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Notes on Ethylene Oxide and Plasma Sterilization

Ethylene Oxide (ETO) Gas Sterilization

  • Names you may hear:

    • Generic name: ethylene oxide
    • Brand name: Anproline
    • Common abbreviation: ETO

  • Key hazards and disadvantages:

    • Carcinogenic
    • Flammable and explosive
    • Irritant
    • Handling and regulatory burden (OSHA)

  • Mode of action:

    • Ethylene oxide gas breaks down microbial metabolic pathways, leading to sterilization
    • Requires proper control of several parameters to be effective

  • Critical operating conditions (must be controlled):

    • Gas concentration
    • Temperature
    • Humidity: maintained at 40% humidity, i.e. 40\%
    • Time (cycle duration)

  • Regulatory and safety considerations:

    • OSHA requires an approved sterilizer and proper handling procedures
    • When loading the ampule or preparing the bag, wear gloves to prevent incidental exposure
    • If exposure occurs, wash hands/affected area thoroughly
    • Ideally: EO sterilizers should be in a separate room with dedicated ventilation to minimize exposure
    • Permissible exposure limit (PEL): the limit is about 1 part ETO to 1000 parts air over an 8-hour period, i.e. \dfrac{1}{1000} ETO per air over 8 hours

  • Equipment involved in EO sterilization (as shown in the course visuals):

    • Approved EO sterilizer (top-right in the setup)
    • Large plastic bag approved for gas sterilization
    • Dosimeters (the two pink long indicators): color-change mechanism that shows whether sterilization parameters were met
    • Humidichip: provides the necessary 40% humidity within the load
    • Important handling note: Humidichips must be placed in a plastic tube so they don’t get crushed by packs; if two packs rest directly on a Humidichip, it won’t release humidity properly
    • Humidichip sleeve: plastic sleeve around the Humidichip component
    • Ampule: contains the liquid ethylene oxide (the source of EO gas)

  • Loading and cycle steps (summary from the video walkthrough):

    • Load instruments/packs into the gas-permeable bag
    • Place the bag into the EO sterilizer chamber
    • The bag is vacuumed to remove air prior to EO exposure
    • Break or activate the ampule to release ethylene oxide into the bag
    • The sterilizer runs its cycle (EO exposure occurs)
    • The cycle has to be conducted with proper temperature, pressure, humidity, and time
    • After cycle completion, purge the air from the system and evacuate residues via the purge system
    • A biological indicator (BI) can be used inside the bag to verify stability in newer machines; not all EO sterilizers include BI options
    • For newer devices, push-button ampoules may replace glass ampoules in older systems
    • The dosimeter’s indicator (blue line across) should confirm that the cycle conditions were met
    • The bag is then detached from the machine and removed for use

  • Key indicators and placement details:

    • Dosimeters: placed in the middle of the bag to ensure EO penetrates to the center
    • Humidichip: placed with a plastic sleeve; the Humidichip should not be crushed and should be loaded so it can provide accurate humidity (
    • The package may include a purge exhaust setup and an explicit purge step during the cycle
    • A biological indicator may be included to verify effectiveness; newer systems may support this
    • After cycle, verify the dosimeter’s indicator (blue line across) to confirm process completion

  • Cycle duration and scheduling:

    • Not a quick cycle; typically requires a long cycle of 12 to 24 hours minimum (i.e., 12\text{–}24\ \text{hours})
    • Many facilities load EO packs at the end of a shift; items may be ready the next day

  • Why EO is used (advantages):

    • Does not require high temperature, so it’s compatible with heat-sensitive plastics
    • Can sterilize very sharp items without dulling like steam autoclaving can
    • Suitable for delicate or heat-labile instruments and certain plastics or components

  • Limitations and drawbacks (disadvantages):

    • Carcinogenic and toxic handling hazards
    • Requires stringent handling, room separation, and ventilation
    • Expensive equipment and ongoing operating costs; long cycle times
    • Regulatory and safety training requirements (ETO certification is recommended or required in many settings)

  • Cost considerations:

    • EO sterilizers are still costly to purchase and operate; approximate current market value is around \$6{,}000 (industry ranges can vary by capacity and features)

  • Practical notes and takeaways:

    • Because EO risk is significant, there is a push toward safer alternatives where feasible (e.g., plasma hydrogen peroxide systems)
    • Certification and ongoing training are important for staff safety; EO-specific certification is often a recommended (and sometimes free) credential
    • The process involves several components that ensure proper humidity, gas distribution, and safe handling of materials

  • Plasma sterilization (introduction and contrast)

  • What is plasma sterilization?

    • Plasma sterilizers use a low-temperature hydrogen peroxide gas-plasma mechanism
    • The plasma is a charged, energized state of matter produced under strong electric/magnetic fields (e.g., lightning-like energy)
    • The process generates reactive species that rapidly sterilize without high heat
    • Ethically advantages include increased safety for staff and patients and reduced chemical residuals

  • Key advantages of plasma systems:

    • Faster cycle times (typically a couple of hours up to a few hours, not days)
    • Safe handling with non-carcinogenic residues; uses hydrogen peroxide (H2O2) as the sterilant
    • Compatible with many plastics and other materials that are heat-sensitive
    • Leaves no toxic residues; byproducts are primarily oxygen and water

  • Key limitations of plasma sterilizers:

    • Limited penetration into lumens or long narrow channels; effectiveness can be reduced for devices with wide or deep lumens or complex internal geometries
    • Not universally effective for all instrument sets with complex internal pathways; newer models have improved capability, but this remains a design consideration

  • Market and cost considerations for plasma systems:

    • Historically very expensive (often around \$50{,}000 in the past for larger systems)
    • Prices have come down; larger systems capable of handling more packs can be around \$30{,}000, smaller tabletop units around \$15{,}000$-$\$\$20{,}000 (varies by model and capacity)

  • How a typical plasma cycle works (STERRAD-style example):

    • The STERRAD low-temperature hydrogen peroxide gas plasma sterilization process is a dry, rapid process that is safe for patients, employees, instruments, and the environment
    • Five phases (as described in the course):
    • Vacuum phase: chamber is evacuated to reduce internal pressure in preparation for the process
    • Injection phase: a measured amount of liquid hydrogen peroxide is injected and vaporizes, dispersing H2O2 into the chamber
    • Diffusion phase: H2O2 vapor diffuses and permeates the chamber to expose all load contents
    • Plasma phase: a radio-frequency (RF) plasma discharge is initiated; the H2O2 vapor is broken apart to form a plasma cloud containing UV light and free radicals, which inactivate remaining microorganisms
    • Post-plasma phase: RF power is turned off; activated components recombine to form non-toxic byproducts such as oxygen and water
    • In some STERRAD models (e.g., STERRAD 5,100 S), all phases are repeated to achieve the required Sterility Assurance Level (SAL) of 10^{-6}
    • Vent phase: after the reaction, filtered air is drawn into the chamber to equalize pressure, allowing the door to be opened
    • No aeration or cool-down is required due to low-temperature technology; instruments are ready for immediate use

  • Practical implications of choosing EO vs plasma:

    • EO is versatile for heat-sensitive items and can maintain sharpness, but carries carcinogenic and explosive hazards and long cycle times
    • Plasma is faster and safer to handle in terms of chemical exposure but may not sterilize devices with lumens or complex internal channels as effectively
    • Institutions may choose based on instrument geometry, material compatibility, throughput needs, and safety considerations

  • Indicators and monitoring (key concepts):

    • Biological indicators (BI): uses bacteria to test whether the sterilization process successfully killed microorganisms
    • Incubation-based confirmation; considered the most definitive indicator of sterility
    • Chemical indicators (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; involves a color change and is a critical QA check for autoclave vacuum integrity
    • Physical monitors: display readouts on the sterilizer (temperature, pressure, cycle status); used to detect operational issues in real-time

  • Indicator usage and QA expectations:

    • BI should be run at least weekly as part of routine QA; if implants are involved, BI should be included in implant packaging to guarantee sterility
    • CI alone cannot guarantee sterility; CI confirms parameters but not sterility
    • Bowie-Dick tests are tied to autoclave vacuum integrity and should be used in appropriate systems
    • Technicians are typically responsible for performing these tests and reading results

  • Practical exam-style points to remember:

    • Which type of indicator guarantees sterility? -> Biological Indicator (BI)
    • Do chemical indicators guarantee sterility? -> No, they indicate that parameters were met but do not guarantee sterility
    • What does a Bowie-Dick test assess? -> Vacuum function and leak detection in pre-vacuum autoclaves

  • Additional context and real-world relevance:

    • EO and plasma sterilization are considered complementary technologies in modern practice, chosen based on device material, design, and required throughput
    • Proper training and certification are essential for safety and regulatory compliance
    • The shift toward plasma sterilization reflects a trend toward safer, faster, and environmentally friendlier low-temperature options, while EO remains a viable option for certain devices that cannot withstand high temperatures

  • Important cross-references to foundational concepts:

    • Comparison to steam-autoclave sterilization: EO avoids high heat (benefits for plastics and sharpness) but introduces chemical hazards; autoclaves are effective for many devices but can dull cutting instruments
    • Role of indicators (BI, CI, Bowie-Dick) is a core concept across sterilization modalities; understanding their limitations is essential for interpreting sterilization success

  • Ethical and practical implications:

    • Employee safety and patient safety hinge on proper handling, ventilation, PPE, and certification for EO processes
    • Choosing the appropriate sterilization method has ethical implications related to material integrity, device performance, and infection control
    • The cost vs. benefit of adopting plasma methods vs EO involves budgeting, training, and workflow optimization to minimize risk and maximize throughput

  • Quick recap of key numbers and definitions (LaTeX):

    • Humidity target: 40\%
    • EO exposure limit: 1:1000\ \text{(ETO:air)} over 8\ \text{hours}
    • EO cycle length: 12\text{–}24\ \text{hours} (minimum)
    • Sterility Assurance Level for plasma cycles (STERRAD example): 10^{-6}
    • Estimated EO sterilizer cost: \$6{,}000 (rough approximate figure)
    • Typical plasma system price range (range examples): \$15{,}000\text{–}\$30{,}000 for tabletop to larger units; older large systems around \$50{,}000

  • Note on structure and preparation for lab exams:

    • Be prepared to identify the type of indicator that guarantees sterility (BI)
    • Distinguish between chemical indicators (pass/fail of process parameters) and sterility indicators (BI)
    • Understand the purpose of Bowie-Dick tests and where they are applied (pre-vacuum autoclaves) and what a color change indicates
    • Recognize the main pros/cons of EO vs plasma sterilization and the contexts in which each is preferred

  • Final takeaway:

    • EO is a robust, low-temperature option with broad material compatibility but comes with significant safety, regulatory, and time barriers; plasma offers faster cycles with safer chemical profiles but may be unsuitable for devices with complex lumens
    • A thorough QA regime using BI, CI, Bowie-Dick, and physical monitors is essential to ensure true sterilization and equipment performance