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

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.