Sterilization is a process that aims to destroy and remove all-living microorganisms, and viable spores from an object. Medical devices can be sterilized by a variety of processes including moist heat, dry heat, gamma radiation, UV, hydrogen peroxide, and ethylene oxide. However, most of the medical devices are sensitive to heat. Hence, heat sterilizations are not preferred by manufacturers.

Ethylene oxide (EO) gas which is a colorless, flammable, explosive, toxic gas with a slight odor was discovered in 1859. However, the bactericidal properties of the EO gas had not known until World War 2. The idea of using EO as a bactericidal agent for the sterilization of heat and humidity-sensitive materials were suggested and EO sterilization has been used since the 1960s for medical device sterilization.

Most medical devices, which are heat, and humidity-sensitive materials, are sterilized with ethylene oxide. It is easily used in polymers such as plastic or resin, metal or glass materials, multi-layer packaging, or medical devices with hard-to-reach spaces. Fifty percent of sterile medical devices are sterilized with ethylene oxide in the US market. This indicates that ethylene oxide sterilization is widely used by manufacturers due to its inertness to medical devices.

EO is a direct alkylating agent that inactivates the microorganism by an alkylation reaction with cellular constituents of organisms. The alkylation pathway occurs by the addition of alkyl groups to DNA, RNA, and proteins. These chemical moieties are not present in most of the medical device’s composition; therefore, exposure to EO does not cause any adverse effects on medical devices.

The ethylene oxide sterilization process generally consists of 3 steps: Preconditioning, sterilization, and ventilation.

Preconditioning: It is the process of preparing the device to keep the product stable at the appropriate temperature (usually 30-50 ᵒC) and 40-80% relative humidity.

Sterilization: Before starting sterilization, a preliminary leak test is performed under a vacuum. In case of leakage, the device will not start the sterilization process. If there is no leakage, the preconditioning process starts. After the preconditioning process, the vacuum process is performed again and the leak test is repeated for safety. Then, the sterilization process begins by flowing EO gas into the sterilization cabinet. The gas flows into the sterilization cabinet until the safe vacuum value. It uses 100% pure Ethyl oxide (EO) or EO: CO2 (Ethylene Oxide – carbon dioxide) mixture as a sterilization agent. EO gas is discharged after the products are exposed to EO gas with the sterilization process.

Ventilation: After sterilization, the products are washed with air after waiting for a while. It is an important step to prevent EO residue on the products due to the toxic and explosive properties of ethylene oxide.

Things to do to work safely with Ethylene Oxide:
– EO gas is flammable and explosive. It should not be exposed to high temperatures and pressure.
– Before working with ethylene oxide, protective measures determined by the "National Institute for Occupational Safety and Health (WIOSH)" should be applied.
– Only trained personnel should enter the EO sterilization area.
– Warning signs must be hung.
– Ethylene oxide level should be kept under constant control.
– In case of gas leakage, an extraordinary action plan should be ready.
– Authorized personnel should work with personal protective equipment.

Advantages of ethylene oxide sterilization:
– It can be used in all medical equipment and instruments that are sensitive to heat and humidity.
– It is suitable for most medical instruments.
– It is easy to apply.
– Applicable to packaged materials.
– Less damage to tools.

Disadvantages of ethylene oxide sterilization:
– Sterilization process is time-consuming.
– Liquids cannot be sterilized by EO.
– It is prone to user error.
– It is a toxic, flammable, and explosive gas.

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