oximeters monitor oxygen saturation.

With capnography, apnea periods in the patient are reflected immediately on

occurrence with breath-to-breath feedback; by contrast, pulse oximetry has a lag time

during breath-to-breath changes. Because a patient often is given supplemental oxygen,

this actually may mask an apnic event keeping the oxygen saturation artificially high

during apnic episodes. Best practice: to use pulse oximetry in conjunction with

capnography to understand the patient’s overall status.

Clinical Applications

Intuba tion Ver ificat ion, the most common problems with airway management

and ventilation can be detected using capnography. The American Heart Association

has identified capnography as a tool for secondary confirmation of intubation. Pediatric

Advanced Life Support (PALS) also calls for the use of ETCO2 to confirm

endotracheal tube placement for all patients with a perfusing rhythm.

Transpor tat ion, it is recommended that capnography be used during transportation

of ventilated patients to immediately identify endotracheal tube dislodgement. ETCO2

should also be used continuously to monitor the intubated pediatric patients due to a

higher, more anterior glottic opening and a shorter trachea which makes dislodgement

of the tube more likely. Capnography can also assist in determining proper ventilation

with bag-valve-mask devices when hyper or hypoventilation is common. Transferring

a mechanically ventilated or pulmonary-challenged patient to other diagnostic

departments within the hospital involves extra attention. These high risk patients

should be given a real-time, breath-to-breath pulmonary assessment that only

capnography can provide.

CPR, capnography is a valuable tool during CPR. CO2 levels fall abruptly because of

the absence of cardiac output (blood flow) and pulmonary blood flow. Studies have

shown, the closer to normal the ETCO2 levels are the more effective cardiac output is

during resuscitation. Lower ETCO2 levels observed during resuscitation may signal a

need for changes in CPR techniques (rate/depth/force) of compression.

7

Predic tor of Dea th/Surviva l, capnography can confirm the futility of resuscitation.

A study in the New England Journal of Medicine concluded: An end-tidal carbon

dioxide level of 10mmHg or less measured 20 minutes after the initiation of advanced

cardiac life support accurately predicts death in patients with cardiac arrest associated

with electrical activity but no pulse. Cardiopulmonary resuscitation may reasonable be

terminated in such patients2. Likewise, case studies have shown that patients with high

initial end tidal CO2 reading were more likely to be resuscitated than those who didn’t.

The greater the initial value, the likelier the chance of a successful resuscitation.

Procedura l Seda t ion, is used for patients of all ages. Medications are administered

to raise pain thresholds, decrease anxiety and to provide amnesia during procedures

while minimally depressing the patient’s level of consciousness. Medications used

during these events often depress the respiratory system. Monitoring ETCO2 will

provide a breath by breath analysis of the patient’s ventilation status and allow the

clinician to intervene before the patient experiences an acute respiratory event. When

possible clinicians should obtain baselines values and observe the waveform. During

the procedure, clinicians should observe for changes in the waveform in addition to

values and reassess patient whenever necessary.

Pain Management, patient controlled analgesia (PCA) is an attractive short-term

option for pain management/relief. However, judging a patients response is difficult.

Oversedation and respiratory depression represent the most significant potential for

harm associated with PCA. Although pulse oximetry is commonly used to monitor

falling arterial oxygen saturations, capnography should be used as a more reliable

indicator of respiratory depression. The Joint Commission has established standards

of care for patient safety that require respiratory monitoring for patients using patient-

controlled analgesia to minimize the risk that the patient's respiratory system does not

become depressed due to overmedication.

Asthma, ETCO2 can be used to assess the severity of an asthma/COPD exacerbation

and the effectiveness of intervention. Bronchospasm will produce a characteristic

“shark fin” wave form, as the patient has to struggle to exhale. Asthma values change

with severity. With mild asthma the CO2 will drop (<35) as the patient hyperventilates

to compensate. As the asthma becomes severe, and the patient is tiring and has little

air movement, the CO2 numbers will rise to dangerous levels (>60). If treatment is

successful the “shark fin” will be eliminated and return the ETCO2 levels to normal

or near normal.

Head Injury Pa tients . Hyperventilation can increase blood pressure, and, with

head injury patients, increased blood pressure can exacerbate cerebral edema.

Monitoring of ETCO2 can assist the clinician in maintaining stable CO2 levels,

thus avoiding secondary injury from accidental increased cerebral edema.

Vent i lat ion, in most patients the ETCO2 correlates well with the PaCO2.

Understanding this, capnography can function as an excellent adjunct to other

monitoring methods, including arterial blood gas analysis and oximetry. While

ETCO2 levels in very ill patients should be interpreted with caution, trends in ETCO2

correlate with changes in the PaCO2 and can provide an early warning of metabolic

or cardiorespiratory problems such as shunting, dead space, bronchoconstriction or

pulmonary embolism. Capnography allows for the trending of the ETCO2 value and

its subsequent comparison with ABG values.

8

Vent i lator Weaning, capnography can assist clinician in successful weaning

ensuring that the patient is clinically stable and without clinically significant residual

effect of any anesthetic agents or sedatives. When ETCO2 values are considered in

combination with standard weaning criteria/parameters, the chance of a successful

extubation increases. ETCO2 value during weaning can indicate if the patient is

experiencing a hypercapnic episode and may decrease the number of ABG’s needed.

“Some clinicians utilized ETCO2 as a marker of the metabolic rate and, therefore, as a

way of determining optimal ventilator settings during the weaning process.”3 Patients

with higher metabolic rates (ie. sepsis) may be difficult to wean under these conditions

making it often difficult to predict the success of weaning. Trauma/Shock, monitoring ETCO2 can provide an early warning sign of shock. A

patient with a sudden drop in cardiac output will show a drop in the ETCO2 numbers

that may be irregardless of any change in breathing. “A patient with low cardiac output

caused by cardiogenic shock or hypovolemia resulting from hemorrhage won’t carry as

much CO2 per minute back to the lungs to be exhales. This patient’s ETCO2 will be

reduced. It doesn’t necessarily mean the patient is hyperventilating or that their arterial

CO2 level will be reduced. Reduced perfusion to the lungs alone causes this

phenomenon. The patient’s lung function may be perfectly normal.4

9

Capnogram

The “normal” capnogram is a waveform that represents the varying CO2 level

throughout the breath cycle over time

Waveform Characteristics:

A-B Baseline (respiratory baseline, value should be zero)

B-C Expiratory Upstroke (sharp rise, mixture of air with gas from the alveoli)

C-D Expiratory Plateau (alveolar gas exhaled, should be straight)

D End-Tidal Concentration (end tidal value at the end of a normal exhaled

Breath)

D-E Inspiration Begins (sharp down stroke, patient inspires)

Increasing ETCO2 level

An increase in the level of ETCO2 from previous levels

Possible Causes:

• Decrease in respiratory rate (hypoventilation)

• Decrease in tidal volume (hypoventilation)

• Increase in metabolic rate

• Rapid rise in body temperature

1 0

Decreasing ETCO2 level

A decrease in the level of ETCO2 from previous levels

Possible Causes:

• Increase in respiratory rate (hyperventilation)

• Increase in tidal volume (hyperventilation)

• Decrease in metabolic rate

• Decrease in core body temperature

Rebreathing

Elevation of the baseline indicates rebreathing (may show increase in ETCO2)

Possible Causes

• Faulty expiratory valve on ventilator or anesthesia machine

• Inadequate inspiratory flow

• Malfunction of system

• Partial rebreathing

• Insufficient expiratory time

1 1

Muscle Relaxants

Curare Clefts are seen in the plateau portion of the capnogram. They appear when the

action of the muscle relaxants begin to subside and spontaneous ventilation returns.

Characteristics:

• Depth of the cleft is inversely proportional to the degree of drug activity

• Position is fairly constant on the same patient but not necessarily present with

every breath

Endotracheal Tube in the Esophagus

A normal capnogram is the best available evidence that the ET tube is correctly

positioned and that proper ventilation is occurring. When the ET tube is placed in the

esophagus, either no CO2 is sensed or only small transient waveforms are present.

1 2

Obstruction in Breathing Circuit or Airway

Obstructed expiratory gas flow is noted as a change in the slope of the ascending limb

of the capnogram (expiratory plateau may be absent)

• Obstruction in the expiratory limb of the breathing circuit

• Presence of a foreign body in the upper airway

• Partially kinked or occluded artificial airway

• Bronchospasm

Apnea

Complete loss of waveform indicating no CO2 present, since this occurred suddenly

consider

• Dislodge ET tube

• Total obstruction of ET tube

• Equipment malfunction, check all connections

1 3

References

1. Fletcher, R. Invasive and noninvasive measurement of the respiratory deadspace

in anesthetized children with normal and abnormal pulmonary circulation. Anesth

Analg 1988;67:442-7

2. New England Journal of Medicine, July 1997: 337: 301-306

3. Taskar, V., John, J., Larsson, A., Wetterberg, T. & Johnson, B. (1995). Dynamics of

carbon dioxide elimination following ventilator resetting. Chest, 88: 196-202.

4 Baruch, K. Capnography in EMS (2003). JEMS

1 4

Post Test

1. ETCO2 and cardiac output are:

a) Directly related

b) Inversely related

c) Not related

d) Both inversely and directly related

2. In normal, healthy lungs, ETCO2 is usually 2-5 mmHg_____ than the PaCO2:

a) Higher

b) Lower

3. ETCO2 levels decrease during a cardiac arrest because of the absence of cardiac

output:

a) True

b) False

4. Widening of the ETCO2 and PaCO2 gradient indicates the patient condition may be:

a) Improving

b) Staying the same

c) Becoming worse

d) None of the above

1 5

5. While using ETCO2 in conjunction with a patient transport the clinician can

continually assess the patient for airway patency and assess ventilation efforts:

a) True

b) False

6. Metabolism has a direct correlation with ETCO2:

a) True

b) False

7. ETCO2 will ___________ with the return of spontaneous circulation:

a) Stay the same

b) Increase

c) Decrease

d) All the above

8. Positive End Expiratory Pressure (PEEP) will generally __________ ETCO2:

a) Increase

b) Decrease

c) Stay the same

d) None of the above

9. On a capnogram elevation of the baseline indicates rebreathing:

a) True

b) False

1 6

10. All of the following are possible causes for an increase in ETCO2 except:

a) Hypoventilation

b) Rapid rise in body temperature

c) Increased metabolic rate

d) Decrease in heart rate

Date: Participant Name (mandatory, please print): Hospital: Hospital Address: AARC Member Number (mandatory): State of Residence (mandatory): Please return completed tests and evaluations to: Lisa Cifaldi Smiths Medical PM, Inc. Patient Monitoring and Ventilation N7W22025 Johnson Drive Waukesha, WI 53186

or

Fax: 262-542-0718

Post Test Answer Key

1. a

Cardiac output

Cardiac ouput and ETCO2 are directly related. If cardiac output is low the ETCO2

will also be low

2. b

Lower

ETCO2 is 2-5 mmHg lower in individuals with normal ventilation and perfusion

3. a

True

CO2 levels fall abruptly because of the absence of cardiac output during a cardiac

arrest

4. c

Becoming worse

Widening of the gradient indicates a worsening of the patient’s condition

5. a

True

Capnography can immediately identify endotracheal tube dislodgement and

provide a breath by breath patient assessment

6. a

True

ETCO2 is a reliable indicator of metabolic changes such as fever and sepsis

7. b

Increase

Due to an increase in flow (cardiac output) with the return of spontaneous

Circulation, ETCO2 will also increase

8. b

Decrease

Peep will generally decrease ETCO2 and widen the gradient

9. a

True

Elevation of the baseline indicates rebreathing and may show an increase in

ETCO2

10. d

Decrease in heart rate

This will not increase the ETCO2

17

Course Sponsor: Smiths Medical MDPM Course Title: Capnography

Part 1: Teaching Effectiveness of the Presenter(s)

Please rate the teaching effectiveness of the presenters using the scale below: 1 = Poor 2 = Fair 3 = Good 4 = Excellent 5 = Superior

Presenters (in program order) Organization Delivery Content Course Content via self-learning packet

Part 2: Your Achievement of Educational Objectives

Please rate the degree to which you believe you achieved the educational objectives for each

module by placing a check mark in the appropriate box corresponding to each: I achieved this activity s educational

objectives Objectives for each module Strongly

Agree Agree Disagree Strongly

Disagree Carbon Dioxide Physiology

1. Metabolism 2. Circulation 3. Respiratory

Alveolar –Arterial Gradient 1. Ventilation Perfusion Relationship 2. Dead space ventilation 3. Shunt perfusion

Clinical Applications Capnogram

1. Normal waveform interpretation 2. Clinical examples

Part 3: Program Integrity Indicate your agreement with the following statement by checking the appropriate response: The content of this course was presented without bias of any commercial product or drug

Strongly Agree____ Agree _____ Disagree_____ Strongly Disagree____ Comment:

18

Smiths Medical PM, Inc. Patient Monitoring and Ventilation N7W22025 Johnson Drive, Waukesha, WI 53186 USA

Phone: 262-542-3100 Fax: 262-542-0718 Toll-Free USA: 800-558-2345

www.smiths-medical.com BCI and the Smiths Medical design mark are trademarks of the Smiths Medical family of companies. The symbol ® indicates the trademark is registered in the U.S. Patent and Trademark Office and certain other countries. All other names and marks mentioned are the trade names, trademarks or service marks of their respective owners. © 2008 Smiths Medical family of companies. All rights reserved. capnography ceu rev. 01 04/08