Pulmonary effusion is just a colloquial term, the medical name is pleural effusion, the normal human chest cavity would have a few milliliters of fluid, the pathological state, but also increased to hundreds or even thousands of milliliters or more. There are more causes of pleural effusion. For example, pneumonia, tuberculosis, hypoproteinemia caused by various diseases, cancer, autoimmune diseases, bleeding from chest trauma, etc. Pneumonia, if left untreated or treated poorly, can lead to eventual pleural effusion. Patients with tuberculous disease have pleural effusions that are mostly clear fluid and yellowish in color. Patients with tuberculous abscess chest slowly also form fibrous plates due to the absorption and mechanization of cloudy pus, which adheres to the surrounding tissues leading to thoracic collapse and deformity and may eventually require surgery to remove the fibrous plates. Pleural effusion caused by cancer, where the fluid color is mostly bloody, should be combined with other symptoms and examinations to identify the primary disease for targeted treatment. Pleural effusion due to autoimmune diseases occurs less frequently and its color is mostly clear and transparent. Traumatic pleural effusions are mostly caused by ruptured blood vessels in the chest wall or chest cavity that bleed. Therefore, pulmonary effusion, which is caused by excessive fluid occupying the chest cavity with limited capacity, leads to compression of the lung and difficulty in air entering the body, which will produce initial symptoms such as chest tightness and difficulty in breathing. If not treated in time, it will subsequently lead to other more serious consequences.