# Interfinger Differences in Pulse Oximetry Signal-Derived Peripheral Perfusion Index: A Single-Center Exploratory Study

## TL;DR

This study finds that the index and ring fingers have the most consistent pulse oximetry readings, which could help avoid probe-related issues in clinical settings.

## Contribution

The study identifies the index and ring fingers as having the least fluctuation in peripheral perfusion index values.

## Key findings

- The index and ring fingers showed the smallest difference in pulse amplitude index (PAI) values.
- Middle and ring fingers also showed minimal differences, but with higher variability than index-ring pairs.
- All other finger combinations had statistically significant differences in PAI values.

## Abstract

Introduction: Peripheral perfusion monitoring is crucial for the management of critically ill patients because abnormal peripheral perfusion is associated with a poor prognosis. The peripheral perfusion index (PPI), derived from pulse oximetry, quantifies peripheral perfusion but varies across fingers. A pulse oximeter probe may cause burns when worn at the same site. Therefore, changing the site has been recommended. However, changes in PPI values owing to probe replacement reduce the reliability of clinical and research applications. No two fingers with equivalent PPI values have been identified yet. This study assessed the interfinger differences in PPI by measuring the five fingers simultaneously and identified the two fingers with the least fluctuation in values.

Methods: A total of 30 healthy volunteers were included in this single-center prospective exploratory study. For PPI measurements, the pulse amplitude index (PAI) was measured using a pulse oximeter on a bedside monitor (Life Scope PT; Nihon Kohden Corp., Tokyo, Japan). The tape-type disposable pulse oximeter probes were attached to each of the five fingertips of the dominant hand, and measurements were conducted in three rooms with different temperatures (16°C, 22°C, and 28°C) to induce thermoregulatory responses and capture a wide range of PAI values. The primary endpoint was the PAI in pairs of two fingers each (a total of 10 pairs). Paired t-tests with Bonferroni correction were used to compare finger pairs, with statistical significance defined as p < 0.005.

Results: The combination with the least difference in PAI was the index-ring finger combination (0.07% ± 1.89%, p = 0.74), followed by the middle-ring finger (0.45% ± 1.93%, p = 0.03) and index-middle finger combinations (0.52% ± 2.05%, p = 0.02). All other finger combinations showed statistically significant differences (p < 0.001).

Conclusion: PPI values measured using the pulse oximeter showed the smallest interfinger difference between the index and ring fingers. If changing the finger to which the probe is attached during clinical or research use is needed, it may be possible to consistently measure the PPI values by alternately attaching the probe to the index and ring fingers.