What is the purpose of the water seal chamber in a chest tube drainage system?

• A. To collect drainage
• B. To prevent air from flowing to the client
• C. To provide suction
• D. To measure pleural pressure

Answer: (B)

The water seal chamber acts as a one-way valve between the pleural space and the atmosphere. A small column of sterile water creates a barrier that air from the chest must bubble through as it flows out through the drainage system. This setup allows air and fluids to exit the chest while preventing outside air from being drawn back into the pleural space during inhalation, which would risk reintroducing a pneumothorax. The pattern of bubbling in the water seal can also help identify an ongoing air leak. It's important to note that drainage collection happens in a separate chamber, and suction (when used) is provided by the suction control chamber; the water seal itself does not collect drainage or provide suction.