Which of the following is a unit used for suction pressure in chest tube management?

• A. Inches of water
• B. Centimeters of water (cm H2O)
• C. Millimeters of mercury
• D. Pascal

Answer: (B)

Suction pressure in chest tube management is expressed in centimeters of water (cm H2O) because the negative pressure applied to the pleural space is a small, fluid-based pressure best described by how high a column of water would need to rise. This unit aligns with how bedside suction regulators and the water-seal drainage systems are calibrated, making it easy to set and monitor safely. Other units don’t fit this context: millimeters of mercury measures gas pressure in vacuums and isn’t practical for the small, liquid-based pressures used here; pascals are SI units that aren’t commonly used on the bedside for chest tube suction; inches of water can be used in some systems but cm H2O is the standard in modern practice.