Pulse oximetry, or blood oxygen saturation, has a normal range of 95% to 100%, with greater than 90% considered good and less than 90% considered hypoxic. Oxygen saturation is the ratio of the actual oxygen content of hemoglobin to the maximum amount of oxygen bound to hemoglobin in the blood of the finger, as checked by an instrument. It fluctuates between 95% and 100% in normal people. Oxygen saturation may decline due to body movement, external environment, and disease. When it is lower than 95% and not lower than 90%, the oxygen saturation is average and mild hypoxia may exist. When the oxygen saturation is lower than 90%, it is a hypoxic state, which requires active oxygen intake and searching for the etiology of hypoxia, including insufficient oxygen supply to the body and oxygen use disorder. Normal oxygen saturation is 95%~100%, which may fluctuate a little due to instruments, environment and body activities. If hypoxia occurs, it is recommended to seek medical attention promptly and follow the guidance of specialized doctors.