Lung effusion, or pleural effusion, is mainly related to fluid exudation and leakage, and the causes of the corresponding conditions mainly include intrapulmonary infections, tumors, decreased cardiac function, and trauma. 1. Intra-pulmonary infection: Infectious diseases such as pneumonia and tuberculosis will cause stimulation to the pleura, which will lead to the exudation of liquid from capillaries into the chest cavity, and then accumulate in the chest cavity and cause effusion. 2. Tumor: Intra-lung tumor mainly refers to lung cancer, which will cause invasion to the surrounding pleura and affect the blood vessels, which will also cause the fluid to accumulate in the pleural cavity, and further lead to the production of pleural effusion. 3. Decrease in heart function: Decrease in systolic and diastolic function of the heart will affect the return of blood, causing the increase of venous pressure in the capillaries, leading to blood leakage, and will also cause corresponding changes. 4. Trauma: Trauma directly damages the capillaries and lymphatic vessels, causing fluid to enter the chest cavity directly, resulting in pleural effusion. The presence of a large amount of pleural effusion accompanied by obvious respiratory limitation, need to consult a doctor in time for observation, after diagnosis of the condition under the guidance of the clinician to carry out standardized treatment.