Ethylene Oxide Sterilization in Healthcare Facilities
All of us involved in patient care, face the challenge of protecting patients and healthcare staff from infectious disease. We must therefore employ effective agents to disinfect and sterilize instruments and equipment.
Ethylene oxide (EO) sterilization plays an important role in an effective healthcare infection control program because of its reliability and gentleness.
Comparison of Various Methods of Sterilization
- Steam sterilization — The most widely used healthcare sterilant in the world, steam effectively kills micro-organisms, works quickly and is cheap. Although it leaves no residue and is non-toxic, steam uses both pressure and high temperatures to achieve sterility, which can be very damaging to sensitive equipment.
Liquid disinfectants sterilization — Liquid disinfectants, such as glutaraldehyde and peracetic acid, are widely used in healthcare facilities; however, they can’t be used for all medical materials. The cycle times and concentrations typically used only provide disinfection, which can fail to kill resistant microorganisms. The solutions are highly corrosive, toxic, and cannot be used with barrier packaging. The moment an instrument is removed from the liquid, its sterility is compromised.
Ethylene Oxide sterilization — Over 20,000 healthcare facilities worldwide use ethylene oxide sterilizers to process sensitive instruments which cannot be adequately sterilized by other methods. EO, a potent, anti-microbial agent, can kill all known viruses, bacteria and fungi, annihilating even the most sterilization-resistant types of microorganisms, bacterial spores. Tough on microbes, ethylene oxide still treats most medical materials gently, even with repeated use. The ability to seal items in all-plastic packaging permits sterility maintenance for an indefinite period following gas sterilization.
As with any other sterilization process, ethylene oxide must be used carefully. Because ethylene oxide is a toxic substance, users must pay attention to correct usage guidelines to avoid adverse effects for operators or patients. Since the gas actually dissolves in porous substances, aeration is required after sterilization to remove residues. Because pure ethylene oxide is a flammable ether, care must be taken to prevent its ignition.
Instruments Frequently Gas Sterilized in Healthcare Facilities
Fiberoptic endoscopes, surgical telescopes
Ophthalmic instruments
Plastic instruments (e.g., specula, syringes)
Anesthesia masks and circuits
Rubber and plastic tubing (e.g., catheters)
Electrical equipment (e.g., drills, pumps, motors)
Respirators and inhalation therapy supplies
Surgical staplers/staples, sutures, sharps
Some of these items may be steam-autoclaved, but the high heat, moisture and pressure of the process often causes rapid deterioration in their quality. Many plastic instruments, such as speculi, can be reused almost indefinitely when they are gas sterilized. Similarly, fiberoptic endoscopes may be resterilized with gas, without any adverse effect.
History of EO Use
Ethylene oxide boasts nearly a seventy-year history of use in healthcare facilities and the medical device industry. First described as an insecticide in 1928, it became widely used in the U.S. as a fumigant for imported agricultural products during the subsequent decades. In the early 1950s, Dr. Charles Phillips, working at the U.S. Army research center at Fort Dietrick, Maryland, thoroughly investigated the microbicidal potential of ethylene oxide. He published a series of articles leading to its adoption as a sterilant by the medical device industry. Today, American medical device manufacturers sterilize over half the goods they produce with ethylene oxide.
Like many other beneficial chemicals, ethylene oxide is produced through the petroleum refining process. Although medical, cosmetic and spice sterilization consume approximately 8 million pounds of EO annually in the U.S., the most common application for the chemical is in making other chemicals. The chemical industry outputs a total of 9 billion pounds of ethylene oxide for this purpose. EO is a crucial ingredient in the production of ethylene glycol, which is the main ingredient in automotive antifreeze. Other important products ethylene oxide plays a key role in manufacturing include soaps, detergents and shampoos.
Characteristics of EO
EO is a tiny molecule in which two carbon and four hydrogen atoms are joined to one oxygen atom in a highly strained ring. Because of the chemical’s very low boiling point (10.4ºC), it becomes active at room temperature. It vaporizes and permeates rapidly through packaging, dissolving in substances like plastic and rubber. EO readily kills all types of microorganisms under ordinary atmospheric conditions. Its fragile molecular bonds allow it to quickly react with a wide variety of compounds. The resulting chemical reaction is called alkylation.
Requirements for EO Sterilization
Effective sterilization requires careful attention to the six main conditions for ethylene oxide use.
- Although highly penetrative, ethylene oxide must have an unobstructed path to be able to sterilize the interior of devices. Complex instruments must be disassembled for sterilization, so the gas may penetrate the most remote recesses. Caps, plugs or stylets must be removed prior to sterilization.
- Biological matter residues on instruments can shield microorganisms from EO’s lethal effects. Thoroughly wash and dry instruments prepared for gas sterilization to meet the standard of surgical cleanliness.
- Use appropriate wrapping materials for gas sterilization: paper, cloth or EO-permeable plastic. These materials allow EO to diffuse into the package to sterilize the contents. If the instruments will be used in an operating room, they may be double-wrapped, according to the traditional method for sterilization. Paper or cloth wrapping materials are not impervious to microorganisms and therefore typically require reprocessing at predetermined intervals.
- A sufficient dose of ethylene oxide must be used for an adequate length of time to kill the most resistant microorganisms.
- Adequate humidity must be present to facilitate the process. Desiccated organisms may become resistant to ethylene oxide sterilization.
- The dose of ethylene oxide required depends on the temperature of the process. The higher the temperature, the lower the dose of EO that will be necessary to sterilize.
Personnel Considerations when using EO
As in all sterilization procedures, it is important that all staff involved in the operation of the sterilizer are fully instructed in the correct operating procedure before using the equipment.
Training manuals and other relevant reference materials must be readily available. AAMI (the Association for the Advancement of Medical Instrumentation) produced a document entitled “Good Hospital Practice: Ethylene Oxide Gas-Ventilation Recommendations and Safe Use” in 1992, much of which is still valid today. This document provides detailed advice on how to operate an EO sterilization system safely.
Note: The use of personnel monitors is recommended by AAMI and is now an OSHA regulatory requirement. These devices measure the average exposure to EO over a given period of time.
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