Comparing Perfusion Index Between Fingers During Short-Term Hypoxemia: Implications for SpO2 Monitoring

Current modern pulse oximeters allow monitoring of perfusion index (PI), which is a non-invasive measure of peripheral perfusion. Although PI is a relatively newly measured vital parameter, it has already found application in many areas of clinical medicine. The aim of the study was to experimentally compare simultaneously measured PI between fingers on all five fingers of the hand during short-term hypoxaemia. Forty-three healthy volunteers (age 23.0 ± 1.8 years, BMI 24.3 ± 4.4 kg·m−2) successfully completed a whole breathing experiment with induced hypoxaemia. PI and peripheral blood oxygen saturation (SpO2) were measured continuously with a monitor of oxygenation Masimo Radical-97 (Masimo Corp., Irvine, CA, USA). The lowest median PI values during the initial stabilization phase were measured on the little finger (1.4%) and the highest on the thumb (2.1%). During the final stabilization phase, a significant increase in PI was observed with the following median values: 2.1% for the little finger, 3.0% for the ring finger, 3.2% for the middle finger, 3.1% for the index finger and 3.7% for the thumb. The relative increase in PI, comparing the median values between the final stabilization phase and the initial stabilization phase, ranged from 50% to 75% on average. Due to the differences in PI between fingers, the PI value should always be considered when measuring SpO2 to avoid possible misdiagnosis.