Dr .Gihan A Tarabih . MD,
ASS.Prof. of Anethesia And SICU,
Mansoura Faculty of Medicine.
Respiratory Monitoring= Rapid progress
with greater safety in Anesthesia field
and better ICU outcome.
Oximetry
Early Warning: When do you want the
patient’s parachute to open?
Capnography( 4-10 minutes)
capnography
Pulse Oximetry (30-60 seconds)
Pulse Oximetry
ECG( 10 seconds)
ECG
No monitor = free fall!
ASA Standard Care
 During all anesthesia care the
following parameters will be
continually monitored:
1-oxygenation
2-ventilation
3-circulation
4-temperature
CAPNOGRAPHY-OXIMETRY
Why use them?
Main Anesthesia Enemies
Cardiac arrest
Pulmonary embolism
Hypoxia
Hypoventilation
Severe hypotension
Objectives
► The physiology involved
►
How it works
►
Indications
► Application in clinical practice
Physiology of respiration
Oxygen/Carbon dioxide interaction: Perfusion and Ventilation
Ventilation
O2
CO2
CO
CO
22
Perfusion
O2
Physiology of respiration
Oxygen/Carbon dioxide interaction: Metabolism
Oxygen -> lungs -> alveoli -> blood
breath
CO2
lungs
Oxygen
CO2 produced by cellular metabolism
diffuses across the cell membrane into the
muscles + organs
circulating blood.
5-10% carried in solution
CO2
Oxygen
20-30% bound to haemoglobin
60-70% carried as bicarbonate in the red blood cell
energy
blood
CO2
cells
Oxygen
+
Glucose
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).
Pulse Oximetry
How does it really work?
Why should I care?
Oximetry History
 Became standard of care in the
1980’s
 1935 Carl Matthes
first oximeter
 1940
J.R. Squires
self calibrating oximeter
Oximetry History
(Cont’d)
 1940’s 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
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).
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
PULSE OXIMETRY: WHAT
DOES IT DO?
 MEASURES/DISPLAYS
- O2 SAT OF HbG
- PULSE RATE
- INDICATES PERFUSION
- PULSATE FLOW
Various forms of pulse ox’s
What are the Normal?
 97-100% sat :Good gas exchange .
 90-95% sat :
Mild hypoxia
 <90% sat :
Severe hypoxia
 Not all patients are the same
- COPD
- Anemia
Pros of Pulse Oximeters
PROS
 Non-invasive
 Allows continuous measurement in
real time
 Easy to use
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.
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
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.
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.
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)
Pulse Oximetry
 Principle of operation -1
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
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.
HERTZ)
(CYCLES/SEC =
 FREQUENCY - # WAVES PER
SECOND.
(CYCLES/SEC)
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.
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.
Beer - Lambert Law
Incident
light
Transmitted
light
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
Beer-Lambert Law
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).
Spectrophotometry
 Beer-Lambert Law:
BEER-LAMBERT LAW
Homogenous
Solution
Iin1
Iout1
L
Iout1
= A1 = e [HbO2] L
Iin1
Non-Homogenous Iin1
Solutions
Iout1
L
A1 = eo [HbO2] + er [Hb] L
Beer’s –Lambert Law for
Spo2
SPO2 Reading
More light is absorbed
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.
WHERE DO WE USE
PHOTOSPECROMETRY?
 Pulse OXIMETRY
 Capnography
 Capnometry
 Co-OXIMETRY
 Mass Spectrometry
 Serum Glucose (glycolated Hb
2Ac)
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.
PULSE OXIMETRY: HOW
DOES IT WORK? (cont.)
ABSORBENCE CAN BE CALCULATED
* EXTINCTION CO-EFFICIENTS
* OPTICAL DENSITY EQUATIONS
* BEERS-LAMBERT EQUATION
Concept of Pulse Oximetry
Pulse Oximetry principles
Two main
principles:
 First Principle of operation – 1
Infrared absorption by oxygenated and deoxygenated haemoglobin at 2 different
wavelengths
RBC’s & Hemoglobin
 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.
Pulse Oximetry

First principle of SPo2:
two wavelengths (660 and 960 nm)
calculates functional saturation (physiologic saturation)
Pulse Oximetry
 First Principle of operation Wavelength of red
and infrared light
emitted by the 2
LEDs
Hb EXTINCTION
CURVES
ISOBESTIC POINTS
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
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)
Characteristics of Common Hb
Species
Spectrophotometric
Name
Symbol
Normal (%)
Oxy
Reduced
Adult
Fetal
Carboxy
Sulf
Meth
O2Hb
RHb
HbA
HbF
COHb
SulfHb
Methb
97
<1
97
85
2-5%
<0.5
1.5%
Peak (nM)
530
585.2
530
NA
594.5
618
620
ABSORPTION SPECTRA
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.
Second principle of Pulse
oximetry
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.
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
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
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).
Patient Environments
 Ambient Light
 Excessive Motion
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
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%
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!
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
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%.
 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!
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)
How is saturation related to
oxygen levels?
Normal
PaO2
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
Spo2 IS GOOD
FRIEND WHEN IT
IS BAD AND IS
BAD FRIEND
WHEN IT IS
GOOD
Has pulse oximetry
improved the
outcome of patients
receiving
anesthesia?
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
Hypoxemia
 Decreased oxygen in arterial blood
Results in decreased cellular oxygenation
Anaerobic metabolism
Loss of cellular energy production
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
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
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!
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
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!
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
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
Value OF Wave of Plathemography
Pulse Oximetry- CVS monitoring
Normo-volaemic
Significant blood loss
After fluid replacement
Summary
 Uses spectrophotometry based on the BeerLambert 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).
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.
 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
Clarck Electrode
Respiratory Monitors
=Great advance in
patient monitoring
with best outcome
Questions