Ethylene Oxide (which is normally represented as "EO" or "EtO") is an organic compound that, at normal room temperature, exists as colorless gas having a faintly sweet odor. The relative instability of its molecular bonds makes it highly reactive and, thereby, extremely flammable and explosive in a wide range of concentrations. However, this same instability and reactivity results in Ethylene Oxide causing alkylation to microorganisms at the cellular level, preventing microbial DNA from reproducing and thereby killing the organism. Ethylene Oxide is compatible with a diverse range of materials and leaves no residue, making it particularly suitable as a sterilizing agent for the healthcare industry and as a fumigant for the processing of agricultural products and the storage of valuable documents.
Ethylene Oxide is a very effective sterilant for products that cannot tolerate heat, moisture or abrasive chemicals as well as products which contain materials that are structurally modified by exposure to radiation. More than 50% of the medical devices manufactured throughout the world today are sterilized by the Ethylene Oxide gas sterilization process.
The Gas Sterilization Process
Products or devices to be sterilized are packaged with a breathable barrier material. This barrier material blocks microorganisms from passing through, but is sufficiently porous to allow the diffusion of the Ethylene Oxide gas to all surfaces of the products being sterilized. Prior to being sterilized the products are generally preconditioned to increase the temperature of the materials and humidity level at the material surface. Preconditioning maximizes the effectiveness of the sterilization process.
The Ethylene Oxide gas sterilization process takes place in a sealed vacuum chamber at very carefully controlled vacuum levels and environmental conditions. While the products are exposed to the gas under vacuum, the temperature, humidity, and gas concentration are carefully maintained at levels that have been validated to result in sterility. The products are exposed to the gas for a time period that is at least twice as long as the time proven to result in a 100% microorganism kill rate.
Following exposure, the sterilized products are actively degassed in several "wash" cycles by successively raising the chamber pressure by the introduction of either Nitrogen or air and lowering the pressure by evacuation. The number and nature of the required wash cycles are determined by how readily the products and their packaging release the sterilizing gas. This process removes almost all of the Ethylene Oxide from the products and returns the chamber to a condition safe to remove the sterilized products.
After sterilization, the products generally are aerated at elevated temperatures for a period known to reduce residual Ethylene Oxide concentrations to acceptable levels.
Why Gas Sterilization?
Gas sterilization is an appropriate sterilization choice for any products that are compatible with Ethylene Oxide and that can be packaged with a breathable microbial barrier sufficient to permit gas diffusion into and out of the package. Typical products include:
- Stents and other implantable devices
- Catheters, IVs and other tubing products
- Bandages and other types of wound dressings
- Surgical gowns and drapes
- Electronic equipment
- Procedure Trays and Packaged medical kits
- Veterinary Supplies
- Spices, Nuts, and other Agricultural Products
The Ethylene Oxide gas sterilization process has been commonly used in the health care industry for over 70 years. It is the most frequently used sterilization process due to its effectiveness, low cost and compatibility with a wide range of materials.