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Vaporized hydrogen peroxide sterilization


Hydrogen peroxide sterilization is a low temperature chemical sterilization process that uses hydrogen peroxide vapor as the sterilizing agent. Hydrogen peroxide will oxidize critical molecules and kill the micro- organism. Vaporized hydrogen peroxide cycles typically operate at temperatures of approximately 50°C to 55°C which are well below the temperatures used in steam sterilization processes. The critical variables for VH2O2 sterilization processes are tem- perature, exposure time, and concentration of hydrogen peroxide. The concentration of hydrogen peroxide is more complicated than it sounds. VH2O2 sterilization is a chemi- cal process which means that hydrogen peroxide molecules must directly contact a microorganism to kill it. So, to sterilize a device, every microorganism on the device must be contacted directly by the hydrogen peroxide. Hydrogen peroxide is in a vapor state, which means it tends to easily con- dense into liquid on surfaces, like water vapor on the mirror in the bathroom after a hot shower. The condensed liquid hydro- gen peroxide will not further penetrate into the devices and may reduce the amount of vaporized hydrogen peroxide available in the rest of the chamber. In addition, hydro- gen peroxide itself is a somewhat unstable molecule, and will tend to break down into other chemicals. (For example, the hydrogen peroxide solution in your home medicine cabinet is in a light-proof, brown bottle and must be stored in a cool place, to protect the unstable hydrogen peroxide molecule). These properties of vaporized hydrogen peroxide make it very important to properly maintain the sterilizer and also to follow the instructions for use (IFUs) provided by both the device manufacturer and the sterilizer manufacturer.


There are many different VH2O2 cycles


available in the VH2O2 sterilizers used in healthcare today. Some cycles use a gas plasma exposure to reduce the amount of residual hydrogen peroxide after the cycle is complete. Each cycle is intended for a specific set of medical devices, and careful adherence to the sterilizer manufacturer’s


and medical device manufacturer’s cycle recommendations is critical.


Sterilization Quality Control The sterile processing team must decide if each instrument load has been correctly processed and is safe and ready for use on patients. The challenge is that you cannot see if the devices are sterile, and there is no practical way to do microbiological testing on each device to determine if it is sterile. However, you can perform other types of tests on each sterilizer cycle to provide information on whether the expected and required conditions were achieved in that cycle. While these quality control (QC) tests cannot absolutely confirm sterility, they can provide information on the sterilizer cycle performance that can be used to decide on whether the devices in that cycle can be considered safe and ready for patient use. The quality control programs for health-


care sterilization processes are typically based on testing the sterilizer and process with a combination of physical monitors, chemical indicators (CIs), and biological indicators (BIs). Each of these monitoring tools provides different information about the sterilization process that, when com- bined and evaluated by a knowledgeable individual, can provide the information needed to decide whether to release the load contents for patient use.


The physical monitors are sensors that


are located in the sterilizer chamber and measure physical parameters such as tem- perature and pressure and provide a cycle printout. This information is useful for ensuring that the correct cycle was selected and confirming that no cycle errors occurred. The physical monitors provide basic infor- mation from distinct points in the chamber wall and are not able to provide informa- tion related to loading or information from inside the sterilizer load. Chemical indica- tors use reactive inks that will respond to specific process conditions with a chemical or physical change that can be interpreted by the user (e.g., a change in ink color or a moving front). Chemical indicators are placed on both the outside and inside of packages and provide information on the


Table 1 – AAMI Monitoring Recommendations for Routine Release of Loads STEAM


VH2O2 Physical monitoring


Chemical indicators - external Chemical indicators - internal


a. Non-implant loads Every cycle


Every package Every package


Biological indicators inside a PCD Optionala Every cycleb


b. Loads containing an implant Every cycle


Every package Every package


Daily, preferably every cyclea Every cycleb


SELF-STUDY SERIES


physical quality of the process from those locations in the load. Biological indicators are placed inside process challenge devices (PCDs) in the most challenging location in the chamber and provide the only direct measurement of the lethality (killing power) of the cycle. In the BI/PCD system the BI’s spores are intended to represent the micro- organisms on the medical devices. The PCD is separate and represents the challenge to the process provided by the device packag- ing and the load. The BI/PCD combination then provides a representative challenge to the process like the organisms on devices inside of the load, yet the BI/PCD is easy to retrieve and test without opening any packaged devices. A “pass” result for all these indicators (physical, chemical, bio- logical) provides a sound rationale that the process was correct and effective, and the load contents are safe for patient use. Performance and labeling requirements for biological indicators for steam are well defined in ISO standards, but currently there are no standards defining the performance requirements for biological indicators for VH2O2 processes. This means that the end user should rely on regulatory clearances by the FDA to provide confidence that the biological indicators they are using will per- form appropriately in the labeled cycles. The FDA makes the determination regarding suitability of BIs for specific VH2O2 cycles through the regulatory clearance.


Recommended Practices AAMI standards provide recommended quality control monitoring practices for load release for steam and VH2O2 cycles.4,5


The recommendations are


summarized in Table 1. The monitoring recommendations for


load release for steam and VH2O2 are quite similar. It should be noted that BI/PCDs are optional for testing of non-implant loads in steam while BI/PCD testing is preferred for every cycle in VH2O2. Many health- care facilities monitor every cycle in both processes with a BI in a PCD to provide the highest level of quality control and a uniform standard of care for all patients.


Summary


By preventing cross contamination between patients, sterilization processes used in healthcare facilities are an essential part of an infection prevention program. Steam and vaporized hydrogen peroxide processes are both effective when used properly. Quality control testing using physical monitors, chemical indicators, and biological indica- tors inside of PCDs provides information


hpnonline.com • HEALTHCARE PURCHASING NEWS • December 2023 25


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


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