Chest Drainage Systems

A chest drain is not simply a tube that “takes fluid out.” It restores a pressure relationship that the lung needs in order to remain expanded. Normally, the pleural space contains only a thin film of fluid and has sub-atmospheric pressure. This negative pressure keeps the visceral and parietal pleura closely apposed. Air entering the pleural space, blood, pus, or a large volume of fluid disrupts that relationship. The lung may partially or completely recoil. The drainage unit creates a controlled exit route. In a water-seal system, air can leave the pleural space but atmospheric air cannot freely travel back toward the patient. The water seal therefore functions as a one-way valve. Fluid moves by gravity into the collection chamber. Suction, when prescribed, adds negative pressure through the suction-control mechanism; it is not automatically required for every patient. A useful mental model is a one-way doorway between the pleural space and the collection unit: material can leave, but the room should not refill with outside air. That doorway is safe only when the unit remains upright, intact, and below the...