Chemical Indicators 101: Applications for Use
By John A. Kurowski, BS, RN
Since the first steam sterilizer was created by Charles Chamberland in 1880, researchers have worked on methods to monitor sterilization processes. It was not until the late 1940s and early 1950s that biological and chemical indicators were used routinely to monitor the process. At that time, it was stated that no single quality-assurance monitoring method assures that any item is sterile: rather, it assures that the conditions for sterilization to occur were met. That very statement remains valid in todays healthcare environment.
As sterilization processes have evolved and become more complex, so have the monitoring systems that we use. Sterility assurance programs may consist of the following tools that healthcare management can use:
- Physical monitoring
- Chemical indicators/integrators
- Biological indicators
- Sterilizer preventative maintenance
- Load record keeping This article discusses chemical indicators/integrators (CIs).
Chemical indicators are defined by the Association for the Advancement of Medical Instrumentation (AAMI) as sterilization process monitoring devices designed to respond with a chemical or physical change to one or more of the physical conditions within the sterilizing chamber. CIs are often used to detect sterilizer malfunction/failures resulting from improper loading of the sterilizer, incorrect packaging, deficiencies of the sterilizing agent, or malfunction of the sterilizer itself.
Remember, the pass reading of a CI does not mean that the item or items in the sterilizer load are sterile; it means that the parameter or parameters for sterilization that the CI was designed to measure have been met. The use of CIs is only one portion of an effective quality assurance program. They should be used in conjunction with a biological indicator (spore test), physical monitors, a sterilizer preventative maintenance program, and accurate record keeping for each sterilization load.
Chemical Indicator Classifications
AAMI ST-60 defines five classes of CIs and the specific performance requirements for each.
Process Indicators (Class 1): The most basic of chemical indicators, they are also known as throughput indicators. These CIs are intended for use with individual items to be sterilized. They are designed to demonstrate that the item has been exposed to a sterilization process and to distinguish between processed and non-processed items. Examples of Class 1 indicators are tape and the indicators found on paper or plastic peel pouches.
Indicators for Use in specific Tests (Class 2): Also known as specialty indicators, Class 2 indicators are designed for use in specific test procedures as defi ned by relevant sterilization standards. Examples of Class 2 indicators are the Bowie Dick and Dart products used in steam sterilizers. These indicators test for the presence of air in the steam sterilizing chamber. A positive test would mean that air, which inhibits the conditions necessary for sterilization, has either not been removed during the cycle or has entered the chamber through leaks in the system. Maintenance must be performed on the steam sterilizer to prevent the presence of air in the chamber during a sterilization cycle.
Single-parameter Indicators (Class 3): These indicators react to one of the critical process parameters of sterilization and indicate exposure to a sterilization cycle at stated values of the chosen parameter. Critical parameters typically chosen for steam sterilization processes are time or temperature.
Multi-parameter Indicators (Class 4): These indicators are more accurate by design than Class 3 indicators. They react to two or more critical parameters of the sterilization process and indicate exposure to the sterilization cycle at stated values of the chosen parameters. Time and temperature are examples of steam sterilization parameters, and time and concentration of ethylene oxide are chosen for EO sterilization.
Integrating Indicators (Class 5): These indicators, known as integrators, are designed to react to all critical parameters over a specified range of sterilization cycles. Their performance has been correlated to the performance of a biological indicator (BI) under its labeled conditions for use. This class of indicator can be used in place of the BI in many applications, thereby reducing the overall cost of sterile processing.
Use of Chemical Indicators
When considering which class of indicator to use, you must consider your external and internal chemical monitoring needs for your various sterilization systems.
External indicators are simply used to distinguish between processed and unprocessed items. A Class 1 indicator in the form of tape, an indicating label, or the indicator legend on a paper or plastic peel pouch is appropriate and should be placed on each package that is intended for sterilization. The external CI usually exhibits a simple visual color change that shows the package has been exposed to physical conditions present during a sterilization process.
Internal indicators need to be used within each package that will be sterilized. Depending on the complexity of the pack and devices within them, a Class 3, Class 4, or Class 5 CI can be used. All internal CIs should be placed in an area of the package that is determined to be the least accessible to sterilant contact. This may not always be in the center of the package.
AAMI states that a Class 5 indicator may serve as the basis for the release of processed items, excluding implants.
Integrator challenge packs utilize a Class 5 chemical integrator within an appropriate challenge pack to monitor sterilization loads. The challenge packs are placed within the sterilization load, outside the packs, in the sterilization chamber, and have been correlated to the kill achieved in the AAMI 16 towel BI test pack. The result of the chemical integrator may be used to release the load, excluding implantable devices.
Results of external indicators and chemical integrator challenge packs can be read at the end of the sterilization cycle when the package is retrieved from the sterilizer. However, internal indicators must be interpreted at the time of use. Therefore all healthcare personnel should be trained on the proper interpretation of a positive and negative result and what to do if a negative result occurs.
Be an Informed Consumer
In order to be an educated consumer you must be familiar with the parameters you wish to monitor, which will help you select the type or class of indicator(s) to purchase. Healthcare management should ask the indicator manufacturer for reliability data and for the safety and overall performance characteristics of their products. Questions to ask include:
- Are the indicator results easy to interpret?
- Can you store the indicator results for a period of time?
- What sterilization parameters will the indicator detect?
- Is it biologically correlated? If so, what are the specifics (organism, D-value, population)?
- Does the indicator have a shelf life and what are the required storage conditions?
By asking these simple questions, you will ensure the correct choice of indicators to meet your quality assurance needs.
John A. Kurowski, BS, RN, is a global clinical education manager for STERIS Corporation. He provides education and training to STERIS employees and healthcare facilities in the areas of infection prevention, the proper use of STERIS products, and proper cleaning, decontamination, and sterilization techniques and procedures. He has been a featured speaker for both the local and national Association of periOperative Room Nurses (AORN), the Association for Professionals in Infection Control and Epidemiology (APIC), and the Society for Gastroenterology Nurses and Associates (SGNA). He is an active member of these organizations.