An oxygen saturation between 85% and 90% is dangerous and indicates that the patient’s respiratory gas exchange function is severely compromised. Oxygen saturation, is the degree of arterial blood oxygen and blood hemoglobin combination of a test indicator. A decrease in oxygen saturation generally indicates a lack of oxygen, a sign of respiratory dysfunction and abnormalities in the body’s gas exchange function. In general, when the blood oxygen saturation level is 85%-90%, the patient will have shortness of breath, body weakness, decreased physical fitness and other physical discomfort symptoms appear. If an acute respiratory infection occurs and the blood oxygen saturation level is between 85% and 90%, it indicates that the respiratory function is seriously impaired, which may lead to damage to the heart, brain and other important organs. At this point, active treatment is required, usually using oxygen infusion, hyperbaric chamber and other treatments. If the disease continues to be unrelieved, even respiratory intubation or mechanical ventilation treatment is required. When blood oxygen saturation is low, it is important to seek medical attention and follow the doctor’s instructions for examination and treatment.