Which finding indicates that a chest-tube drainage system is functioning properly?

• A. The presence of tidaling in the water-seal chamber.
• B. Continuous absence of bubbling.
• C. No drainage for 24 hours.
• D. Constant negative pressure.

Answer: (A)

Tidaling in the water-seal chamber shows the chest-tube system is patent and connected to the pleural space. As the patient breathes, intrapleural pressure changes cause the water level in the seal to rise and fall—this movement is tidaling. It demonstrates that air and fluid can move between the pleural space and the drainage system, which is the normal function of the setup. If tidaling stops, it can signal a blockage, kinking, or lung re-expansion with no pressure change, indicating a potential problem with drainage. Other signs aren’t as reliable indicators of proper function: lack of bubbling in the suction area doesn’t definitively prove the system is working, no drainage for a day can mean obstruction or that the lung has shrunk or resolved, and constant negative pressure is a setting, not a direct, always-present sign of correct operation. So the presence of tidaling best reflects that the chest-tube drainage system is functioning properly.