Pleural effusion refers to the accumulation of fluid in the thoracic cavity. What is the harm of not pumping out pleural effusion depends on the amount of the patient’s pleural effusion, if it is a small amount of pleural effusion, there is generally no harm, if it is a medium or large amount of pleural effusion, it may cause lung compression to the patient, affecting the normal gas exchange. 1. small amount of pleural effusion: generally speaking, a small amount of pleural effusion does not pump out the patient’s lung function will not have a significant impact, if the patient does not have obvious symptoms such as chest pain, fever, etc., you can not need to pump out the fluid, and wait for the body to absorb on its own. 2. Medium or large amount of pleural effusion: when the patient’s pleural effusion reaches a medium amount, or even a large amount of pleural effusion, it will cause lung compression on the patient, affecting the normal gas exchange, and then the patient will have symptoms such as chest pain, chest tightness, and panic, etc., and if it is not pumped out, it may lead to infections, respiratory difficulties, and other hazards, and in severe cases, tissue and organ lesions may also occur. It is recommended that when the amount of pleural effusion reaches moderate or above, it is best to draw out the pleural effusion for laboratory examination and culture, etc., to clarify the cause of the disease, and carry out drainage and other therapeutic measures under the guidance of the doctor.