Notes on Ethylene Oxide and Plasma Sterilization

Ethylene Oxide (ETO)

A gas sterilant known for being carcinogenic, flammable, explosive, and an irritant, used for heat-sensitive items.

Mode of Action (ETO)

Ethylene oxide gas breaks down microbial metabolic pathways, requiring proper control of gas concentration, temperature, humidity (40\%), and time to be effective.

Permissible Exposure Limit (PEL) for ETO

Approximately 1 part ETO to 1000 parts air (\dfrac{1}{1000} ETO per air) over an 8-hour period.

Humidichip

A component used in ETO sterilization bags to provide the necessary 40\% humidity within the load. Must be placed in a plastic tube to avoid crushing.

Dosimeter (ETO)

A pink, long indicator that changes color (e.g., a blue line appears) to confirm that sterilization parameters were met during an ETO cycle.

ETO Cycle Duration

Typically requires a long cycle of 12\text{–}24\ \text{hours} minimum.

Advantages of ETO Sterilization

Does not require high temperature (compatible with heat-sensitive plastics), can sterilize very sharp items without dulling.

Plasma Sterilization

Uses a low-temperature hydrogen peroxide gas-plasma mechanism to generate reactive species that rapidly sterilize without high heat, primarily producing oxygen and water as byproducts.

Advantages of Plasma Systems

Faster cycle times (a couple of hours), safe handling with non-carcinogenic residues, compatible with many heat-sensitive materials, leaves no toxic residues.

Limitations of Plasma Sterilizers

Limited penetration into lumens or long narrow channels, potentially less effective for complex internal geometries.

Sterility Assurance Level (SAL) for STERRAD Plasma Systems

Achieves a SAL of 10^{-6} in models like STERRAD 5,100 S.

Biological Indicator (BI)

Uses bacteria to test whether the sterilization process successfully killed microorganisms; considered the most definitive indicator of sterility, confirmed by incubation-based results.

Chemical Indicator (CI)

Shows that a cycle parameter was reached (e.g., temperature, exposure) but does not guarantee sterility.

Bowie-Dick Test

Used in pre-vacuum autoclaves to verify vacuum function and identify air leaks, involving a color change as a critical QA check.