2. Learning Objectives
by the end of this section the students able to
• Differentiate between oxygenation
and ventilation
• Define end-tidal CO2
• Identify phases of a normal capnogram
• Recognize patterns abnormal capnogram
3. Physiologic aspects and the need for capnography
Respiration
The respiratory process consists of three main events:
1. Cellular metabolism of food into energy—O2 consumption and CO2
production.
2. Transport of O2 and CO2 between cells and pulmonary capillaries, and
diffusion from/into alveoli.
3. Ventilation between alveoli and atmosphere
INTRODUCTION
5. introduction
• Oxygenation: The process of getting oxygen
into the body and to the tissues for
metabolism, is monitored with pulseoximetry.
• Ventilation: the process of eliminating CO2
from the body, is monitored with
capnography.
6. Capnography
Continuous measurement of patient’s inhaled and exhaled
[CO2]
Waveform display more informative than the value
Useful for evaluation of
– Esophageal intubation
– Disconnect in breathing circuit
– Rebreathing of CO2
– Cardiac arrest
– Malignant Hyperthermia / Thyroid storm
– Hypotension
– PE
ETCO2 underestimates PaCO2 due to deadspace ventilation
7. Capnography- Continuous analysis and recording of
Carbon Dioxide concentrations in respiratory gases.(
I.E. waveforms and numbers)
Capnograph a device that measures CO2 and displays a waveform.
Partial pressure (mmHg) or volume (% vol) of CO2 in
the airway at the end of exhalation
Breath-to-breath measurement provides
information within seconds
8. -CO2 dilates the cerebral blood vessels
increasing ICP by increasing the volume
of blood in the intracranial vault
Titrating CO2 levels to 30-35 mmHg
range in head injured patient can help
relieve the untoward effects of raised ICP
9. CO₂ plays a role in metabolic, cardiovascular
and respiratory systems.
Monitoring CO₂ concentration gives
indication of subtle pathological
disturbances of metabolic, cardiovascular
and respiratory systems.
10. Normal arterial and end-tidal CO2
values
Arterial CO2 (PaCO2) sample (ABG)
PaCO2values: 35 to 45 mmHg
End-tidal CO2 (EtCO2)From capnograh
values: 30 to 43 mmHg
4.0 to 5.7 kPa
4.0 to 5.6%
Mixed venous blood gas PeCO2
Normal range: 46-48mmHg
Generally; ETCO2 < PACO2 < PaCO2
11. Arterial to end-tidal CO2 gradient
the difference b/n aCO2(from ABG) and ACO2(EtCO2
2 to 5 mmHg.
This difference is termed the PaCO2—PEtCO2 gradient
or the a—ADCO2 and can be increased by:
COPD (causing incomplete alveolar emptying)
ARDS(causing V/Q mismatch)
A leak in the sampling system or around the ET tube
12. The format for reported end-
tidal CO2 can be classified as
1. Quantitative (an actual numeric value) OR
usually can be displayed in units of mmHg, % or kPa
2. Qualitative (low, medium, high):
usually present as a bar graph,
while colorimetric devices are
presented in a percentage range
grouped by color
13.
14.
15. Capnography (cont)
How does it work?
CO2 : 2 dissimilar atoms absorbs infrared radiation
with wavelength of 4.3 mm
Infrared lamp = stable source
IR absorption number of CO2 molecules in chamber
Remaining infrared radiation falls on thermopile detector
which produces heat
→ converted to an electrical output to produce a waveform
Converted to real time waveform (note delay due to sampling
time)
16. Components
1. sampling chamber
A main-stream version
positioned within the patient’s gas stream
B. side-stream version
Connected to the distal end of the breathing system
2. A photodetector
measures light reaching it from a light source after
passing through two chambers.
One acts as a reference whereas the other one is the
sampling chamber
19. SpO₂ and EtCO₂
• Oxygen Saturation
• Reflects Oxygenation
• SpO2 changes lag when
patient is hypoventilating or
apneic
• Should be used with
Capnography
• Carbon Dioxide
• Reflects Ventilation
• Hypoventilation/Apnea
detected immediately
• Should be used with pulse
Oximetry
Pulse Oximetry Capnography
20. Why Use Capnography?
Verify and document ET tube placement
Immediately detect changes in ET tube position
Assess effectiveness of chest compressions
Earliest indication of ROSC
Indicator of probability of successful resuscitation
Optimally adjust manual ventilations in patients
sensitive to changes in CO2
21. Ventilation- Rate and gas exchange
Minute ventilation- Total volume of gas entering
lungs per minute
Alveolar Ventilation- Volume of gas that reaches
the alveoli
Dead Space Ventilation- Volume of gas that does
not reach the respiratory portions ( 150 ml)
22. The Capnography
• Monitors changes in
Ventilation - asthma, COPD, airway edema,
foreign body, stroke
Diffusion - pulmonary edema, alveolar damage,
CO poisoning, smoke inhalation
Perfusion - shock, pulmonary embolus, cardiac
arrest, severe dysrhythmias
25. Capnogram Waveform
Phase Termed Variables Gas from
phase I A→B Baseline A = completion of inspiration Large airways
Oropharynx
nasopharynx
B = beginning of expiration
phase II B→C Expiratory
upstroke
C = slowing of exhaled flow Intermediate airways mixes with
phase I air
phase III C→D Alveolar plateau D = end expiration = ETCO2 Mixed gas displaced by alveolar
gas
phase IV D→E Inspiratory
downstroke
E= end inspiration Inspiratory gas has little CO2
27. There is no carbon dioxide at the beginning of
exhalation. The air is from the trachea, mouth
and nose.
This upper airway area is often called “dead
space” because there is no gas exchange in
the upper airway.
An extension of the airway such as an ET tube,
expands the “dead space”.
30. Capnogram Phase one
the ending of inhalation and the beginning
of exhalation.
This baseline is normally at zero and shows
the amount of carbon dioxide in the dead
space.
31. Capnogram Phase II (Ascending Phase)
carbon dioxide from the alveoli begins to
reach the upper airway and mix with the
dead space air.
This causes a rapid rise in the amount of CO2
that is now detected in exhaled air.
33. Capnogram Phase III (Alveolar Plateau)
The carbon dioxide from the alveoli has reached
the airway exit. The exhaled air is now rich in CO2.
In normal ventilation of health lungs, the
concentration of CO2 in the air is uniform.
the alveolar plateau is flat with a slight upward tilt
this shows uniform concentration of carbon
dioxide in the pulmonary system.
34. Phase III cont..
The end of phase three is also the end of
exhalation.
Termination of the breath cycle contains the
highest concentration of CO2 and is labeled the
“end-tidal CO2”.
This is the number seen on the monitor.
Normal EtCO2 is 35-45mmHg.
35. Capnogram Phase IV(Descending Phase)
Shows the beginning of the next inhalation.
Oxygen fills the airway and the carbon dioxide
level quickly drops to the baseline.
37. Possible causes to Decreasing EtCO2 level
Increase in respiratory rate (hyperventilation)
Increase in tidal volume (hyperventilation)
Decrease in metabolic rate
Fall in body temperature
Rebreathing
Obstruction in breathing circuit or airway
38. Possible causes to increases EtCO2
Decrease in respiratory rate (hypoventilation)
Decrease in tidal volume (hypoventilation)
Increase in metabolic rate
Rapid rise in body temperature (malignant
hyperthermia)
39. How would your capnogram change if you
intentionally started to breathe at a rate of 40?
Frequency
Duration
Height
Shape
40. 1. Rate: increased frequency of waveforms
2. Duration: the waveform cycle shortens
3. Amount: the peak or height of the plateau will
lower as the CO2 is blown off
4. The shape of the waveform should remain in the
normal box-like pattern.
42. In the normal metabolic state
hyperventilation is seen as the increase RR
leads to a depletion of CO2 in the exhaled air
When would a rapid RR not show a decline in
EtCO2?
• Metabolic states in which there is
hyperventilation and high production of
carbon dioxide such as fever, DKA, etc.
43. EtCO2
would a slow RR not show an increase in EtCO2?
• In Slow metabolic states in which there is a lower
production of carbon dioxide such as severe
hypothermia.
ETCO2 underestimates PaCO2 due to deadspace ventilation
45. • When would a slow RR not show an increase in
EtCO2?
• In Slow metabolic states in which there is a lower
production of carbon dioxide such as severe
hypothermia.
47. Bronchospasm
In an asthma attack, the alveoli are unevenly filled
on inspiration and empty asynchronously during
expiration.
The waveform often referred to as the “shark fin”.
48. Shark Fin
Asthmatic Waveforms
COPD patients have a difficult time exhaling gases
This is represented on the capnogram by a shark fin appearance
49. Factors that affect CO2 levels:
INCREASE IN ETCO2 DECREASE IN ETCO2
Increased muscular activity Decreased muscular activity
Increased cardiac output Decreased cardiac output
Exhausted Sodalime Bronchospasm
Hypoventilation Hyperventilation
Malfunctioning exhalation valve Circuit leak or partial obstruction
Decreased minute ventilation Hypothermia
Bicarbonate infusion Poor sampling technique
Tourniquet release Pulmonary embolism
drug therapy for bronchospasm
Increased minute ventilation
50. A capnogram that does not touch the baseline is
indicative of a patient who is rebreathing CO2
through insufficient inspiratory or expiratory flow.
51. Rebreathing
A capnogram that does not touch the baseline is indicative of a patient
who is rebreathing CO2 through insufficient inspiratory or expiratory flow
69. Recap
Phase I Inspiration ends and exhalation begins, dead
space air is eliminated first, no CO2 is present.
Phase II Alveolar air begins to mix with dead space air,
a sharp upstroke is produced.
Phase III Alveolar air predominates and the CO2 level
plateaus as the exhalation continues.
The EtCO2 is noted at the end of exhalation
Normal range is 35-45mmHg (5% vol)
70. Phase IV Inspiration occurs, CO2 level quickly
returns to baseline.
Normal baseline is at zero.
The pattern repeats with each breath.
71.
72. DEFINETION
• Hypoxia is O2 deficiency at the tissue level.
• A pathological condition in which the whole body
as a whole or a region of the body is deprived of
adequate oxygen supply.
• It is the decrease below normal levels of oxygen in
inspired gases, arterial blood, or tissues, without
reaching anoxia.
73. CAUSES OF HYPOXIA
High altitude.
Low hemoglobin level.
Decreased oxygen supply to an area.
Low oxygen carrying capacity.
Poor tissue perfusion.
Impaired ventilation.
Decreased diffusion of oxygen.
75. Hypoxic hypoxia
SYNONYMS
Hypoxemic hypoxia OR Arterial hypoxia
DEFINITION: Hypoxic hypoxia is a result of
insufficient oxygen available to the lungs or
decreased oxygen tension
77. Major causes of Hypoxic hypoxia
1. Low oxygen tension in inspired air.
2. Respiratory disorders associated with
decreased pulmonary ventilation.
3. Respiratory disorders associated with
inadequate oxygenation of blood in lungs.
4. Cardiac disorders
78. CAUSE
Low oxygen tension in inspired air
High altitude.
Breathing in closed space.
Breathing gas mixture containing low pO2
80. CAUSE
Respiratory disorders associated with
inadequate oxygenation of blood in lungs.
Emphysema.
Fibrosis.
Pulmonary hemorrhage.
Pneumonia.
Bronchiolar obstruction.
Bronchiectasis.
81. CAUSE
Cardiac disorders.
Congestive heart failure.
Low cardiac output
Hypoxic hypoxia is characterized by reduced
oxygen tension in arterial blood while all the
other features are normal.
82.
83. • Hypoxia in which arterial pO2 is normal but
the amount of haemoglobin available to carry
oxygen is reduced.
84. Anemic hypoxia
• CAUSE
Decreased no. of RBCs
Decreased haemoglobin content in blood
Formation of altered haemoglobin
Combination of haemoglobin with gases other than
O2 and CO2
85. • Anemic hypoxia is characterized by low
oxygen carrying capacity of blood while the
other features remain normal.
86. • Stagnant /Ischaemic
hypoxia
• Hypoxia in which the blood flow to the tissues
is so low or slow that adequate oxygen is not
delivered to them despite a normal arterial pO2.
88. • Stagnant hypoxia is characterized by
decreased velocity of blood flow while the
other features remain normal.
89.
90. o Hypoxia in which the amount of oxygen
delivered to the tissues is adequate , but
because of the action of a toxic agent the
tissue cells cannot make use of the oxygen
supplied to them.
91. o Cyanide poisoning:
Cyanide destroys the cellular oxidative
enzymes completely paralyzing the
cytochrome oxidase system.
94. TYPES OF
HYPOXIAS
CAUSES
• Hypoxic hypoxia
•Anemic hypoxia
Stagnant hypoxia
Histotoxic hypoxia
• Decreases inspired pO2;
decreased pulmonary
ventilation ; defective V/P ratio
• Total Hb content decreases due
to anemia;
• haemorrhage; presence of
abnormal Hb
• Circulatory failure;
haemorrhage; heart failure
• Cyanide poisoning
95. TYPES OF
HYPOXIA
ARTERIALpO2
ARTERIALO2
CONTENT
ARTERIAL % -
O2 SATURATION
OF
HEMOGLOBIN
Hypoxic
hypoxia
Decreased Decreases Decreases
Anemic
hypoxia
Normal Markedly
reduced
Decreases
Stagnant
hypoxia
Normal Normal Normal
Histotoxic
hypoxia
Normal Normal Normal
96. TYPES OF
HYPOXIA
A-V PO2
DIFFERENCE
CYANOSIS STIMULATION
OF
PERIPHERAL
CHEMORECEP
TORS
Hypoxic
hypoxia
Decreases Present Present
Anemic
hypoxia
Normal Absent Absent
Stagnant
hypoxia
More than
normal
Present Present
Histotoxic
hypoxia
Less than
normal
Absent Present
97. • Anemic hypoxia is characterized by low
oxygen carrying capacity of blood while the
other features remain normal.
98. • Ischaemic hypoxia.
• Hypoxia in which the blood flow to the tissues
is so low or slow that adequate oxygen is not
delivered to them despite a normal arterial pO2.
100. • Stagnant hypoxia is characterized by
decreased velocity of blood flow while the
other features remain normal.
101.
102. o Hypoxia in which the amount of oxygen
delivered to the tissues is adequate , but
because of the action of a toxic agent the
tissue cells cannot make use of the oxygen
supplied to them.
103. o Cyanide poisoning:
Cyanide destroys the cellular oxidative
enzymes completely paralyzing the
cytochrome oxidase system.
106. TYPES OF
HYPOXIAS
CAUSES
• Hypoxic hypoxia
•Anemic hypoxia Stagnant
hypoxia Histotoxic hypoxia
• Decreases inspired
pO2; decreased
pulmonary
ventilation ;
defective V/P ratio
• Total Hb content
decreases due to
anemia;
• haemorrhage;
107. TYPES OF
HYPOXIA
ARTERIALpO2
ARTERIALO2
CONTENT
ARTERIAL % -
O2 SATURATION
OF
HEMOGLOBIN
Hypoxic
hypoxia
Decreased Decreases Decreases
Anemic
hypoxia
Normal Markedly
reduced
Decreases
Stagnant
hypoxia
Normal Normal Normal
Histotoxic
hypoxia
Normal Normal Normal
108. TYPES OF
HYPOXIA
A-V PO2
DIFFERENCE
CYANOSIS STIMULATION
OF
PERIPHERAL
CHEMORECEP
TORS
Hypoxic
hypoxia
Decreases Present Present
Anemic
hypoxia
Normal Absent Absent
Stagnant
hypoxia
More than
normal
Present Present
Histotoxic
hypoxia
Less than
normal
Absent Present
109. Stagnant /Ischaemic hypoxia
• DEFINITION
Hypoxia in which the blood flow to the tissues is
so low or slow that adequate oxygen is not
delivered to them despite a normal arterial pO2