Understanding the Ethylene Oxide (EtO) Sterilization

Sterilization of operation theaters and surgical instruments is one of the fundamental principles of surgery. If the sterilization is not taken into consideration or if it is done improperly, the patients’ lives are at risk. One can see many variations for different modes of sterilization and its related practices. For example, surgical instruments are commonly sterilized using autoclave machines and radiation. In contrast, steam and ethylene oxide are used to fix surgical drapes.

Ethylene oxide sterilization may seem an unconventional mode of sterilization since it is a gas. However, it is widely used to sterilize moisture and heat-sensitive medical devices. There are two major EtO mixtures available for sterilization:

1. EtO-carbon dioxide mixture, and

2. EtO-hydrofluorocarbons (HCFC) mixture.

EtO Sterilization for Medical Devices

Mode of Action of EtO

EtO performs its microbicidal action by alkylating the microbes’ DNA, RNA, and protein structure. Alkylation refers to replacing hydrogen atoms with an alkyl group, thus preventing normal replication and metabolism within the microbial cells.

EtO Sterilization Cycle

An EtO sterilization cycle has the following five stages:

1. Preconditioning and humidification

2. Gas introduction

3. Exposure

4. Evacuation, and,

5. Air washes

Mechanical aeration for 8 to 12 hours at 50 to 60°C reduces the hazardous EtO residue in exposed absorbent materials. Most current EtO sterilizers do sterilization and aeration simultaneously in the same chamber. These EtO sterilizers limit potential EtO exposure during door opening and load transfer to the aerator.            

Why is Aeration Important After EtO Sterilization?

Many materials absorb EtO easily. As a result, they require aeration after sterilization to eliminate any leftover EtO. Various guidelines recommend that the residual levels of EtO should be checked in devices after sterilization.

Benefits of EtO Sterilization

EtO sterilization offers the following benefits:

  • Sterilization at low temperatures protects the product and packaging.
  • EtO is effective against germs, even resistant spores.
  • Good diffusion: The gas can pass through sheets and difficult-to-reach areas of the goods being disinfected.
  • EtO can sterilize plastics that would otherwise melt in an autoclave.
  • Materials sterilized using EtO are not subjected to high temperatures, moisture, or radiation. This implies that EtO can sterilize a wide range of materials, especially polymeric components often used in the manufacturing of medical devices.

Medical Devices and EtO Sterilization

For most of the medical devices, sterilization with EtO is the only plausible method. EtO sterilization sterilizes the device. It is safe, as devices are not harmed during the process. Some of the medical devices that may only get sterilized because of EtO are:

  • Those made from specific polymers, such as resin or plastic;
  • Those having different layers of packaging;
  • Those made from metal or glass, and
  • Those devices that need to be placed in hard-to-reach spaces. Catheters are examples of such devices.

FDA and Standards for EtO Sterilization

The Food and Drug Authority (FDA) of USA has enacted two consensus standards regarding EtO sterilization. These standards are:

  • ANSI AAMI ISO 10993-7:2008(R)2012), and
  • ANSI AAMI ISO 11135:2014

These standards can be helpful for hospitals and healthcare settings that want to sterilize their medical devices with EtO. This is because these standards explain the process of development, validation, and control of EtO sterilization processes for medical devices. They also explain the acceptable levels of EtO residue after sterilization.

The Future of EtO Sterilization

The trend of EtO sterilization will continue to grow. For example, the demand for medical devices in the USA is speeding up. It is projected that by 2040, around 21% people will be over the age of 65 in the USA. This implies that the aging population will require a greater number of medical devices, and EtO sterilization will be one way to ensure these devices’ safety.

Similarly, there is a profound backlog of pending surgical cases. The rise in these cases was seen after the Covid-19 pandemic, during which all the elective surgeries were canceled. Now, in order to resolve these cases, there is a need for additional devices in the market. This means that the medical device manufacturers must speed up their manufacturing and delivery process so that devices can get into the market quicker. In this scenario, EtO sterilization can play a very important role.

Disadvantages of EtO Sterilization

Regarding EtO sterilization, it is essential to mention that it should only be used when no other options are available. Practicing this precaution is necessary because EtO also has many disadvantages. Some of its ill effects on the human body include:

  • Blurry vision,
  • Sore throat,
  • Nausea,
  • Difficulty in breathing,
  • Muscle weakness, and
  • Nerve damage.

Apart from these disadvantages, Ego is known as a carcinogenic. It also possesses abortional tendencies, especially for healthcare workers who receive high exposure to the gas.

Ethylene Oxide Residual Analysis

The major side effect of using EO as a sterilization agent is that it can leave a residue on the devices being processed. The residues that may be found after processing are as follows:

  • Ethylene Oxide (EO) – the residue that may remain after processing has been completed
  • Ethylene Chlorohydrin (ECH) – the residue that may form when EO comes into contact with free chloride ions
  • Ethylene Glycol (EG) – the residue that may form when EO comes into contact with water

As stated in the previous section, EtO residues can pose serious health risks if present in excessive amounts. Therefore, regulatory agencies and industries have strict limits and guidelines regarding the permissible levels of ethylene oxide residues to ensure device safety.

The analysis typically involves collecting samples from the target material or environment, followed by extraction and concentration of ethylene oxide residues. Various analytical techniques, such as gas chromatography (GC) coupled with mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTIR) are then employed to identify and quantify the ethylene oxide residues present.

The standard reference for this analysis is ISO 10993 Part 7: Ethylene oxide sterilization residuals. It specifies allowable limits for residual ethylene oxide (EO) and ethylene chlorohydrin (ECH) in individual EO-sterilized medical devices and procedures for the measurement of EO and ECH, and methods for determining compliance so that devices may be released.

Important Factors to be Considered During EtO Sterilization

The following factors play an important role in affecting EtO sterilization:

  • Exposure time: It varies according to the materials being used or sterilization, relative humidity, gas concentration, and temperature.
  • Gas concentration: The adequate range for gas concentration during sterilization is 4000 to 1200 mg/l.
  • Relative humidity: During the sterilization procedure, the humidity ranges are 35% to 85%.
  • Temperature: The adequate temperature range for EtO sterilization is 50-60◦ C.      

Do You want to Implement EtO Sterilization System? We can help!

EtO sterilization requires proper measures and equipment, especially ensuring that the devices stay clear from any residual EtO. You can schedule a call with our consultants to learn more about the sterilization process. Not only will they explain the intricacies of the sterilization process, but they will also help you in establishing an EtO sterilization setup. Moreover, they are well-versed in FDA’s regulations and other similar laws concerning EtO sterilization. With their help, you can show the compliance of your sterilization process and increase your market. To schedule a meeting with our consultants, contact us today.

About the Author

Waqas Imam

S. M. Waqas Imam is associated with TS Quality as a Regional Partner. He is also an ambassador of Medical Device Community. He is an Industrial Engineer by qualification and served the manufacturing industry since 2011. He is also IRCA CQI Lead Auditor of ISO 9001 and other management system standards. He had served as Quality Assurance and Regulatory Affairs Manager in QSA Surgical Pvt. Ltd. and Ultimate Medical Products. He managed requirements of ISO 13485:2003, EU directives, CE marking and FDA. He also served as Expert Blog Writer for 13485Academy and wrote expert articles on various topics of ISO 13485:2016.