chapter 5; patient monitor – spo2 parameter quick points ... · chapter 5; patient monitor –...

Chapter 5; Patient Monitor – SpO2 Parameter

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QUICK POINTS

• There are four vital sign measurements which

measure the body’s most basic function which are

body temperature (BT), blood pressure (BP), pulse

heart rate (HR) and respiration rate (RR). SpO2 is

commonly considered to be the fifth vital sign.

• Pulse oximetry is a noninvasive method to monitor a

patient’s peripheral oxygen saturation (SpO2). The

SpO2 method uses a sensor placed on the patient's

extremity (finger, ear or toe). This method is an

alternative to an invasive arterial oxygen saturation

(SaO2) performed using a blood gas analyzer.

• The SpO2 probe has dual light-emitting diodes (red

and infrared) and a light sensor. The pulse oximeter

measures the difference between oxygenated and

deoxygenated hemoglobin absorbed by the body to

calculate the SpO2 level. A healthy person's range is

between 95 to 100%.

• Patient monitors with the SpO2 parameter may have

the following options:

Pulse rate and plethysmograph waveform (pleth)

Low/high saturation level and pulse rate

Trending and sensor off alert

• Common issues the biomed will experience with the

SPO2 parameter include broken probes and user

errors.

• Specific to the SPO2 parameter, the biomed verifies

saturation value accuracy, pulse rate accuracy, pulse

tone changes with saturation level changes and

ensures numerous alarms/alerts are working.


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PATIENT MONITOR – SPO2 PARAMETER

CHALLENGE QUESTIONS

1. What is the definition of pulse oximetry?

2. How does a patient monitor pick up the SpO2 rate

and/or waveform from a patient?

3. How does the SpO2 monitor calculate the pulse

oxygen saturation?

4. If the SpO2 monitor calculates an SpO2 value of

97%, what does this mean?

5. How does the pulse oximeter detect the patient's

heart rate?

6. What does the pleth waveform show?

7. If the heart rate tone is not changing with the SpO2

level, why?

8. How does a biomed deal with a user complaining

about an erratic SpO2 reading and/or waveform?

9. Outline the specific tests a biomed performs on the

SPO2 parameter during a PM.


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CLINICAL INFORMATION and

PARAMETER DETECTION

How does the body get oxygen?

The heart's right atrium receives deoxygenated

blood from the body. It pumps this blood to the right

ventricle which pumps this blood towards the lungs to pick

up oxygen. We breathe air into the lungs which contains

about 21% oxygen. The oxygen is absorbed in the blood

where it attaches to hemoglobin for transport through the

bloodstream. This oxygenated blood from the lungs returns

to the heart's left atrium. It pumps this blood to the left

ventricle which pumps the oxygenated blood to the body.

How is the oxygen saturation measured?

A probe is placed on the body's extremity, usually

the finger. Alternatively, there are ear lobe and toe probes

available. The probe has dual light emitting diodes (LED)

which are red (660nm) and infrared (940nm) and a light

detector. The light is passed through a patient's extremity and

monitored by the detector. With each contraction of the

heart's left ventricle, there is an increase in arterial blood

flow with oxygen-rich hemoglobin which was picked up

from the lungs. The oxygenated hemoglobin

(oxyhemoglobin or HbO2) absorbs more of the infrared

light. The deoxygenated hemoglobin (deoxyhemoglobin or

Hb) absorbs more of the red light. The pulse oximeter

measures the difference between oxygenated hemoglobin

(bright red blood) and deoxygenated hemoglobin (darker red

blood) absorbed by the body via the light detector. Using this

ratio, the pulse oximeter can then calculate the oxygen

saturation. If the SpO2 monitor calculates an SpO2 value of


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98%, this means the person has 98% oxygenated and 2%

non-oxygenated hemoglobin. In summary, oxygen

saturation tells you the percentage of the total hemoglobin

that is carrying oxygen. Persistent low SpO2 is called

hypoxemia and can lead to health issues including organ

failure. Blood oxygen saturation is an indicator of heart and

lung health.

What is the difference between reflectance and

transmission probes?

There are two probe designs which are either the

reflectance or transmittance detection. The reflectance

probe design has the emitter and photo detector next to each

other. The light travels from the emitter through the patient's

tissue and the light that is not absorbed by the hemoglobin

bounces off the patient tissue and then measured by the

detector. The transmission probe design has the emitter and

photo detector opposite each other. The light travels from the

emitter, through the patient's tissue and the light that is not

absorbed by the hemoglobin travels through the patient's

tissue and then measured by the photo detector. The

transmission method is the most common type of probe

design.

How is the pulse rate and plethysmograph detected?

The pulse oximeter can detect the patient's heart

rate by counting pulses of blood flow (peripheral arterial

pulses) that travels through the probe. The pleth waveform

is created by displaying the real-time peripheral arterial

pulse, as it passes through the SpO2 extremity sensor. The

pleth waveform shows:


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• The systolic phase which occurs when the heart has

contracted

• The diastolic phase which shows when the heart is

relaxed, and the ventricles are filling with blood

• The dicrotic notch which shows the closure of the

aortic valve

A SpO2 finger sensor and the plethysmograph waveform

Are all SpO2 probes the same?

No, there are a few different pulse oximeter

probes available. Ensure the probe type is designed to work

with the pulse oximeter.


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COMMON FEATURES OF THE SpO2 PARAMETER

SpO2 saturation display:

The SpO2 saturation level represents the

peripheral oxygen saturation of the patient's blood, as a

percentage. A normal value is between 95 to 100%.

SpO2 saturation low/high alarm:

If the SpO2 saturation level becomes too high or

too low, the SpO2 saturation high or low alarm will give an

audible and/or visual signal to the user. This SpO2 saturation

level alarm value is adjustable by the user.

Pulse rate display and tone:

The pulse rate is displayed in beats per minute

(BPM) and represents the mechanical contractions of the

heart by measuring the flow of blood at an extremity. In

comparison, patient monitors with the ECG parameter

measure the electrical activity of the patient's heart between

two electrodes, placed on the patient's skin. In a healthy

person, the ECG and SpO2 pulse rates are about the same

value. Patient monitors with both parameters available (ECG

and SpO2), give the user the option to use either the ECG or

SpO2 source to obtain the patient's heart rate. This allows the

user to display the patient's heart rate using an electrical or

mechanical method which the user selects, depending upon

the patient's condition. If the user monitors the pulse rate

using the SpO2 parameter, the tone of the heart rate will

change with the patient's peripheral blood oxygen saturation

level. If the user selects to monitor the heart rate using the

ECG parameter, the heart rate's tone will not change.


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Pulse rate low/high alarm:

If the pulse rate becomes too high or too low, the

pulse rate high or low alarm will give an audible and/or

visual signal to the user. This pulse rate alarm value is

adjustable by the user.

Plethysmograph waveform display (pleth):

The pleth waveform shows the arterial pulse flow

passing through the SpO2 sensor. The monitor displays the

real-time flow of the arterial pulses which shows the systolic

phase, dicrotic notch and diastolic phase.

Trending SpO2 level and/or pulse rate:

The SpO2 level and/or pulse rate can be saved

automatically at specific intervals. Trending of a patient's

SpO2 level and/or pulse rate allows the user to view them

over time.

Sensor off patient alert:

It is not uncommon for the SpO2 extremity sensor

to fall off the patient. Most patient monitors with the SpO2

parameter will signal the user if the SpO2 probe falls off the

patient.

Battery operation:

Many portable SpO2 monitors have an internal

battery allowing a mobile ability.


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Patient Monitor: SpO2 parameter

A SpO2 Portable Patient Monitor


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USER SETUP: SpO2 PARAMETER

1. The user admits the patient on the patient monitor

via:

a. manually entering the patient information.

OR

b. selecting the patient from a list on the patient

monitor obtained electronically, via other hospital

systems.

2. The user attaches the SpO2 probe.

3. The user may adjust the low/high oxygen saturation

alarms.

4. The user may turn on the pleth waveform.

5. The user will select either the heart rate source to

come from the ECG parameter or from the SpO2

parameter.

6. The user may adjust the low/high heart rate alarms.

7. The user may set up trending, etc.


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HOW TO TEST/PM THE SpO2 PARAMETER

Always refer to the manufacturer's service manual for a

complete recommended PM guideline. Following is a

generic guideline only!

Perform a visual inspection:

• The biomed checks the overall monitor looking for

obvious issues such as a broken case, etc.

• The biomed checks the SpO2 probe to ensure it is in

good order and do not have any cracks in the cables.

Ensure all user controls are operational:

• The biomed checks all the user controls are

functioning during your tests.

• A biomed will often find user controls not working

during their testing. If a button/control is not

working, repair it prior to placing the patient monitor

back into service.

Ensure the date and time are accurate:

• It is very important all systems including patient

monitors are at the same time to correlate patient

treatment. Correct the date/time if required.

Review error logs:

• Always check the error logs accumulated by the

patient monitor during use, if available.

• Most patient monitors in service mode allows the

biomed to review these logs which may include basic

to very detailed information. Often these logs will


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give the biomed information showing operational

issues the user may be unaware of during use.

Ensure SpO2 saturation level accuracy:

• Connect the SpO2 probe to a SpO2 simulator which

gives a known calibrated saturation level (%).

• Ensure the SpO2 monitor's saturation level is

accurate compared to the simulator's calibrated

saturation level. You should test the SpO2 saturation

level accuracy at a few different saturation levels

available from the simulator, usually the lowest,

highest and a few in-between. Ensure the SpO2 is

within the manufacturer's accuracy.

• Test the SpO2 on yourself. Get to know your own

SpO2 saturation level and pleth waveform. This

method can be used for a fast-functional SpO2 test.

SpO2 Simulator


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Ensure SpO2 saturation high/low alarms are working:

• To test the high SpO2 saturation level alarm, set the

SpO2 simulator at a higher saturation level than the

current high SpO2 saturation alarm setting. Ensure

the high SpO2 saturation alarm signals the user by an

audible and/or visual indicator.

• To test the low SpO2 saturation level alarm, set the

SpO2 simulator at a lower saturation level than the

current high SpO2 saturation alarm setting. Ensure

the low SpO2 saturation alarm signals the user by an

audible and/or visual indicator.

Ensure pulse rate accuracy:

• Connect the SpO2 probe to a SpO2 simulator which

gives a known calibrated value (BPM).

• Ensure the pulse rate is accurate compared to the

SpO2 simulator. The biomed should test the pulse

rate accuracy at the lowest/highest value and a few

in-between. Ensure the pulse rate is within the

manufacturer's accuracy.

Ensure pulse rate high/low alarms are working:

• To test the high pulse rate alarm, set the SpO2

simulator at a higher pulse rate than the current high

pulse rate alarm setting. Ensure the high pulse rate

alarm signals the user by an audible and/or visual

indicator.

• To test the low pulse rate alarm, set the SpO2

simulator at a lower pulse rate than the current high

pulse rate alarm setting. Ensure the low pulse rate


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alarm signals the user by an audible and/or visual

indicator.

Ensure the pulse tone changes with the saturation level:

• Enable the heart rate source to come from the SpO2

parameter. Vary the SpO2 saturation level and ensure

the pulse tone changes with the SpO2 saturation

level. At a saturation level of 100%, the tone should

be noticeably different when compared to a lower

value such as 90%.

Ensure the pleth waveform can be displayed:

• If the pleth waveform is available, ensure the user

can enable/disable the plethysmograph waveform

display.

Ensure the battery is working (if available):

• If testing a portable SpO2 monitor and it contains an

internal battery, refer to the manufacturer’s guideline

for testing the battery capacity.

• If the battery tests fail, replace the battery!

• Often the manufacturer will recommend routine

replacement of the battery.

Ensure the monitor is electrically safe: (IEC)

• Measure the ground resistance (0.15 OHM max.)

• Measure the chassis leakage (500ua max.)

• Leakages should be within the manufacturer’s or

local government specifications, whichever is less.


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Always perform a final functional check:

• As a final test, the biomed should do a quick SpO2

functional test to ensure proper operation, prior to

placing it back into service.

• All operation, controls and alarms should operate as

per the manufacturer's design.

Ensure your documentation is accurate:

• All repairs and performance tests need to be

documented so that they can be retrieved at any time.

• This documentation should include all parts used for

repair and that all the above tests showing the

equipment is within manufacturers' and local

authorities acceptable limits.

• These documents may be used legally to validate the

proper maintenance was performed by the biomed.

Ensure the documentation is accurate!

What do I do if any of my checks fail?

• If any device maintained by the biomed fails a

functional test and/or electrical safety, it is the

biomed's responsibility to pull it out of service!

• Failure means a patient safety issue exists!

• Fix the issues prior to placing the patient monitor

back into service!


188

QUICK SERVICE TIPS

Broken probe:

• It is NOT uncommon for the re-usable patient probe

to get an intermittent break in the wire, most often

near the probe. Bending the wire to look for these

breaks may reveal them quickly as the SpO2 value

and/or pleth waveform will be erratic. Also observe

the red LED which may turn on/off as you bend the

probe wires (the red LED should always be on

normally).

• If you suspect the SpO2 probe as the issue, the

quickest way to fix the issue is to swap the suspected

bad sensor with a known working SpO2 probe. The

suspected bad probe can then be tested in the

Biomedical department.

Movement artifacts:

• SpO2 probes are very susceptible to movement of the

extremity, usually a finger probe. If there is

movement at the site of where the probe is placed,

there may be movement artifact.

• Shivering or the patient experiencing seizures are

common movement artifact issues.

• Movement artifacts can easily be seen by looking at

the pleth waveform which will be distorted.


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Improper SpO2 placement:

• Unfortunately, this is a common issue.

• The user must place the probe properly on the

patient, so the 2 light sources pass through the

patient's extremity. The light source must emit the

light through the patient and the detector must see

this light as it passes through or bounces off the

patient.

Improper probe size:

• If the probe placed on the patient is too large, the

LEDs may not line up properly resulting in an

inaccurate reading.

• If the probe placed on the patient is too small or too

tight, this can cause venous pulsations causing

interference. This may result in “low” readings.

Light interference:

• In a hospital setting, occasionally other strong light

sources may interfere with the SpO2 monitor. These

can include such devices as Operation Room (OR)

lights which are very bright.

• An easy way to eliminate this issue is to cover the

probe!

Nail polish:

• Nail polish, especially “red”, may absorb some light

emitted from the LEDs. This would result in

inaccurate readings as the red will interfere with the

red emitter/detector.


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• Advise the user to remove the nail polish from the

probe site.

Medical conditions that may interfere:

• There are certain medical conditions that may

interfere with accurate readings. These include

peripheral vasoconstriction (poor circulation),

hypothermia, shock and anemia.

• Be aware of these and other patient conditions that

may cause inaccurate readings.

User setup/operational errors:

• It is not uncommon for the user to be unaware of how

to set up the SpO2 alarms available, heart rate source,

pleth waveform, trending, etc. The biomed may need

to assist/train the user on operation of the patient

monitor with the SpO2 parameter.

Probe type:

• As there are different type of pulse oximeter probes,

verify the user has not replaced the probe with the

incorrect type. Verify the probe type required for the

pulse oximeter.

NOTE: the majority of patient monitor SpO2 parameter

service calls will be one of the above issues!


191

PATIENT MONITOR - SpO2 PARAMETER

CHALLENGE ANSWERS

1. Pulse oximetry is a noninvasive method to monitor a

patient’s peripheral oxygen saturation (SpO2).

2. The SpO2 method uses a sensor placed on the

patient's extremity (finger, ear or toe).

3. The SpO2 probe has dual light-emitting diodes (red

and infrared) and a light sensor. The pulse oximeter

measures the difference between oxygenated

hemoglobin (oxyhemoglobin) and deoxygenated

hemoglobin (deoxyhemoglobin) absorbed by the

body to calculate the SpO2 level.

4. If the SpO2 monitor calculates an SpO2 value of

97%, this means the person has 97% oxygenated and

3% non-oxygenated hemoglobin.

5. HR is calculated by counting peripheral arterial

pulses that travels through the probe.

6. The pleth waveform shows the systolic phase, the

diastolic phase and the dicrotic notch.

7. The heart rate tone is not changing with the SpO2

level because the user has selected the heart rate

source as the ECG parameter. The tone changes if the

heart rate source is using the SpO2 parameter. The

tone will then change with the patient’s saturation

level.

8. An erratic SpO2 reading and/or pleth waveform most

often is caused by patient movement or a faulty

SpO2 probe. If the biomed suspects the SpO2 probe

as the issue, the quickest way to fix the issue is to

swap the suspected bad sensor with a known working


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SpO2 probe. The suspected bad probe can then be

tested in the Biomedical department.

9. The specific tests a biomed performs on the SPO2

parameter during a PM includes:

• Ensure SpO2 value accuracy.

• Ensure SpO2 high/low alarms are working.

• Ensure pulse rate accuracy.

• Ensure pulse rate high/low alarms are working.

• Ensure the pulse tone changes with the saturation

level.

• Ensure the pleth waveform can be displayed.

• Ensure the battery is working (if available).

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