Perfusion Index (PI) is a measurement obtained from a pulse oximeter that indicates the strength of the pulse signal detected by the device. It is a non-invasive way to assess 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 normal range of PI values is 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.

PI is useful for quickly evaluating the appropriateness of a sensor application site for pulse oximetry. It is also used to determine the successful onset of anesthesia and can serve as an objective pain indicator. In particular, this application is more common with patients who are unable to communicate their discomfort levels...