Proper sterilization of instruments and materials is a critical aspect of infection control. Historically, health care professionals have sought a means to effectively and reliably manage sterilization by monitoring the parameters needed for sterilization (time, temperature & sterilant contact). Since microorganisms can not be seen with the naked eye, the major difficulty in sterilization is determining WHEN an item is considered STERILE. In earlier days, a raw potato was sometimes placed in the sterilizer along with the load being processed and afterwards examined to see if it was cooked. If it was, then the load was considered sterile. As sterilization processes became more sophisticated, more scientific monitoring practices replaced this rather crude (but tasty) method. Today, an overall sterility assurance program involves the use of the following management tools:
- Mechanical/Electronic Controls
- Chemical Indicators/Integrators
- Biological Indicators (spore tests)
- Sterilizer Maintenance
- Record Keeping
Mechanical or electronic controls are the easiest for sterile processing personnel to use and interpret, and they provide the earliest indication of unsatisfactory sterilization conditions. While most sterilizers come with time, temperature and pressure gauges, these readings are limited as they only tell us what is happening at the probe site (usually in the drain) and not inside the packs being processed. AAMI (Association for the Advancement of Medical Instrumentation) guidelines state that sterile processing personnel should review and record these readings after each and every sterilization cycle. Most older sterilizers use analog (mechanical) controls, while newer sterilizers usually have digital (electronic) controls. Compared to analog controls, digital controls have proven to be much more reliable; therefore, you should upgrade where possible. There are also new technology digital monitoring systems available that monitor all the parameters of the sterilization process through a real time system with adjustable alarms to alert the user to any changes to the vessel, pumps, valves or temperature variances. These systems graph the physical parameters of the sterilization process which can be visually observed by the user.
Experienced practitioners use chemical indicators (CIs) as an adjunct to biological indicators in an effort to achieve a system of checks and balances. Inexpensive compared to biological indicators (BIs), AAMI guidelines state that an external and internal CI should be used with every pack. The FDA classifies CIs as Class II medical devices requiring standards and AAMI under Sterilization of health care products - Chemical indicators - Part 1: General requirements, Part 4.5, has established the following classifications.
- Class I - Process Indicators are for external use to show processed vs. unprocessed items and can usually be found in the form of tape or labels, as well as printed directly on some sterilization packaging.
- Class II - Bowie-Dick Indicators are used to show the pass/fail in Steam vacuum type sterilizers with the presence of air. Quality assurance is attained by performing an air removal test with an indicator sheet placed inside a towel pack (AAMI specified) or with a commercially prepared test pack that already includes an indicator sheet. AAMI standards state the Bowie-Dick test must be carried out each day the vacuum steam sterilizer is used, in an empty chamber.
- Class III - Temperature Specific Indicators are designed to reveal the attainment of specific minimum temperature at that location within the sterilizer chamber or load. This type is not sensitive to other sterilization parameters, such as time or sterilant.
- Class IV - Multi-Parameter Indicators are much more accurate by design, as they provide an integrated response to all the parameters needed to achieve sterilization, by either a specified color change or migration along a wick to indicate pass or fail.
- Class V - Integrating indicators are designed to react to all critical parameters over a specified range of sterilization cycles. The stated values are those required to achieve a stated inactivation by referring to a stated test organism with stated D and, if applicable, z values.
The third tool used to manage sterilization involves the use of bacterial spores. Biological Indicators (BIs)are considered the highest level of sterility assurance because they actually test the sterilizer's ability to kill specific strains of highly resistant organisms. Commercially available BIs are non-pathogenic (harmless) and are specific for the type of sterilization process being monitored.
For example, Steam, ChemiClave™ and STERIS™ System 1 sterilization processes are tested with Geobacillus stearothermophilus spores, while EO gas, Dry heat and STERRAD™ gas plasma sterilization processes are tested with Bacillus atrophaeus spores. BIs are available in the following four (4) formats:
- Spore strips are available in a variety of concentrations and spore populations allowing the user to select a specific SAL (sterility assurance level). After processing, the spore strip envelope is opened and the BIs aseptically transferred into a tube of sterile culture media, then incubated for up to 7 days at a preset temperature (Geobacillus stearothermophilus = 55-60ºC or Bacillus atrophaeus = 35-37ºC). Special Note: While this type of BI format can be used for other sterilization processes, it is required for ChemiClave, STERIS System 1 and STERRAD processes.
- Self-Contained vials are available as single or dual species for use with Steam or EO gas processes. A glass ampule of sterile media is surrounded by a plastic vial with a spore strip inside. After processing, the user activates the BI by crushing the vial (manually or with a device) to let the media come into contact with the spore strip, then incubates at the appropriate temperature. No media color change of a processed BI indicates negative (STERILE) results, providing an unprocessed BI that is used as a Control cultures positive. Incubation time varies from 24 hours to 7 days depending on the Manufacturer. Special Note: One Manufacturer offers rapid read-out systems whereby a chemical enzyme is read at 1 or 3 hours depending on the system and the BI can be incubated for 48 hours. Another offers an immediate read-out system whereby a chemical integrator, cleared as equal in performance to a BI, is read immediately and the BI is incubated for 48 hours.
- Sealed Glass Ampules are available with Geobacillus stearothermophilus spores for use with Steam processes. This form has the spores and media mixed together; therefore, no vial crushing or activation is required after processing. No media color change or visible turbidity (spore growth) of a processed BI indicates negative (STERILE) results. Providing an unprocessed BI used as a Control cultures positive. Spore growth will usually occur within 8-12 hours; however, 48 hours incubation is recommended. Spore growth is evidenced by a yellow color change in the media along with visible turbidity at the bottom of the vial.
- Spore Suspension is available in 10 ml pharmaceutical vials directly from Manufacturers and is used for cycle and/or direct inoculation of product for process validation. Geobacillus stearothermophilus, Bacillus atrophaeus and B. pumilus spores are commonly stocked by suppliers.
For consistency in testing, AAMI guidelines recommend placing the BI inside a "Test Pack" to properly challenge the sterilization cycle. Test packs can be made in-house by the user per AAMI guidelines or purchased pre-made from suppliers. Unlike the Bowie-Dick test pack, which is always run in an empty sterilizer, the BI Test Pack should be run in a fully loaded chamber along with other packs. Place the BI test pack in the area of the sterilizer that is least favorable to sterilization (normally in the front bottom section, near the drain). Depending on the sterilizer being tested (Steam vs. EO gas) and the type of monitoring (routine vs. installation), pack assembly and testing procedures vary.
BI Testing Frequency
BI testing frequency varies among health care users and suppliers. For example, medical device manufacturers are required by the FDA to spore test every load processed in Steam or EO gas. A minimum of 10 BIs must be located throughout the load and it can not be released until full incubation of the BIs, along with an unprocessed Control for 7 days. Some hospitals in Europe do not test with BIs at all, while most U.S. hospitals follow AAMI guidelines which recommend daily testing of Steam and every load of EO gas or any load that includes an implant.
Private offices and clinics seldom test more often than monthly, except in the dental market where the ADA recommends weekly testing and a number of States have mandated weekly testing of all sterilizers. If your facility is considering a new technology sterilization process, be sure to ask the manufacturer for detailed information regarding the type of BI to use, format, test pack design and frequency of testing. In some cases, you may be required to have Product Testing done to validate certain items and/or materials to make sure they are compatible with the new process. The Manufacturer of the sterilizer, the Manufacturer of the items, and/or an independent testing laboratory should be able to assist you.
Regardless of the testing frequency you choose or the type of sterilizer being tested, if any of the processed BIs culture positive (show spore growth), then that means the sterilizer is suspect and the following actions should be taken:
- Report results to supervisor
- Recall and resterilize all "suspected non-sterile" items
- Verify spore growth via gram stain
- Determine cause of failure and correct
- Retest sterilizer before using again
Each Manufacturer provides users who purchase their sterilizers with a Manual that includes comprehensive care and maintenance instructions. According to AAMI guidelines, all sterilization equipment must receive periodic and routine maintenance to ensure accurate and reliable operations. The following maintenance procedures are considered the fourth management tool:
- Routine Maintenance - daily inspections and cleaning in accordance with the manufacturer's recommendations. This generally includes the cleaning of gaskets, chart pens, chamber drain screens and internal/external surfaces.
- Preventive Maintenance - periodic preventive maintenance in accordance with the manufacturer's instructions.
- Scheduled Maintenance - this level of maintenance should include lubrication of appropriate parts and replacement of expendable parts, i.e. steam traps.
- Calibration - periodic calibration of items such as pressure and temperature gauges, timers, recording and control devices must be carried out by qualified personnel as specified in the manufacturer's instruction manual.
The fifth management tool is Record keeping, which is considered an absolute essential for any facility involved in the sterilization of instruments and materials for disbursement. In the event of a recall, there must be a system in place for finding and reprocessing the items in question. This is accomplished by keeping accurate records of each and every sterilizer's performance. Maintenance records must be kept showing such things as: model and serial number of each sterilizer, date of servicing, reason for the service request, what was done, what parts were used, etc. In addition, evidence is required to document that items processed did indeed get sterilized. While each facility may have varying methods of how to logically keep or file records of their sterilizers' performance, all sterilization records should include the following:
- Date, sterilizer #, load #
- Lot number, general contents of load
- Exposure time, temperature & pressure
- Operator's name or initials
- Chemical indicator results
- Biological indicator results
- Bowie-Dick test results (Steam vacuum)
As we've seen, sterilization of instruments and materials can and must be managed through the use of various tools. With the very real and growing concern over infectious hepatitis and AIDS, it is more important than ever that you select the proper sterilization process and document that sterilization has indeed taken place for each item you process.