EFHSS Questions and Answers - Question Q00681

Why would sterilised packs be wet only on the inside; and what pressure should the chamber fall to in mbars?

Dear Ivette

There are numerous factors that can cause "wet packs".
Wet packs/moisture found on the outside of a package is generally the result of mechanical problems. Internal moisture is more complex. Since there is no simple monitor or indicator indicating wetness inside a pack it can't be detected until the pack is opened for use. Consequently it is important to evaluate wet packs situations. Potential causes of interior moistor can be:

• Defective vacuum drying system
• Insufficient drying time
• Material wet before packaging
• Overloaded trays, large packs
• Metal items positioned in a way allowing water pool or trap steam inside
• Material not permitted to cool ans equilibrate to room temperature

If after a thorough evaluation of the process and the technique no source of your wet pack problem(s) is found, you may consider to modify together with your sterilizer service the post-vacuum cycle from the usual post-vacuum (0.8 bar /10 minutes) to several vacuum differing in time.
In Praxis the following specialized post-vacuum program to solve wet packs, is working very satisfactory:

• First Evacuation -0.8 bar / 5 minutes
• Back to Atmosphere level for 2 minutes
• Second Evacuation -0.8 bar / 5 minutes
• Back to Atmospheric level for 4 minutes
• Third Evacuation -0.8 bar / 5 minutes
• Back to Atmospheric level for 5 minutes
• Fourth Evacuation -0.8 bar for 2 minutes
• Back to Atmospheric level - End of the cycle

You can shorten or make addings, until your packs are 100% dry!
If you look for standards for drying requirements, there are no clear guidelines. EN 868, "Packaging materials and systems for medical devices which are to be sterilized - Part 8 Reusable sterilization containers" discusses in Annex F how to test load drying. The EN describes the loading of the pack and how to weigh the pack before and after sterilization and drying cycle. The Norm allows a weight increase (or water content) as long as it is less than 0.2%.
I hope this is of some help!

Kind regards
Josy Holdener