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Transcutaneous measuring principles – tc and saturation RTC, June 2006 Radiometer Medical ApS, Åkandevej 21, DK-2700 Brønshøj, Tel: +45 38 27 38 27, www.radiometer.com 1 Agenda • Saturation - sO2, pO2(a), ODC - SpO2 - Light emission - Light detection - Animations - Calibration curves - Cautions/limitations • tc - New illustrations - New animations • Summing up - table 2 Methods of measuring blood gas 3 sO2 and pO2 http://www.nellcor.com/_Catalog/PDF/Edu/MON_F.a.00838v1 ClinicalMonoPul.pdf 4 sO2 and the ODC • sO2 vs. pO2(a) • Standard ODC: - sO2= 90 % corresponds to pO2(a)= 60 mmHg • Abnormal/critical ODC: - Shifts due to temperature, pH, 2,3-DPG, pCO2(a) At a constant pO2 of 45 mmHg/6 kPa, sO2 may be either 80 % or 88 % depending on whether arterial pH is 7.25 or 7.40 Conclusions: • sO2 is not suited for detection of hyperoxemia (high pO2(a)) • sO2 cannot be used to predict pO2(a) 5 Definition of saturation, sO2 O 2 Hb sO 2 100% O 2 Hb HHb • Arterial oxygen saturation • Utilization of oxygen transport capacity • Normal range 95-99 % • When sO2 is below normal range, the patient can benefit from supplemental oxygen • NO information about tHb, ventilation or O2 release to tissue • Available from BG CO-ox analyzers, BG analyzers, pulse oximeters 6 What does pulse oximetry measure? • Arterial oxygen saturation • SpO2 • Measuring range 70-100 % • SpO2 based on empirically determined sO2(a) calibration curves • I.e. SpO2 is NOT identical to sO2(a), which is measured by CO-ox analyzers - From measured O2Hb and HHb • And SpO2 is NOT identical to sO2(e), which is estimated by BG analyzers - From pO2(a) and pH-corrected standard ODC - E.g. ABL5 7 Light emission - hemoglobin absorption • Dual light source - Red light 660 nm - Infrared light 900 nm - Alternating diode cycles • O2Hb absorbs more IR light - I.e. it looks more red • HHb absorbs more red light - I.e. it looks less red http://www.nellcor.com/_Catalog/PDF/Product/OxiMaxTechNote.pdf 8 Light detection – pulse amplitude • Photodetector - One detector for both wavelengths • Isolate absorption from pulsating arterial blood - I.e. discard the ”base line” absorption http://www.nellcor.com/_Catalog/PDF/Product/OxiMaxTechNote.pdf 9 Baseline animation 10 sO2 animation 11 From light absorption to SpO2 • Red-to-infrared pulse Modulation Ratio (R) • Ratio translated to SpO2 from calibration curve http://www.nellcor.com/_Catalog/PDF/Product/OxiMaxTechNote.pdf 12 Choosing the right calibration curve • Curve defined for each • • • • sensor Each LED has its own characteristics Grouped and paired with a corresponding resistor Resistor housed in sensor plug Monitor recognizes resistor value and chooses the appropriate calibration curve 13 SpO2– when to be cautious? • Extreme hypoxemia (< 70 %) and hyperoxemia (> 95 %) • Sensor matching to site • DysHb – SpO2 may be normal despite low tHb • Anemia – SpO2 may be normal despite low tHb • Dye used for medical purposes - E.g. Methylene blue (likewise for CO-oximetry) • Low perfusion (likewise for tc) • Hypothermia (likewise for tc) - Peripheral constriction - Shivering (motion artifacts) • Medication (likewise for tc) - Peripheral constriction • Light interference • Nail polish 14 tc – new sensor illustrations • E5250 • Single tcpO2 • E5280 • Combi tcpO2/tcpCO2 • E5260 • Single tcpCO2 15 tc – new E5250 animation 16 tc – new E5260 animation 17 tc – new E5280 animation 18 tc– new physiological measuring princ. animation 19 Table to summarize BG CO-ox analyzer Transcutaneous Pulse oximetry Parameters pO2(a) pCO2(a) sO2(a) tcpO2 tcpCO2 SpO2 Pulse Translation • Oxygen uptake • Distribution of O2 from • Saturation lungs to skin • Ventilation • Utilization of O2 • pO2(a) – 0-800 mmHg – 0-107 kPa • pCO2(a) – 5-250 mmHg – 0.67-33.3 kPa • sO2(a) – 0-100 % • tcpO2 – 0-800 mmHg – 0-99.9 kPa • tcpCO2 – 5-100 mmHg – 0.7-13.3 kPa • SpO2: 70-100 % • Accurate • Non-invasive • Ease of use • Continuous • Non-invasive • CO2 monitoring • Continuous • Snapshot • Clinical understanding • Poor detection of • Invasive • Calibration and • Ventilation Measuring range Benefits Drawbacks • Expensive • Doctors/lab stabilization period transport capacity • Pulse: 20-250 bpm hyperoxemia > 95 % • Poor detection of severe hypoxemia < 70 % • No pCO2 20 Radiometer Training Center, June 2006 Radiometer Medical ApS, Åkandevej 21, DK-2700 Brønshøj, Tel: +45 38 27 38 27, www.radiometer.com 21