Case8 For Better SpO2 Monitoring - PI (Pulse-amplitude Index)

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

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Pulse-amplitude Index (PI)

The Pulse-amplitude Index, PI, indicates the percentage of the pulsatile signal as a proportion of the entire transmitted infrared signal. It fluctuates depending on the size of transmitted signal and the size of the pulsatile signal obtained from the probe attached to the 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 an SpO2 probe is inappropriately attached, the intensity of the transmitted light decreases, meaning the PI value becomes low.

When the PI is low, any of the following situations might be happening.

  • Measurement site is cold
  • SpO2 probe is attached too tightly
  • The patient is in a condition of shock
  • The patient is a premature baby

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