Limitations and Causes of Inaccurate Readings on a Pulse Oximeter

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If you are familiar with pulse oximeters, you probably know just how useful they can be. If you are not familiar with them, don’t worry, because we are about to explain everything that you need to know.

One thing which many people are concerned about is that pulse oximeters may produce inaccurate readings.

While these devices are generally reliable, there are various limitations they have, limitations which can cause fairly inaccurate readings on a pulse oximeter. So, what exactly are these devices and why might they not be accurate?

What do Pulse Oximeters Read?

There are two main things which pulse oximeters tell you. For one, they inform you of what your current heartbeat is. In normal healthy adults, the average resting heart rate is between 60 and 100 beats per minute, and the lower your resting heart rate is, the less your body has to work to supply oxygen to your body.

Speaking of oxygen, the main purpose of pulse oximeters is to measure the level of saturated oxygen in the blood. Your body’s all cells, tissues, and organs needs oxygen to function.

A healthy adult should have a blood oxygen saturation level of 95% or higher, with anything below that being a signal of heart- or lung-related health issues. Therefore, knowing just how much oxygen your blood is carrying is vital for determining the state of your health.

Average Margin of Error for Pulse Oximeters

It is normal for pulse oximeters to have some deviations when it comes to the readings. On average, the normal deviation for the readings provided by these devices is +/- 2%. This means that if a pulse oximeter indicates that you have a blood oxygen saturation level of 97%, it could actually be as high as 99% or as low as 95%.

This is perfectly normal and it can be caused by a variety of factors. However, this deviation can be much more extreme, and in essence, there are many factors which can greatly decrease the accuracy of the readings, well beyond this average deviation range.

Limitations and Causes of Inaccurate Readings

There are a variety of limitations which pulse oximeters have, and they can all be causes which lead to inaccurate readings. So, why might your pulse oximeter not be displaying the correct Sp02 level in your blood?

Excessive Movement

One of the leading causes of inaccurate readings in pulse oximeters is excessive movement on the part of the person being measured. Pulse oximeters need to be kept in place to get an average Sp02 level. If you move around too much, the pulse oximeter moves around or slips off, or if the patient moves from low to high light areas (or vice versa), it can greatly impact the readings.

Improper Placement

Just like the previous cause, this one also has to do with human error. If the pulse oximeter is not applied properly, it can also lead to highly inaccurate readings. For one, if being applied to a finger, if the finger is too large, it may cause the pulse oximeter to apply too much pressure to the given area, which in turn decreases blood flow, and thus causes inaccurate readings. There are right ways and wrong ways to use a pulse oximeter.

Inaccurate Readings on a Pulse Oximeter

Nail Polish

Yes, this one also qualifies as human error. Nail polish is thick and it absorbs light. Using a pulse oximeter on a finger that has nail polish on it is virtually guaranteed to produce false and inaccurate results.

Skin Pigmentation

Yet another factor that can affect readings is skin pigmentation. The darker the skin, the more light the skin absorbs. Because pulse oximeters use light to measure blood oxygen levels, if too much light is being absorbed by the skin, it may very well cause false readings. This can be especially problematic for people with darker skin, especially when already suffering from low Sp02 levels.

Carbon Monoxide

Carbon monoxide is another thing which can cause inaccurate readings. Carbon monoxide molecules attach themselves to hemoglobin, which replace the oxygen molecules. Pulse oximeters cannot distinguish between the two. For instance, if your hemoglobin carries 85% oxygen and 10% carbon monoxide, the reading would show as 95%.

Blood Volume Deficiencies

Another thing which can cause inaccurate readings is if you are suffering from some sort of blood volume deficiency. If you are suffering from a reduction in blood flow, the pulse oximeter will not be able to get an accurate reading.

Electromagnetic Signals

Electromagnetic signals released by other electronic devices may also interfere with pulse oximeter readings.

Conclusion

The unfortunate reality is that there are a lot of factors which an affect the accuracy of pulse oximeter readings, so when using one of these devices, you must be sure it is properly placed and that there are no underlying obstacles that might affect a reading.

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