Understanding Perfusion Index in Pulse Oximeter

Understanding Perfusion Index in Pulse Oximeter

Pulse Oximeters have known to be used for the measurement of oxygen saturation in arterial blood. Perfusion Index (PI) derived from pulse oximetry represents a measure of peripheral perfusion that can be measured continuously and noninvasively. PI is the ratio of pulsatile blood flow to non-pulsatile static blood flow in a patient’s peripheral tissue. It works primarily by the amount of blood at the monitoring site, not by the level of oxygenation in the blood.

The PI is useful for quickly evaluate the appropriateness of a sensor application site for pulse oximetry. PI’s values range from 0.02% (weak pulse) to 20% (strong pulse). A site with a high PI number generally indicates an optimal monitoring site. PI is a relative number and varies depending on patients, physiological conditions, and monitoring sites. Therefore, each patient’s “normal” PI is unique.

Reliability of PI has improved to a level where clinicians are beginning to explore various ways, they can utilize PI to care for their patients.

Perfusion index has been considered a useful tool for accurately monitoring changes in peripheral perfusion in real time caused by certain anaesthetics. Increase in PI is an early indicator that general and epidural anaesthesia has initiated peripheral vasodilatation which typically occurs before the onset of the anaesthetic effect. Detection of a spike in PI is a sign to the physician of the successful onset of anaesthesia. Conversely, no increase in PI in a patient given anaesthesia may be an early warning of anaesthetic failure. As an objective indicant of pain levels in patients, the PI has been used to determine proper management of pain, especially in patients unable to communicate their discomfort to the clinician.

In the neonatal acute care setting, a low PI has been shown to be an objective indicator of severe illness. In conjunction with oxygen saturation and pulse rate, a diminished PI becomes an important indicator of a critical state of neonatal health. It is superior to qualitative approach such as foot warmth.

Understanding PI has emerged as an important bedside diagnostic and monitoring tool with applications in multiple clinical settings. Other uses of PI can be found throughout various literature. As we learn more about PI, more clinical applications are being discovered.

Note: The content on this page is strictly informational and should not be considered as any form of medical advice. Please consult a medical professional for any queries.


  • My pulse rate is 72 and PI% is 23. Is it good

    By S. K. KHEMKA

  • My pulse rate is 72 and PI% is 23. Is it good

    By S. K. KHEMKA

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  • The perfusion index (PI) is a measurement that indicates the strength of the pulse signal detected by a pulse oximeter. It is a non-invasive way to assess peripheral perfusion and tissue oxygenation. The PI value is calculated as the ratio of the pulsatile blood flow to the non-pulsatile blood flow in the peripheral tissue, expressed as a percentage. A higher PI value indicates better peripheral perfusion, while a lower value suggests poor perfusion. Pulse oximeter use two different wavelengths of light to measure the oxygen saturation (SpO2) and PI. The red light is absorbed by oxygenated hemoglobin, while the infrared light is absorbed by deoxygenated hemoglobin. The pulse oximeter uses the difference in the absorption of these two wavelengths to determine the SpO2 and PI.

    By Rajan

  • Pi 1.2 is that bad

    By Jilly

  • Sp o2 is 98, pulse 70, pi%9.8

    By Satish murthy

  • I am a first responder in UK, and find this article very informative, I of course would like to read more informative information on PI%. Please advise on details of more articles with Perfusion in pulse oximetry. Thanks

    By C Sterry

  • I am a first responder in UK, and find this article very informative, I of course would like to read mor informative information on PI%. Please advise on details of more articles with Perfusion in pulse oximetry. Thanks

    By C Sterry

  • Spo2% 98 bpm 70 pI% 10.5 is this okay for a 74 year old

    By Earvin

  • My Sp02% is 96, my PRbpm is 79 and my PI%% is 12.03 is this ok? As I feel strange,

    By tracy crawford

  • I recently read the article in Pulse Oximeter and it really helped me understand this important medical tool. It was written in an easy to understand way and provided helpful diagrams to illustrate the concepts. The article covered all the key points of a pulse oximeter and its application in patient monitoring. I am so glad I found this resource, as it was incredibly informative and beneficial for my understanding of pulse-oximeter . Highly recommend this article to anyone looking for more information!

    By sonu

  • Is a reading for your pi 9.3 a good reading

    By Sue

  • SpO2 98% PI 0.5 My Father Pls tell about above Is it Good

    By Aalok Deviprasadji Agrahari

  • SpO2 % 98 PRbpm 101 PI% 6.7 Is this normal?

    By kulajit Borah

  • Excellently explained

    By Peerzada Zakir Hussain

  • the higher the number the better accuracy, read the article. please tell me you work and don't steal from others that work.

    By ravindra is returd

  • My sister is a terminally ill with lung cancer. her blood preasure is 126/72.The PI is 0.13. she is under palliative care with a fantanyl patch. what would be the PI when she started her organ failures.

    By Jay

  • HillSulky

    By HillSulky

  • My age 74+ have pace maker Suffering coug 98 62 pi 15.3%

    By Samarendra Sur

  • Pi is no use by the layman really ! Main thing is oxygen saturation and temperature plus of course pulse rate . Get an oxymeter and a temperature gauge monitor daily it could be a life saver !

    By David Porter

  • All fine

    By God

  • I am not a doctor but as I understan PI index is related with the quality of the location which you are taking measurements.

    By Tbreva

  • What are normal ranges for Hemoglobin Saturation SpO2; and perfusion index PI, and the plethysmograph for a person age 80?

    By FAB

  • My age us 72+Fiabatic and undetgone angiopladty 3 years back. Oxygen levek 96 pulse rate 74. Pl % 5.4.is it normal

    By A. Sukumaran

  • %SPO97 bpmPR63 PI%8.4 - is it good?

    By Bon S.S.

  • Poi.5 Spo298 Pbm 83

    By Lekha

  • Rate 77 96% pi 6.1 is the 6.1 good?

    By Julie

  • Oxymetter pi 8rbpm 69 spo2 93

    By Skaliappan

  • Spo2 93 prb 63 pi11

    By Skaliappan

  • Oxymetter pi 8rbpm 69 spo2 93

    By Skaliappan

  • My PI is 1.2%, while oxygen 98 & pulse 74.... I have piles problems & presently suffering from cough n cold attack too... .


  • Very good

    By Ahmed

  • The article does not indicate what should be the PI for a normal healthy person. 0.2 to 20 ii's so wide that it means nothing.

    By Ravindra

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