non-invasive oxygen monitoring pulse oximetry & conjunctival oxygen monitoring
TRANSCRIPT
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Non-Invasive Oxygen Monitoring
Pulse Oximetry &
Conjunctival Oxygen Monitoring
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OBJECTIVES
• At the end of this module, the student will be able to…
• define terms associated with pulse oximetry. • explain the theory of operation of a pulse
oximeter. • differentiate between functional and fractional
saturation.• list the indications, limitations, advantages,
disadvantages and contraindications for use of a pulse oximeter.
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OBJECTIVES
• At the end of this module, the student should be able to…• list some of the things that affect the accuracy
of a pulse oximeter.• explain when co-oximetry would be more
appropriate than pulse oximetry.• describe patient application for each of the
noninvasive monitors.
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ASSIGNMENTS
• Read: • Egan Chapter 16, pgs. 377 – 383• AARC Clinical Practice Guidelines - Pulse
Oximetry• Articles on Pulse Oximetry (look on website)
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Circle of OxygenationLungs
Uptake
PaO2
Dissolved Oxygen
Blood
Carrying
SaO2
Carried Oxygen
Heart
Pumping
DO2
Oxygen Delivery
Tissues
Utilization
O2
Oxygen Consumption
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Hypoxia Develops Rapidly
SaO2
%PaO2
mmHg 4 —> 2 L/minA
Central Apnea
Obstructive Apnea
Hypoxia + Obstructive Apnea
from Hanning,"Oximetry and Anaesthetic Practice", 1985
0 1 2 3 40
20
40
60
80
100
120
98
97
9695
90
8070
5030
10
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Pulse Oximetry
The Fifth Vital Sign
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Oxygen Content• The total amount of oxygen present in
arterial blood.• Dissolved oxygen (PaO2)
• Attached to hemoglobin (SaO2)• Measured by co-oximeter• Estimated by pulse oximeter• Calculated by blood gas analyzer
• Actual amount of hemoglobin (Hb)
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Oxygen Carrying Capacity
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The Science behind Oximetry
• Spectrophotometry• Lambert-Beer Law• Light Transmission Spectra and Oximetry• Light Emitting Diode (LED) technology
• Optical Plethysmography
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Spectrophotometry• Spectrophotometry is the measurement of
the amount of light that is absorbed as it passes through a substance.• Reflected• Absorbed• Transmitted
• Spectrophotometry is an application of Beer’s (Beer-Lambert) law.
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Absorption Spectrum
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Schematic block diagram of a pulse oximeter
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Wavelength Selection
• Two wavelengths are selected for analysis.• A red light at about 660 nanometers (nm).• An infrared light at about 940 nanometers.
• So how do we get such specific measurements?
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Light Emitting Diode Technology
• A pulse oximeter sensor is made up of two different parts:• An light emitting diode • A photodetector
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Misalignment of the sensor by inserting finger too far.
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Optical Plethysmography
• Plethysmography is the measurement of changes in volume in a particular part of the body.
• Originally designed to measure vascular perfusion.
• Changes in volume at a site is due to the pulsation of arterial blood.
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Output signal generated by pulse oximeter. Saturation is based on the ratio of light absorption
during pulsatile and baseline phases.
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Functional vs. Fractional Saturation
• SpO2 SaO2
• Functional Saturation (SpO2)
• Fractional Saturation (SaO2)
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Measurement vs. Monitoring
• Measurement: A one time snapshot. Example: ABG sample or a “spot-check” SpO2.
• Monitoring: Ongoing measurements.Example: Continuous pulse oximetry
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Golden Rule For Safety Monitors
• SAFE• ACCURATE
• RELIABLE• CONVENIENT
“Always detect danger”
and
“No false goodness”
•A Safety Monitor must beA Safety Monitor must be::
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Technical Limitations
• Calibration Assumptions
• Optical Interference
• Absorption Interference
• Signal Artifact
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Calibration Assumptions
• Calibration curves
• Accuracy range
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Optical Interference
• Ambient Light
• Optical Shunt
• Optical Cross-Talk
• Edema
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Absorption Interference
• Anemia • Skin Pigmentation• Nail Polish• Carbon Monoxide• Methemoglobin• Intravascular Dyes
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Signal Artifact
• Artifact can cause errors in measurement.
• Artifact may obscure the signal
• Causes:• Low perfusion
• Hypotension• Cold
• Motion Artifact
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The Solution?
• Improvements in technology that:• Improve the signal to noise ratio present in low
perfusion.• Improve the ability of the oximeter to “read”
through motion.
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Sensor Application
• Properly place sensor.
• Single use sensor are meant for a single patient.
• Use sensor as designed.
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Patient Application - Sites
• Adults & children• Finger• Toe• Ear lobe• Cheek• Tongue• Nose
• Small children & babies• Wrist• Upper arm• Across foot
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Pulse oximetry probes
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Reporting Results
• Four things to verify prior to reporting results:
• Waveform
• Signal strength
• Heart rate• Clinical Correlation
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Plethysmograph – Pulse oximeter tracing
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Oxyhemoglobin Dissociation Curve
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Contraindications (relative)
• When arterial blood gases are indicated for measurement of pH or PaCO2.
• When CO-oximetry is indicated for evaluation of total hemoglobin and abnormal hemoglobins• HbCO%• HbMet%
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Maintenance
• Pulse oximeters usually do a self-check when they are first turned on.
• They do not require regular routine manual calibration.
• Wipe probe and monitor with an alcohol soaked cloth between patients.
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Mini Clini - Egan: Page
363
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Conjunctival
• Principles of Operation
• A sensor is inserted under the eyelid.
• It contains a Clark PO2 electrode similar to a blood gas analyzer.
• It is used mainly in to OR for short-term application.
• Conjunctival PO2 is reported and correlates to the arterial PaO2.
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Conjunctival PO2 (PcjO2)