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.

Department of Biomedical Technology Faculty of Biomedical Engineering Czech Technical University Prague 27201 Kladno Czech Republic

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