When you go to the hospital to measure the blood oxygen saturation, have you noticed which finger the blood oxygen sensor is clipped on? The index finger or the middle finger? Many nurses naturally clip the blood oxygen sensor on our index finger. But is the measurement from the index finger the most accurate?


As a standard monitoring indicator during anesthesia, monitoring of pulse oximetry is not a new technology. Since its implementation in the 1980s, its pulse oximeters have also incorporated more advanced technologies due to technological advancements, but these have primarily been efforts aimed at the accuracy of blood oxygen readings. In 2015 researchers published an interesting study showing the effect of each finger on the measurements.


The volunteers of this study are all healthy people, excluding some special circumstances such as pregnant women, people with low blood pressure. During the monitoring period, everyone used the same monitor, the same measurement posture, and the measurement was performed in the same location. Blood oxygen saturation measurements were taken on each of the ten fingers. Oxygen saturation was highest in the middle finger of the right hand in 370 results from 37 volunteers, while two left-handed volunteers had the highest level in the middle finger of the left. In a survey of medical staff, about 80% of medical staff will clip the blood oxygen sensor on the index finger. Because the index finger is supplied with blood by the deep palmar arch, which belongs to the artery, but the middle finger is supplied by the ulna as well as the artery. The study also showed that each finger had a different perfusion index, with the middle finger showing the highest perfusion index regardless of whether it was normal or hypoperfused. Due to the limited number of volunteers, no significant differences in blood oxygen saturation were measured between the fingers.


The researchers say the study of differences in blood oxygen saturation between fingers may not be clinically important, but in the context of low perfusion, it is meaningful. If you are accustomed to using the right hand, the middle finger of the right hand undoubtedly has the highest blood oxygen saturation. So the researchers say they believe the middle finger of the dominant hand may provide the most accurate blood oxygen saturation measurement.


Next time you go to the hospital to measure your blood oxygen saturation, if you think the result is not very accurate, you can try to measure it again with the middle finger of your dominant hand to see if your blood oxygen saturation is normal.