Inter-Finger Variability of SpO₂ During Hypoxemia and Step Resaturation

Area of Science:

• Medical Devices
• Physiology
• Clinical Measurement

Background:

• Pulse oximetry is a standard non-invasive method for monitoring peripheral blood oxygen saturation (SpO2).
• Previous research indicates potential variability in SpO2 readings based on the finger used.
• No prior studies have comprehensively compared all fingers for SpO2 during simultaneous monitoring under induced hypoxemia.

Purpose of the Study:

• To investigate inter-finger variability of SpO2 measurements.
• To assess SpO2 dynamics during sequential desaturation and step resaturation across all fingers.

Main Methods:

• Healthy participants (n=43) underwent short-term induced hypoxemia via inhalation of low-oxygen gas mixtures (14%, 12%, 10%).
• Continuous SpO2 monitoring was performed simultaneously on all fingers using Masimo Radical-97 pulse oximeters.
• Randomized finger sensor placement was employed during the desaturation and resaturation phases.

Main Results:

• The thumb consistently showed lower SpO2 values (0.6%–0.7%) compared to other fingers during desaturation.
• This systematic difference is within the accepted clinical accuracy range of pulse oximeters.
• No significant differences in SpO2 dynamics were observed between fingers during step resaturation.

Conclusions:

• A systematic difference exists in SpO2 measurements between the thumb and other fingers during desaturation.
• This thumb-to-finger variability should be considered alongside oximeter performance and sensor placement.
• Understanding inter-finger differences is crucial for accurate SpO2 interpretation in clinical settings.