Pulmonary encephalopathy is mainly caused by hypoxia and carbon dioxide retention.
Carbon dioxide retention can cause hypercapnia, and the breathing of patients with chronic hypercapnia is maintained mainly 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 centre disappears, leading to obstructed breathing, increased carbon dioxide retention and deterioration of the patient’s condition.