Inter-Finger Variability of SpO₂ During Hypoxemia and Step Resaturation

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.