What is the meaning of negative pressure drainage 24 hour drainage volume

The amount of blood that flows through a drain in a day. Negative pressure drainage 24 hours of drainage is through the drainage device a day and the flow surface of the amount of blood, negative pressure drainage device is through the drainage tube to exert negative pressure way, so that the surgical area of the exudate or a small amount of bleeding drainage out of the body. Commonly when the drainage flow is less than 50ml per 24 hours, it can be removed.