Pulmonary effusion, or pleural effusion, has many causes. The main causes are pneumonia, tuberculosis, cancer, autoimmune diseases, as well as hypoproteinemia due to various diseases, heart failure due to heart disease, chest trauma and chest hemorrhage. Pneumonia patients with poorly controlled inflammation can lead to the occurrence of eventual exudative pleural effusions, which can gradually increase with respiratory distress and fever if not disposed of in a timely manner. Tuberculosis diseases such as tuberculosis, tuberculosis pleurisy, tuberculosis abscess thorax, etc., have different manifestations depending on the duration of the disease. Most patients with tuberculosis are affected by the pleura, and the pleural effusion results from the accumulation of inflammatory fluid in the chest cavity over time. Most of them are clear fluid or yellowish. In the case of pleural effusion caused by cancer, the fluid is mostly blood-colored, which may be caused by the invasion of the pleura by cancer. Pleural effusions caused by autoimmune diseases are less common and are mostly clear and transparent in color. Hypoproteinemia, which reduces the colloid osmotic pressure in the human blood, therefore causes fluid to collect in the chest cavity and form pleural effusion. Traumatic pleural effusions are mostly caused by rupture and bleeding of the chest wall or blood vessels in the chest cavity. Therefore, pulmonary effusion, or pleural effusion in medical terms, has more causes and requires different subsequent treatments depending on the etiology.