The Process of EO Sterilization
The EO sterilization procedure was first used by the medical industry to sterilize medical equipment between the 1940s and the mid-1990s (Wikipedia 2021). In the United States, it is still widely used as a method of sterilizing medical devices. Even in the United Kingdom, dental implants are one of the few dental procedures that still use the EO sterilization technique. There have been many changes to the procedure over time; however, many of these changes have only increased the safety of the procedure overall.
Before discussing the sterilization technique in terms of the medical device itself, it is important to discuss the equipment itself. An
EO kit contains two major components: an oxidizing agent, usually in the form of a carrier solution, and an inlet filter or diatomaceous earth (DE). Typically, the kit will also contain some instructions and safety materials. These materials generally include the type of device to be used, sterile equipment to handle the unit, storage media for the EO solution, packaging for the product, and other miscellaneous information about EO sterilization. The sterilization needle is generally standard and may vary slightly from manufacturer to manufacturer, although all needles are manufactured with a stainless steel construction.
The oxidizing agent is typically either iodine or nitrous oxide. Both serve the same purpose, which is to create a chemical reaction that causes rapid deterioration of the viable material during the contact time. It is important to note that some variations of the EO sterilization method actually use chlorine to achieve the same results. Iodine is the most commonly used sterilizer due to its long shelf life and relatively low cost. Nitrous oxide, on the other hand, is less expensive but less effective.
As part of the sterilization process, the kit will provide storage media for the EO solution. This is typically sterile packaging like serum-free cotton wool or glassine or polyethylene film. This packaging can be a little tricky to use initially. Once the proper temperature is achieved during storage, it will be easy to use. The glassine or polyethylene film, however, will prevent any air or moisture from reaching the solution as well as hindering any airborne contaminants like bacteria and viruses. A good rule of thumb for EO sterilization packaging is to ensure the glassine or polyethylene film is enclosed in a plastic bag during transport.
The inlet filter or diatomaceous earth (DE) serves as the primary contact point between the solution and the medical device. This component is also the most effective method of EO sterilization as it efficiently chokes and kills any pathogens that make it into the sterilized area. Unlike some of the other methods used in EO sterilization, DE does not use heat to kill or sterilize pathogens. Instead, it relies on physical contact for this reaction. For EO to work effectively, it must come into contact with the air in the medical device.
Depending on the kind of device being used, different kinds of media may be needed. Some medical devices require absolute humidity (or CI) neutral media, while others rely on relative humidity (RH). Relative humidity is calculated using the percentage of water vapor in the air mass over the dry weight of the device. For instance, if a medical device with a dry weight of 10 g is kept in an environment with a CI of 20% and a relative humidity of 40%, then this device would be considered relative humid. Relative humidity affects the PH level of the EO and therefore affects the gas concentration that is released during sterilization.
The key step of all EO cycle parameters sterilization is proper and complete mixing. The mixing process actually varies depending on the type of device being used. EO that is used in medical equipment such as endoscope pads usually contain borate-based solution. The borate-based solution is mixed with dimethylbenzene, which serves as an oxidizing agent. This process allows bacteria to adhere to the surface of the device as it ferments with the oxygen in the medium.
Different kinds of media can be used for EO sterilization. In some cases, an autoclave is used for this purpose. This is because the temperature and pressure of an autoclave can affect the chemical properties of the media that are being used. One example of such media includes deep vacuum nitrogen soft cycles. These media include carbon sheet, shallow vacuum nitrogen soft cycles, and ice water autoclaves.
