What is a Chemical Indicator?

Chemical Indicators

Chemical Indicators (CIs), as defined by AAMI and ISO, are devices used to monitor the presence or attainment of one or more of the parameters required for a satisfactory sterilization process or used in a specific test of sterilization equipment. For example, when placed inside packs, CIs are used to confirm that sterilant achieved good penetration in the items being sterilized. CIs are used as internal and external indicators and as part of routine performance testing and load release. It is important to note that CIs alone do not confirm that an item is sterile.

They must be used as part of comprehensive quality control program, that also includes the use of biological indicators and physical monitors, to assure that the conditions for sterilization were met.

When CIs are used as part of a comprehensive quality control program they can capture failures, such as malfunctioning equipment and technician errors, that could result in a non-sterile device. The use of CIs in sterilization provides confidence in the effective reprocessing of medical devices.

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How Do Chemical Indicators Work?

Chemical indicators are used to monitor whether the parameters to achieve sterilization have been met for a specific sterilization process. Chemical indicators use one or more chemicals that undergo either a physical or chemical change, that is visible to the human eye, after exposure to predetermined critical parameters such as time, temperature and sterilant.

VERIFY Steam Integrating Indicator
VERIFY HPU Chemical Indicator 

An example of a CI design that changes physically is a steam indicator strip where the CI uses a chemical pellet that changes from a solid phase to a liquid phase when it is exposed to steam. Once in a liquid state, the material wicks along a paper strip and is visible through the window in the CI.

The second type of CI utilizes one or more chemical reactions to bring about a chemical change. The chemical present in the indicator ink reacts to one or more of the critical parameters of the sterilization process and undergoes a chemical reaction to alter and change the color of the indicator ink to its endpoint color.

This physical or chemical change is observed and interpreted as a pass or fail result and can help Sterile Processing Staff and Surgical Technologists decide whether or not to release a set of instruments for use.

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Chemical Indicators for Sterilization

Chemical indicators should be used in all types of sterilization processes including: steam, hydrogen peroxide, and ethylene oxide. Sterile Processing Department (SPD) staff should always follow the manufacturer's instructions for use and healthcare compliance organizations' guidelines and requirements when using chemical indicators for sterility assurance monitoring.

Chemical indicators are required when using a steam sterilization process to verify that the critical parameters of the cycle were met, and sterilization was achieved. The way CIs are used with an autoclave process depends on the indicator Type and sterilization cycle. Chemical indicators should be used in conjunction with physical monitors and any other appropriate measure of sterility assurance.

What are the different Types of Chemical Indicators for Sterilization?

ANSI/AAMI/ISO 11140-1:2014 defines six types of chemical indicators:

Type 1 Chemical Indicators

Type 1 chemical indicators are also known as Process Indicators. These types of indicators are external and indicate whether an instrument set has been fully exposed to the sterilization process.1 Indicator tape and labels placed on the outside of a peel pack are examples of Type 1 chemical indicators.

Type 2 Chemical Indicators

Type 2 chemical indicators are indicators for use in specific tests. These types of chemical indicators are used in specific procedures defined by sterilization standards.1 For example, Bowie Dick tests are used for a steam sterilizer with a pre-vacuum cycle to check the efficiency of the air removal and steam penetration in the autoclave chamber.

Type 3 Chemical Indicators

Type 3 chemical indicators are known as Single-Variable Indicators. These CIs react to one of the critical parameters (e.g., time, temperature, pressure) of the sterilization process, and indicate exposure to a sterilization cycle at stated values of the specific parameters.1

Type 4 Chemical Indicators

Type 4 chemical indicators, also known as Multi-Variable Indicators, react to two or more critical parameters of the sterilization process, and indicate exposure to the cycle at stated values of the chosen parameters.1 Time and temperature are examples of critical parameters that would be chosen for a steam sterilization process.

Type 5 Chemical Indicators

Type 5 chemical indicators are also known as Integrating Indicators, or Integrators. These CIs are designed to react to all critical parameters over a determined range of sterilization cycles1. The performance of Type 5 Indicators have been correlated to the performance of biological indicators.

Type 6 Chemical Indicators

Type 6 chemical indicators are known as Cycle Specific Indicators and are designed to react to all critical parameters for specified sterilization cycles.1 For example, each Type 6 CI for a steam sterilization monitors the specific temperature and time of a chosen sterilization cycle.

Where to Buy Chemical Indicators?

Healthcare facilities should purchase CIs from a reliable, accessible source for easy reordering. CIs can be purchased from companies that offer sterilization and infection prevention products. Factors that may be considered when deciding which CIs to purchase include sterilization modality being monitored, performance, brand name, cost, range and variety of products, validated applications and ease of use. Refer to ISO 14161 for more information on supplier selection.

1 https://university.steris.com/course/indicators-disinfection-and-sterilization/

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