dr.gihan a tarabih. md, ass.prof. of anethesia and sicu, mansoura faculty of medicine
TRANSCRIPT
Oximetry
Respiratory Monitoring= Rapid progress with greater safety in Anesthesia field and better ICU outcome.
Early Warning: When do you want the patient’s parachute to open?
Capnography( 4-10 minutes)
Pulse Oximetry
Pulse Oximetry (30-60 seconds)
ECG
ECG( 10 seconds)
No monitor = free fall!
capnography
ASA Standard CareASA Standard Care
During all anesthesia care the following parameters will be continually monitored:1-oxygenation
2-ventilation
3-circulation
4-temperature
Main Anesthesia EnemiesMain Anesthesia Enemies
Pulmonary embolism
Severe hypotension
Cardiac arrest
Hypoxia
Hypoventilation
► ► Application in clinical practiceApplication in clinical practice
Objectives
► How it works
► The physiology involved
Indications►
O2
CO2 O2
CO2
CO2
Physiology of respirationPhysiology of respirationOxygen/Carbon dioxide interaction: Perfusion and Ventilation
Ventilation
Perfusion
OxygenOxygen -> lungs -> alveoli -> blood
muscles + organs
OxygenOxygen
cells
OxygenOxygen
OxygOxygenen ++GlucoGlucosese
energy
COCO22
blood
lungs
COCO22
breath
COCO22
Physiology of respirationPhysiology of respirationOxygen/Carbon dioxide interaction: Metabolism
CO2 produced by cellular metabolism diffuses across the cell membrane into the circulating blood.
5-10% carried in solution
20-30% bound to haemoglobin
60-70% carried as bicarbonate in the red blood cell
OxygenationOxygenation 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).
Oximetry HistoryOximetry History
Became standard of care in the 1980’s
1935Carl Matthesfirst oximeter
1940J.R. Squiresself calibrating oximeter
Oximetry History Oximetry History (Cont’d)(Cont’d)
1940’s Glen Millikenaviation 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 ReviewTerminology 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 SaturationOxygen Saturation
Percentage of hemoglobin saturated with oxygen
Normal SpO2 is 95-98% Suspect cellular perfusion compromise
if less than 92% SpO2Insure adequate airway
Provide supplemental oxygen
Monitor carefully for further changes and intervene appropriately
PULSE OXIMETRYPULSE OXIMETRY: : WHAT WHAT DOES IT DO?DOES IT DO?
MEASURES/DISPLAYS - O2 SAT OF HbG
- PULSE RATE
- INDICATES PERFUSION
- PULSATE FLOW
What are the Normal?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 OximetersPros of Pulse Oximeters
PROS Non-invasive Allows continuous measurement in
real time Easy to use
Cons of Pulse OximetryCons of Pulse OximetryCONS 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 Pros/Cons of an arterial blood gas 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
ObjectivesObjectives
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 Indications for Pulse OximetryOximetry
Uses of Pulse Oximetry generally fall into two categoriesReal Time Indicator of hypoxemia
End point for titration of therapeutic interventions.
TechnologyTechnology 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 bedRequires physiological pulsatile waves to measure
saturationRequires a pulse or a pulse wave (Adequate CPR)
Pulse OximetryPulse OximetryOptical plethysmography
detects pulsatile changes in blood volume
Spectrophotometrymeasures pulsatile hemoglobin saturation
Assumptionsall pulsation is arterial
light passes through pulsatile beds
DEFINITIONSDEFINITIONS 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)
DEFINITIONSDEFINITIONS((contcont......)) 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.
BEERBEER--LAMBERT LAWLAMBERT LAWASSUMPTIONSASSUMPTIONS::
LIGHT PASSES AS A COHERENT BEAM - DOES NOT SCATTER.
SOLUTIONS ARE HOMOGENEOUS - TISSUE DENSITY IS CONSTANT.
OPTICAL PATH LENGTH IS CONSTANT.
Physics (Beer-Lambert law)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 LawBeer-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).
BEERBEER--LAMBERT LAWLAMBERT LAW
L
Iin1 Iout1
Iin1 A1=
Iout1 = HbO2] L
HbO2] + r Hb] L A1=
Iin1 Iout1
HomogenousSolution
L
Non-HomogenousSolutions
PhotospectrometryPhotospectrometryPhotospectrometry 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 WHERE DO WE USE PHOTOSPECROMETRY?PHOTOSPECROMETRY?
Pulse OXIMETRY Capnography Capnometry Co-OXIMETRY Mass Spectrometry Serum Glucose (glycolated Hb 2Ac) ?
PULSE OXIMETRYPULSE OXIMETRY: : HOW DOES HOW DOES IT WORK?IT WORK?
I.R. PHOTOSPECTROMETRY: - HEMOGLOBIN ABSORBS LIGHT.
- THE ABSORBED LIGHT VARIES WITH:
* OXYGEN SATURATION
* TYPE OF HEMOGLOBIN
* LENGTH OF THE OPTICAL PATH.
PULSE OXIMETRYPULSE OXIMETRY: : HOW HOW DOES IT WORK? DOES IT WORK? ((contcont.).)
ABSORBENCE CAN BE CALCULATED
* EXTINCTION CO-EFFICIENTS
* OPTICAL DENSITY EQUATIONS
* BEERS-LAMBERT EQUATION
Pulse Oximetry principlesPulse Oximetry principles
First Principle of operation – 1Infrared absorption by oxygenated and de-
oxygenated haemoglobin at 2 different wavelengths
Two main principles:
Oxygenated blood and deoxygenated blood absorb different light sourcesOxyhemoglobin absorbs more infrared light
Reduced hemoglobin absorbs more red light
Pulse oximetry reveals arterial saturation my measuring the difference.
Pulse OximetryPulse Oximetry First principle of SPo2:
two wavelengths (660 and 960 nm)
calculates functional saturation (physiologic saturation)
Pulse OximetryPulse Oximetry First Principle of operation -
Wavelength of red and infrared light emitted by the 2 LEDs
How does it work?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 SaO2CALCULATION 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 Characteristics of Common Hb SpeciesSpecies
Spectrophotometric
Name Symbol Normal (%) Peak (nM)
Oxy O2Hb 97 530
Reduced RHb <1 585.2
Adult HbA 97 530
Fetal HbF 85 NA
Carboxy COHb 2-5% 594.5
Sulf SulfHb <0.5 618
Meth Methb 1.5% 620
Pulse OximetryPulse Oximetry
Second Principle of operation - 2The 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 for pulse Second principle for pulse oximetryoximetry
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 OximetryPulse 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 Second principle for Spo2 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 OximetryPulse 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).
Ambient LightingAmbient 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 ERRORSOURCES 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%
HypothermiaHypothermia
Severe peripheral vasoconstriction may prevent oximetry detection
Shivering may result in erroneous oximetry motionPulse 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 ERRORSOURCES OF ERROR
Skin PigmentationDarker 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 ERRORSOURCES 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 ERRORSOURCES 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)
PULSE OXIMETRYPULSE OXIMETRY:: HOW ACCURATE ISHOW ACCURATE IS: : O2 SAT?O2 SAT?
VERY ACCURATE - BETWEEN 85-100% SATURATION (+/- 1-2 %) POOR - BELOW 85% (ALGEBRAIC
DECREASE IN ACCURACY)
INDISCRIMINATE - BETWEEN 98 -100% SATURATION
Has pulse oximetry Has pulse oximetry improved the improved the
outcome of patients outcome of patients receiving receiving
anesthesia?anesthesia?
Clinical Value Of Spo2Clinical 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
HypoxemiaHypoxemia
Decreased oxygen in arterial bloodResults in decreased cellular oxygenation
Anaerobic metabolism
Loss of cellular energy production
PathophysiologyPathophysiology
Oxygen is exchanged by diffusion from higher concentrations to lower concentrations
Most of the oxygen in the arterial blood is carried bound to hemoglobin97% of total oxygen is normally bound to
hemoglobin
3% of total oxygen is dissolved in the plasma
Inadequate Oxygen Inadequate Oxygen TransportTransport
AnemiaReduces red blood cells reduce oxygen carrying capacity
Inadequate hemoglobin results in the loss of oxygen saturation
PoisoningCarbon monoxide on-loads on the hemoglobin more
readily preventing oxygen saturation and oxygen carrying capacity
ShockLow blood pressures result in inadequate oxygen
carrying capacity
AnemiaAnemia
Low quantities of erythrocytes or hemoglobinNormal 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!
CarboxyhemoglobinCarboxyhemoglobin
Carbon monoxide has 200-250 greater affinity for the hemoglobin molecule than oxygenBinds 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 oximetryErroneously high reading may present
Hypovolemia/HypotensionHypovolemia/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 ManegementHypoxia 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 OXIMETRYPULSE OXIMETRY::HOW ACCURATE IS HOW ACCURATE IS - - PULSEPULSE??
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
Pulse Oximetry- CVS monitoring
Normo-volaemic
Significant blood loss
After fluid replacement
Value OF Wave of Plathemography
SummarySummary 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).
SpO2 and PaO2SpO2 and PaO2
SpO2 indicates the oxygen bound to hemoglobinClosely corresponds to SaO2 measured in
laboratory testsSpO2 indicates the saturation was obtained
with non-invasive oximetry PaO2 indicates the oxygen dissolved in
the plasmaMeasured in ABGs or Clarck electode.
Normal PaO2 is 80-100 mmHgNormally
• 80-100 mm Hg corresponds to 95-100% SpO2• 60 mm Hg corresponds to 90% SpO2• 40 mm Hg corresponds to 75% SpO2