In a three-chamber chest drainage system, what is the purpose of the water-seal chamber?

• A. To provide active suction to drain air.
• B. To act as a one-way valve that prevents air from re-entering the pleural space.
• C. To store the collected fluid indefinitely.
• D. To measure drainage volume.

Answer: (C)

The water-seal chamber provides an underwater barrier that acts as a one-way valve. Air from the pleural space can escape through the water as bubbles, but the water column prevents air from re-entering the chest, protecting against backflow and re-collapse. This makes it the key component for allowing drainage while preventing air from re-entering, not for storing fluid. The collection chamber handles fluid drainage, and the suction-control chamber supplies regulated negative pressure. Observing bubbling in the water seal helps detect an air leak.