By Nancy Chobin, RN, AAS, ACSP, CSPM, CFER
Q: I am reviewing AAMI ST79 2010. We recently had two autoclaves installed in our new facility. As I recall, we must do testing as the following:
- Three leak tests
- Three Bowie–dick tests
- Three biological tests
Should this testing be followed by product testing? Can you please refresh my memory on this?
A: The Association for the Advancement of Medical Instrumentation (AAMI) recently updated its Comprehensive Guide to Steam Sterilization and Sterility Assurance in Healthcare Facilities (ST-79) 2017. You should make sure you have this updated document available for reference.
AAMI's ST-79 states, “It is recommended that biological monitoring of steam sterilization cycles be performed routinely (weekly, preferably daily), for every load containing implants, and for qualification testing. Qualification testing is performed when a new sterilizer is installed, when a sterilizer is relocated, when a sterilizer malfunctions, when a sterilizer or its utilities has had a major repair, and after sterilization process failure that requires a major repair.”
If your sterilizer is designed to be used with multiple types of cycles (e.g., gravity displacement at 250 degrees Fahrenheit [121 degrees Celsius], dynamic-air-removal at 270 degrees Fahrenheit to 275 degrees Fahrenheit [132 degrees Celsius to 135 degrees Celsius], etc. then each type of cycle should be biologically monitored at least weekly, preferably daily (per ANSI/AAMI ST79).
If there are cycles on the sterilizer that are never used, they should be removed from the list of cycles so that they do not have to be tested and so that personnel do not inadvertently select an incorrect cycle. I is not necessary to test every cycle time (e.g., 8 minutes, 12 minutes) for each specific type of cycle (e.g., dynamic-air-removal at 270 degrees F Fahrenheit to 275 degrees Fahrenheit [132 degrees Celsius to 135 degrees Celsius]), just the shortest time for each type of cycle (e.g., 4 minutes at 270 degrees Fahrenheit [132ºC], 3 minutes at 275 degrees Fahrenheit [135 degrees Celsius]).
Sterilizer Qualification Testing: BI PCD testing (Process Challenge Device or test pack) should also be performed when a sterilizer is installed or relocated, after a malfunction requiring a major repair of the sterilizer or its utilities, and after a sterilization process failure necessitating major repairs. To establish a baseline for the sterilizer’s performance, the BI PCD tests should be performed before the Bowie-Dick tests. All of the test results must be satisfactory before the sterilizer can be put into use or back into routine use.
According to AAMI, the testing in this order represents the greatest challenge to the sterilizer. Also, the table refers to sterilizers larger than 2 cubic feet of chamber size.
The Definitive Guide to Steam Sterilization Cycles states, “Vacuum leak tests, (which are different from the Bowie-Dick tests) are used to determine the air-tight integrity of a pre-vacuum autoclave’s chamber and plumbing system. This test does not use a test pack, it is performed in an empty sterilizer. This test exposes the autoclave’s plumbing and components to vacuum conditions and measures how much vacuum depth was lost over a given period of time. A typical Vacuum Leak Test Cycle will consist of three vacuum/pressure pulses followed by a 15-minute dwell period at deep vacuum. Upon completion of the cycle, a leak rate will be displayed on the autoclave’s control screen in units such as psia/min, kPa/min, mbar/min, or mmHG/min. The pass/fail criteria for a Vacuum Leak Test is ultimately determined by the specifications of the user, but industry standards call for an average leak rate of 1mmHG/min or less."
You should consult with your sterilizer manufacturer regarding the frequency of performing this test. Test results should be documented and saved. As noted in the table above, this testing is not needed when qualification testing is performed.
Product testing, as defined by AAMI, “Consists of a series of procedures used to verify that manufacturer's written instructions for use (IFU) can be successfully performed in the user facility." There are specific guidelines for performing product testing. You should consult AAMI ST-79 for additional information.
For sterilizers with a chamber size of less than 2 cubic feet (table-top steam sterilizer), sterilizer qualification testing after installation, relocation, major repairs, or a sterilization process failure necessitating major repairs should be performed with a BI PCD in a fully loaded chamber. This type of testing creates the greatest challenge to the limited amount of sterilant that enters the chamber of a table-top sterilizer. The PCD should be placed on its edge if it is a small pack or flat if it is a tray or large pack and positioned in the coldest area of the sterilizer chamber, as determined by the sterilizer manufacturer. This placement creates the most severe challenge to the sterilizer. The “cold point” in a sterilizer varies somewhat, but it is normally in the center of the load towards the front of the chamber.
For qualification testing of table-top sterilizers, three consecutive cycles should be run, one right after the other, according to the sterilizer manufacturer’s instructions. This testing should be performed for all cycles being routinely used, as in the case of routine BI monitoring. At the end of each cycle, the CI should be removed from the PCD and the results recorded. The BI should be removed from the PCD and incubated according to the BI manufacturer’s instructions. The remainder of the items in the test load should be quarantined until the BI results are known.
For other methods of sterilization (e.g., low-temperature gas plasma, ozone), you should consult with the sterilizer manufacturer regarding the testing of these sterilizers.
In summary, Qualification testing after sterilizer installation, relocation of major repair is recommended to ensure the sterilizer is performing properly in your facility with your utilities. The AAMI recommended protocol for this testing should be included in a policy and procedure for staff reference. I have found it helpful to make a reference sheet for staff (laminated) and posted near the sterilizers with the testing needed. Documentation of all qualification testing is required to verify compliance with this standard.
Nancy Chobin, RN, AAS, ACSP, CSPM, CFER, is a sterile processing consultant and educator.
ANSI/AAMI: ST79:2017. Comprehensive Guide to Steam Sterilization and Sterility Assurance in Healthcare Facilities.
Basics of Sterile Processing 6th Edition. Sterile Processing University, LLC. Lebanon, N.J.
The Definitive Guide to Steam Sterilization Cycles. Consolidated Sterilizer Systems. www.consterile.com.