What is the typical suction pressure used in many systems, and when is suction applied?

• A. -5 cm H2O; suction is applied when indicated
• B. -20 cm H2O; suction is applied when indicated (persistent air leak, incomplete expansion, or significant drainage)
• C. -40 cm H2O; suction is applied after 24 hours
• D. -10 cm H2O; suction is applied only for effusion

Answer: (B)

Suction is used in chest drainage to actively remove air and fluid and help the lung re-expand by creating negative pressure in the pleural space. The typical setting is about -20 cm H2O, and suction is applied when there are practical indications such as a persistent air leak, incomplete lung expansion, or significant drainage. This level provides enough negative pressure to assist drainage without risking tissue injury or worsening a leak. Using too little suction (for example, much less than -20) may not achieve re-expansion or adequate drainage, while too much suction (a much higher negative pressure) can cause pain, tissue injury, or harmful negative pressures. The indications—persistent air leak, incomplete expansion, or significant drainage—mirror common clinical scenarios where active suction aids recovery.