Ethylene oxide sterilization gas is the most commonly used sterilization method at room temperature. Ethylene oxide sterilization is widely applied in the sterilization of medical devices. Due to its active nature, strong bactericidal power, and minimal damage to items, ethylene oxide sterilization is currently one of the primary sterilization methods. This article will discuss the sterilization process, principles, and advantages and disadvantages of ethylene oxide sterilization.

Properties of Ethylene Oxide Gas

Ethylene oxide is an organic compound with the chemical formula C2H4O. It is a toxic carcinogen that was previously used to manufacture disinfectants. Ethylene oxide is highly flammable and explosive, making it difficult to transport over long distances, resulting in strong regional variability.
At temperatures above 40 degrees Celsius, ethylene oxide begins to polymerize, making it difficult to store. To enhance safety, it is typically stored and used with carbon dioxide or other inert gases as diluents.

Principle of Ethylene Oxide Sterilization

Ethylene oxide (EO) can eliminate various microorganisms, including bacterial vegetative cells, spores, viruses, and fungal spores, making it a broad-spectrum sterilant. It is generally believed that this is due to its ability to undergo non-specific alkylation reactions with the proteins, DNA, and RNA of microorganisms. To date, all available data indicate that the sterilizing effect of EO is irreversible, meaning that EO is a sterilant rather than a disinfectant. Furthermore, based on various clinical and research results, EO is the most effective chemical sterilant among all chemical disinfectants or sterilants. Ethylene oxide can inhibit the activity of certain microbial enzymes, including phosphoactivase, peptidase, cholinesterase, and cholinesterase. Ethylene oxide also undergoes alkylation with DNA and RNA, leading to the inactivation of microorganisms.

How does ethylene oxide work?

Ethylene oxide (EtO) is considered a powerful sterilant. But how exactly does it kill microorganisms?
The simple answer is that ethylene oxide tears apart cell membranes, causing microorganisms to die.
Ethylene oxide is a colorless, flammable gas. When ethylene oxide reacts with different chemicals, an alkylation reaction occurs. An alkylation reaction is a chemical reaction where hydrogen atoms are replaced by hydroxyethyl radicals. This process causes amino acids in proteins to change their shape.
These proteins typically penetrate cell membranes, forming channels between the inside and outside of cells. When these proteins change shape, it causes the cell membrane to rupture, thereby killing (dissolving) microorganisms.

Ethylene Oxide Sterilization Process

Ethylene oxide sterilization (EtO sterilization) is a widely used low-temperature sterilization method for medical devices, pharmaceutical packaging, and laboratory equipment. The process utilizes the chemical action of ethylene oxide gas to destroy microbial DNA, thereby achieving sterilization. The following are the main steps of ethylene oxide sterilization:  

Preparation stage:

Cleaning: Before sterilization, ensure that the items to be sterilized are free of dirt, grease, etc., to ensure sterilization effectiveness.  
Packaging: Items are packaged in breathable materials, typically sterile packaging bags, to ensure that the gas can penetrate every part of the items.

Gas introduction:

Place the items to be sterilized into the ethylene oxide sterilization chamber and use a vacuum system to remove air, reducing oxygen concentration to minimize reactions between the gas and air.  
Then, introduce ethylene oxide gas into the sterilization chamber to ensure thorough contact with the items.

Sterilization stage:

At appropriate temperatures (typically 30°C to 60°C) and humidity levels (approximately 40% to 60%), ethylene oxide gas comes into contact with the surface of the items and, through chemical reactions, destroys the DNA of microorganisms, rendering them incapable of reproduction.  
The sterilization process lasts several hours, with the exact duration depending on the material, size, and sterilization requirements of the items.

Ventilation stage:

After sterilization is complete, the ethylene oxide gas is vented from the sterilization chamber, and residual ethylene oxide gas is thoroughly removed through the ventilation process.  
This process typically takes several hours to ensure that the sterilized items are completely non-toxic and safe for use.

Testing and verification:

After the entire sterilization process, the sterilization effectiveness is verified using biological or chemical indicators to ensure that all target microorganisms have been inactivated.  
The advantage of ethylene oxide sterilization is that it is suitable for temperature-sensitive items that cannot withstand high temperatures, such as plastics, rubber, and certain electronic devices. However, since ethylene oxide gas is toxic, strict adherence to safety regulations is required during operation.

Advantages, Disadvantages, and Applications of Ethylene Oxide (EO) Sterilization

Advantages of EO Sterilization

Can be used for sterilizing items that are not heat-resistant or moisture-resistant.
Ethylene oxide can eliminate all microorganisms, including bacterial spores.
High penetrability, suitable for sterilizing hard-to-reach areas such as thin, long tubes.
Minimal damage to items, widely used for sterilizing heat-sensitive precision instruments.
During sterilization, items can be wrapped in various materials for storage and transportation. Upon opening the packaging, the items can be used immediately, eliminating the risk of cross-contamination.

Disadvantages of EO Sterilization  

Long sterilization cycle time.  
EO is flammable and explosive; leakage must be strictly prevented during storage and sterilization. Safe sterilization equipment must be selected, and safe operation and storage procedures must be followed.

Clinical Applications of EO

Ethylene oxide (EO) is widely used in clinical settings for the sterilization of various devices and instruments. Commonly sterilized devices include:  
Endoscopic equipment: such as arthroscopes, gastroscopes, bronchoscopes, cystoscopes, etc.
Medical equipment: such as anesthesia equipment, dialysis equipment, heart-lung machines, ventilators, etc.  
Surgical instruments: such as electric drills, electrosurgical units, dental drills, microsurgical instruments, bone drills, etc.  
Rubber products: such as catheters, surgical gloves, endotracheal tubes, etc.  
Plastic products: such as heart valves, etc.

Conclusion

In conclusion, ethylene oxide sterilization is a highly effective method for sterilizing a wide range of heat-sensitive medical devices and equipment. By utilizing ethylene oxide gas to disrupt microbial DNA and proteins, this process ensures thorough sterilization without damaging delicate materials. Despite its efficiency, proper handling, ventilation, and post-sterilization aeration are crucial to ensure safety and eliminate residual toxicity. As a result, ethylene oxide remains a vital sterilization method in healthcare and laboratory settings, particularly for complex or sensitive items that cannot withstand high temperatures.