Respiratory failure can be classified according to its causes into four types. The first type involves diseases of the airway such as bronchial inflammation, bronchiectasis, and foreign body obstruction, leading to insufficient ventilation. The second type is due to lung tissue diseases, such as pneumonia, severe tuberculosis, emphysema, diffuse pulmonary fibrosis, adult respiratory distress syndrome, etc., causing a state of hypoxia and carbon dioxide retention due to ventilatory defects. The third type includes pulmonary vascular diseases, such as pulmonary vascular embolism and pulmonary infarction, which cause part of the venous blood to flow into the pulmonary veins, resulting in hypoxia. The fourth type involves diseases of the thoracic cage such as chest trauma, surgical trauma, pneumothorax, and pleural effusion, which affect daily activities and lung expansion, leading to insufficient lung ventilation and resulting in respiratory failure.