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.


  • 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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