On the equipment for oxygen intake, there is a flow meter that patients need to adjust themselves. So, what is the flow rate of oxygen for patients on long-term oxygen therapy? Prof. Shen Ning: For patients with chronic obstructive pulmonary disease, we put a lot of emphasis on low-flow oxygenation. What do you mean by low flow rate? Generally speaking, the flow rate for patients with chronic obstructive pulmonary disease is below 2 liters/minute. There are scales on the flow meter, and adjusting the flow rate at 1-2 liters/minute is fine. However, in some cases, such as when the patient is really severely hypoxic, the flow rate can be raised for a short time. So what is the concentration of oxygen intake? Is it pure oxygen? Prof. Shen Ning: We generally require low concentration of oxygen for patients with chronic obstructive pulmonary disease, with oxygen concentration below 35%. Oxygen concentration and oxygen flow rate are related and can be learned by converting the relationship, generally the oxygen concentration of 3.5 l/min flow rate is 35%. In the home, the oxygen concentration generated by the oxygen machine is above 90%, and by adjusting the oxygen flow rate, the oxygen concentration inhaled by the patient can be reduced to less than 35%, which will not be pure oxygen. Low-flow, low-concentration oxygen intake can fully achieve the purpose of treatment. Do patients with chronic obstructive pulmonary disease use nasal catheters for oxygen inhalation instead of using masks like some inpatients? Prof. Shen Ning: Using nasal cannula to administer oxygen is the most routine method at home because it is simple to operate and easy to clean and maintain. And if you are in the hospital, we will have some other devices to provide long-term oxygen to the patients. Why do you always emphasize low-flow, low-concentration oxygen? Prof. Shen Ning: Because if the oxygen concentration is too high, it may lead to carbon dioxide retention, which means that the patient with chronic obstructive pulmonary disease inhales more oxygen and cannot get rid of the carbon dioxide. Some people are worried that long-term oxygen inhalation will not lead to oxygen toxicity? Prof. Shen Ning: There is indeed a possibility if 100% pure oxygen is inhaled for a long time, but oxygen therapy uses nasal catheter oxygen, and even if the oxygen flow is adjusted to the maximum, oxygen toxicity is unlikely to occur. Carbon dioxide retention may occur when the oxygen concentration is too high, but it is not oxygen toxicity. What are the manifestations of carbon dioxide retention? Prof. Shen Ning: In mild cases of carbon dioxide retention, carbon dioxide will anesthetize the central nervous system, and the patient will initially experience sleep inversion, such as being quite alert during the day but now sleeping all the time, while not being able to sleep at night. When the condition is very severe, the patient may become comatose. How can patients or family members detect the possible presence of carbon dioxide retention at an early stage? Prof. Shen Ning: In the early stage of carbon dioxide retention, the patient only has some behavioral changes, such as problems with sleep. And these problems are often easy to be ignored by patients or family members, thinking that it is due to the long time of illness, low activity, poor sleep, etc. And once a coma occurs, it is already very serious by the time they get to the hospital. Therefore, it is difficult for the patients themselves or their families to find out by themselves whether carbon dioxide retention has occurred. Therefore, the most important thing is to avoid the occurrence of carbon dioxide retention, and the most fundamental means is not to easily adjust up the oxygen flow and oxygen concentration. Is it possible to detect carbon dioxide retention by regular review? Prof. Shen Ning: Patients will have their blood gases checked during the review, which will clearly show the partial pressure of oxygen and carbon dioxide. If the patient has carbon dioxide retention, it will be clearly shown at the review. However, in most cases, if patients strictly follow the oxygen therapy regimen prescribed by their doctors, carbon dioxide retention rarely occurs. However, when the condition of a patient with chronic obstructive pulmonary disease worsens, carbon dioxide retention may also occur due to aggravated infection, heart failure, sputum blockage and asphyxia, and so on.