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Dr .Gihan A Tarabih . MD,

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Title: Dr .Gihan A Tarabih . MD,


1
??? ???? ?????? ??????
Dr .Gihan A Tarabih . MD, ASS.Prof. of
Anethesia And SICU, Mansoura Faculty of Medicine.
2
Respiratory Monitoring Rapid progress with
greater safety in Anesthesia field and better ICU
outcome.
Oximetry
3
Early Warning When do you want the patients
parachute to open?
Capnography( 4-10 minutes)
capnography
Pulse Oximetry (30-60 seconds)
Pulse Oximetry
ECG( 10 seconds)
ECG
No monitor free fall!
4
ASA Standard Care
  • During all anesthesia care the following
    parameters will be continually monitored
  • 1-oxygenation
  • 2-ventilation
  • 3-circulation
  • 4-temperature

5
CAPNOGRAPHY-OXIMETRY
  • Why use them?

6
Main Anesthesia Enemies
Cardiac arrest
Pulmonary embolism
Hypoxia
Hypoventilation
Severe hypotension
7
? Application in clinical practice
Objectives
? The physiology involved
? How it works
Indications
?
8
Physiology of respiration
Oxygen/Carbon dioxide interaction Perfusion and
Ventilation
Ventilation
O2
CO2
CO2
O2
CO2
Perfusion
9
Physiology of respiration
Oxygen/Carbon dioxide interaction Metabolism
Oxygen -gt lungs -gt alveoli -gt blood
Oxygen
breath
CO2 produced by cellular metabolism diffuses
across the cell membrane into the circulating
blood.
CO2
muscles organs
lungs
5-10 carried in solution 20-30 bound to
haemoglobin 60-70 carried as bicarbonate in the
red blood cell
Oxygen
CO2
cells
energy
blood
Oxygen Glucose
CO2
10
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11
Oxygenation
  • Objective
  • ensure adequate oxygen concentration in inspired
    gas and blood
  • Montoring
  • 1-inspired gas oxygen analyzer with alarms (GA)
  • 2-Arterial oxygen saturation(Spo2).
  • 3-Arterial oxygen tension(Po2).

12
Pulse Oximetry
  • How does it really work?
  • Why should I care?

13
Oximetry History
  • Became standard of care in the 1980s
  • 1935 Carl Matthes
  • first oximeter
  • 1940 J.R. Squires
  • self calibrating oximeter

14
Oximetry History (Contd)
  • 1940s Glen Milliken
  • aviation ear oximeter for use in avitation
    research to investigate high altitude hypoxic
    problems.
  • -1964 Robert Shaw(surgeon) built a self
    caliberating ear oximeter Which was marketed by
    Hewlett Packard in 1970 for use in physiology and
    cardiac cathterization laboratories

15
Terminology Review
  • SpO2 Non invasive oxygen saturation
  • SaO2 Arterial (invasive)Oxygen Saturation
    (oxygen bound to the hemoglobin molecules)
  • PaO2 Arterial Partial Pressure, oxygen
    dissolved in the plasma (only about 3 of total
    content) or PO2
  • CaO2 Total amount of oxygen in the blood or the
    (SaO2 PaO2).

16
Oxygen Saturation
  • Percentage of hemoglobin saturated with oxygen
  • Normal SpO2 is 95-98
  • Suspect cellular perfusion compromise if less
    than 92 SpO2
  • Insure adequate airway
  • Provide supplemental oxygen
  • Monitor carefully for further changes and
    intervene appropriately

17
PULSE OXIMETRY WHAT DOES IT DO?
  • MEASURES/DISPLAYS
  • - O2 SAT OF HbG
  • - PULSE RATE
  • - INDICATES PERFUSION
  • - PULSATE FLOW

18
Various forms of pulse oxs
19
What are the Normal?
  • 97-100 sat Good gas exchange .
  • 90-95 sat Mild hypoxia
  • lt90 sat Severe hypoxia
  • Not all patients are the same
  • - COPD
  • - Anemia

20
Pros of Pulse Oximeters
  • PROS
  • Non-invasive
  • Allows continuous measurement in real time
  • Easy to use

21
Cons of Pulse Oximetry
  • CONS
  • Measures Hb saturation rather than the actual
    level of Hb. Only measures oxygenation status.
  • Does not detect carbon dioxide levels in the
    blood. CO2 determines the ventilation status.
  • Measurements are not always accurate. Inaccuracy
    may occur due to nail polish, light interference,
    poor peripheral perfusion, intravenous dyes, the
    presence of carboxyhemoglobin and
    hemoglobinopathies.

22
Pros/Cons of an arterial blood gas
  • PROS
  • Accurate
  • The gold standard for measuring respiratory status
  • CONS
  • Invasive
  • Not easy to perform on a patient
  • Does not reflect measurements in real time status

23
Objectives
  • Understand how a pulse oximetry works
    (technology)
  • Define normal and abnormal pulse oximetry
    readings.
  • State the indications and limitations when using
    a pulse oximetry in anesthesia ,POCU and ICU.

24
Indications for Pulse Oximetry
  • Uses of Pulse Oximetry generally fall into two
    categories
  • Real Time Indicator of hypoxemia
  • End point for titration of therapeutic
    interventions.

25
Technology
  • The pulse oximeter has Light-emitting diodes
    (LEDs) that produce red and infrared light
  • LEDs and the detector are on opposite sides of
    the sensor
  • Sensor must be place so light passes through a
    capillary bed
  • Requires physiological pulsatile waves to measure
    saturation
  • Requires a pulse or a pulse wave (Adequate CPR)

26
Pulse Oximetry
  • Principle of operation -1

27
Pulse Oximetry
  • Optical plethysmography
  • detects pulsatile changes in blood volume
  • Spectrophotometry
  • measures pulsatile hemoglobin saturation
  • Assumptions
  • all pulsation is arterial
  • light passes through pulsatile beds

28
DEFINITIONS
  • WAVE LENGTH - DISTANCE FROM ONE PEAK TO THE NEXT.
    (NANOMETERS)
  • INTENSITY - OF ENERGY PACKETS GENERATED IN 1
    SECOND. (HEIGHT OF THE WAVE). (LUX)
  • CYCLE - ACTIVITY FROM ONE PEAK TO THE NEXT.
    (CYCLES/SEC HERTZ)
  • FREQUENCY - WAVES PER SECOND. (CYCLES/SEC)

29
DEFINITIONS(cont...)
  • LIGHT EXTINCTION/ABSORPTION - THE ABILITY OF A
    SUBSTANCE TO ABSORB SPECIFIC PORTIONS OF THE
    LIGHT SPECTRUM.
  • WAVE THEORY - LIGHT IS A CONTINUOUS STREAM OF
    ENERGY WHICH VARIES IN AMPLITUDE AT SPECIFIC
    FREQUENCIES.
  • PACKET THEORY- LIGHT IS BUNDLES OF ENERGY
    MOVING AT SPECIFIC FREQUENCIES.

30
BEER-LAMBERT LAW ASSUMPTIONS
  • LIGHT PASSES AS A COHERENT BEAM - DOES NOT
    SCATTER.
  • SOLUTIONS ARE HOMOGENEOUS - TISSUE DENSITY IS
    CONSTANT.
  • OPTICAL PATH LENGTH IS CONSTANT.

31
Beer - Lambert Law
Incident light
Transmitted light
32
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33
Physics (Beer-Lambert law)
  • Beer s law
  • The concentration of a liquid is exponentially
    related to the intensity of light that will pass
    through it.
  • Lambert s Low
  • The distance of light travelled through the
    liquid is exponentially related to the intensity
    of light that will pass through it.
  • Oxygenated hemoglobin absorbs a different
    wavelength of light than does deoxygenated blood

34
Beer-Lambert Law
35
Beer-Lambert Law
  • I trans I inc . A
  • A DCE
  • Where
  • I trans intensity of transmitted light .
  • I inc intensity of incident light.
  • ???A fraction of light absorption.
  • D distance light transmitted
    throught the liquid (path length).
  • C concentration of
    solute(hemoglobin).
  • E extinction
    coefficient of the solute (a constant for a
    given solute at spcified wavelenght).

36
Spectrophotometry
  • Beer-Lambert Law

37
BEER-LAMBERT LAW
Iin1
Iout1
Homogenous Solution
L
Iout1

A1

e HbO2 L
Iin1
Iin1
Iout1
Non-Homogenous Solutions
L
38
Beers Lambert Law for Spo2
SPO2 Reading
More light is absorbed
39
Photospectrometry
  • Photospectrometry is a method of
  • using light emission or absorption to
  • determine the composition of
  • substances. It generally involves the
  • use of light emitters and receptors
  • coupled with signal analyzers.

40
WHERE DO WE USE PHOTOSPECROMETRY?
  • Pulse OXIMETRY
  • Capnography
  • Capnometry
  • Co-OXIMETRY
  • Mass Spectrometry
  • Serum Glucose (glycolated Hb 2Ac)
  • ?

41
PULSE OXIMETRY HOW DOES IT WORK?
  • I.R. PHOTOSPECTROMETRY
  • - HEMOGLOBIN ABSORBS LIGHT.
  • - THE ABSORBED LIGHT VARIES WITH
  • OXYGEN SATURATION
  • TYPE OF HEMOGLOBIN
  • LENGTH OF THE OPTICAL PATH.

42
PULSE OXIMETRY HOW DOES IT WORK? (cont.)
  • ABSORBENCE CAN BE CALCULATED
  • EXTINCTION CO-EFFICIENTS
  • OPTICAL DENSITY EQUATIONS
  • BEERS-LAMBERT EQUATION

43
Concept of Pulse Oximetry
44
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45
Pulse Oximetry principles
Two main principles
  • First Principle of operation 1
  • Infrared absorption by oxygenated and
    de-oxygenated haemoglobin at 2 different
    wavelengths

46
RBCs Hemoglobin
47
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48
  • Oxygenated blood and deoxygenated blood absorb
    different light sources
  • Oxyhemoglobin absorbs more infrared light
  • Reduced hemoglobin absorbs more red light
  • Pulse oximetry reveals arterial saturation my
    measuring the difference.

49
Pulse Oximetry
  • First principle of SPo2
  • two wavelengths (660 and 960 nm)
  • calculates functional saturation (physiologic
    saturation)

50
Pulse Oximetry
  • First Principle of operation -

Wavelength of red and infrared light emitted by
the 2 LEDs
51
Hb EXTINCTION CURVES
  • ISOBESTIC POINTS

52
How does it work?
  • Since there are only two frequencies of light,
    only two substances can be distinguished.
  • This comparison is defined as functional
    saturation OR
  • SPo2 oxyhemoglobin
  • -------------------
  • oxyhemoglobin reduced hemoglobin

53
CALCULATION OF SaO2
  • O2 Hb FRACTION
    02Hb___________________________

  • O2Hb RHb MetHb HbF COHb
  • O2 SAT OF AVAILABLE Hb
  • O2 SAT 02Hb______
  • O2Hb RHb
  • The difference between O2 sat and O2 Hb fraction
    is (MetHb HbF COHb HbX)

54
Characteristics of Common Hb Species

  • Spectrophotometric
  • Name Symbol Normal ()
    Peak (nM)
  • Oxy O2Hb 97
    530
  • Reduced RHb lt1
    585.2
  • Adult HbA 97
    530
  • Fetal HbF 85
    NA
  • Carboxy COHb 2-5
    594.5
  • Sulf SulfHb lt0.5
    618
  • Meth Methb 1.5
    620

55
ABSORPTION SPECTRA
56
Pulse Oximetry
  • Second Principle of operation - 2
  • The success of pulse oximetry depends on its
    ability to measure the saturation of the arterial
    blood by analysis of infrared absorption of
    vascular bed throughout the whole pulsatile pulse
    cycle.

57
Second principle of Pulse oximetry
58
Second principle for pulse oximetry
  • Light is absorbed by the tissues and does not
    vary with the cardiac cycle
  • During the cardiac cycle there IS a small
    increase in arterial blood
  • Light absorption is increased during this phase.

59
Pulse Oximetry
  • 2th -Principle of operation

The variable absorption due to pulse added volume
of arterial blood is used to calculate the
saturation of arterial blood
60
Second principle for Spo2
  • What is the amount of light absorbed by the
    peak of the cardiac cycle

This is the only area that changes with Wave of
blood associated with the pulse
This area remains constant and therefore
irrelevant
61
Pulse Oximetry
  • Main Limitations of SPo2
  • Ambient light
  • Patient movement or shivering.
  • Hypothermia.
  • Peripheral shut down.
  • Hypovlemia and shock.
  • Carbon monoxide poisoning(carboxy HB).
  • Other dysfunctional Hemoglobins(met HB).
  • Skin pigmentation.
  • Dye injection(methylene blue).

62
Patient Environments
  • Ambient Light
  • Excessive Motion

63
Ambient Lighting
  • Any external light exposure to capillary bed
    where sampling is occurring may result in an
    erroneous reading
  • Most sensors are designed to prevent light from
    passing through the shell
  • Shielding the sensor by covering the extremity is
    acceptable

64
SOURCES OF ERROR
  • Sensitive to motion
  • Standard deviation is certified to 4 down to 70
    saturation
  • Sats below 85 increase the importance of error
    in the reading
  • Calibration is performed by company on normal
    patients breathing various gas mixtures, so
    calibration is certain only down to 80

65
Hypothermia
  • Severe peripheral vasoconstriction may prevent
    oximetry detection
  • Shivering may result in erroneous oximetry motion
  • Pulse rate on oximeter must coincide with
    palpable pulse rate to be considered accurate
  • Treat the patient according to hypothermic
    guidelines and administer oxygen accordingly!

66
SOURCES OF ERROR
  • Skin Pigmentation
  • Darker color may make the reading more variable
    due to optical shunting.
  • Dark nail polish has same effect blue, black,
    and green polishes underestimate saturations,
    while red and purple have no effect
  • Hyperbilirubinemia has no effect
  • Low perfusion state(hypotension-shock).
  • Ambient Light
  • Delay in reading of about 10 seconds

67
SOURCES OF ERROR
  • Methylene blue and indigo carmine underestimate
    the saturation
  • Dysfunctional hemoglobin
  • Carboxyhgb leads to overestimation of sats
    because it absorbs at 660nm with an absorption
    coefficient nearly identical to oxyhgb
  • Methgb can mask the true saturation by absorbing
    too much light at both 660nm and 940nm.
    Saturations are overestimated, but drop no
    further than 85, which occurs when methgb
    reaches 35.

68
  • Suspect the presence of carboxyhemoglobin in
    patient with
  • - Smoke inhalation
  • - Intentional and accidental CO poisoning
  • - Heavy cigarette smoking
  • Treat carboxyhemoglobin with high flow oxygen
    irregardless of the pulse oximetry reading!

69
SOURCES OF ERROR
  • Affect of anemia is debated
  • Oxygen-Hemoglobin Dissociation Curve
  • Shifts in the curve can affect the reading
  • Oximetry reading could correspond to a PaO2 of
    60mmHg (90 saturation) or 160mmHg (99
    saturation)

70
How is saturation related to oxygen levels?
Normal PaO2
71
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72
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73
PULSE OXIMETRY HOW ACCURATE IS O2 SAT?
  • VERY ACCURATE - BETWEEN
  • 85-100 SATURATION (/- 1-2 )
  • POOR - BELOW 85 (ALGEBRAIC DECREASE IN
    ACCURACY)
  • INDISCRIMINATE - BETWEEN 98 -100 SATURATION

74
  • Spo2 IS GOOD FRIEND WHEN IT IS BAD AND IS
    BAD FRIEND WHEN IT IS GOOD

75
Has pulse oximetry improved the outcome of
patients receiving anesthesia?
76
Clinical Value Of Spo2
  • Review the signs and symptoms of respiratory
    compromise
  • Understand the importance of adequate tissue
    perfusion
  • Define hypoxia and describe the clinical signs
    and symptoms

77
Hypoxemia
  • Decreased oxygen in arterial blood
  • Results in decreased cellular oxygenation
  • Anaerobic metabolism
  • Loss of cellular energy production

78
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79
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80
Pathophysiology
  • Oxygen is exchanged by diffusion from higher
    concentrations to lower concentrations
  • Most of the oxygen in the arterial blood is
    carried bound to hemoglobin
  • 97 of total oxygen is normally bound to
    hemoglobin
  • 3 of total oxygen is dissolved in the plasma

81
Inadequate Oxygen Transport
  • Anemia
  • Reduces red blood cells reduce oxygen carrying
    capacity
  • Inadequate hemoglobin results in the loss of
    oxygen saturation
  • Poisoning
  • Carbon monoxide on-loads on the hemoglobin more
    readily preventing oxygen saturation and oxygen
    carrying capacity
  • Shock
  • Low blood pressures result in inadequate oxygen
    carrying capacity

82
Anemia
  • Low quantities of erythrocytes or hemoglobin
  • Normal value of hemoglobin is 11-18 g/dl
  • Values as low as 5 g/dl may result in 100 SpO2
  • Anemic patients require high levels of oxygen to
    compensate for low oxygen carrying capacities!

83
Carboxyhemoglobin
  • Carbon monoxide has 200-250 greater affinity for
    the hemoglobin molecule than oxygen
  • Binds at the oxygen binding site
  • Prevents on-loading of oxygen
  • Fails of readily off-load at the tissue cells
  • Carboxyhemoglobin can not be distinguished from
    oxyhemoglobin by pulse oximetry
  • Erroneously high reading may present

84
Hypovolemia/Hypotension
  • Adequate oxygen saturation but reduced oxygen
    carrying capacity
  • Vasoconstriction or reduction in cardiac output
    may result in loss of detectable pulsatile
    waveform at sensor site
  • Patients in shock or receiving vasoconstrictors
    may not have adequate perfusion to be detected by
    oximetry
  • Always administer oxygen to patients with poor
    perfusion!

85
Hypoxia Manegement
  • Suspect severe cellular perfusion compromise when
    SpO2 is less than 90
  • Insure airway and provide positive ventilations
    if necessary
  • Administer high flow oxygen
  • Head injured patients should never drop below 90
    SpO2

86
PULSE OXIMETRY HOW ACCURATE IS - PULSE?
  • GOOD BUT CHANGES WITH DEGREE OF PULSATE FLOW
  • CHANGES WITH PULSE PRESSURE
  • REDUCED SENSITIVITY WITH LOW PULSE
    VOLUME/FORCE
  • MAY NOT EQUAL ECG RATE
  • MEASURES MECHANICAL NOT ELECTRICAL ACTIVITY

87
Value OF Wave of Plathemography
Pulse Oximetry- CVS monitoring
Normo-volaemic
Significant blood loss
After fluid replacement
88
Summary
  • Uses spectrophotometry based on the Beer-Lambert
    law
  • Differentiates oxy- from deoxyhemoglobin by the
    differences in absorption at 660nm and 940nm
  • Minimizes tissue interference by separating out
    the pulsatile signal
  • Estimates heart rate by measuring cyclic changes
    in light transmission
  • Measures 4 types of hemoglobin deoxy, oxy,
    carboxy, and met
  • Estimates functional hemoglobin saturation
    (oxyhemoglobin/deoxy oxy).

89
SpO2 and PaO2
  • SpO2 indicates the oxygen bound to hemoglobin
  • Closely corresponds to SaO2 measured in
    laboratory tests
  • SpO2 indicates the saturation was obtained with
    non-invasive oximetry
  • PaO2 indicates the oxygen dissolved in the plasma
  • Measured in ABGs or Clarck electode.

90
  • Normal PaO2 is 80-100 mmHg
  • Normally
  • 80-100 mm Hg corresponds to 95-100 SpO2
  • 60 mm Hg corresponds to 90 SpO2
  • 40 mm Hg corresponds to 75 SpO2

91
Clarck Electrode
92
Respiratory Monitors
Great advance in patient monitoring with best
outcome

93
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94
Questions
95
Thank You
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