Arterial oxygen saturation of 85% may be life threatening. Venous oxygen saturation of 85% is not dangerous. Oxygen saturation is the percentage of the volume of hemoglobin in the blood that is oxygenated to the total volume of hemoglobin that can be combined with oxygen, and is an important physiological parameter of the respiratory cycle. In normal people, arterial oxygen saturation should not be less than 94%, and less than 94% is insufficient oxygen supply. Blood oxygen 80%-85% belongs to severe hypoxia, should be timely treatment, otherwise it will lead to respiratory failure. The normal value of venous oxygen saturation is between 60%-85%, so there is no danger of venous oxygen saturation of 85%. When the supply of oxygen is insufficient, it leads to disorders of cellular metabolism and hypoxia, which have a huge impact on the organism. In the case of hypoxia, first of all, there is a compensatory acceleration of the heart rate, an increase in the number of heartbeats, an increase in cardiac output, and the circulatory system compensates for the lack of oxygen content in a highly dynamic state. At the same time, redistribution of blood flow occurs, selectively dilating the cerebral and coronary vessels to ensure an adequate blood supply. In severe hypoxia, accumulation of lactic acid occurs in the endocardium, which reduces adenosine triphosphate synthesis, leading to myocardial depression, premature contraction, bradycardia, decreased blood pressure and cardiac output, and arrhythmias such as ventricular fibrillation or even leading to cardiac arrest. When the blood oxygen is 85%, it is necessary to actively carry out oxygen therapy and observe the patient’s vital signs changes. If cough, sputum, dyspnea and other symptoms appear, timely resuscitation is needed, and mask high-flow oxygen or other non-invasive assisted ventilation should be given immediately. If the patient is comatose and cannot regain consciousness after oxygen administration, the patient should be given endotracheal intubation and ventilator-assisted ventilation, and 100% pure oxygen therapy, and then change to appropriate concentration of oxygen therapy after the primary disease and hypoxia improve. If obvious discomfort occurs, it is recommended to consult a doctor in time.