Proper operation and monitoring of office sterilizers

June 1, 2007
Question: Our mail-in spore testing service informed us that our office autoclave had failed its last spore test.

by Charles John Palenik, MS, PhD, MBA

Question: Our mail-in spore testing service informed us that our office autoclave had failed its last spore test. I am not sure what happened. Do you have any ideas?

Answer: Not being on-site makes answering your question a bit difficult; however, there are some points that could prove useful.

Biological monitoring (spore testing) provides the main guarantee of sterilization. The process uses biological indicators that contain highly resistant bacterial spores. The goal is to kill the test spores. Failure allows them to grow when cultured. This is a “positive spore test,” and is a significant event that requires immediate action. To respond correctly, however, identifying the cause of the failure is necessary.

Sterilization failure involves two factors: mechanical malfunction and/or operator error. Many sterilizers have automated features that inform if there is a problem. Some even help identify the likely cause. Mechanical problems include improper temperature, pressure, or insufficient exposure time. Using incorrect or expired solutions in a chemical vapor sterilizer also could cause improper functioning.

Chemical indicators provide a type of early warning system. Chemical monitoring uses heat-sensitive chemicals to assess the physical conditions present during sterilization. These indicator chemicals change color and/or form when exposed to certain temperatures. Examples include autoclave tape, special markings on instrument bags, and pouches as well as tubes of colored materials. Chemical monitors offer instant feedback. Although most measure a single operational parameter, such as temperature, failure to change color or form after processing should cause instant alarm.

Most sterilizer failures are the result of operator error. A wide variety of misadventures might be involved. This could include insufficient cleaning of instruments, improper instrument packaging or sterilizer loading, or incorrect sterilizer operation. If debris remains after instrument cleaning, insulation of microorganisms from direct contact with the sterilizing agent could occur. Inadequate cleaning probably is not the cause of your sterilization failure. However, since you are reviewing your instrument processing procedures, it also would be helpful to check on cleaning.

Packaging materials must be compatible with the sterilizer used. Incorrect packaging prevents penetration of the sterilizing agent. For example, aluminum foil or closed containers do not readily allow steam passage. Conversely, paper, paper/plastic pouches, and wrapped perforated cassettes allow proper steam movement. Using excessive packaging material also can be problematic. Unnecessary wrapping also retards penetration. Cloth wraps absorb chemicals and prevent sufficient vaporization required for sterilization.

Overloading a sterilizer increases heat-up time and retards movement of sterilizing agents into the center of the sterilizer load. Crowding of packages and cassettes also jeopardizes sterilizer effectiveness. Separation between packages or cassettes increases chances of sterilization success.

Be sure your sterilizer achieves the correct temperature and pressure, and that the proper operational parameters are applied for the required cycle time.

Since a sterilization failure has occurred, you should follow certain steps to assure proper operation of your unit. First, remove the unit from service until you can determine the cause of the problem. A review of sterilization procedures should follow. Many of the major problems have already been described. You also should review the training for the people operating the sterilizer. Is there someone new? Is everyone familiar with the required operating procedures?

Again, most sterilization failures are due to operational difficulties, rather than a mechanical malfunction. After review, make all necessary changes and retest the unit. Evaluation should include not only biologic monitoring but also chemical indicators, as well as observation of the unit’s gauges, dials, lights, and digital readouts. These procedural changes should resolve the problem. If chemical and mechanical monitoring indicates proper operation and the spore test is negative, you can return the unit to service. If the spore test is positive, contact a service company for evaluation. It may be necessary to replace the sterilizer. You must monitor a repaired unit prior to its use on patient-care items. In this case, the unit must successfully kill three consecutive BI challenges that are run in an empty chamber.

The Organization for Safety and Asepsis Procedures, OSAP, is a global dental organization dedicated to promoting infection control and safety policies and practices supported by science and research. Additional information about proper operation and monitoring of office sterilizers is available on the OSAP Web site at www.osap.org.

Dr. Charles John Palenik is the assistant director of Infection Control Research and Services at the Indiana University School of Dentistry. Dr. Palenik is the co-author of the popular “Infection Control and Management of Hazardous Materials for the Dental Team.” In 2003, he was chairman of the Executive Board of OSAP, dentistry’s resource for infection control and safety. Questions about this article or any infection-control issue may be directed to [email protected].

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