# Inter-Finger Variability of SpO2 During Hypoxemia and Step Resaturation

## TL;DR

This study finds that measuring blood oxygen saturation on the thumb gives slightly lower readings than other fingers during low oxygen conditions, but the difference is within acceptable clinical accuracy.

## Contribution

The study is the first to compare all fingers for SpO2 under hypoxemia and during step resaturation with randomized sensor placement.

## Key findings

- SpO2 measured on the thumb was 0.6% to 0.7% lower than on other fingers during desaturation.
- No differences in SpO2 dynamics were observed between fingers during step resaturation.

## Abstract

Background: Pulse oximetry is a non-invasive method for continuous monitoring of peripheral blood oxygen saturation (SpO2) to estimate arterial oxygen saturation. Previous studies suggested that SpO2 measurements show variability depending on the particular finger that is used for measurement. To date, no study has compared all fingers for SpO2 under hypoxemia and during continuous simultaneous monitoring with randomization of finger sensor placement. Objectives: The aim of this study was to assess the inter-finger variability of SpO2 values during sequential desaturation and step resaturation. Methods: Forty-three out of forty-five healthy participants (age 23.0 ± 1.8 years, BMI 24.0 ± 4.4 kg·m–2) completed the experimental assessment with short-term induced hypoxemia by consecutive inhalation of three prepared gas mixtures with reduced oxygen concentrations (14%, 12%, and 10%). SpO2 was measured continuously with the Masimo Radical-97 (Masimo Corp., Irvine, CA, USA) pulse oximeters. Results: The SpO2 measured on the thumb was lower than all other fingers by 0.6% to 0.7% SpO2, a systematic difference that is less than the clinically accepted accuracy of oximeters. No difference in SpO2 dynamics was found between any of the fingers during step resaturation. Conclusions: A systematic difference in measured SpO2 exists between the thumb and the other fingers during desaturation, which should be considered at least as well as the impact of the performance of a particular oximeter, sensor placement or anatomical variability.