Which factor may affect the accuracy of pulse oximetry readings in a client with dyspnea?

Measurement of peripheral oxygen saturation (SpO2) is used to identify early hypoxia in patients and evaluate the effectiveness of oxygen therapy. Nurses should be aware of the procedure for using a pulse oximeter to measure SpO2 levels and the normal range for SpO2 readings.

A pulse oximeter is used to measure SpO2 levels, and involves placing a probe on the patient’s finger, toe or ear lobe.

A SpO2 level of less than 90% is a clinical emergency. If the SpO2 level is below 94%, the nurse should assume the patient is hypoxic until proven otherwise, and therefore they may require supplemental oxygen administration.

Nurses should be aware of the factors that might affect SpO2 readings, including anaemia, peripheral vasoconstriction, dark skin tone and skin discolouration.

Nursing Standard. doi: 10.7748/ns.2017.e9940

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A Pulse Oximeter is a handheld clip device used to measure one's oxygen saturation. Pulse Oximetry is the process of using the device to measure the oxygen saturation. It helps indicate how well oxygen is being sent to parts of your body away from your heart, like the periphery

Due to its portability, it can easily be used at rest, and can also be used during exercise.

Pulse oximeters can be used in critical care settings, like emergency rooms and hospitals, used to monitor patients before, during, and/or after rehabilitation exercise therapy, or can be used in the home setting.

The pulse oximeter can be used to monitor oxygen saturation in the blood, in a variety of conditions. Some of these conditions include:

Reasons to use a pulse oximeter could be:

• Assess the effectiveness of lung medication or beathing medicine
• Evaluate if someone needs help breathing (with a supplemental oxygen supply), especially if they are short of breath
• Evaluate the effectiveness of a ventilator or supplemental oxygen supply
• Monitor oxygen saturation level before and after a surgery with sedation
• Monitor oxygen saturation levels prior to, during, and after physical activity or exercise therapy, especially for respiratory patients

The pulse oximeter is a gentle clamp, which provide two digital readings: your heart rate, and oxygen saturation. A picture of this device can be seen at the top of this page.

It is placed around the fingertip, and the outputs are displayed within seconds. The device consists of a cold light source which shines a light through the fingertip. The device analyzes the light that is passing through the fingertip, and will determine the percentage of oxygen in the red blood cell. This is done by measuring changes in light absorption between oxygenated and deoxygenated blood, at two different wavelengths. The ratio of these is calculated and compared to measurements of arterial oxygen saturation to achieve the pulse oximeter's measurement of arterial saturation.

This is a non-invasive device, and does not involve any pain discomfort to administer. This can be seen in the picture of the device, on the right.

The device can be used on the fingers, ears, nose, or toes , but is generally used on the finger.

• When placing the pulse oximeter on your (or someone's) fingertip, ensure that the hand is warm, is placed below heart level, the particular finger is clean without any fingernail polish or jewelry, and that you are relaxed.
• Sit still and do not move your hand with the device.
• Wait a few seconds for the the digital readings to settle. This will show a proper estimate of your heart rate and oxygen saturation.

Normal oxygen saturation (SpO2) levels for healthy individuals should be between 95% - 100%.

SpO2 values below 95% (90.1%-94.9%) are considered to be abnormal, and caution should be taken at these values.

Patients with an SpO2 reading of less than 90% are said to be hypoxemic.

Patients with an SpO2 reading of less than 85%would be severely hypoxemic. These patients would most likely need an external oxygen supply.

Note that oxygen saturation levels can be slightly lower for individuals at higher altitudes.

This is an oxygen saturation curve. Note that at the very top (95%-100%) the partial pressure of oxygen has plateaued, and is the highest. It is also seen that below 80%, the partial pressure rapidly or exponentially decreases.

There are many factors which may cause an inaccurate or unreliable reading. Such factors may include:

• Poor Circulation
• Cool skin temperature
• Have dark nail-polish
• Long nails or unclean nails
• Low perfusion state
• Anemia
• Tobacco usage
• Patient motion
• Dark skin pigmentation - it is seen that individuals wit a darker skin colour have a lower SpO2 reading from the pulse oximeter
  

These factors may result in an unintended low oxygen saturation measurement. It is also good to note that the accuracy of the device is the lowest when SpO2 values are below 80%.

There are no risks or dangers of having the device administered.

If and when someone is measuring their oxygen saturation at home using a pulse oximeter, attention should be given to the following signs or symptoms:

• Cyanosis (blueness) of the face, lips, or nails
• Shortness of breath (SOB), difficulty breathing, or progressive cough
• Restlessness and discomfort
• Chest pain or tightness
• fast or racing pulse rate

Here is a detailed video explaining the pulse oximeter:

Interesting fact: There has been an increased usage of pulse oximeters as a result of Covid-19. Patients with (or suspected symptoms of) covis-19, who are using a pulse oximeter, should pay attention to all signs and symptoms when judging the accuracy and reliability of the device.

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