Pulmonary encephalopathy is mainly caused by hypoxia and carbon dioxide retention.
Carbon dioxide retention can cause hypercapnia, and the breathing of patients suffering from chronic hypercapnia is mainly maintained by the stimulation of hypoxia. If high concentrations of oxygen are inhaled and the hypoxic state is relieved, the stimulating effect of hypoxia on the respiratory center disappears, resulting in obstructed breathing, increased carbon dioxide retention and deterioration of the patient’s condition.