Case8 For Better SpO2 Monitoring - PI, Pulse-amplitude Index

The SpO2 value is often affected by the patient’s condition, artifacts created by external devices or by inappropriate attachment of probes, while monitoring continuously.
Nihon Kohden’s monitor has several features for better SpO2 measurement. Let us introduce one of the features here: PI, Pulse-amplitude Index.
For other three features, please see in each page. Signal Quality Index, Sensitivity Mode, and Response.

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Pulse-amplitude Index (PI)

The Pulse-amplitude Index, PI, indicates the percentage of pulsatile signal in the entire transmitted infrared signal. It fluctuates depending on the size of transmitted signal and the pulsatile signal obtained from a probe attached to a patient.

PI on the display


Pulsatile and entire transmitted signals

PI can be used as an index to confirm the circulation of the attachment site as well as to check the condition of an attachment site of SpO2 probe so if the attachment site is too thick or if a SpO2 probe is inappropriately attached, transmitted light intensity decreases, meaning the PI value becomes low.

When the PI is low, following situation might be happening.

  • Measurement site is cold
  • SpO2 probe is attached too tight
  • A patient in shock condition
  • A patient is a premature baby

In case the PI value is low, confirm the probe attachment condition as it may block blood flow of the measurement site due to the high pressure if the probe is attached too tight.
In case the PI value is low, but the probe is properly attached, change the probe attachment site for more reliable SpO2 measurement.
In case SpO2 value and PI value are dropping simultaneously, there is a possibility that the SpO2 probe might have deviated from the correct attachment position.