Blood oxygen saturation can be divided into arterial oxygen saturation and venous oxygen saturation, in which the normal value of human arterial oxygen saturation is about 95%-100%, and the normal value of venous oxygen saturation is about 75%. While oxygen saturation mostly refers to arterial oxygen saturation, therefore, the oxygen saturation of 91% is lower compared to the normal value. Oxygen saturation mainly refers to the proportion of oxygenated hemoglobin bound to oxygen in the blood out of the total hemoglobin, which is an important indicator for determining vital signs. If the oxygen saturation level is 91%, which is lower than normal, it mostly suggests that the test subject has different degrees of hypoxia and should be given appropriate oxygen support. Clinically, oxygen saturation of 94% or less is considered to be insufficient oxygen supply, and less than 90% suggests that the person is in a state of severe hypoxia, which may result in hypoxemia or respiratory failure. Therefore, when the oxygen saturation is 91%, oxygen therapy should be given in time, and if necessary, a ventilator can be used to assist respiration, to avoid a continuous decrease in saturation to below 90%. If the oxygen saturation test result is 91%, you need to pay attention to it, you can go to the hospital in time for examination, to clarify the causes of low oxygen saturation, and then carry out targeted treatment as soon as possible, so as to avoid delaying the condition and preventing the worsening of symptoms, which may lead to danger.