Transcript Transcutaneous measuring principles

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
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Agenda
• Saturation
- sO2, pO2(a), ODC
- SpO2
- Light emission
- Light detection
- Animations
- Calibration curves
- Cautions/limitations
• tc
- New illustrations
- New animations
• Summing up - table
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Methods of measuring blood gas
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sO2 and pO2
http://www.nellcor.com/_Catalog/PDF/Edu/MON_F.a.00838v1 ClinicalMonoPul.pdf
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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)
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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
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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
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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
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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
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Baseline animation
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sO2 animation
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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
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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
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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
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tc – new sensor illustrations
• E5250
• Single tcpO2
• E5280
• Combi
tcpO2/tcpCO2
• E5260
• Single tcpCO2
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tc – new E5250 animation
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tc – new E5260 animation
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tc – new E5280 animation
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tc– new physiological measuring princ. animation
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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
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Radiometer Training Center, June 2006
Radiometer Medical ApS, Åkandevej 21, DK-2700 Brønshøj, Tel: +45 38 27 38 27, www.radiometer.com
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