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The Pulse Oximeter by Dr. Arpit Patel.pptx

PULSE OXIMETRY

Health & Medicine◦
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PULSE OXIMETRY PRESENTOR: DR. ARPIT PATEL MODERATOR: DR. C. MALLIKA ma’am
What is Pulse Oximetry ?  Pulse oximetry is a non-invasive means of measuring oxygen saturation of arterial blood. Oxygen saturation is defined as the amount of hemoglobin that is bound to O2 divided by the amount of total hemoglobin that is available to bind with O2.  Mandatory for any anesthetic even cases with moderate sedation.  Pulse oximetry, sometimes called the fifth vital sign, is a non invasive method of measuring haemoglobin saturation (Sp02) by using a light signal transmitted through a tissue  A low Sp02 can provide a warning sign of hypoxemia before other signs such as cyanosis or a change in heart rate are observed.
PARTS OF PULSE OXIMETER
TECHNIQUES:  Combines the principles of oximetry and plethysmography to measure saturation.  Sensor containing light sources (2/3 light emitting diodes)  A light detector (photodiode) placed across the finger, toe, earlobe or any perfused tissue that can be transilluminated.  When light source and detector are placed on the opposite side, transmittance oximetry is used.  When light source and detector are placed on the same side of patient (eg: forehead) backscatter of light is recorded by the detector.  Oximetry depends on the observation that oxygenated and reduced hemoglobin differ in their absorption of red and infrared light (lambert-beer law).
OPERATING PRINCIPLES  The pulse oximeter estimates Sp02 from the differential absorption of red and infrared light in tissue.  Oxyhemoglobin absorbs more infrared light (940nm)  Deoxyhemoglobin absorbs more red light (660nm)– thus appears blue/cyanotic to the naked eye.  Thus the change in the light absorption during arterial pulsations is the basis of oximetric determinations.  The ratio of red and infrared wavelengths is analyzed by microprocessor to provide spo2  Greater ratio--- lower is arterial hemoglobin saturation.  Pulse oximetry computes ratio between these two signals and relates this ratio to arterial oxygen saturation using an empirical algorithm.  Whereas the arterial pulsations are identified by plethysmography, allowing corrections for light absorption by venous blood and tissue.
The basic principle of pulse oximetry employs an alternate current (AC) amplifier to process pulsatile light transmission from arteries while rejecting non pulsatile light transmission.
PRINCIPLES  ABSORPTION SPECTRO PHOTOMETRY  BEERT LAMBERT LAW All atoms and molecules absorb specific wavelength of light. ABSORPTION SPECTROPHOTOMETRY
BEER-LAMBERT LAW Absorbance is directly proportional to concentration of the solution. /I) A – absorbance ) l - Length of light path through the cell (cm) c – concentration (mol/litre)
PLETHYSMOGRAPHY
Types of pulse oximetry  Transmission Pulse Oximetry: Most common type, light beam transmitted through vascular bed is detected on opposite side.  Reflectance Pulse Oximetry: Relies on light is reflected to determine oxygen saturation.
Sites of SpO2 probe application ADULTS and CHILDREN INFANTS and NEONATES • Finger • Thumb • Toe • Pinna • Lobe of Ear • Palm • Sole
Applications of pulse oximetry 1. Monitoring oxygenation for adult and children in critical areas A. Anaesthesia I. In operation room or general anaesthesia II. Monitored anaesthesia care or during conscious sedation B. PACU C. Intensive care units D. Emergency Department
Applications of pulse oximetry 2. Monitoring oxygenation in neonatal areas A. Intensive care B. Newborn nursery C. Delivery suites 3. Transport A. Internal (within the hospital) B. External I. Ambulance II. Air transport
Applications of pulse oximetry 4. Diagnostic lab 5. Home care patients 6. Controlling oxygen administration 7. Avoiding hyperoxemia 8. Monitoring peripheral circulation 9. Determining systolic blood pressure 10. Locating arteries 11. Monitoring vascular volume and sympathetic tone 12. Intrapartum fetal monitoring
A sudden decrease in spo2 1. Disconnection. 2. Fat / Pulmonary embolism. 3. O2 delivery failure. 4. Hypoxia gas mixture. 5. ETT obstruction. 6. Pulmonary edema. 7. Anaphylaxsis / Malignant hyperthermia.
Monitoring oxygenation 1. Reduction in number of hypoxic events (especially during induction and emergence) 2. To detect inadvertent Bronchial intubation by fall in Spo2, not a reliable method especially if supplemental oxygen is used. 3. Regional and monitored anaesthesia care 4. Post anaesthesia care unit 5. Transport
Monitoring peripheral oxygenation 1. Detects arm position that compromises circulation. 2. Detects decreased perfusion in toe in lithotomy position. 3. Brachial artery compression during shoulder arthroscopy. 4. Compromised peripheral circulation distal to site of fracture. 5. To evaluate effects of sympathetic block as indicated by SPO2 due to vasodilation.
ADVANTAGES OF PULSE OXIMETRY  Simple to use, user friendly.  Accuracy.  Non - invasive.  Require no warm up time.  Independence from gases and vapours.  Fast response time.  Continuous measurements.
 Tone modulator - variable pitch of tone.  Convenient.  Light weight.  Fast start time within a few beats after application of probe.  Economical.  Separate respiratory and circulatory variables.
Limitations and disadvantages  Poor function with poor perfusion.  Difficulty in detecting high oxygen partial pressures.  Delayed hypoxic event detection.  Erratic performance with dysrhythmias.  Motion Artifact
INACCURACY is seen in Different Haemoglobin:  Methheamoglobin 1.<1% of the total Haemoglobin. 2.Oxidation product of Hb that forms a reversible complex with oxygen and impairs the unloading of oxygen to tissues. 3.Congenital or acquired . 4.Drugs causing Meth Haemoglobinemia include nitrobenzene, benzocaine, prilocaine, and dapsone. 5.Absorbs light equally at red and infrared wavelengths that are used by most pulse oximeters.
 Carboxyhemoglobin: 1. An increase in Hb CO may occur during laser surgery in the airway, but the levels are not high enough to keep pulse oximeter from reliably estimating saturation. 2. Pulse oximeters that differentiate between oxyhemoglobin and carboxyhemoglobin and that can measure carboxyhemoglobin are now available.  Fetal hemoglobin: Hb F does not appear or affect the accuracy to a clinically important degree, although very high levels may cause it to read slightly low.  Hemoglobin S Inaccurate readings.  Sulfheamoglobin May be caused by drugs such as metaclopramide, dapsone and sulfonamides– artificially lower oxygen saturation.
Recent Advances  Error Correction Two most common errors with pulse oximetry are motion artifacts and signal loss secondary to hypoperfusion. Recently quite a few manufacturers have incorporated new technologies of signal analysis reducing these inaccuracies.  Multi-wavelength Pulse Oximeters Eight-wavelength pulse oximeter capable of measuring several species of Hb has been developed. It claims capability to accurately measure MetHb and COHb.  Reflectance Pulse Oximetry Reflectance oximetry has been used to monitor fetal oxygen saturation with scalp probes and has shown to decrease surgical intervention in the face of non- reassuring fetal status.58 Esophageal probes have been designed and have shown success in measuring SpO2 during cardiothoracic surgery when finger probes have failed.
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