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 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 Pulmonary embolism Severe hypotension Cardiac arrest Hypoxia Hypoventilation

► Application in clinical practice Objectives ► How it works ► The physiology involved Indications ►

O2O2 CO 2 O2O2 Physiology of respiration Oxygen/Carbon dioxide interaction: Perfusion and Ventilation Ventilation Perfusion

Oxygen Oxygen -> lungs -> alveoli -> blood muscles + organs Oxygen cells Oxygen Oxygen +Glucose energy CO 2 blood lungs CO 2 breath CO 2 Physiology of respiration Oxygen/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

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  1935Carl Matthes first oximeter  1940J.R. Squires self calibrating oximeter

Oximetry History (Cont’d)  1940’sGlen Milliken aviation ear –oximeter for use in avitation research to investigate high altitude hypoxic problems 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  SpO 2 : Non invasive oxygen saturation  SaO 2 :Arterial (invasive)Oxygen Saturation (oxygen bound to the hemoglobin molecules)  PaO 2 : Arterial Partial Pressure, oxygen dissolved in the plasma (only about 3% of total content) or PO 2  CaO2:Total amount of oxygen in the blood or the (SaO 2 + PaO 2).

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?  % 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. (CYCLES/SEC = HERTZ)  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

 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 L I in1 I out1 I in1 A 1 = I out1 =    HbO 2 ] L    HbO 2 ] +  r  Hb] L A 1 = I in1 I out1 Homogenous Solution L Non-Homogenous Solutions

Beer’s –Lambert Law for Spo2 More light is absorbed SPO 2 Reading

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  First Principle of operation – 1 Infrared absorption by oxygenated and de- oxygenated haemoglobin at 2 different wavelengths Two main principles :

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 = 0 2Hb___________________________ 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 (%) Peak (nM) Oxy O2Hb Reduced RHb < Adult HbA Fetal HbF 85 NA Carboxy COHb 2-5% Sulf SulfHb < Meth Methb 1.5% 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 P a O 2 of 60mmHg (90% saturation) or 160mmHg (99% saturation)

How is saturation related to oxygen levels? Normal PaO 2

PULSE OXIMETRY: HOW ACCURATE IS: O2 SAT? PULSE OXIMETRY: HOW ACCURATE IS: O2 SAT?  VERY ACCURATE - BETWEEN % SATURATION (+/- 1-2 %)  POOR - BELOW 85% (ALGEBRAIC DECREASE IN ACCURACY)  INDISCRIMINATE - BETWEEN % 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 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 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

Pulse Oximetry- CVS monitoring Normo-volaemic Significant blood loss After fluid replacement Value OF Wave of Plathemography

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).

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 mmHg Normally mm Hg corresponds to % 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