module g2 - pulse oximetry

7/31/2019 MODULE G2 - Pulse Oximetry

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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 thenoninvasive monitors.


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ASSIGNMENTS

Read:

Egan Chapter 16, pgs. 377 383

AARC Clinical Practice Guidelines - PulseOximetry

Articles on Pulse Oximetry (look on website)


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Circle of Oxygenation

Lungs

Uptake

PaO2

DissolvedOxygen

Blood

Carrying

SaO2

Carried

OxygenHeart

Pumping

DO2

Oxygen Delivery

Tissues

Utilization

O2

OxygenConsumption


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Hypoxia Develops Rapidly

SaO2%

PaO2mmHg

4 > 2 L/minA

Central Apnea

Obstructive Apnea

Hypoxia + Obstructive Apnea

from Hanning,"Oximetry and Anaesthetic Practice", 1985

0 1 2 3 4

0

20

40

60

80

100

12098

97

9695

90

8070

50

3010


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Pulse Oximetry

The Fifth Vital Sign


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Oxygen Content

The total amount of oxygen present inarterial 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 ofthe amount of light that is absorbed as it

passes through a substance.

Reflected Absorbed

Transmitted

Spectrophotometry is an application ofBeers (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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Misalignmentof the sensorby insertingfinger 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. Saturationis 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 readthrough 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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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)

module g2 - pulse oximetry

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