Sterilization indicators, chemical

Industrial sterilization cycles tend to vary considerably, not only from manufacturer to manufacturer, but often from product type to product type, depending on the bioburden present on a given load. Chemical indicators have historically been used only to differentiate between sterilized and nonsterilized packages. More recent developments have resulted in the availability of chemical dosimeters of sufficient accuracy to permit their appHcation either as total monitors or as critical detectors of specific parameters. 

Table 23.1 Examples of chemical indicators for monitoring sterilization processes...

Gaseous sterilization Ethylene oxide (EO) Reactive chemical Indicator paper impregnated with a reactive chemical which undergoes a distinct colour change on reaction with EO in the presence of heat and moisture. With some devices rate of colour development varies with temperature and EO concentration Gas concentration, temperature, time (selected devices) NB a minimum relative humidity (rh) is required for device to function... 

In prevacuum autoclaves, problems are created by the removal of air and the air-insulation systems. A specific test called the Bowie Dick test (12), was developed to evaluate the abflity of prevacuum sterilizers to provide rapid and even steam penetration which includes the abflity to eliminate air from the chambers, and prevent air from lealdng back during the prevacuum phase. The test utilizes a pack of specific constmction (or its proven equivalent) placed in the empty chamber and exposed to specific test conditions (9,12). The pack contains a chemical indicator sheet. A correctly fimctioning sterilizer produces a uniform color change. A nonuniform color change indicates poor steam penetration and the possible presence of air which requires the attention of a qualified mechanic. The daily testing of all porous load sterilizers is recommended (1,9,10). 

Biological indicators (Bis) for use in thermal, chemical or radiation sterilization processes consist of standardized bacterial spore preparations which are usually in the form either of suspensions in water or culture medium or of spores dried on paper, aluminium or plastic carriers. As with chemical indicators, they are usually placed in dummy packs located at strategic sites in the sterilizer. Alternatively, for gaseous sterilization these may also be placed within a tubular helix (Line-Pickerill) device. After the sterilization process, the aqueous... 

Chemical indicators for dry-heat sterilization are available either in the form of pellets enclosed in glass ampuls, or in the form of paper strips containing a heat-sensitive ink. The former displays its end point by melting, the latter by a color change (see CHROMOGENIC materials). 

Biological and chemical indicators used alone are not acceptable as proof that a sterilization process has been effective. They will show when sterilization has failed, but not necessarily prove that the process has been successful. 

Chemical indicators are available for heat, ethylene oxide and radiation sterilization, usually in the form of. adhesive tapes or patches, color spot cards,small tubes or sachets. They change color as a result of chemical reaction brought about by the sterilization process. It is possible for the change to take place before the sterilizing time has been completed, and hence, with the exception of plastic dosimeters used in radiation sterilization, they are unsuitable to be used as proof of sterilization. 

Biological and chemical indicators used alone are not acceptable as proof of sterility. 

Puntambekar, S. S. Water-based chemical indicator ink for ethylene oxide sterilization process and method for its use. U.S. Pat. Appl. Publ. US 2003235654, 2003 Chem. Abstr. 2003,140, 43618. 

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