Dr.Gihan A Tarabih. MD, ASS.Prof. of Anethesia And SICU, Mansoura Faculty of Medicine.

Dr .Gihan A Tarabih . MD,

ASS.Prof. of Anethesia And SICU,

Mansoura Faculty of Medicine.

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

CAPNOGRAPHY-OXIMETRYCAPNOGRAPHY-OXIMETRY

Why use them?

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).

Pulse OximetryPulse Oximetry

How does it really work?Why should I care?

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

Various forms of pulse Various forms of pulse ox’sox’s

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)


Principle of operation -1

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.

Beer - Lambert Law

Incident light

Transmitted light

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 Law

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).

Spectrophotometry Spectrophotometry

Beer-Lambert Law:

BEERBEER--LAMBERT LAWLAMBERT LAW

L

Iin1 Iout1

Iin1 A1=

Iout1 = HbO2] L

HbO2] + r Hb] L A1=

Iin1 Iout1

HomogenousSolution

L

Non-HomogenousSolutions

Beer’s –Lambert Law for Beer’s –Lambert Law for Spo2Spo2

More light is absorbed

SPO2 Reading

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

Concept of Pulse OximetryConcept of Pulse Oximetry

Pulse Oximetry principlesPulse Oximetry principles

First Principle of operation – 1Infrared absorption by oxygenated and de-

oxygenated haemoglobin at 2 different wavelengths

Two main principles:

RBC’s & HemoglobinRBC’s & Hemoglobin

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

Hb EXTINCTION Hb EXTINCTION CURVESCURVES

ISOBESTIC POINTS

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

ABSORPTION SPECTRAABSORPTION SPECTRA


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 of Pulse Second principle of Pulse oximetryoximetry

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.


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


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 EnvironmentsPatient Environments

Ambient Light Excessive Motion

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!


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!


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 How is saturation related to oxygen levels?oxygen levels?

Normal PaO2

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

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

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

Clarck ElectrodeClarck Electrode

Respiratory MonitorsRespiratory Monitors

=Great advance in patient monitoring with best outcome

QuestionsQuestions

Dr.Gihan A Tarabih. MD, ASS.Prof. of Anethesia And SICU, Mansoura Faculty of Medicine.

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Transcript of Dr.Gihan A Tarabih. MD, ASS.Prof. of Anethesia And SICU, Mansoura Faculty of Medicine.