CMDRT - Certified Medical Device Reprocessing Technician Low-Temperature Sterilization Questions and Answers 2 — Questions and Answers

Question 1: What is ethylene oxide (ETO) sterilization and when is it used in medical device reprocessing?

A type of steam sterilization at low pressure
A chemical sterilization method using ETO gas for heat-sensitive and moisture-sensitive devices that cannot withstand steam sterilization (Correct answer)
A radiation-based sterilization technique
A manual cleaning method using ETO liquid

Correct answer: A chemical sterilization method using ETO gas for heat-sensitive and moisture-sensitive devices that cannot withstand steam sterilization

ETO sterilization uses ethylene oxide gas to sterilize medical devices that would be damaged by the high temperatures and moisture of steam sterilization, such as flexible endoscopes, certain plastics, electronics, and battery-powered devices.

Ethylene oxide (ETO) sterilization is a low-temperature chemical sterilization method that uses ETO gas (C2H4O) to achieve sterilization at temperatures typically between 37°C and 63°C. It is primarily used for heat-sensitive and moisture-sensitive medical devices that cannot tolerate the 121-134°C temperatures of steam sterilization. Common applications include flexible endoscopes (when sterilization rather than HLD is required), electronic devices, battery-operated instruments, fibre-optic cables, certain plastics and rubber materials, and power tools with lubricated components. The ETO sterilization cycle involves several phases: preconditioning (humidity and temperature), gas exposure (at defined concentration, temperature, humidity, and time), gas evacuation, and aeration (a prolonged phase to remove residual ETO from devices, as ETO is toxic). CSA Z314.3 requires that ETO sterilization follow the sterilizer and device manufacturer's validated parameters.

Question 2: What is hydrogen peroxide gas plasma sterilization?

Sterilization using liquid hydrogen peroxide
A low-temperature sterilization method that uses hydrogen peroxide vapour converted to a plasma state by radiofrequency energy to sterilize medical devices (Correct answer)
A type of ultraviolet light sterilization
A steam sterilization process with added hydrogen peroxide

Correct answer: A low-temperature sterilization method that uses hydrogen peroxide vapour converted to a plasma state by radiofrequency energy to sterilize medical devices

Hydrogen peroxide gas plasma (such as STERRAD systems) uses a combination of hydrogen peroxide vapour and low-temperature plasma (ionized gas) to achieve sterilization at temperatures around 45-55°C, suitable for many heat-sensitive devices.

Hydrogen peroxide gas plasma sterilization (commonly known by the brand name STERRAD) is a widely used low-temperature sterilization technology in Canadian healthcare facilities. The process works in several phases: a vacuum is drawn in the sterilization chamber, liquid hydrogen peroxide (58%) is injected and vaporized, the peroxide vapour diffuses throughout the chamber and contacts all device surfaces (achieving the kill phase), then radiofrequency energy is applied to create a plasma state — an energized cloud of ions, electrons, and reactive species that further enhance microbial killing and break down peroxide residuals into water vapour and oxygen. The entire cycle takes approximately 28-75 minutes depending on the cycle type and chamber size, at temperatures of 45-55°C. This method is compatible with many metals, plastics, and rubber materials. However, it cannot be used for items with lumens below certain diameter/length specifications, cellulose-containing materials (paper, linen, cotton), or liquids.

Question 3: What are the primary safety hazards associated with ethylene oxide sterilization?

ETO is completely safe with no hazards
ETO is a toxic, carcinogenic, mutagenic, and flammable gas requiring strict exposure controls and monitoring (Correct answer)
ETO only causes mild skin dryness
The only hazard is the heat generated during the cycle

Correct answer: ETO is a toxic, carcinogenic, mutagenic, and flammable gas requiring strict exposure controls and monitoring

ETO is classified as a known human carcinogen and is mutagenic, making it a significant occupational health hazard. Canadian OELs are very low, and strict engineering controls, monitoring, and safety protocols are required.

Ethylene oxide presents multiple serious occupational health and safety hazards. It is classified as a known human carcinogen (Group 1) by the International Agency for Research on Cancer (IARC) and Health Canada. Key hazards include: (1) Carcinogenicity — chronic exposure is linked to lymphatic and hematopoietic cancers; (2) Mutagenicity — ETO causes genetic mutations and chromosomal damage; (3) Acute toxicity — exposure causes respiratory irritation, nausea, headache, and neurological effects; (4) Reproductive toxicity — associated with spontaneous abortion and other reproductive effects; (5) Flammability — ETO is highly flammable and can form explosive mixtures with air. Canadian OELs for ETO are extremely low (typically 1 ppm TWA). Facilities using ETO sterilizers must have dedicated ventilated rooms, continuous air monitoring, personal dosimetry for exposed workers, emergency response procedures, and a comprehensive ETO safety program. The prolonged aeration phase after sterilization is critical to remove residual ETO from devices before patient use.

Question 4: Why is aeration important after ethylene oxide sterilization?

To cool the instruments down
To remove residual ethylene oxide gas absorbed by device materials, which is toxic to patients and staff (Correct answer)
To dry the instruments
Aeration is optional and can be skipped

Correct answer: To remove residual ethylene oxide gas absorbed by device materials, which is toxic to patients and staff

ETO gas is absorbed by many materials during sterilization. Without adequate aeration, residual ETO on devices can cause burns, irritation, hemolysis, and other toxic reactions in patients, and poses an inhalation hazard to staff.

Aeration is a mandatory and critical phase of the ethylene oxide sterilization process. During the gas exposure phase, ETO molecules are absorbed into the materials of the medical devices — particularly plastics, rubber, and other polymeric materials. If devices are used on patients before adequate aeration, the residual ETO can cause severe adverse reactions including: chemical burns to tissue, hemolysis of blood (if devices contact the bloodstream), mucosal irritation, and potentially more serious systemic toxicity. For staff, handling inadequately aerated items can cause skin and respiratory exposure. CSA Z314.3 requires that aeration follow the device and sterilizer manufacturer's validated parameters, which typically specify minimum aeration times at defined temperatures. Aeration times can range from 8 to 12 hours (or longer) in a dedicated mechanical aerator at 50-60°C, or significantly longer at room temperature (which is not recommended). Items must never be removed from the aeration cycle prematurely, even under urgent operational pressure.

Question 5: Which types of materials are NOT compatible with hydrogen peroxide gas plasma sterilization?

Stainless steel instruments
Cellulose-based materials (paper, cotton, linen), liquids, and devices with long narrow lumens below specified dimensions (Correct answer)
Titanium instruments
Silicone tubing within specifications

Correct answer: Cellulose-based materials (paper, cotton, linen), liquids, and devices with long narrow lumens below specified dimensions

Cellulose-based materials absorb hydrogen peroxide and prevent plasma formation. Liquids are not compatible because the process requires a deep vacuum. Long narrow lumens may not allow adequate peroxide penetration to achieve sterilization.

Hydrogen peroxide gas plasma sterilization has specific material compatibility limitations that CMDRT professionals must understand. Incompatible materials include: (1) Cellulose-containing materials — paper, cotton, linen, and cardboard absorb hydrogen peroxide, preventing it from reaching all device surfaces and interfering with plasma formation. This means standard peel pouches (which have a paper side) and woven textile wraps cannot be used; only polypropylene wraps (like Tyvek pouches) or the manufacturer's specific packaging are acceptable. (2) Liquids — the deep vacuum phase would cause liquids to boil or evaporate. (3) Powders — can absorb or scatter the peroxide. (4) Devices with lumens narrower or longer than specified limits — the peroxide vapour cannot adequately penetrate very narrow or very long channels. Each sterilizer model has specific lumen diameter-to-length restrictions that must be consulted. (5) Certain nylon and polyurethane materials may degrade with repeated processing. Always verify compatibility using the sterilizer manufacturer's compatibility guide and the device manufacturer's IFU.

Question 6: What biological indicator is used to monitor ethylene oxide sterilization cycles?

Geobacillus stearothermophilus
Bacillus atrophaeus (formerly B. subtilis var. niger) (Correct answer)
Staphylococcus aureus
Escherichia coli

Correct answer: Bacillus atrophaeus (formerly B. subtilis var. niger)

Bacillus atrophaeus spores are used as the biological indicator for ETO sterilization because they are highly resistant to ETO gas. If the sterilization process kills these resistant spores, it confirms that less resistant organisms were also eliminated.

Biological indicators (BIs) are the gold standard for monitoring sterilization efficacy because they directly test whether the process has killed highly resistant microbial spores. Different sterilization methods use different BI organisms based on resistance characteristics. For ethylene oxide sterilization, the standard BI organism is Bacillus atrophaeus (ATCC 9372, formerly classified as Bacillus subtilis var. niger). These spores exhibit high resistance to ETO gas, making them an appropriate challenge to the sterilization process. If the sterilization cycle successfully kills the required population of B. atrophaeus spores (typically a minimum 6-log10 reduction), it provides confidence that all other microorganisms — which are less resistant to ETO — have also been eliminated. For comparison, steam sterilization uses Geobacillus stearothermophilus spores, and hydrogen peroxide gas plasma also uses G. stearothermophilus. CSA Z314.3 requires that BIs be used with every ETO sterilization load, with the BI placed in the most challenging location within the load.

CMDRT - Certified Medical Device Reprocessing Technician Low-Temperature Sterilization Questions and Answers 2

What is ethylene oxide (ETO) sterilization and when is it used in medical device reprocessing?