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Perfusion Index PI Oximetry


What is PI?

-  Perfusion Index, or PI, is a relative assessment of the pulse strength at the monitoring site.

- PI display ranges from .02% (very weak pulse strength) to 20% (very strong pulse strength).

- Perfusion Index is a numerical value that indicates the strength of the IR (infrared) signal returning from the monitoring site.

- The LED-based Masimo pulse oximeters such as Rad-5 and Rad-5v display PI as the Pulse

Amplitude Index (PAI) where the height of the bar represents the pulse strength.  Low PAI is

indicated by the lower two bar segments turning red.

- PI is a relative number and varies between monitoring sites and from patient to patient, as

physiologic conditions vary.


How do I use PI in a clinical setting?

- During sensor placement, use PI to quickly evaluate the appropriateness of an application site,

looking for the site with the highest PI number.

- Placing the sensor at the site with the strongest pulse amplitude (highest PI number) improves

performance during motion.  Monitor the trend of the PI for changes in physiologic conditions.

- Changes in sympathetic nervous tone affect smooth muscle tone, thereby altering levels of perfusion.


How does PI work?

- Meditech  infrared signal is influenced primarily by the amount of blood at the monitoring

site, not by the level of oxygenation in the blood.

- The ratio of AC (pulsatile) to DC (non-pulsatile) components of the IR (infrared) signal correspond to the pulsatile and the non-pulsatile amounts of blood.

- The relationship of the pulsatile to the non-pulsatile amounts of blood at any particular site corresponds to PI at that site.


Has PI been clinically validated?

- Preliminary data suggest high PI values correspond with health and low PI values with illness

on neonates.



1. Hager H, Reddy D, Kurz A. Perfusion Index - A Valuable Tool To Assess Changes in Peripheral Perfusion Caused by Sevoflurane?

Anesthesiology 2003;99:A593

2. De Felice C, Latini G, Vacca P, Kopotic RJ. The pulse oximeter perfusion index as a predictor for high illness severity in neonates.  

Eur J Pediatr 2002; 161:561-562

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