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Infection Control Report® by Chris H. Miller, Ph.D. | Sterilization monitoring Part 1: Instrumentally clean
There is indirect evidence that dental office infection control measures work—occupationally acquired hepatitis B among healthcare workers has significantly dropped within the last decade; there have been no reports of hepatitis spread to dental patients within the past several years. Although some of this undoubtedly is traceable to the hepatitis B vaccine, this is at least in part due to enhanced glove use and greater care in handling contaminated sharps. Hard to measure There are few ways we can actually measure how good a job we’re doing as we perform asepsis procedures in the office. For example, we can’t readily test for microbial killing as we disinfect an operatory surface. Nonetheless, we can assess one of the most important parts of our infection control programs—the sterilization process. We can monitor this by mechanical, chemical and biological means to help ensure the safety of the instruments we use for patient treatment. Often thought of as the destruction of all life, sterilization actually is defined as the destruction of high levels of bacterial spores—the most difficult type of microbe to kill. We use this microbe for testing. Numerous scientific studies have shown that certain conditions of time and temperature or chemical action do kill high levels of bacterial spores, so measuring these physical parameters during sterilizer runs also can help assess the efficacy of the sterilization process. MANAGING MONITORING Three methods of monitoring are recommended by the CDC to determine the effectiveness of sterilization in the dental office. They are mechanical, chemical and biological monitoring. 1. Mechanical monitoring The CDC recommends that every sterilization load in the dental office needs to be mechanically monitored (see “Ensuring sterilization effectiveness,” page 128). This means that the physical parameters (cycle time, temperature, and pressure) for each sterilizer run should be documented. This challenge is met by sterilizer models that provide a mechanical print-out, because the measures are automatically recorded on tape (Figure 1). Sterilizer models with no mechanical print-outs need gauge results carefully observed to ensure the correct parameters are attained (Figure 2). Although correct print-out results alone do not ensure sterilization, any incorrect results can be an early indicator of problems with the sterilization cycle. Sterilizer temperatures Steam sterilizers have sterilizing temperatures ranging from 121°C (250°F) to about 134°C (273°F), and operate from about 3 minutes to 30 minutes, depending upon the cycle selected (e.g., wrapped, unwrapped, or rubber & plastics). Shorter cycles use a higher temperature; longer cycles use a lower temperature. Dry heat sterilizers operate at about 160°C (320°F) for about 1 to 2 hours at temperature. Special forced-air dry heat sterilizers may operate at higher temperatures with shorter times. The unsaturated chemical vapor sterilizer operates at about 134°C (273°F) for 20 minutes. All times mentioned are for the cycle’s sterilization segment only, excluding “heat-up,” “come-down,” or “dry” times. 2. Chemical monitoring
The CDC recommends that each package be chemically monitored as it is processed through a sterilizer (see “Ensuring sterilization effectiveness”). While sterilizing conditions inside each package need monitoring, one also needs to show that the package itself has been processed through a heat sterilizer. To meet these conditions, place a chemical indicator inside each package (Figure 3). If this indicator cannot be seen from the outside of the package—that is, if the package is wrapped with opaque material—attach another chemical indicator to the package’s exterior. These acts identify the package itself has been processed through a sterilizer, and indicate that the package’s interior (containing the instruments) has attained one or more sterilizing conditions. VISIBLE DIFFERENCE Chemical indicators consist of chemicals that change color or form when exposed to certain high temperatures (such as 121°C) alone; or to high temperatures plus other sterilizing conditions, such as length of time and the presence of steam. These indicators are available as autoclave tape, strips, tabs, or packets. Autoclave tape (Figure 4) is sometimes referred to as a process monitor. This indicator type responds to high temperatures alone by changing color or even physical form (e.g., from solid to liquid). Such changes are readily seen by the naked eye. For example, autoclave tape changes color when the sterilizer reaches about 121°C. However, it is important to note that process monitors do not indicate whether a complete sterilization cycle has occurred—they only show that adequate sterilizing temperatures have been reached. A sterilizer could heat up to the proper temperature of 121°C, causing the process indicator to change color; and then immediately malfunction, preventing sterilization. The integrator chemical indicator changes color more slowly than the process monitor, because
it responds to a combination of factors—such as temperature and time; or temperature, time and the presence of steam. Integrators usually come in strips or tabs. RESULTS RIGHT AWAY The main advantage of using the mechanical or chemical monitoring methods is the results are visible and available immediately. This is in contrast to biological monitoring (presented next), which can take from 1 to 7 days before results are known. 3. Biological monitoring The CDC recommends that every sterilizer be biologically monitored at least once a week. Although the biological monitoring process takes the longest time to obtain results, this method offers the highest guarantee that sterilization has occurred. The bacterial spores used as part of this monitoring process are more difficult to kill than other microbes, including the hepatitis, HIV, herpes and influenza viruses, TB, MRSA, and streptococci. CONTINUED ON PAGE 2
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