Patients with emphysema are recommended to choose a 5L oxygen machine as it is more appropriate, because the main symptom of emphysema is shortness of breath after activity, and patients often have difficulty in breathing and lack of oxygen. At the initial stage, it is mainly hypoxia, which is manifested as type I respiratory failure, and then it is necessary to give to improve the oxygen flow, and it is more appropriate to apply the oxygen machine. At this time, the main purpose is to increase the oxygen flow to make the patient’s oxygen saturation reach more than 90%, so the oxygen flow can be increased appropriately, and it is more appropriate to use 3-5L oxygen flow. If in more severe emphysema, combined with type II respiratory failure, it is necessary to appropriately reduce the oxygen flow rate and give low-flow oxygen, applying 1-3L/min oxygen flow rate is more appropriate. So if it is an initial emphysema patient with type I respiratory failure, it is recommended to choose at least a 5L oxygen concentrator, while a patient with type II respiratory failure can also choose a 3L oxygen concentrator if the family conditions are limited.