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Pulse oximeters
- 1. PULSE OXIMETERS - Dr.Vinai Theerthaan
- 2. PULSE OXIMETERS Pulse Oximeter is a Simple, Non-Invasive, Reliable, Reasonably Accurate, Cheap, Continuous, Risk free method of measuring ARTERIAL OXYGEN SATURATION It is also called as “FIFTH VITAL SIGN” (PR + BP + RR + Temp + PULSE OX)
- 4. SPECTROPHOTOMETRY Based on BEER – LAMBERT’S LAW BEER LAW : INTENSITY of transmitted Light DECREASES exponentially as the CONCENTRATION of the Substance INCREASES LAMBERT’s LAW : INTENSITY of transmitted Light DECREASES exponentially as the DISTANCE travelled through the Substance INCREASES BEER – LAMBERT’s LAW : Ie = Io x e -Dca Where , Ie – Intensity of transmitted ight Io – Intensity of Incident Light D – Distance light is transmitted C – Concentration of the medium a – extinction coefficient ( Constant )
- 5. OXY Hb – absorbs more INFRARED LIGHT ( 940nm ) REDUCED Hb – absorbs more RED LIGHT ( 660nm )
- 6. PULSE OX has two LED ( Red and Infrared LED ) and one PHOTODETECTOR Pulse ox works out the SpO2 using the RATIO of AMOUNT OF RED LIGHT ABSORBED to the AMOUNT OF INFRARED LIGHT ABSORBED
- 7. PLETHYSMOGRAPHY DC component – During “DIASTOLE” – Absorption caused by : NON PULSATILE ARTERIAL BLOOD VENOUS BLOOD TISSUE BONE PIGMENTS AC component – During “SYSTOLE” – INCREASED Absorbance due to increase in path length due to PULSATILE EXPANSION of Arteries SpO2 = f ( AC660/DC660) / (AC940/DC940)
- 8. Ambient Room Light Functional SaO2 = [O2Hb / (O2Hb + Reduced Hb)] x 100 Measured by Conventional Pulse Oximetry Fractional SaO2 = [O2Hb / (O2Hb + Reduced Hb + COHb + MetHb)] x 100 Measured by Laboratory Co-Oximeters
- 9. Types TRANSMISSION PULSE OX REFLECTANCE PULSE OX - Commonly Used - To overcome signal transmission problems during hypoperfusion - Common site : Forehead - Source of Inaccuracy : Excessive edema, Poor Skin Contact, Motion Defect
- 10. EQUIPMENT PROBE : Reusable and disposable, Slide-on and Tape-on ( Less Motion defect but not shielded from ambient Light) CABLE CONSOLE : Stand alone and Multiparameter monitor Displayed values are averages of past 3-6 seconds PULSE BEEP : Beep after detecting Plethysmographic pulse which coincides with Heartbeat Pitch is proportional to SpO2
- 11. Models Fingertip Wrist Handheld Tabletop
- 12. Sites for Measurement Adults : finger, thumb, toe, pinna, lobe of ear Neonates and Infants : palm, soles Less common sites : cheek, tongue
- 13. Uses During Anaesthesia Post operative care ICU Emergency Dept NICU New born care During Transport ( Ambulance) In Labs ( PFT / Sleep Lab) Home care patients Intrapartum fetal monitoring (Scalp probe) Monitoring vascular volume and sympathetic tone
- 14. Advantages Accuracy Independence Fast response time Non invasive Continuous Convenience Tone modulation User friendliness Light weight and compact Probe variety Battery operated Economy
- 15. Safe Limitations Motion artefacts (shivering / transport / nerve stimulants) Poor perfusion (BP cuff / improper position / hypotension / hypothermia / hypovolemia) Skin pigmentation Nail polish (black / blue / green) Artificial nails Irregular rhythms Electromagnetic interference
- 16. Unsafe Limitations Calibration assumptions ( <80% is derived by extrapolation, thus less accurate) Delay in detection of hypoxia (delay in change in alveolar O2 tension and change in SpO2) Probe positioning ( optical shunting effect) Ambient light interference Abnormal Hb (COHb – 10-20% in smokers / 1%rise in COHb Overreads SpO2 by 1%) Venous pulsations IV Dyes (methylene blue - Increased absorption @ 660nm – low SpO2) Rapid Blood Transfusion ( decreases SpO2) Increased FiO2 – hypoventilation and hypercarbia without decrease Hb O2 Saturation
- 17. Recent Advances 8 Wavelength Pulse Ox Reflectance Oximetry – To monitor fetal O2 saturation (scalp Probe) Esophageal Probe – used in Cardio thoracic Surgery