A pleural effusion of 4.5 centimeters may be 500 to 800 milliliters of fluid if it is in the chest of an adult. A pleural effusion of 4.5 centimeters may be 500 to 800 milliliters of fluid in an adult, which is a large amount of fluid. In a child, the amount of fluid may be less than 500 to 800 milliliters, but the pleural effusion is much more serious compared to the small chest cavity of a child. A pleural effusion of 4.5 centimeters, in both adults and children, is a moderate to large amount of pleural effusion that requires treatment, which can be done by puncture and aspiration or closed chest drainage to relieve the symptoms while actively looking for the cause of the condition and treating the cause. For moderate to large amounts of pleural effusion of 4.5 centimeters or more, it is recommended to go to the thoracic surgery department of a regular hospital as soon as possible for treatment to avoid delaying the condition.