What type of fluid is used to fill the water-seal drainage before insertion?

• A. Normal saline
• B. Sterile saline
• C. Antibiotic solution
• D. Sterile water

Answer: (D)

A water-seal drainage system relies on a one-way barrier created by a column of fluid in the seal chamber. Air from the pleural space can escape through the chest tube, but outside air cannot re-enter because it would have to push through the fluid column. Therefore, the seal is filled with sterile water. Sterile water is the standard choice because it provides a pure, non-solute barrier and maintains sterility, avoiding introduction of solutes or contaminants. Using other fluids like saline isn’t preferred for the seal, since the system is designed around a water column. Filling with sterile water ensures the seal functions properly from the moment the chest tube is inserted.