PULSE OXIMETRY

ABDUL RS BUKHARI, D.Sc., PMP

11/12/2015

WHAT IS PULSE OXIMETRY? Pulse oximetry is the non-invasive measurement

of the oxygen level in the arterial blood and the pulse rate. Why interested in arterial blood?

Oxygen saturation (SpO2). Oxygen saturation is defined as the amount of oxygen dissolved in blood (oxyhemoglobin).

SpO2 is the general indicator of oxygen delivery to the peripheral tissues (such as the finger, earlobe, nose, and other tissues).

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REVIEW OF BLOOD CIRCULATION

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SYSTEMIC LOOP

WHAT IS PERCENTAGE SPO2• Blood carries the oxygen to the various organs in our body by means of Hemoglobin molecules( Hb) in the red blood cells. •Each Hemoglobin molecule can combine with up to 4 Oxygen molecules. Suppose there are 100 Hb molecules having a total of 360 Oxygen molecules ( some Hb molecules may have 4 O2 molecules bound, others may have 3, 2 or none).•SpO2= 360/400 = 90% oxygenation

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OXYGENATED HEMOGLOBIN (HbO2)AND

DEOXYGENATED HEMOGLOBIN(Hb)What is the difference between the Oxygenated Blood and the Deoxygenated Blood

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OXYGENATED HEMOGLOBIN (HbO2)AND

DEOXYGENATED HEMOGLOBIN(Hb)

The color of HbO2 is _____________ The Color of Hb is ________________ What about the light absorption

characteristics of the two hemoglobins? Will it be the same or different ?

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PRINCIPLE OF PULSE OXIMETRY

The principle of pulse oximetry is based on the light absorption characteristics of oxygenated and deoxygenated hemoglobin.

VIS/IR absorption in hemoglobin (blood)changes with O2 binding.

Oxygenated hemoglobin is red. Will it allow more of red light to pass through or the infrared light?

Deoxygenated (or reduced) hemoglobin is dark red. Will it allow more of red light to pass through or the infrared light? 11/12/201

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VIS/IR ABSORPTION IN HEMOGLOBIN (BLOOD)CHANGES

HbO2 absorbs more infrared light and allows more red light to pass through.

Hb absorbs more red light and allows more infrared light to pass through.

Wave length of red light is in 600-750 nm range.

Wave length of Infrared light is in the 850-1000 nm range

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BEER-LAMBERT LAW

There is another factor that is component of BEER LAMBART LAW,

the absorbance of light is directly proportional to the thickness of the media through which the light is being transmitted

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constant light absorbers always present: Skin, Tissue, Venous Blood, and the Arterial Blood When heart contracts it pushes the blood through the arterial system. There is a surge of arterial blood momentarily causing an increase in the blood volume with each heart beat The results ? Less absorption or more absorption? If light signals received at the photo detector are looked at 'as a waveform', there should be peaks with each heartbeat and troughs between heartbeats.

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RED LED IR LED

Photo Detector

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What does the absorption of light at trough represent? The light absorption at the trough includes all the constant absorbers , subtracted from the light absorption at the peak Then, in theory, the resultants are the absorption characteristics due to added volume of blood only; which is arterial blood Since peaks occur with each heartbeat or pulse, the term "pulse oximetry“ is used.

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tA

tpart AAA

PULSE OXIMETRY EQUATION AND LOOKUP TABLE

The ratio R of pulse to constant portions at the two wavelengths 940 and 660 nm is calculated as below:

940940

660

DCAC

DCAC

R

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LOOKUP TABLE

The above ratio is compared to a "look-up" table (made up

of empirical formulas) that convert the ratio to an SpO2 value.

Typically a ratio of 0.5 equates to approximately 100% SpO2, a ratio of 1.0 to approximately 82% SpO2, while a ratio of 3.5 equates to 0% SpO2.

Most manufacturers have their own look-up tables based on calibration curves derived from healthy subjects at various SpO2 levels and are stored in the system.

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BLOCK DIAGRAM PULSE OXIMETRY SYSTEM

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50µ S at I1KHz

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DESIGN TRENDSAdvances in digital signal processing using

microcontroller technologies has enabled vendors to create special algorithms to implementation design by utilizing software techniques rather hardware components. to extract the oxygen saturation data from even those patients who are suffering from severe heart diseases and having blood perfusion issues. Low perfusion performance and Motion Artifact Rejection have become standard features of every pulse oximetry design.

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NORMAL AND ABNORMAL WAVE FORMS

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 COMMON PROBLEMS AND SOLUTIONS

PROBLEM CAUSE SOLUTION

Blood gas reading (CO oximetry) from clinical laboratory is different than pulse oximetry reading

1. Values have changed due to time between blood drawing and pulse oximeter readings

2. Blood gas sampling technique not correct

3. SaO2 calculated from PaO2 by analyzer

4. Dysfunctional hemoglobins such as carboxyhemoglobin or methemoglobin

5. Intracardiac shunting such as congenital heart condition results in differing SaO2 reading in different parts of the body

6. Dye injected into the body for another medical test

1. Use blood gas analyzer in close time proximity

2. Check blood drawing and transport technique

3. Check analyzer

4. Do not rely on pulse oximeter

5. Be consistent in measurement location

6. Wait till the dye disperses before relying on pulse oximetery data

Reading intermittent

1. Nail polish on finger measuring O2 sat

2. Skin pigmentation

3. Ambient light interference

4. Electrical/electromagnetic interference

1. Remove nail polish or chose a different site

2. If lower pigmentation site available, use it

3. Shield probe from interfering light source or remove light source

4. Remove interfering source

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Reading intermittent with baseline wander1. Motion artifact

2. Wrong probe for application site used

1. Reduce motion if possible (e.g. blanket over shivering patient); use a newer pulse oximeter with motion artifact reduction

2. Use correct probe

Reading intermittent; waveform low Poor perfusionFind a site with better perfusion or use a newer pulse oximeter with more senstivity

Reading periodically goes away and device alarms NIBP cuff on same side of patient as finger probe Change probe to finger on side without NIBP monitoring

Readings high, waveform good Anemia Check red blood cell count

Unit on; No reading or waveform; red LED light on 1. Defective cable or probe/cable unit

2. Defective pulse oximeter

1. Replace the cable or probe/cable unit

2. Replace pulse oximeter

Unit on; No readings of waveforms; red LED light is off

1. Defective probe

2. Defective cable or probe cable unit

3. Defective pulse oximeter

1. Replace probe

2. Replace cable or probe/cable unit

3. Replace pulse oximeter

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LIMITATIONS Decreased blood flow to the peripheral vessels very small

fingers or very large fingers Light shining directly on the oximetry probe Irregular signal caused by Movement, shivering of the area to

which the probe is attached Severe anemia (decreased red blood cells) Extreme warmth or coolness of the area to which the probe is

attached Excessive sweating of the area to which the probe is attached  Recent injection of contrast dye

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PULSE OXIMETRY ROLE IN PRIMARY CARE

Diagnosing and managing a severe chronic obstructive pulmonary disease (COPD) .

Grading the severity of an asthma attack. Assessing severity and oxygen requirements for patients with Pneumania

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AnesthesiaIn OR/General AnesthesiaMonitoring Care During Conscious Sedation

PACU

Intensive Care Units

Neonatal

Intensive Care

Newborn Nursery

Delivery Suites

Transport

Internal (within the Hospital)External

Ambulance/Air Transport

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Diagnostic Lab

PFT LabExercise LabSleep Lab

Home Care Patients

Other Patient Conditions

Blood Flow Assessment

Cardiopulmonary Arrest

Asthma

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QUESTION?

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