The Principles of Medical Device Decontamination

Chemical Indicator (CI) formats

CIs usually come in the form of a reactive ink printed on a substrate. The substrate may be paper or plastic-based and in the form of an adhesive label or tape which can be fixed onto the outside of surgical instrument sets and sterile packs. The ink might be printed directly onto sterile packaging materials such as paper bags or pouches. There are also special kinds of chemical indicators, called “moving front” CIs. These CIs consist of a pellet of dye which is placed within an indentation on a foil base. A paper wick is then placed in contact with the dye pellet and the whole assembly then sandwiched between a semi permeable membrane and the foil base. An adhesive label is then usually placed over the semi permeable membrane with informational material printed on it. CIs have also been supplied in other formats in which they are incorporated into some form of test device which is then used in a special test to ensure the sterilizer is functioning correctly, for example the Bowie and Dick test.

The use of CIs

CIs are used to monitor various aspects of a sterilization process and can be divided into three categories based on how they are employed:

• External CIs • Internal CIs • Special test CIs

External type 1 CIs are placed on the outside of every sterile pack to give a clear indication whether the pack has been exposed to a sterilization process or not. These types of indicators do not provide any evidence that the pack is sterile, but simply that the pack has been put through a process. The purpose of such indicators is to ensure that instrument packs which have not been processed are not released from the SSD or used by the clinical practitioner in for example the operating theatre. Internal CIs of type 4, 5 and 6 are placed inside sterile packs during assembly. They are designed to indicate that a sterilising agent has penetrated through the packaging materials and appropriate conditions have been met at the point of placement. It is important to understand that such indicators alone cannot be used to judge if the pack is sterile; other factors must also be considered. Internal CIs are primarily interpreted

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