Proper cleaning, rinsing, and drying of medical devices are critical steps to successful low temperature sterilization. While the importance of cleaning is obvious to most people, why is drying so significant?
To understand this, we should first discuss how water behaves under low pressure. Low temperature sterilization starts by evacuating the chamber of all its air. Lower pressure favors the passage of water into the vapor phase – it evaporates. This water vapor is in turn removed from the chamber by the sterilizer pump. This results in a longer time for the sterilizer to achieve its target pressure, potentially triggering a cycle abort if this takes longer than the prescribed duration.
Then there is more. Zooming in on a single water molecule, it requires heat to free itself from the liquid phase and get into the vapor phase. This heat is taken from other nearby water molecules that make up the larger droplet or from the load. This process cools down the droplet and its immediate surroundings. The water droplet can even freeze! These cold spots cause excessive and localized condensation of the hydrogen peroxide solution. This can reduce the cycle lethality and even leave residual sterilant droplets in the load at the end of the cycle.
How dry is dry enough? A good guideline is that no visible water should be present, even tiny droplets. But be mindful that water gets trapped in all sorts of locations where it is not visible: in the body of some devices, under tray corners/brackets/gaskets, and even in damaged instruments. All this hidden water also needs to be removed prior to sterilization.
Drying is important because water in the load can result in annoying cycle aborts and create risks for the SPD workers and patients. Fortunately, with the right tools, processes, and education, drying problems can be solved.