What is a Normal PI on a Pulse Oximeter?

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If you bought a pulse oximeter to use at home, a device designed to measure the amount of saturated oxygen in the blood, you might have come across the term “normal PI.” PI stands for “perfusion index,” and it is an indication of the strength of your pulse, but there is more to it than that. Let’s take a look at what is a normal PI on a pulse oximeter and what it tells you.

Perfusion Index

The perfusion index represents the ratio of the pulsatile blood flow to the non-pulsatile static blood flow in the peripheral tissues and limbs, such as toes, finger tips, and ear lobes. This might all sound very complicated, but what it really means is that the perfusion index measures the strength of the pulse at the site where the sensor is connected, which in this case is the pulse oximeter.

Measuring the Perfusion Index

The most widely used monitoring tool to keep track of the perfusion index is the pulse oximeter. The perfusion index is calculated by dividing the pulsatile signal (AC) by the non-pulsatile signal (DC), multiplied by 100.

This is then expressed as a percentage which ranges from 0.02% to 20%. The perfusion index can also be an indication of how reliable the reading from the pulse oximeter is. What is important to note is that pulse oximeter readings can be highly inaccurate if your perfusion index is too low, generally speaking, if your perfusion index is below or at 0.4%.

Due to the lack of pulse, the pulse oximeter cannot accurately measure the amount of oxygen in the blood. With that said, most people who are in good health have no need for a pulse oximeter that includes the perfusion index, as a low perfusion index is usually associated with bad health.

Keep in mind that if you need a pulse oximeter with the perfusion index included, these extra sensors required to measure the perfusion index will also add more to the price of the pulse oximeter. In essence, the perfusion index is a measure of the strength of the pulse or the blood flow to a given area of the body, generally small extremities like toes, fingers, and ear lobes.

What is a Normal PI on a Pulse Oximeter

Using the Perfusion Index with Pulse Oximeters

The reason having a perfusion index on your pulse oximeter is a good idea is because it can help increase the accuracy of the readings which the pulse oximeter gives you in relation to your blood oxygen levels.

Simply put, the stronger your pulse is at the monitoring site (where the pulse oximeter is attached), the more accurate the readings of it will be.

The perfusion index can help you determine how appropriate the application site is; it can help you find the best location to attach the pulse oximeter. Generally speaking, you want to apply the sensor to the area that has the highest percentage. If your earlobe has a perfusion index rating of 3%, and your finger has a rating of 15%, then the finger is where you want to attach the pulse oximeter.

Low vs. High Perfusion Index

So, besides telling you that your pulse may be strong or weak in an extremity such as your fingers or toes, what does the perfusion index indicate? What does it mean when you have a high or low perfusion index?

When it comes to a high perfusion index, it means that you are OK; a high perfusion index indicates that the strength of the pulse to an area such as your toes is very strong. This means that your veins and arteries are working properly, and that an ideal amount of blood is flowing to those areas.

However, if you have a low perfusion index, this can be a sign of poor health, and generally is; however, a low blood perfusion reading can be caused by an improperly placed sensor, cold temperatures, and dirty sensors, but it is more often associated with poor health. Simply put, if you have a weak pulse in your fingers and toes, it means that blood is not flowing to those areas properly, and that is a sign of poor health.


Being familiar with the perfusion index is important, particularly if you are using a pulse oximeter to measure your blood oxygen levels. Keeping track of the perfusion index is synonymous with keeping track of the state of your health.

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