comparison

1. CAPNOGRAPHY
VS
PLETHYSMOGRAPHY
PRESENTED BY DR. SOURAV MONDAL
MODERATED BY DR. ARVIND RATHIYA, MD
DEPT OF ANAESTHESIOLOGY, S.S.M.C , REWA , M.P.

2. CAPNOGRAPHY

3. • Capnography was first introduced by Karl Luft,
a German bioengineer, in 1943 with an infrared
CO2 measuring device he called URAS, or “Ultra
Rot Absorption Schreiber”
• It was big, heavy and very impractical to use
• Today capnography is successfully used in
almost all areas of health care.
HISTORY

4. CAPNOGRAPHY
(Quantitative ETCO2 Detectors)
• Capnography is a recording
of CO2 concentration versus
time.
• It is a form of noninvasive
monitoring of the end-tidal
carbon dioxide (ETCO2)
levels in the patient’s
exhaled breath.

5. Capnography provides instantaneous information about
Ventilation
• How effectively CO2 is being eliminated by the pulmonary system
Perfusion
• How effectively CO2 is being transported through the vascular system
Metabolism
• How effectively CO2 is being produced by cellular metabolism

6. STANDARD REQUIREMENTS OF
CAPNOMETER
• The CO2 reading shall be within ±12% of the value or ±4mm of Hg
(0.53kPa) , whichever is greater .
• The manufacturer must disclose any interference caused by ethanol,
acetone , methane , helium , tetrafluoroethane, and
dicholorodifluromethane as well as commonly used halogenated anesthetic
agents.
• The capnometer must have a high CO2 alarm for both inspired and exhaled
CO2.
• An alarm for low exhaled CO2 is required.

7. METHODS OF MONITORING
 Mass Spectrometry
 Infrared Spectrography – Most commonly
used in the hospital setting
 Chemical Colorimetric Analysis – Most
commonly used in the pre-hospital setting

8. MASS SPECTROMETRY
• It is a technique by which
concentrations of gas in a sample
can be determined according to
charge- mass ratio.
• A gas sample is passed through
an ionizer and molecules become
positively charged ions. Because
all of the ions generated carry the
same positive charge , this allows
separation based solely on mass.
• A detector then counts the no.of
ions of each mass & the results
are translated into concentrations.

9. INFRARED SPECTROGRAPHY
PRINCIPAL: Carbon Dioxide selectively
absorbs a known amount of infrared
light of a specific wavelength (4.26 µm).
The amount of light absorbed is directly
proportional to the concentration of
carbon dioxide molecules.
A predetermined amount of infrared
light is sent from the emitting side of the
sensor through a gas sample and
collected on the receiving side of the
sensor. The infrared light received is
compared to the infrared light
transmitted. The difference is then
converted by calculations into either
partial pressure or percentage of total
gas concentration that we see on the
monitor.
Infrared Spectrography

10. Chemical colorimetriC analysis
CHEMICAL COLORIMETRY ANALYSIS
CO2 NOT PRESENT CO2 PRESENT

11. •Consists of pH-sensitive indicator enclosed in housing. When the indicator is
exposed to carbonic acid it becomes more acidic & changes colour. During
inspiration the colour returns to resting state.
•The inlet and outlet ports are 15mm, so the device can be placed between
patient and the breathing system or resusciation bag
TECHNOLOGY
HYGROSCOPIC – contains hygroscopic filter paper that is impregnated with a
colourless base & an indicator that changes colour as a function of pH. A
purple/mauve colour indicates low (<0.5%) CO2 level, beige colour indicates a
moderate (0.5%- 2%) level while a yellow colour indicates high(>2%) level
HYDROPHOBIC – shows a colour change from blue to green to yellow when
exposed to CO2. Liquid water may cause improper functioning of the device.

12. TYPES OF
CAPNOMETERS
The 2 Types of Capnometers
Mainstream
Sidestream
The infrared sensor is in
the direct path of the gas
source, and connected to
the monitor by an
electrical wire.
The sample of gas is
aspirated into the monitor
via a lightweight airway
adapter and a 6ft length of
tubing. The actual sensor
is inside the monitor.

13. MAINSTREAM
CAPNOMETERS
ADVANTAGES
Mainstream – Advantages
Mainstream
 No sampling tube to
become obstructed.
 No variation due to
barometric pressure
changes.
 No variation due to
humidity changes.
 Direct measurement
means waveform and
readout are in ‘real-time’.
There is no sampling delay.
 Suitable for pediatrics and
neonates.

14. MAINSTREAM
CAPNOMETERS
DISADVANTAGES
Mainstream – Disadvantages
Mainstream
 The airway adapter sensor puts
weight at the end of the
endotracheal tube that often
needs to be supported.
 In older models there were
minor facial burns reported.
 The sensor windows can
become obstructed with
secretions and water rainout.
 Sensor and airway adapter can
be positional – difficult to use
in unusual positions (prone,
etc).

15. SIDESTREAM
CAPNOMETERS
ADVANTAGES
Sidestream – Advantages
 Sampling capillary tube and
airway adapter is easy to
connect.
 Can be used with patient in
almost any position (prone,
etc).
 Can be used in awake
patients via a special nasal
cannula.
 CO2 reading is unaffected by
oxygen flow through the
nasal cannula.

16. SIDESTREM CAPNOMETERS
DISADVANTAGES
Sidestream – Disadvantages
 The sampling capillary tube
can easily become obstructed
by water or secretions.
 Water vapor pressure
changes within the sampling
tube can affect CO2
measurement.
 Delay in waveform and
readout due to the time it
takes the gas sample to travel
to the sensor within the unit.

17. Physiology of Capnography
• During cellular respiration, small
amounts of CO2 produced , is excreted
via exhalation
• When no cellular respiration is
occurring, even if ventilation is, there
will be no CO2 exhaled
– In poor perfusion states (cardiac
arrest) no CO2 is transported to the
lungs to be exhaled, so a low
reading will occur
– In poor ventilation states
(hypoventilation) CO2 is retained,
so a high reading will occur

18. End-tidal CO2
 The peak partial pressure of CO2
during exhalation (the highest
level of expired CO2 reached
during exhalation) is known as
the end-tidal CO2 (ETCO2).
– Normally occurs at the end
of the alveolar plateau
 ETCO2 is a reflection of alveolar
ventilation, CO2 production and
pulmonary blood flow.
 Normal value is 35-45 mmHg

19. Clinical Application of ETC02
• Verification of endotracheal
tube placement
• Continuous monitoring of
tube location during transport
• Gauging the effectiveness of
resuscitation and prognosis
during cardiac arrest
• Titrating ETC02 levels in
patients with suspected
increases in intracranial
pressure
• Determining adequacy of
ventilation

20. Waveform Displays
(Quantitative Device)
 The waveform is divided into
4 phases.
 Phases I, II and III occur
during and reflect the three
phases of exhalation.
 Phase IV occurs during and
reflects inspiration

21. Capnogram: Phase I
Phase I (A-B) occurs
during exhalation of air
from the anatomic dead
space, which normally
contains no CO2.
This part of the curve is
normally flat, providing a
steady baseline.

22. Capnogram: Phase II
Phase II (B-C) occurs
during alveolar washout
and recruitment, with a
mixture of dead space
and alveolar air being
exhaled.
Phase II normally
consists of a steep
upward slope.

23. Capnogram: Phase III
 Phase III (C-D) is the alveolar
plateau, with expired gas
coming from the alveoli.
 In patients with normal
respiratory mechanics, this
portion of the curve is flat,
with a gentle upward slope.
 The highest point on this
slope (D) represents the
ETCO2 value.

24. Capnogram: Phase IV
 Phase IV (D-E) occurs during
inspiration, where the ETCO2
level normally drops rapidly
to zero.
 Unless CO2 is present in the
inspired air, as occurs when
expired air is rebreathed ,
this part of the waveform is a
steep, downward slope.

26. VOLUME CAPNOGRAM
It is a graphic display of CO2 concentation/ partial pressure
versus exhaled volume. The inspiratory phase in not defined in
volume capnogram.
ADVANTAGES
Allows estimation of relative contributions of anatomical dead
space and alveolar dead space
More sensitive
Allows for determination of total mass of CO2 exhaled during
a breath & provides estimation of VCO2

27. ABNORMAL CAPNOGRAMS

28. Causes of an Elevated ETCO2
• ↑CO2 PRODUCTION &
DELIVERY TO LUNGS
 ↑metabolic rate
 Fever
 Sepsis
 Seizures
 Malignant hypothermia
 Thyrotoxicosis
 ↑Cardiac output (during CPR)
 Bicarbonate administration
• ↓ALVEOLAR VENTILATION
 Hypoventilation
 Respiratory centre depression
 Partial muscular paralysis
 Neuromuscular disease
 COPD
• EQUIPMENT MALFUNCTION
 Rebreathing
 Exhausted C02 absorber
 Leak in ventilator circuit
 Faulty inspiratory/ expiratory valve

30. Causes of a Decreased EtCO2
• ↓ CO2 PRODUCTION AND
DELIVERY TO LUNGS
 Hypothermia
 Pulmonary hypoperfusion
 Cardiac arrest
 Pulmonaryembolism
 Haemorrhage
 Hypotension
• ↑ALVEOLAR VENTILATION
 Hyperventilation
• EQUIPMENT MALFUNCTION
 Ventilator disconnect
 Esophageal intubation
 Complete airway obstruction
 Poor sampling
 Leak around ETT cuff

37. INCOMPETENT INSPIRATORY
UNIDIRECTIONAL VALVE
• The waveform shows
a prolonged plateau
& a slanting
inspiratory
downstroke
• The inspiratory phase
is shortened & the
baseline may or may
not reach zero.

38. LEAK IN SAMPLING LINE DURING PPV
• Will result in upswing at
the end of Phase III.
• The brief peak is caused
by the next inspiration ,
when positive pressure
pushes undiluted end-
tidal gas through the
sampling line.

40. Pulse oximetry
(photoplethysmography+
oximetry)

41. PULSE OXIMETRY
Pulse oximeters combines
the principle of oximetry and
plethysmography to
noninvasively measure oxygen
saturation in arterial blood

42. History
• In early 1940 GLEN MALKIKAN coined the term
oximeter.
• MATHEES- father of oximetry
20 papers in1934 –1944
• HERTZMAN 1937 –use of photoelectric finger
plethsmography
• 1975 –concept of pulse oximetry –Japan
• In 2008 modification continued and term High
Resolution Pulse Oximetry come into existence

43. Introduction
• Also called the fifth vital sign
• Low SpO2 provide warning of hypoxemia before other signs such as
cyanosis or a change in heart rate are observed.
• Until the 1980s, noninvasive oximeters, known oximeters, were large,
expensive, and cumbersome. They required “arterialization”.
• Technical advances, including LEDs, miniaturized photodetectors, and
microprocessors, allowed the creation of a new generation of oximeters.
• These differentiate the absorption of light by the pulsatile arterial
component from the static components, so they are called Pulse
Oximeters.

44. Oxygen Saturation
• Saturation is defined as ratio of O2 content to oxygen
capacity of Hb - expressed as percentage.
• Desaturation leads to Hypoxemia – a relative
deficiency of O2 in arterial blood. (PaO2 < 80mmHg –
hypoxemia)
• (SaO2< than 76% is life threatening.)

45. FRACTIONAL SATURATION
This is the ratio of oxygenated Haemoglobin to sum of
all haemoglobin species in blood.
Fractional saturation = HbO2
-
--------------------------
HbO2+ Hb+ Met Hb +CO Hb

46. FUNCTIONAL SATURATION
This is the of ratio between HbO2 to
all the functional haemoglobin

47. PLETHYSMOGRAPHY
• Pulse oximeters show pulsatile change in
absorbance in a graphical form. This is called the
“plethysmographic trace” or “pleth”
• Because absorption of light is proportional to the
amount of blood between the transmitter & the
photodetector , changes in the blood volume are
reflected in pulse oximetry trace. Hence pulse
oximeter can also be used as a
photoplethysmograph

48. PRINCIPLES
• All atom and molecules absorb specific wavelength of light. This
property is the basis for an optical technique known as
spectrophotometry.
Beer-Lambert Law
It states that if a known intensity of light illuminates a chamber of
known dimensions , then the concentration of a dissolved substance can
be determined if the incident and transmitted light is measured :
It = Iie –dcα
Solved for C,
C= (1/dα)ln[Ii/It]

49. Substances have a specific pattern of absorbing
specific wavelength – EXTINCTION COEFFICIENT
Uses two lights of wavelengths
660nm –deoxy Hb absorbs ten times as oxy Hb
940 nm – absorption of oxyHb is greater
Lab oximeters use 4 wavelengths to measure 4 species
of haemoglobin

50. Operating Principles
• The pulse oximeter computes the ratio between the
two signals and relates this ratio to the arterial
oxygen saturation, using an empirical algorithm.
• Pulse oximeters discriminate between arterial blood
and other components.
• The oximeter pulses the red and infrared LEDs ON
and OFF several hundred times per second

51. • The rapid sampling rate allows recognition of the peak and trough of
each pulse wave.
• At the trough, the light is transmitted through a vascular bed that
contains mainly capillary and venous blood as well as intervening
tissue.
• At the peak, it shines through all these plus arterial blood.
• A photodiode collects the transmitted light and converts it into
electrical signals.
• The emitted signals are then amplified, processed, and displayed on the
monitor.

52. Accuracy
• A clinically acceptable level of arterial
oxygenation(SaO2 above 70%),the oxygen saturation
recorded by pulse oximeters (SpO2) differs by less
than 3% from the actual saturation.
• Pulse oximetry also show a high degree consistency
of repeated measurements.

53. PHYSIOLOGY OF PULSE OXIMETRY
• Pulse Oximetry uses light to work out oxygen saturation.
Light is emitted from light sources which goes across the
pulse oximeter probe and reaches the light detector.
• If a finger is placed in between the light source and the
light detector, the light will now have to pass through the
finger to reach the detector. Part of the light will be
absorbed by the finger and the part not absorbed reaches
the light detector.

54. The amount of light
absorbed depends on the
following:
concentration of the light
absorbing substance.
length of the light path in the
absorbing substance

55. Types of Oximetry
Transmission Pulse Oximetry
• light beam is transmitted through
a vascular bed and is detected on
opposite side of that bed
Reflectance Pulse Oximetry
• relies on light that is reflected to
determine oxygen saturation. The
probe have the emitters &
detectors on the same side.
advantage - its signal in low
perfusion is better.
limitations -The probe design must
eliminate light that is passed directly
to the probe or is scattered in the
outer surface of the skin. The signals

56. Equipment
Probes
• The probe (sensor, transducer) comes in contact
with the patient.
• It contains one or more LEDs (photodiodes) that
emit light at specific wavelengths and a
photodetector.
• The LEDs provide monochromatic light.
• Probes may be reusable or disposable.

57. •Self-adhesive probes are less likely to come
off if the patient moves.
• Probes are available in different sizes.
•The photocell should be aligned with the
probe
•Contamination should be reduced.

58. Cable
• The probe is connected to the oximeter by an
electrical cable.
Console
• Many different consoles are available . Most
oximeters that are used in the operating room are
part of a physiologic monitor.
• Most stand-alone units are line operated but will
work on batteries, making them useful during
transport.

59. • Most instruments provide an audible tone whose
pitch changes with the saturation.
• Alarms are commonly provided for low and high
pulse rates & for low and high saturation.
• ASA standards for Basic Anesthetic Monitoring
require that the variable pitch pulse tone and low
threshold alarm be audible.

60. Oximeter Standards
• There must be a means to limit the duration of
continuous operation at temperature above
41°C .
• The accuracy must be stated over the range of
70% to 100% SpO2.
• There must be an indication when the SpO2
or pulse rate data is not current.

61. • It must be provided with an alarm system
• There must be an alarm for low SpO2 that is not less
than 85% SpO2 .
• An indication of signal inadequacy must be provided
if the SpO2 or pulse rate value displayed is
potentially incorrect.

62. Sites of probe placement
Fingers
Toe
Ear
Nose
Tongue
Cheek
Esophagus
Forehead

63. MISC
• Pharyngeal pulse oximetry by using a pulse oximeter
attached to a laryngeal mask may be useful in patients with
poor peripheral perfusion.
• Flexible probes may work through the palm, foot, penis,
ankle, lower calf, or even the arm in infants
• Pulse oximetry may be used to monitor fetal oxygenation
during labor by attaching a reflectance pulse oximetry probe
to the presenting part . A disadvantage is that the probe has
to be placed blindly and may be positioned over a
subcutaneous vein or artery, which will affect the reliability of
the readings

64. uses
• Monitoring oxygenation: PACU,
transport.
• Detect inadvertent bronchial
intubation
• Managing one lung anaesthesia
• Weaning from artificial ventilation
• Controlling 02 administration
• Monitoring peripheral circulation
• Determining systolic blood
pressure
• Locating vessels ( eg: axillary
artery)
• Avoiding hyperoxaemia
• Monitoring vascular volume
• Monitoring sympathetic
tone(dicrotic notch)
• Pulse rate
• Arrhythmias
• Neonatal care(one element of
suggesting congenital heart
diseases)

65. ADVANTAGES
• Accuracy
• Independence from gases and vapours
• Fast response time
• Non invasive
• Continuous Measurements
• Separate Respiratory and circulatory variables
• Convenience
• Fast start time

66. • Tone modulation
• User –friendliness
• Light weight & compactness
• No heating required
• Battery operated
• Probe variety
• Economy

67. Limitations and Disadvantages
Failure to Determine the Oxygen Saturation
Factors that are reported to contribute to higher failure rates
include ASA physical status III , IV or V patients, orthopedic,
vascular, and cardiac surgery; electrosurgery use; hypothermia;
hypotension; low hematocrit and motion
Poor Function with Poor Perfusion
Readings may be unreliable or unavailable if there is loss or
diminution of the peripheral pulse (proximal blood pressure cuff
inflation, external pressure, improper positioning, hypotension,
hypothermia, Raynaud's phenomenon, low cardiac output,
hypovolemia, peripheral vascular disease).

68. Erratic Performance with Dysrhythmias
Double- or triple-peaked arterial pressure waveform
that confuses the pulse oximeter, so it may not provide
a reading
Carboxyhaemoglobin
COHb has an absorption spectrum similar to that of
02Hb at 660nm, so most pulse oximeters give falsely
elevated readings.

69. Methaemoglobin
Methaemoglobin absorbs light equally at the red and infrared
wavelengths that are used by most pulse oximeters. When compared
with functional saturation, most pulse oximeters give falsely low
readings for saturations above 85% and falsely high values for
saturations below 85% .
Sulfhaemoglobin
• Sulfhaemoglobinemia may be caused by drugs such as
metoclopramide , phenacetin, dapsone and sulfonamides.
Sulfhaemoglobin causes the pulse oximeter to display artifactually
low oxygen saturation

70. Mixing Probes
SpO2 measurements may not be accurate if one
manufacturer's probe is used with a different
manufacturer's instrument
Bilirubinemia
Severe hyperbilirubinemia can cause an artifactual
elevation of metHb and carboxyhaemoglobin when
using in vitro oximetry but does not affect pulse
oximetry readings.

71. Low Saturations
Pulse oximetry becomes less accurate at low oxygen
saturations . This inaccuracy is greater in patients with dark skin.
It should be used with caution in patients with cyanotic heart
disease.
Malpositioned Probe
• Prominent pulsations of venous blood may lead to
underestimation of the SpO2.
• High airway pressures during artificial ventilation may cause
phasic venous congestion, which may be interpreted by the
oximeter as a pulse wave.

72. Nail polish and coverings
• All colour of nail polishes especially black, dark blue & purple may cause
significantly lower saturation readings
Electrical Interference
• Electrical interference from an electrosurgical unit can cause the oximeter
to give an incorrect pulse count .
• Steps to minimize electrical interference include – keeping the oximeter
probe & console as far from the surgical field as possible; locating
electrosurgery ground plate as close as possible to the surgical site ;not
plugging in the electrosurgical apparatus and pulse oximeter into the
same power circuit
Severe Anaemia -The pulse oximeter may overestimate SpO2, especially at
low saturations, in patients with severe anemia.
Skin Pigmentation -pigmentation does not make a significant difference in
pulse oximeter accuracy

73. Problem of movement
• Pulse oximeters are very vulnerable to motion, such
as a patient moving his hand. As the finger moves,
the light levels change dramatically. Such a poor
signal makes it difficult for the pulse oximeter to
calculate oxygen saturation.
• Lengthening the averaging time will increase the
likelihood that enough true pulses will be detected
to reject the motion artifacts.

74. Problem of optical shunting
• If the probe is of the wrong size or has not being
applied properly, some of the light , instead of going
through the artery, goes by the side of the artery
(shunting).
• This reduces the strength of the pulsatile signal
making the pulse oximeter prone to errors. It is
therefore important to select the correct sized probe
and to place the finger correctly in the chosen probe
for best results.

75. PROBLEMS OF TOO MUCH AMBIENT LIGHT
• If the ambient light is too strong, the LED light signal
gets "submerged" in the noise of the ambient light.
This can lead to erroneous readings. Therefore, it is
important to minimise the amount of ambient light
falling on the detector.

76. Problem of not detecting hyperoxia
• Haemoglobin is not the only way oxygen is carried in
blood. Additional oxygen can also be dissolved in the
solution in which red blood cells travel (plasma).
• The problem is that the pulse oximeter cannot "see"
the extra dissolved oxygen. So even if the patient’s
blood contains extra oxygen, the saturation will still
show 100 %.

77. Methods to improve signals
• Application of vasodilating cream
• Digital nerve block
• Administration of intraarterial vasodilators
• Placing a gloves filled with warm water over patient
hand.
• Warming cool extremities
• Trying an alternative probe site.
• Trying a different probe
• Trying a different machine

78. Patient Complications
• Corneal Abrasions
• Pressure and Ischemic Injuries
• Burns
• Electric Shock

79. CAPNOGRAPHY VS PLETHYSMOGRAPHY
–
a comparison & conclusion

80. • Oxygenation is monitored by pulse oximetry whereas Ventilation is
monitored with capnography
• Oximeters measure saturated haemoglobin in peripheral blood and
provide additional information about the adequacy of lung perfusion and
oxygen delivery to the tissues. However, pulse oximetry is a late indicator
of O2 supply, and is less sensitive than capnography. It does not afford a
complete picture of ventilatory status.
• Capnography continuously and nearly instantaneously measures
pulmonary ventilation and is able to rapidly detect small changes in
cardio-respiratory function before oximeter readings change.
• Hypoventilation & hypercarbia may occur without a decrease in Hb O2
saturation, so pulse oximeter cannot be relied on to detect leaks,
disconnections or esophageal intubations ; whereas capnography can be
reliably used in these conditions.

81. THANK YOU