When removing fluid from a vial, what must be done to prevent vacuum formation?

To prevent vacuum formation when removing fluid from a vial, it is essential to insert an amount of air that is equal to the fluid volume being withdrawn. This action balances the pressure inside the vial. When fluid is removed from a sealed vial, a negative pressure or vacuum can develop as the liquid occupies less space than before. By injecting air equal to the volume of fluid taken out, you maintain an equilibrium of pressure, ensuring that the liquid can be easily withdrawn without creating suction that might lead to difficulties in drawing out the fluid or potential contamination.

The process not only aids in maintaining the integrity of the vial’s contents but also minimizes the risk of damaging the vial or creating an unsafe situation, such as allowing air contaminants to enter. Understanding this principle is crucial for safe and effective sterile compounding practices.