The purpose of a chest drainage device is to help reestablish normal vacuum pressures by removing air or fluid in what manner?

• A. In a closed, one-way fashion
• B. In an open, bidirectional fashion
• C. In a valve-controlled two-way fashion
• D. In a passive capillary fashion

Answer: (A)

The main idea is to reestablish negative intrapleural pressure by letting air or fluid escape without letting it flow back in. A chest drainage system achieves this with a closed setup that provides a one-way path for drainage. The underwater seal (or a one-way valve) allows air and fluid to leave the pleural space and enter the collection chamber, but it prevents air from re-entering the pleural space as atmospheric conditions change or suction is interrupted. This one-way, closed design maintains the vacuum needed for the lung to re-expand.

Open or bidirectional systems would risk air or fluid flowing back into the pleural space, defeating the suction. A two-way valve could still allow backflow under certain pressures, and a passive capillary approach doesn’t generate the needed suction or control.