Low oxygen saturation should be given etiological treatment, as follows: 1. Firstly, when the oxygen saturation is low, the airway obstruction condition should be removed, the airway blockage should be lifted, and the back patting to remove sputum should be strengthened; 2. Find the cause, if it is caused by infection factors, choose appropriate and sensitive anti-infective drugs for treatment, whether anti-bacterial, fungal or viral treatment, which is the necessary treatment measure to treat lung infection; 3. Perform Oxygen therapy, in the hospital oxygen therapy means relatively more, there are nasal plug oxygen, mask oxygen, non-invasive mechanical ventilation, invasive mechanical ventilation, which are the treatment means to improve hypoxia. In severe ARDS patients or patients with heart failure who have decreased oxygen saturation and hypoxemia, ECMO can also be used clinically to improve the oxygen supply. Oxygen therapy should pay attention to the setting of supply oxygen flow rate and oxygen concentration supply. Oxygen flow rate less than 4L/min belongs to low flow rate oxygen supply, and greater than 4L/min belongs to high flow rate oxygen supply. Oxygen concentration less than 30% belongs to low concentration oxygen absorption, oxygen concentration more than 50% belongs to high concentration oxygen absorption, and between 30%-50% belongs to medium concentration oxygen absorption oxygen therapy.