Low-Temperature Sterilization: EO, Hydrogen Peroxide Gas Plasma, and Other Modalities

Why Low-Temperature Sterilization?

Many devices used in modern healthcare cannot survive the high heat and moisture of steam sterilization. Flexible endoscopes, battery-powered handpieces, rubber components, and certain plastics would be damaged or destroyed in a steam autoclave. Low-temperature sterilization methods use chemical sterilants — either a gas or a plasma — to achieve sterility at temperatures generally below 60 °C (140 °F). The two most widely used low-temperature technologies in US hospitals and sterile processing departments are ethylene oxide (EO) gas sterilization and hydrogen peroxide gas plasma sterilization.

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Ethylene Oxide (EO) Sterilization

How It Works

Ethylene oxide is a colorless, flammable gas that kills microorganisms by alkylation — it chemically alters the DNA and proteins of bacteria, spores, viruses, and fungi, preventing reproduction and destroying viability. EO penetrates deeply into porous materials and through packaging, making it effective for complex, lumened, or tightly packaged devices.

Critical Parameters

Four parameters must be controlled for an EO cycle to achieve sterilization:

1. Concentration — the amount of EO gas in the chamber

2. Temperature — typically in the range of 37–63 °C, depending on the system

3. Humidity — adequate moisture (relative humidity) is essential; dry cells resist EO penetration

4. Exposure time — the period during which the device is in contact with the gas

After the sterilization phase, devices must undergo aeration — a degassing period in a dedicated aerator or built-in aeration phase — to remove residual EO from materials before they are safe for patient use. Aeration times vary by device material and system; always follow the manufacturer's instructions for use (IFU) and your department's written procedures.

Material Compatibility

EO is compatible with a broad range of materials, including rubber, latex, many plastics, polyethylene, nylon, and most metals. It is one of the few methods suitable for long, narrow-lumen devices and moisture-sensitive items. However, it is not appropriate for liquids or items that cannot withstand a vacuum cycle.

Safety Precautions for EO

EO is a known human carcinogen and is highly toxic even at low concentrations. OSHA regulates worker exposure limits, and facilities must maintain engineering controls (dedicated exhaust systems, monitors, sealed systems). As a sterile processing technician, you must:

• Never handle EO cartridges without facility-approved PPE: nitrile gloves, safety glasses or a face shield, and a lab coat at minimum
• Follow the written procedure for cartridge loading — do not puncture or force a cartridge
• Know the location of the Safety Data Sheet (SDS) for EO before performing any task
• Know your facility's emergency exposure response: evacuate the area, notify a supervisor, and seek immediate medical evaluation if exposure is suspected
• Understand that symptoms of EO exposure include eye and mucous membrane irritation, headache, nausea, and dizziness

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Hydrogen Peroxide Gas Plasma Sterilization

How It Works

Hydrogen peroxide (H₂O₂) gas plasma systems use vaporized hydrogen peroxide and radiofrequency or microwave energy to create a plasma state — a cloud of reactive free radicals. These free radicals disrupt the cell membranes and metabolic processes of microorganisms, achieving sterilization. At the end of the cycle, the plasma collapses back into water vapor and oxygen, leaving no toxic residue. Aeration is not required.

Critical Parameters

• Hydrogen peroxide concentration — delivered from a sealed cassette; concentration is controlled automatically by the machine
• Pressure (deep vacuum) — the chamber must achieve and maintain a specified vacuum level for the sterilant to vaporize and penetrate
• Cycle time — typically 28–75 minutes depending on cycle type and device load
• Lumen diameter and length — these are the most clinically important compatibility constraints. Each system has strict limits on the minimum internal diameter and maximum length of lumens it can sterilize. Exceeding these limits means the sterilant cannot adequately reach interior surfaces.

Loading Constraints — Lumens

This is a critical point for every technician. Before placing any lumened device in a hydrogen peroxide gas plasma sterilizer, you must consult the device IFU and the sterilizer manufacturer's IFU. Many flexible endoscopes and long, narrow-bore instruments are not compatible with hydrogen peroxide gas plasma because the lumen geometry prevents adequate sterilant penetration. Placing an incompatible device in the cycle risks a failed sterilization with no visible sign of failure — a serious patient safety risk.

Material Compatibility

Hydrogen peroxide gas plasma is compatible with most metals, many plastics, cameras, lenses, and battery-powered devices. It is not compatible with:

• Cellulose-based materials (paper, cotton, linen) — these absorb the sterilant and cause cycle failures
• Liquids
• Powders
• Devices with very long or very narrow lumens that exceed system specifications

Cassette Handling and Cycle Operation

H₂O₂ is delivered in sealed cassettes that are inserted into the machine. Handle cassettes according to the SDS and facility policy. If a cassette is punctured or leaks, concentrated hydrogen peroxide is a strong oxidizer that can cause skin and eye burns. Wear gloves and eye protection at all times during cassette handling.

To operate the cycle: load the device according to tray configuration guidelines (do not overload), insert the cassette as directed, select the correct cycle program, and start the cycle. After the cycle ends, review the printout to confirm all critical parameters were met (cycle complete, no aborts, parameter readings within range). A cycle that aborted or shows out-of-range readings must not be released — quarantine the load and notify your supervisor.

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Comparing the Two Methods

| Feature | EO | H₂O₂ Gas Plasma |

|---|---|---|

| Temperature | ~37–63 °C | ~37–44 °C |

| Aeration needed | Yes | No |

| Cycle time | Hours (plus aeration) | ~28–75 minutes |

| Lumen compatibility | Broad | Restricted by diameter/length |

| Residual | Toxic — must aerate | None (water + oxygen) |

| Cellulose compatible | Yes | No |

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Safety First — Always

For both methods: locate and read the SDS before your first task, don required PPE before handling any sterilant or cassette, and know your facility's emergency response plan. Patient safety depends on correct method selection, proper loading, verified cycle completion, and proper aeration where required.