Type II respiratory failure refers to hypercapnic respiratory failure. Respiratory failure is a syndrome in which pulmonary ventilation and/or gas exchange is severely impaired for various reasons, so that sufficient gas exchange cannot be maintained even at rest, resulting in hypoxemia with (or without) hypercapnia, which in turn leads to a series of pathophysiological changes and corresponding clinical manifestations. Respiratory failure is categorized into type I and type II respiratory failure, which is judged by the blood gas analysis value. When the partial pressure of oxygen is less than 60 mmHg and the partial pressure of carbon dioxide is more than 50 mmHg, it is classified as type II respiratory failure, which is caused by insufficient alveolar ventilation. The degree of hypoxemia and hypercapnia are parallel to the degree of hyperventilation alone, and the hypoxemia is more severe in the presence of ventilatory dysfunction, as in chronic obstructive pulmonary disease (COPD). Type II respiratory failure indicates that the patient’s condition is more serious.