Perfusion index: Physical principles, physiological meanings and clinical implications in anaesthesia and critical care

Photoplethysmography (PPG) has been extensively used for pulse oximetry monitoring in anaesthesia, perioperative and intensive care. However, some components of PPG signal have been employed for other purposes, such as non-invasive haemodynamic monitoring. Perfusion index (PI) is derived from PPG signal and represents the ratio of pulsatile on non-pulsatile light absorbance or reflectance of the PPG signal. PI determinants are complex and interlinked, involving and reflecting the interaction between peripheral and central haemodynamic characteristics, such as vascular tone and stroke volume. Recently, several studies have shed light on the interesting performances of this variable, especially assessing regional or neuraxial block success, and haemodynamic monitoring in anaesthesia, perioperative and intensive care. Nevertheless, no review has yet been published concerning the interest of PI in these fields. In this narrative review will be exposed first the physiological and pathophysiological determinants of PI, and then the mean to measure this value as well as its potential limitations. In the second part, the existing data concerning usefulness of PI in different clinical settings such as operating theatres, intensive care units and emergency departments will be presented and discussed. Finally, the perspectives concerning the use of PI and mentioned aspects that should be explored regarding this tool will be underlined. (C) 2021 Societefranc , aise d'anesthesie et de reanimation (Sfar). Published by Elsevier Masson SAS. All rights reserved.

Automated summary

Perfusion index (PI), derived from photoplethysmography (PPG) signal, represents the ratio of pulsatile to non-pulsatile light absorbance or reflectance. The determinants of PI are complex and interlinked, involving the interaction between peripheral and central haemodynamic characteristics. Studies have shown PI's potential in assessing regional or neuraxial block success and haemodynamic monitoring in various clinical settings.