Does Measurement Site Matter? A Comparison Between Finger, Forehead, and Toe Pulse Oximetry Measurements in...

Accurate peripheral blood oxygen saturation (SpO₂) measurements are critical for evaluating sleep patients, particularly those with frequent desaturations due to pathological breathing events. We compared synchronised SpO₂ measurements obtained from three anatomical sites (finger, forehead and toe) in patients undergoing routine Type 1 polysomnography (PSG) to assess site-related variability. Continuous and simultaneous pulse oximetry recordings from 41 sleep patients were synchronised with PSG data and scored for SpO₂ desaturations (≥ 3% and ≥ 10 s), signal dropouts and artefact occurrences. Forehead and toe SpO₂ measurements were compared against finger oximetry, the standard PSG oximetry site. Significant differences were observed between anatomical sites for mean SpO₂ (p < 0.01), mean SpO₂ desaturations per hour (p < 0.01) and time spent below an SpO₂ level of 95% during total sleep time (p < 0.01). Forehead pulse oximetry demonstrated the highest mean SpO₂, the fewest SpO₂ desaturations per hour and the least artefact occurrences (p = 0.024), while finger oximetry exhibited the most signal dropouts (p < 0.01). Finger and toe pulse oximetry showed the strongest concordance for SpO₂ desaturations per hour (r = 0.948). Observed differences in SpO₂ measurements are likely due to perfusion variability between peripheral and core circulation during sudden blood pressure oscillations associated with sleep disordered breathing. Our findings highlight that anatomical site choice for measuring SpO₂ during PSG may have significant implications in the severity classification, diagnosis and treatment of sleep disorders; especially for limited channel sleep studies that rely primarily on oximetry. Further research is required to determine which anatomical site reflects true arterial oxygenation in sleep patients.