Pulse OximetryPulse Oximetry

What is it?What is it?

A meter used to measure the concentration of oxygen in the

blood.

A meter used to measure the concentration of oxygen in the

blood.

It is done with an oximeter, a photoelectric device specially

designed for this purpose and a reusable probe.

It is done with an oximeter, a photoelectric device specially

designed for this purpose and a reusable probe.

The oximeter works on the principle that the oxygenated blood is a brighter color of red than the

deoxygenated blood, which is more blue-purple.

The oximeter works on the principle that the oxygenated blood is a brighter color of red than the

deoxygenated blood, which is more blue-purple.

Pulse oximeters display oxygen saturation, pulse rate, pulse

strength, low battery, and alarms. There may be a waveform display

also.

Pulse oximeters display oxygen saturation, pulse rate, pulse

strength, low battery, and alarms. There may be a waveform display

also.

Invented in 1972 by Takuo Aoyagi, an electrical engineer at Nihon

Kohden company in Tokyo.

Invented in 1972 by Takuo Aoyagi, an electrical engineer at Nihon

Kohden company in Tokyo.

What Does it Do?What Does it Do?

Pulse Oximetry provides estimates of arterial oxyhemoglobin saturation

(SAO2) by utilizing selected wavelengths of light to noninvasively

determine the saturation of oxyhemoglobin

Pulse Oximetry provides estimates of arterial oxyhemoglobin saturation

(SAO2) by utilizing selected wavelengths of light to noninvasively

determine the saturation of oxyhemoglobin

What Is Oxyhemoglobin?What Is Oxyhemoglobin?

Hemoglobin is a protein molecule that binds to oxygen. In its oxygen-

loaded form, it is called oxyhemoglobin and is bright red. In

the oxygen-unloaded form it is called deoxyhemoglobin and is

purple-blue.

Hemoglobin is a protein molecule that binds to oxygen. In its oxygen-

loaded form, it is called oxyhemoglobin and is bright red. In

the oxygen-unloaded form it is called deoxyhemoglobin and is

purple-blue.

What is meant by saturation?What is meant by saturation?

The amount of oxygen combined with Hemoglobin, expressed as a

percentage of the oxygen capacity of that hemoglobin.

The amount of oxygen combined with Hemoglobin, expressed as a

percentage of the oxygen capacity of that hemoglobin.

Why is this Important to Know ?

Why is this Important to Know ?

Hemoglobin in the blood is what transports oxygen from the lungs

to the rest of the body where it releases the oxygen for cellular use.

Hemoglobin in the blood is what transports oxygen from the lungs

to the rest of the body where it releases the oxygen for cellular use.

What is good reading?What is good reading?

The oxygen saturation should always be above 95%.

Readings below 85% need medical attention.

The oxygen saturation should always be above 95%.

Readings below 85% need medical attention.

How Does it Work?How Does it Work?

Based on two physical principles:

Based on two physical principles:

The presence of a pulsate signal generated by arterial blood.

Oxyhemoglobin and reduced hemoglobin have different absorption spectra.

The presence of a pulsate signal generated by arterial blood.

Oxyhemoglobin and reduced hemoglobin have different absorption spectra.

What is meant by a pulsate signal?

What is meant by a pulsate signal?

Pulse: The rhythmic contraction and expansion of an artery due to the

surge of blood from the beat of the heart.

Pulse: The rhythmic contraction and expansion of an artery due to the

surge of blood from the beat of the heart.

The oximeter is dependant on a pulsate flow and produces a graph

of the quality of flow.

The oximeter is dependant on a pulsate flow and produces a graph

of the quality of flow.

Where flow is sluggish, the pulse oximeter may be unable to function. The computer within the oximeter is capable of distinguishing pulsatile flow from other more static signals

(such as tissue or venous signals) to display only the arterial flow.

Where flow is sluggish, the pulse oximeter may be unable to function. The computer within the oximeter is capable of distinguishing pulsatile flow from other more static signals

(such as tissue or venous signals) to display only the arterial flow.

What about oxyhemoglobin and reduced hemoglobin

having different absorption spectra?

What about oxyhemoglobin and reduced hemoglobin

having different absorption spectra?

Pulse oximetry uses spectrophotometry based on Beer-Lambert law

Spectrophotometry is the measurement of the amount of light

that is absorbed as it passes through a substance.

Spectrophotometry is the measurement of the amount of light

that is absorbed as it passes through a substance.

The "Beer-Lambert Law" states that there is a linear relationship between the concentration of a solution and

the absorbance.

The "Beer-Lambert Law" states that there is a linear relationship between the concentration of a solution and

the absorbance.

Oxygen saturation is based on the ratio of light absorption during pulsate and baseline phases.

Oxygen saturation is based on the ratio of light absorption during pulsate and baseline phases.

Absorption GraphAbsorption GraphOxygenated hemoglobin

absorbs more infrared light and

allows more red light to pass through.

Deoxygenated (or reduced) hemoglobin absorbs more red light

and allows more infrared light to pass through.

Wavelengths of LightWavelengths of Light

Consists of an emitter and a photo detector.

Consists of an emitter and a photo detector.

There are two methods of sending light through the measuring site:

transmission and reflectance.

There are two methods of sending light through the measuring site:

transmission and reflectance.

The light emitter with red and infraredLED’s shine through a reasonable

translucent site with good blood flow typical adult/pediatric sites are the finger, toe, or top lobe of the ear.

The light emitter with red and infraredLED’s shine through a reasonable

translucent site with good blood flow typical adult/pediatric sites are the finger, toe, or top lobe of the ear.

The transmitted red (R ) and infrared (IR) signals pass through

the measuring site and are received at the photodetector.

The transmitted red (R ) and infrared (IR) signals pass through

the measuring site and are received at the photodetector.

First, the oximeter measures the sum of the intensity of both shades of red,

representing the fractions of the blood with and without oxygen.

First, the oximeter measures the sum of the intensity of both shades of red,

representing the fractions of the blood with and without oxygen.

The oximeter detects the pulse, and then subtracts the intensity of color detected when the pulse is absent.

The oximeter detects the pulse, and then subtracts the intensity of color detected when the pulse is absent.

The remaining intensity of color represents only the oxygenated red

blood. This is displayed on the electronic screen as a percentage of

oxygen saturation in the blood.

The remaining intensity of color represents only the oxygenated red

blood. This is displayed on the electronic screen as a percentage of

oxygen saturation in the blood.

Handheld Pulse OximeterHandheld Pulse Oximeter

Tabletop Pulse OximeterTabletop Pulse Oximeter

Why is it used?Why is it used?

It is used in evaluation of various medical conditions that affect the

heart and lungs.

It is used in evaluation of various medical conditions that affect the

heart and lungs.

It is used to detect hypoxia. Hypoxia is a pathological condition

in which the body as a whole (generalized hypoxia) or a region

of the body (tissue hyoxia) is deprived of adequate oxygen

supply.

It is used to detect hypoxia. Hypoxia is a pathological condition

in which the body as a whole (generalized hypoxia) or a region

of the body (tissue hyoxia) is deprived of adequate oxygen

supply.

Even under ideal conditions, skilled observers cannot detect

hypoxemia until oxygen saturation is below 80%.

Even under ideal conditions, skilled observers cannot detect

hypoxemia until oxygen saturation is below 80%.

Areas of UseAreas of Use

Anesthesia standards require pulse oximetry on all anesthetized patients.

Used with ventilator dependant patients.Frequently incorporated into vital signs

monitors measuring heart rate, blood pressure, and temperature.

It is commonly used in the hospital in the continuous mode for critical applications and intermittently for less critical patients.

Anesthesia standards require pulse oximetry on all anesthetized patients.

Used with ventilator dependant patients.Frequently incorporated into vital signs

monitors measuring heart rate, blood pressure, and temperature.

It is commonly used in the hospital in the continuous mode for critical applications and intermittently for less critical patients.

Benefits of UseBenefits of Use

Low cost (Finger units <$50).Ease of Use (Clip and Press).Degree of Accuracy.

Low cost (Finger units <$50).Ease of Use (Clip and Press).Degree of Accuracy.

For a resting patient under normal conditions, the accuracy of pulse oximeters is about +/- 2% in the

typical range of clinical interest - a SaO2 value of 70% - 100%.

For a resting patient under normal conditions, the accuracy of pulse oximeters is about +/- 2% in the

typical range of clinical interest - a SaO2 value of 70% - 100%.

Limitations of UseLimitations of Use

Intravenous Dyes.Motion.Low Perfusion states.Black or blue nail polish.

Intravenous Dyes.Motion.Low Perfusion states.Black or blue nail polish.

Areas of concernAreas of concern

Sensitive to motion.Readings below 85% have increased

error.Low perfusion state increases error.Ambient light interferes with reading.Delay in reading of about 12 seconds.Dysfunctional hemoglobin.

Sensitive to motion.Readings below 85% have increased

error.Low perfusion state increases error.Ambient light interferes with reading.Delay in reading of about 12 seconds.Dysfunctional hemoglobin.

Since first generation devices, technical advances which have been

made to improve pulse oximetry include:

Since first generation devices, technical advances which have been

made to improve pulse oximetry include:

Calibration resistors and chips embedded into the sensor.

The use of ECG synchronization techniques.Various motion sensing improvements.Specialty sensors for high altitude climbers.Smart alarm systems for pulse oximeters.A reduction in size, cost and power use. Wireless connection via Bluetooth

technology.

Calibration resistors and chips embedded into the sensor.

The use of ECG synchronization techniques.Various motion sensing improvements.Specialty sensors for high altitude climbers.Smart alarm systems for pulse oximeters.A reduction in size, cost and power use. Wireless connection via Bluetooth

technology.

Safety ConsiderationsSafety Considerations

Pulse oximeters are relatively safe devices with a few safety

issues:

Pulse oximeters are relatively safe devices with a few safety

issues:

Infection especially with reusable sensors.Possible heating and minor burns to

sensitive skin due to the red/infra-red LEDs.

Routine electrical safety concerns.

Infection especially with reusable sensors.Possible heating and minor burns to

sensitive skin due to the red/infra-red LEDs.

Routine electrical safety concerns.

Questions?Questions?