7.3 Ozone & Liquid Peracetic Acid Sterilization Systems

7.3 Ozone & Liquid Peracetic Acid Sterilization Systems

Exam Tip: Liquid Peracetic Acid (LPA) and Ozone represent specialized low-temperature technologies. For the CSPDT exam, remember that liquid peracetic acid processed items are wet upon completion and CANNOT be stored—they are for immediate point-of-use only. Ozone requires high humidity (>85% RH) and generates its gas from oxygen.

In addition to Ethylene Oxide and Hydrogen Peroxide, healthcare facilities utilize Ozone ($O_3$) gas sterilization and Liquid Peracetic Acid (LPA) automated immersion systems to process specialized surgical devices. Each technology occupies a specific operational niche in sterile processing, especially regarding scope re-processing and environmental sustainability.

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1. Ozone ($O_3$) Sterilization Systems

Ozone is an allotropic form of oxygen containing three oxygen atoms ($O_3$). It is an extremely powerful oxidizing gas that destroys microorganisms by attacking cell walls, membrane lipids, and intracellular enzymes.

Ozone Generation & Cycle Parameters

Unlike EtO or hydrogen peroxide, which require chemical cartridges or cassettes, Ozone sterilizers generate their own sterilant gas on-site from medical-grade oxygen ($O_2$) and water via electrical corona discharge.

$$\text{3 O}_2 \xrightarrow{\text{High Voltage Electrical Field}} \text{2 O}_3$$

Material Compatibility & Advantages

• Compatible: Stainless steel, titanium, silicone, rubber, rigid lumens, and specialized polymers.
• Incompatible: Natural rubber, latex, neoprene, copper alloys, and cellulose/paper packaging.
• Packaging: Requires Tyvek® pouches or anodized aluminum containers with synthetic filters.
• Biological Indicator: Geobacillus stearothermophilus incubated at 55°C to 60°C.

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2. Liquid Peracetic Acid (LPA) Sterilization Systems

Liquid Peracetic Acid (LPA) is a liquid chemical sterilant used in automated, table-top processor units (such as the STERIS SYSTEM 1E®) designed primarily for point-of-use sterilization of fully immersible surgical instruments, including flexible and rigid endoscopes, video laryngoscopes, and microsurgical tools.

Chemical Mechanism & Cycle Parameters

Peracetic acid ($CH_3CO_3H$) is a potent mixture of acetic acid and hydrogen peroxide. It denatures proteins, disrupts cell wall permeability, and oxidizes sulfhydryl and sulfur bonds in enzymes and proteins.

• Sterilant Concentration: Concentrated liquid peracetic acid diluted with warmed, filtered water to approximately 0.2% peracetic acid solution (pH ~6.4).
• Processing Temperature: Controlled warmth between 50°C and 56°C (122°F to 133°F).
• Cycle Duration: Rapid, total cycle time is approximately 23 to 30 minutes.
• Water Rinsing: The processor performs automated rinses using internal UV-treated, sterile-filtered water to strip all chemical residues from instrument channels.

CRITICAL RULE: Immediate Use Only (No Storage)

WARNING (Exam Essential): Items sterilized in a liquid peracetic acid processor are wet and unbagged at the end of the cycle. Because the instruments are not wrapped in a sterile barrier pouch and remain wet, THEY CANNOT BE STORED. They must be transported in a covered, sterile tray directly to the operating room for immediate patient use ("just-in-time" processing). Storing wet, unsealed instruments leads to immediate recontamination and bacterial growth.

Quality Assurance for LPA Systems

1. Diagnostic Test Cycle: Performed daily prior to processing the first clinical load to verify hydraulic pressure, temperature, and filter integrity.
2. Chemical Concentration Monitoring: Technicians must test the peracetic acid solution using chemical test strips to verify the Minimum Effective Concentration (MEC) before starting a cycle.
3. Biological Indicator: Geobacillus stearothermophilus spore strips contained in a specialized challenge tray, incubated at 55°C–60°C.

Comprehensive Low-Temperature Sterilization Technology Comparison Matrix

Summary Comparison of Low-Temperature Sterilization Technologies

When evaluating low-temperature options for fragile medical instrumentation, sterile processing professionals balance processing time, material compatibility, worker safety, and packaging requirements:

1. Ethylene Oxide: Widely compatible with complex instruments and deep lumens, but carries significant worker hazards, long cycle times, and mandatory 8–12 hour aeration.
2. Hydrogen Peroxide (VHP / Gas Plasma): Rapid, non-toxic, and widely used, but strictly prohibited from contacting cellulose (paper/linen) or wet/liquid items.
3. Ozone: Generated on-site from oxygen with zero chemical consumables, but requires high humidity and a longer 4.5-hour cycle time.
4. Liquid Peracetic Acid: Unmatched turnaround speed (30 minutes) for flexible endoscopes at point-of-use, but items emerge wet and unbagged, prohibiting shelf storage.