1 Radiometer Medical ApS, Åkandevej 21, DK-2700 Brønshøj, Tel: , Transcutaneous measuring principles – tc and saturation RTC, June 2006

2 Agenda Saturation ­ sO 2, pO 2 (a), ODC ­ SpO 2 ­ Light emission ­ Light detection ­ Animations ­ Calibration curves ­ Cautions/limitations tc ­ New illustrations ­ New animations Summing up - table

3 Methods of measuring blood gas

4 sO 2 and pO 2 ClinicalMonoPul.pdf

5 sO 2 and the ODC sO 2 vs. pO 2 (a) Standard ODC: ­ sO 2 = 90 % corresponds to pO 2 (a)= 60 mmHg Abnormal/critical ODC: ­ Shifts due to temperature, pH, 2,3-DPG, pCO 2 (a) At a constant pO 2 of 45 mmHg/6 kPa, sO 2 may be either 80 % or 88 % depending on whether arterial pH is 7.25 or 7.40 Conclusions: sO 2 is not suited for detection of hyperoxemia (high pO 2 (a)) sO 2 cannot be used to predict pO 2 (a)

6 Definition of saturation, sO 2 Arterial oxygen saturation Utilization of oxygen transport capacity Normal range % When sO 2 is below normal range, the patient can benefit from supplemental oxygen NO information about tHb, ventilation or O 2 release to tissue Available from BG CO-ox analyzers, BG analyzers, pulse oximeters

7 What does pulse oximetry measure? Arterial oxygen saturation SpO 2 Measuring range % SpO 2 based on empirically determined sO 2 (a) calibration curves I.e. SpO 2 is NOT identical to sO 2 (a), which is measured by CO-ox analyzers ­ From measured O 2 Hb and HHb And SpO 2 is NOT identical to sO 2 (e), which is estimated by BG analyzers ­ From pO 2 (a) and pH-corrected standard ODC ­ E.g. ABL5

8 Light emission - hemoglobin absorption Dual light source ­ Red light 660 nm ­ Infrared light 900 nm ­ Alternating diode cycles O 2 Hb absorbs more IR light ­ I.e. it looks more red HHb absorbs more red light ­ I.e. it looks less red

9 Light detection – pulse amplitude Photodetector ­ One detector for both wavelengths Isolate absorption from pulsating arterial blood ­ I.e. discard the ”base line” absorption

10 Baseline animation

11 sO 2 animation

12 From light absorption to SpO 2 Red-to-infrared pulse Modulation Ratio (R) Ratio translated to SpO 2 from calibration curve

13 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

14 SpO 2 – when to be cautious? Extreme hypoxemia ( 95 %) Sensor matching to site DysHb – SpO 2 may be normal despite low tHb Anemia – SpO 2 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

15 tc – new sensor illustrations E5280 Combi tcpO 2 /tcpCO 2 E5260 Single tcpCO 2 E5250 Single tcpO 2

16 tc – new E5250 animation

17 tc – new E5260 animation

18 tc – new E5280 animation

19 tc– new physiological measuring princ. animation

20 Table to summarize BG CO-ox analyzerTranscutaneousPulse oximetry ParameterspO 2 (a) pCO 2 (a) sO 2 (a) tcpO 2 tcpCO 2 SpO 2 Pulse Translation Oxygen uptake Ventilation Saturation Distribution of O 2 from lungs to skin Ventilation Utilization of O 2 transport capacity Measuring range pO 2 (a) – mmHg – kPa pCO 2 (a) – mmHg – kPa sO 2 (a) – % tcpO 2 – mmHg – kPa tcpCO 2 – mmHg – kPa SpO 2 : % Pulse: bpm Benefits Accurate Non-invasive Continuous CO 2 monitoring Ease of use Non-invasive Continuous Drawbacks Snapshot Invasive Expensive Doctors/lab Clinical understanding Calibration and stabilization period Poor detection of hyperoxemia > 95 % Poor detection of severe hypoxemia < 70 % No pCO 2

21 Radiometer Medical ApS, Åkandevej 21, DK-2700 Brønshøj, Tel: , Radiometer Training Center, June 2006