SELF-STUDY SERIES


a period of a few seconds and then stays at that color for the remaining exposure time.15 For CIs used in special tests the indica- tor ink will be designed to react to certain conditions occurring in the sterilization process. As an example, in the Bowie and Dick test, the indicator inks will be designed to change color when exposed to a speci- fied temperature (.g. 134o


C) for a defined


period (3.5 minutes) when in the presence of moisture (saturated steam). The sensitiv- ity of the ink towards moist heat conditions is especially important in this test since the concept behind the test is that any residual air within the test device prevents the ingress of moisture and so the ink does not change color.13


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overarching purpose of such indicators is to ensure that instrument packs which have not been processed are not released from the SPD and aid product flow through the SPD. They are also used by the operating room profes- sionals to again ensure that they are using a sterile set which has been processed. Such indicators should have a very clear color change which cannot be misinterpreted. Internal chemical indicators are placed


inside sterile packs during assembly. They are designed to indicate that sterilizing agent has penetrated through the packag- ing materials and appropriate conditions have been met at the point of placement. It is important to understand that such indicators cannot alone be used to judge if the pack is


the Bowie and Dick Test, which employs a chemical indicator placed within a stack of textile material (13). When used daily within the sterilizer, the test is designed to assess the capability of the process to remove air and enable steam penetration. The test is described in many standards and guid- ance documents2, 4


and involves placement


of a chemical indicator A4 sheet placed in the centre of a stack of towels. There are many alternative commercially produced test packs available which have equivalent performance but are more consistent and convenient in use.


Conclusions


Along with Physical measurements and Biological Indicators, Chemical Indicators are one of the three basic types of technol- ogy which can be used to routinely monitor the efficacy of sterilization processes used in industry and the hospital SPD. They can be used to identify unprocessed from processed surgical instrument sets when adhered to the outside of packs thereby avoiding non steril- ized packs being sent to the OR department. They can be used to indicate that sterilizing agent has penetrated through the sterile bar- rier system packaging and stated exposure conditions have been met thereby avoiding inadequately or incorrectly processed loads being used.


Chemical Indicators are therefore an extremely useful and practical tool for ensuring SPD processes are functioning correctly. HPN


This article is part of a three-article series. Part two will be in our December issue.


Figure 3:


Graph showing the color change of some chemical indicators printed on commercially available autoclabe types. The vertical lines show the exposure conditions to whicha type 1 process indicator must show a fail result (red line) and pass result (greenline).


The use of chemical indicators. Chemical indicators are used to monitor various aspects of a sterilization process and can be divided into three categories based on how they are employed: • External chemical indicators • Internal chemical indicators • Special test indicators.


External chemical indicators 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. It is important to understand that 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


sterile; other factors must also be considered.2 Internal pack indicators are primarily inter- preted by the OR practitioners, and it is vital that they are appropriately trained in the interpretation of the CIs and have available appropriate reference material such as wall charts and clear instructions. It is vital that the SPD has a good communication channel with the OR management teams so that any changes in the internal indicators used can be communicated to the end user. Special Test Indicators are used in specific performance tests described in standards and guidance documents to ensure that the sterilizer is performing according to speci- fication. An example of such a CI would be


26 October 2021 • HEALTHCARE PURCHASING NEWS • hpnonline.com References:


1. McDonald, G and Hansen, J. Block’s Disinfection, Sterilization and Preservation, 6th


Ed, 2021, Wolters Kluwer, USA


2. ANSI/AAMI ST79:2017, Comprehensive Guide to steam sterilization and sterility assurance in health care facilities, 2021, AAMI, N Glebe Rod, Arlington VA


3. ISO 11139 : 2018, Sterilization of health care products, Vo- cabulary – Terms used in sterilization and related equipment and process standards, International Standards Organisation, Geneva, Switzerland


4. ISO 17665-1:2006, Sterilization of health care products – Moist Heat – Part 1: Requirements for the development, validation and routine control of a sterilization process for medical devices (ISO 17665-1:2006), International Standards Organisation, Geneva, Switzerland.


5. Underwood, W.B. A textbook of sterilization. 1934, American Sterilizer Co., Erie PA, USA


6. Perkins, J,J. Principles and Methods of Sterilization, 1st Ed, 1956, Charles Thomas Publishers, Springfield Il, USA.


7. Hoyt,J, Chemical indicators for steam sterilization, J Lab and Clin Med, 19, 382-390 (1934) 8. 3M autoclave tape patent


9. Walter,C.W, An evaluation of sterility indicators, Surgery 2, 585-589, 1941


10. Kelsey , J.C. The testing of sterilizers, Lancet, 1(7015), 306- 309, 1958 11. Bunn, J.L and Sykes, I,K. A chemical indicator for the rapid

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