Perfusion Index (PI)

To make informed patient management decisions, physicians often need to be aware of changes in peripheral perfusion and circulatory status. This is especially true in patients who are in a critical condition, or who are anesthetised, undergoing surgery, or in labour. The perfusion index (PI) is the ratio of the pulsatile blood flow to the non-pulsatile or static blood in peripheral tissue. Perfusion Index thus represents a non-invasive measure of peripheral perfusion that can be continuously and non-invasively obtained from a pulse oximeter.

As the sensitivity of certain pulse oximeters has improved, the fidelity and reliability of PI has improved to a level where clinicians are beginning to explore various ways they can utilise PI to care for their patients. Optimal pulse oximetry monitoring accuracy is dependent on the selection of a monitoring site (e.g. fingertip, hand, toe, foot, forehead, ear) characterised by good perfusion with oxygenated blood. The PI provides instant and continuous feedback as to the perfusion status of the selected monitoring site. In clinical scenarios where peripheral perfusion may drop below the minimums required for tissue oxygenation and cellular respiration, the PI alerts the clinician to consider another monitoring site. Optimal monitoring sites are chosen with a relatively high, stable PI of over 3%.

If in doubt, contact your medical team for advice.