Infection Control: Chemical monitoring provides rapid feedback

March 1, 2001
Chemical monitoring of the sterilization process helps assure patient safety.

Instrument cleaning and sterilization is performed to reduce the transfer of microbes from one patient to the next. Thus, monitoring the sterilization process helps assure patient safety. Monitoring involves two main approaches. One (chemical monitoring) provides an immediate indication that the sterilization process appears or does not appear to be working properly. The second (biological monitoring or spore-testing) provides the main guarantee that the sterilization process is working properly. Chemical monitoring will be discussed in this issue and biological monitoring will be described next month.

Chemical monitoring uses heat-sensitive chemicals that provide a rapid visual change when exposed to sterilizing conditions achieved inside a sterilizer. There are two general types of chemical indicators. For discussion purpose, we'll refer to them as rapid-change indicators and slow-change indicators.

The rapid-change chemical indicators change color rapidly after a certain temperature has been reached. One example is the indicator tape (autoclave tape) used to seal packages. The stripes on these tapes are nearly invisible when taped packages are placed in the sterilizer chamber, but turn dark when the temperature approaches 250 F (121 C).

Other examples of this type of indicator are markings (a dot or arrow) on the outside of sterilization bags and pouches. These markings are usually pink, light blue, or light brown, and turn dark when exposed to temperatures approaching 250 F (121 C). Rapid-change indicator inks also may be placed on strips or tabs.

The second type of chemical indicator is the slow-change indicator. It changes color more slowly or only after a combination of physical conditions (temperature and time, or temperature, time, and the presence of steam) have been met. This type of indicator is referred to as an integrator because more than one parameter is involved in the color change. These indicators are usually in the form of a strip or tab that changes color after the sterilizing temperature has been maintained for a few minutes.

The rapid-change indicator provides the least amount of information about the sterilization process. It only indicates exposure to sterilizing temperatures for some unknown length of time. The slow-change indicator (integrator) provides more information, indicating exposure to a combination of temperature and time, which more closely relates to the complete sterilization process.

One important property of both rapid- and slow-change chemical indicators is that they are ready to read as soon as the instrument package is removed from the sterilizer. This allows chemical indicators to serve two important functions.

One, they provide an immediate, easily visible indication that a package or cassette has or has not been processed through a sterilizer. This is why chemical indicators are sometimes referred to as process indicators. For this function to be fully effective, every instrument package should have a chemical indicator on the outside or an internal chemical indicator should be visible from the outside (when see-through packaging/pouches are used). This function will prevent the intermingling of "sterile" and "non-sterile" packages.

In other words, a quick glance at a package, pouch, bag, or cassette with an externally visible chemical indicator will show if it is ready for use, or if it still needs to be processed through the sterilizer. This is important in the sterilization room and at chairside. In the sterilization room, instrument packages waiting to be sterilized usually look just like sterilized instrument packages except for the chemical indicator. On very hectic days, this will help minimize the accidental distribution of nonsterilized packages to chairside. The indicators also help eliminate possible confusion when an office temp or other person not familiar with the sterilizing room may need to retrieve sterile instruments.

Another important aspect of external indicators is to provide sterilization assurance to the hygienist and dentist at chairside. Again, a quick glance at the instrument packages placed on the cart or bracket table in the operatory for the next patient will indicate that the instruments are, indeed, ready to be used.

A second major function of chemical indicators occurs when the indicator is placed inside the package next to the instruments. Such indicators show that the sterilizing agent has actually penetrated the packaging material and at least reached the instruments inside. This is particularly important if new packaging material or wrapping techniques are used or if different loading procedures are used for the sterilizer. Internal (and external) indicators also can help assure that new or temporary personnel in the sterilizing room are properly processing instruments.

Of course, for chemical indicators to serve their functions, proper training of the dental team must occur. The "before and after" colors must be known. A hard-fast rule obviously must be set - instrument packages with unchanged indicators must not be used. Also, procedures must be established to quarantine improperly processed instruments and investigate packaging or sterilization problems identified by unchanged chemical indicators.

In summary, chemical monitoring involves color-change indicators on the inside and outside of instrument packages. Instrument packages showing unchanged indicators have not been properly sterilized and must not be used on patients. Chemical monitoring provides immediate feedback that the sterilization process is apparently functioning properly. This information is only a part of the total monitoring process, but, when coupled with results of routine biological monitoring (spore-testing), gives the necessary data to best assure patient safety.

Chris Miller, PhD, is professor of oral microbiology and executive associate dean at the Indiana University School of Dentistry.

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