AAMI TIR16:2023—Ethylene Oxide Sterilization

Ethylene oxide (EO or EtO) gas is one of the most common ways to sterilize medical devices, as approximately 50% of sterile medical devices are treated with EO—about 20 billion each year. EO sterilization consists of a safe, tightly controlled, highly regulated process that is critical for preventing infections and ensuring patients have safe surgeries and medical treatments. AAMI TIR16:2023— Microbiological Aspects Of Ethylene Oxide Sterilization provides guidelines for the ethylene oxide (EO) sterilization process.

What Does Ethylene Oxide (EO) Mean in Sterilization?

Ethylene oxide (also known as EO or EtO) is a low temperature gaseous process widely used to sterilize a variety of healthcare products, such as single-use medical devices. Sterilization by EO kills microorganisms through exposure to EO gas under vacuum and humidity. Hundreds of thousands of medical, hospital, and laboratory processes rely on EO to sterilize devices and equipment to protect millions of patients from the real risks of infectious diseases caused by bacteria, viruses, and fungi. Medical devices and equipment commonly processed with EO include:

Assembled complex devices
Catheters
Custom procedure packs
Equipment with integrated electronics
Multi-lumen tubing products
Stents
Uterine Monitors
Wound care dressings
Surgical telescopes
Syringes
IV sets
Specula
Electrical equipment
Plastic tubing
Respirators
Heart Valves
Pumps

For the majority of these products, EO sterilization is the most effective and efficient—and often the only viable—sterilization technology. The gentle yet thorough nature of EO allows for the sterilization of many critical medical technologies and devices that would otherwise be destroyed and rendered unusable by other sterilization methods.

What Is AAMI TIR16?

AAMI TIR16:2023 addresses various microbiological aspects of the development and validation of an ethylene oxide (EO) sterilization process. This technical information report (TIR) provides additional guidance to ANSI/AAMI/ISO 11135:2014 for medical device manufacturers, including those that use contract sterilization facilities or contract sterilization operations. Although the information presented was developed for application to medical devices, the content of AAMI TIR16:2023 may also be applied to other relevant products or materials.

This TIR does not address the various factors that can have an effect on the bioburden of the product and on the sterilization process.

How Is Sterilization By Ethylene Oxide (EO) Performed?

The basic ethylene oxide (EO) sterilization cycle consists of five stages (preconditioning and humidification, gas introduction, exposure, evacuation, and air washes). The exposure time for most EO sterilizations is relatively long (around 6 hours). The gas aeration period is also lengthy, up to 24 hours or more. After loading items into an EO sterilization chamber, a vacuum is applied. Next, the chamber is filled to the desired relative humidity. Then an appropriate concentration of EO gas is added. Items undergoing sterilization rest in the EO gas under vacuum and humidity for the desired exposure time. The gas is slowly and safely evacuated from the EO sterilization chamber, and the sterilized items are given ample aeration time to support EO off-gassing.

For sterilization validations, the D value (i.e., the number of minutes exposure to a defined temperature to reduce viable bacteria by 90%) of biological indicators used for EO sterilization validations may range up to 10-fold over the range of relative humidity values. AAMI TIR16:2023 specifies that the D value of the internal process challenge device (PCD) is calculated using the Holcomb-Spearman-Karber Procedure (HSKP) or Limited Holcomb-Spearman-Karber Procedure (LHSKP), or the Stumbo-Murphy-Cochran Procedure (SMCP).

Factors that Affect Ethylene Oxide (EO) Sterilization and Lethality

AAMI TIR16:2023 details that the physical parameters that have a significant effect on the lethality of an ethylene oxide (EO) sterilization process are EO concentration, temperature, EO dwell time, and humidity. These parameters are interrelated and a change in one can often be compensated for by a change in another. Other aspects that could affect lethality are the rate of sterilant injection, vacuum depth, and rate of evacuations during the sterilant-removal phases, as these aspects could impact the overall exposure phase time. Evacuations can be affected by chamber temperature, humidity, sterilant levels, vacuum pump performance, and/or product load configuration.

AAMI TIR16:2023— Microbiological Aspects Of Ethylene Oxide Sterilization is available on the ANSI Webstore and in the Standards Packages: AAMI TIR28 / AAMI TIR16 / AAMI TIR14 – Ethylene Oxide Sterilization Package and AAMI TIR28 / AAMI TIR16 / AAMI TIR17 – Ethylene Oxide Sterilization Package.