Example of a failed Bowie-Dick test.
By Nancy Chobin, RN, AAS, ACSP, CSPM
Q: Recently we had a consultant visit our department. She said I was performing the Bowie-Dick test wrong. I place the test pack on top of a wire basket which is placed over the drain line. This is how I was shown to do the test and we all do it the same way. The consultant could not explain why this is wrong. Can you explain the correct process and why?
A: The Association for the Advancement of Medical Instrumentation (AAMI)'s ANSI/AAMI Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities, ST79:2010, & A1:2010, & A2:2011, & A3:2012, & A4:2013 describes the Bowie-Dick test procedures in detail. You should have a policy and procedure for performing the Bowie-Dick test because it is an important indicator of the sterilizer’s performance.
What is a Bowie-Dick test? It is a test of the sterilizer’s air removal system. According to AAMI, “A Bowie-Dick test is conducted every day, before the first processed load, because it is a sensitive and rapid means of detecting air leaks, inadequate air removal, inadequate steam penetration, and non-condensable gases (e.g., air or gas from boiler additives). Insufficient air removal in a dynamic-air-removal sterilizer, particularly a pre-vacuum cycle, can defeat sterilization and result in nonsterile supplies if undetected.
Bowie-Dick testing should be performed on dynamic-air-removal sterilizers on the pre-vacuum cycle. The test should be performed each day the sterilizer is used and always before the first processed load. If the sterilizer is used continuously, then the test should be performed at the same time each day. If you have a steam-flush-pressure pulse sterilizer, check with your sterilizer manufacturer if Bowie-Dick testing is recommended.
Procedure: The Bowie-Dick test should be performed daily, whenever the sterilizer is in use, and before the first processed load. If your sterilizers remain on continuously, you should perform the test at the same time each day. A Bowie-Dick test pack uses a Class II chemical indicator for the test. Most facilities use a manufactured Bowie-Dick test pack. The pre-assembled pack provides consistency in pack preparation. (NOTE: AAMI ST-79 does provide guidance on preparation of a test pack made at the facility using surgical towels). There are single use Bowie-Dick tests and reusable tests. Always follow the test pack manufacturer’s instructions for use, storage and interpretation.
The test pack’s expiration date should be checked first. Never use an outdated test pack. Then identify the pack with the sterilizer number (if you have more than one steam sterilizer). You can affix a lot control label to the outside of the pack. This will prevent mixing up the tests.
According to AAMI ST-79, “the test pack should be placed horizontally in the front, bottom section of the sterilizer rack or cart, near the door and over the drain, in an otherwise empty chamber. The test pack is the only item on the sterilizer cart. Using anything other than a sterilizer cart does not represent how the loads are run therefore, the pack should always be placed on the cart or bottom rack (for those sterilizers without a cart), The Bowie-Dick test is conducted in an empty chamber to maximize the potential for detecting any air that enters by means of a leak or is not removed because of malfunction of the air-removal system. Other packs in the chamber would entrain a percentage of the air and reduce the sensitivity of the test.
The test is conducted using an abbreviated cycle. Some sterilizers are set-up with a Bowie-Dick test cycle already programmed in. Usually the cycle time is 3.5 to 4.0 minutes with no dry time. The test should never be run longer than that 4-minute exposure. According to AAMI, “If longer exposure times are used, the test should be considered invalid and the results meaningless; even an extra minute could affect the results.”
Most manufacturers recommend a warm-up cycle be run before performing the Bowie-Dick test. Check with your sterilizer and Bowie-Dick test pack manufacturer to see if this is recommended. A sterilizer tested from a “cold start” (after the sterilizer has been turned on and before a load is processed) might produce false failures unless it is preheated to operating temperature by running at least one empty-chamber cycle.
It is important to know how to interpret the Bowie-Dick test results. Depending on the test pack being used, refer to the instructions regarding the expected results. If there is any question as to the result, report this to the supervisor who will determine what action to take.
Bowie-Dick testing is also performed after relocation, installation of major repair of steam sterilizers. See AAMI ST-79 for Qualification Testing procedures.
So, it is important to follow all instructions for performing the Bowie-Dick test. Read the instructions for use for the test pack you are using and always follow AAMI standards.
Reference: ANSI/AAMI Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities, ST79:2010, & A1:2010, & A2:2011, & A3:2012, & A4:2013.
Nancy Chobin, RN, AAS, ACSP, CSPM, is a sterile processing consultant and educator.