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specify a range of stated values covering a range of sterilization temperatures used by practitioners around the world. For example, 121, 132 and 134 o


C are common


exposure temperatures used in various parts of the world and a CI may have stated values for each of these temperatures with appropriate exposure time stated values.


Testing chemical indicators All chemical indicators have to be tested before they are released into use, and this includes every batch produced by a manu- facturer. Type 1, 3, 4, 5 and 6 CIs are tested in a special type of “exposure apparatus” called a Chemical Indicator Evaluating Resistometer (CIER) vessel or Resistometer. CIER vessels are designed for accurate con- trol of the exposure conditions occurring within what is usually a very small chamber - typically 10 to 20l in volume. International standard ISO 18472 7


is the


standard that describes the requirements for CIER vessels. The CIER vessel is also designed to ensure that the required expo- sure conditions (e.g., 132o


C for 4 minutes)


are reached very quickly and that the chamber is vented equally quickly at the end of the exposure period. For example, a typical test carried out within a steam CIER vessel would involve mounting the samples on a sample holder, (which should not inuence the outcome of the results) and plac- ing the samples in the chamber, closing the door, and then draw- ing a vacuum to 45 mB absolute pressure (1.33 inches of mercury). Steam is then admitted to the chamber to the required expo- sure temperature and pressure within 10 seconds. The exposure temperature is then held within a tolerance of +/- 0.5 o


1


3 4 5


C for the


required exposure time (the stated value for the indicator or as prescribed in the standard); at which point the chamber is evacuated to 10mB (3 inches of mercury) within 60 seconds. By using such a test cycle, the indicator is exposed to carefully controlled, constant conditions that are often termed ‘square wave’ condi- tions. This is in contrast to the conditions that would be encountered in a production sterilizer where multiple pulses of vacuum and steam injection would be employed to remove the air trapped within the chamber and load prior to exposure to the steriliza- tion phase where temperature and pressure are maintained relatively constant. These multiple pulses can give rise to some color change in CIs prior to exposure to the ster- ilization phase which is unavoidable and quite normal.


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Testing chemical indicators: pass and fail


As described above, type 3, 4, 5 and 6 CIs will have stated values associated with them that are defined by the manufacturer of the product. When the p-roduct is exposed to these stated values in a CIER vessel, a pass result (called its endpoint) should be observed. Clearly CIs will also show a fail response under certain exposure conditions and ANSI/AAMI ISO 11140-11


prescribes


test conditions under which such a failure response should be observed in the CI. Thus, the CI will be tested for both a pass and a failure response. Generally, the exposure conditions which should be used for test- ing for a failure response are related to the stated values for the indicator. The failure exposure test condition is usually a percent- age reduction in the CI’s stated value for exposure time (and concentration) and a defined reduction in the Cs stated value for temperature. The test requirements for type 1 CI’s are an exception to this approach in that the standard specifies which test conditions should be used for a pass and fail exposure condition .


To illustrate this further, table 3 shows the test conditions for type 1, 3, 4, 5 and 6 steam sterilization CIs.(Table 3)


is to use a type 1 process indicator which should be attached to every pack. This provides evidence to the SPD operators that each and every pack has been processed and to the end user it signals that that particular pack has similarly been processed. Internal pack indicators are vital for indi- cating that sterilant has penetrated into the pack and that sterilizing conditions have been achieved at the point of placement. An internal pack indicator of type 5 or 6 showing a pass result will provide some evidence that the correct conditions have been met, because the performance of these types of indicators are linked to the response of a biological indicator or relate to a recognized sterilization time temperature relationship. Conversely a CI that shows a fail result should sound immediate alarm bells that something has gone wrong during the sterilization cycle, or incorrect packaging materials or accessory items have adversely affected the process. The requirements for the use of internal pack indicators are described in a number of national guidance documents. Thus ANSI/AAMI ST 794


requires the placement


Table 3: The exposure conditions in a steam CIER vessel allowing establishment of the performance to ANSI/AAMI/ISO 11140-1 of various types of a chemical indicator for monitoring steam sterilization


CI Type Pass Exposure Conditions Fail Exposure Conditions Temperatures (or 121 134 SV SV


C) Time (min) Temperatures (or 10 2


SV SV


121 135 Ta


SV


temperature Sv = manufacturers stated value


121 134 SV-2 SV-2


SV >16.5 SV-1 SV >1.2 SV-1 SV SV


SV-1 SV-1


0.3


SV-25% SV-25% SV-15% SV-15% SV-15% SV-6%


C) Time (min) 2


Type 2 are special test indicators for which separate parts of ISO 11140 exist. The manufacturer of a type 5 CI declares SV’s at 121 and 135 o


Standards for using Chemical Indicators Chemical indicators are used in various applications as discussed above. There are a number of standards and local guidance documents which provide information on how and when they should be used. International standards for various sterilization processes and local guidance documents require the use of a system for differentiating processed from non-pro- cessed items.4


Whilst a carefully controlled


segregation system might be used in an industrial manufacturing setting, the most obvious and secure means of complying with this requirement in a healthcare facility


26 December 2021 • HEALTHCARE PURCHASING NEWS • hpnonline.com C and at one other


of a CI in every pack which is to be steam sterilized. The use of such indicators is primarily aimed at the healthcare profes- sionals who will eventually use the packs during patient therapy. The Operating Room (OR) teams will normally carry out a series of checks on instrument sets prior to use. This will include checks to ensure the sterile barrier system is intact with no signs of perforation or staining. If sterilization container systems are used, they will check the tamper evident seal and once opened, the filter systems or valve assemblies to make sure they appear operational. The lid seals will also be checked for integrity. One of the most important checks that will


be carried out is on the process indicator attached to the instrument set to make sure it has changed color. In addition, the OR teams will also check the color change of any internal CI included with the instru- ments. It is vital that such indicators have a very clear endpoint, and that full instruc- tional material is available to the end user to enable correct interpretation of the CI. Any changes in supplier should also be notified to the end users so that appropriate training and instructional material can be made available to those who will interpret CI results.


All of these checks are described in the World Health Organization’s Surgical


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