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ments for CIs used in different sterilization processes including steam (often termed moist heat sterilization), dry heat, ethylene oxide, radiation, low temperature steam and formaldehyde and vaporized hydrogen peroxide sterilization processes. (Table 2, previous page.)


Terminology: endpoint and stated values Each type of C will have a specific func- tion and requirement associated with it. Before considering each of the types of CI, it is imperative that the reader understands two fundamental terms associated with the performance of Cs. he first is the term “endpoint” and the second is the term “stated value” and both are interrelated. The “endpoint” of a CI is the point at which a pass color change result is indicated after eposure to the conditions specified by the manufacturer or the standard, ANSI/AAMI ISO 11140-1.1


The exposure conditions


which give rise to the pass color change or endpoint are called the “stated values”, and there may be one or multiple stated values for each of the process variables the CI responds to depending on which type of indicator is in use. Figure 4 illustrates the endpoint and stated values for a type 5 CI. Endpoint


sv=22.1 min@121C Figure 4: Showing the endpoint on a


moving front CI (the reject/accept line) and the stated values (sv) which give rise to the endpoint being reached.


The six types of CI


Table 2 describes the six types of CI described in ANSI/AAMI/ISO 11140-1.1 Type 1 CIs are designed for placement on the outside of individual packs of sterile medical devices including surgical instru- ment sets. These indicators may be in the form of an indicator tape which is used to secure instrument sets wrapped in eible tray wrap. They may be in the form of an adhesive label which contains information about the pack contents. In some cases, a bar code for use within a track and trace systems and an indicator imprint which changes color with exposure to the steriliza- tion process. They may also be in the form of some other device which has a specific function. For example, some tamper evi- dent sealing systems used with sterilization containers may have a CI printed on them which changes color when exposed to the sterilization process. The indicator may also be printed directly onto packaging materials such as paper bags or paperfilm pouches.


Type 1 chemical indicators provide a very important function because they help ensure non-processed instrument sets are not released into use. Before sets are released from the SPD, operators should be trained to examine every pack to make sure the CI has changed color. Similarly, operating room practitioners must also be trained to do the same. Sadly, reports still appear in the press which recount the use of non-sterilized sets by surgeons.2


It is important to understand


that type 1 CIs are not intended to provide evidence of sterility and should not be regarded as sterility indicators. Type 2 CIs are used in special tests usu- ally related to making sure the sterilizer is performing correctly before it is used for processing loads. A prime example of this type of indicator is the Bowie-Dick type indicators used daily to ensure that a steam sterilizer is achieving adequate air removal and steam penetration when tested using a standardized test load (3, 4). Parts 3, 4, 5 and in the future 6 of ISO 11140 describe the requirements for such indicators. The Bowie-Dick test will be discussed in more detail in part 3. Type 3 CIs are single variable indicators which are designed to respond to just one process variable of the sterilization process. A good example of these types of indicators are the Diack tubes which contain a pellet of wax material sealed inside a glass tube that melts when exposed to the correct steriliza- tion temperature.5


Clearly these types of


indicators have limited utility because in order to know that a sterilization process has been effective, we need evidence that all of the process variables (i.e., those contribut- ing to microbial kill), have been present at a sufficient level during the process. Type 4 CIs are multi-variable indicators,


which are designed to respond to two or more process variables. For a steam ster- ilization process whose process variables are time and temperature in the presence of moisture, a type 4 CI must react to at least two of these variables. It is important to note that the practitioner must make careful choices when using such indicators since in a steam sterilization process, the presence of moisture is vital in ensuring efficacy of the process. So, a type 4 CI, which only responds to time and temperature, may give rise to misleading conclusions because such an indicator would also respond to identical dry heat conditions. The manu- facturer of a type 4 indicator is required to specify the stated values for each of the process variables the indicator responds to however, there is no requirement for the manufacturer to choose a stated value with a relationship to the sterilization process in


SELF-STUDY SERIES


which the indicator might be used (see type 6). Practitioners should be aware of this and ensure that if they are using a Type 4 indi- cator, the stated values are of relevance to the sterilization process they are using. For example, a Type 4 may have stated values of 1 minute at 132 o


clearly has little relevance to a sterilization process that is being operated at 132 o


C in moist heat, which C for


4 minutes. Type 5 CIs are integrating indicators and are designed to respond to all of the variables of a sterilization process. Thus, in a steam sterilization process they must respond to time, temperature, and the pres- ence of moisture (typically in saturated steam; see later section). Conversely, they must not give a ‘pass’ result when exposed to the same time and temperature of expo- sure in the absence of moisture (i.e., dry heat) and they are tested to make sure they do not. Similarly, in an EO process they must respond to the process variables of time, temperature, ethylene oxide concen- tration and humidity, and for vaporized hydrogen peroxide, time, temperature, and hydrogen peroxide vapor concentration. They must not give a pass result if EO gas or humidity are at inadequate levels. Type 5 integrating indicators have a special characteristic in that they provide a result that is similar to one that would be expected from a biological indicator - effectively mimicking the response of a biological indicator.6


With this in mind, the


manufacturer of a steam type 5 indicator must provide at least three stated values. he first should be at an eposure tem- perature of 121 o


C and must be not less than


C and should not be less than 1.2 min- utes, and at least a third must be declared at an equidistant intermediate time and temperature of exposure. The temperature coefficient (theoretical  value) of the color change reaction must then fall between 10 and 27o


16.5 minutes. The second value must be at 135 o


C. All of these requirements mirror


the minimum values that are given for a biological indicator for steam sterilization in ISO 11138.6 Type 6 CIs are emulating indicators and are designed to provide a pass result which has a direct relationship to a time/tempera- ture combination which may be cited in a standard, local guidance, national regula- tion or a pharmacopoeia. As an example, a type 6 steam CI might have stated values of 132 o


C for 4 minutes -- a commonly used time/temperature combination used in the US. In theory, a type 6 CI should only have one set of stated values related to a particular sterilization process. However, it is common practice for manufacturers to


C and 4 minutes, which means it will give a pass result after exposure to moist heat at 132 o


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Self-Study Test Answers: 1. A, 2. B, 3. A, 4. B, 5. B, 6. A, 7. A, 8. A, 9. A, 10. B


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