Low-Temperature Sterilization
Introduction
Low-temperature sterilization, essential for heat and moisture-sensitive medical devices, primarily employs Hydrogen Peroxide (H₂O₂) and Ethylene Oxide (EO) methods.
Efficacy
- EO (Ethylene Oxide): Sterilizes by Alkylation.
- Hydrogen Peroxide: Sterilizes by Oxidation.
- The U.S. Food and Drug Administration (FDA) mandates rigorous testing of each sterilant against a wide range of microorganisms for legal marketing in the U.S.
ETHYLENE OXIDE (EO):
Background: EO gas has been used for over 60 years to sterilize heat and moisture-sensitive medical devices. (some states in the US have stopped using it)
Sterilization Cycle Phases:
Consists of 5 phases.
Preconditioning and Humidification: Prepare the items for sterilization by adjusting temperature and humidity.
Gas Introduction: Introduce EO gas into the sterilization chamber.
Exposure: Maintain the items in the EO gas for a specified duration to ensure sterilization.
Evacuation: Remove the EO gas from the chamber.
Air Washes: Circulate air to purge any remaining EO residues.
- The cycle lasts 2.5 to 3.5 hours, excluding aeration time. After the cycle, items undergo Aeration to remove EO residues before the sterilizer can be unlocked and items removed.
Safety:
EO is toxic and classified by OSHA as a carcinogen and reproductive hazard
EO sterilizers should be well-ventilated, with at least 10 air changes per hour
It is placed in negative pressure rooms
100% EO cartridges should be stored in ventilated flammable liquid storage cabinets
Exposure Monitoring:
Personal monitoring devices attached to employees' clothing within 12 inches from the breathing zone (their nose). OSHA mandates keeping medical surveillance records of employees exposed to high EO levels for the employment duration plus 30 years.
Packaging:
- Compatible:
Paper/plastic or Tyvek peel pouches
Approved fabric wrappers
Medical crepe paper
Polypropylene
Most container systems
- NON-Compatible:
Liquids
Devices with energy sources
Leather items
Aluminum foil
Cellophane
Nylon films
Polyester
PVC (plastic) films
Styrofoam
Reason: EO can permeate many materials but reacts adversely with certain items or materials.
Monitoring:
- Biological monitoring with a Bacillus Atrophaeus spore is required for each EO cycle.
HYDROGEN PEROXIDE GAS PLASMA:
- Background: H₂O₂ gas plasma is a newer sterilization technology, safer than EO, with faster cycle times. The byproducts are non-toxic water vapor and oxygen.
- Efficacy: H₂O₂ gas plasma, using 59% to 95% hydrogen peroxide solution, effectively kills microorganisms by way of Oxidation.
- Penetration: H₂O₂ gas plasma sterilizers utilize deep vacuums and increased concentrations for sterilization.
Sterilization Cycle Phases:
Consists of 5 phases.
Vacuum: Remove air from the chamber and packages, reducing pressure below atmospheric levels.
Injection: Introduce a pre-measured amount of concentrated H₂O₂ into the chamber.
Diffusion: Drive the H₂O₂ vapor into small crevices and lumens of devices.
Plasma: Use radio frequency (RF) energy to create H₂O₂ gas plasma. This phase is repeated twice.
Vent: Introduce air into the chamber through bacterial high-efficiency particulate air (HEPA) filters, returning the chamber to atmospheric pressure.
- Instruments can be used immediately after cooling.
Safety: Technicians should wear recommended PPE when handling items from a canceled cycle.
Packaging:
- Compatible:
Approved containers
Polypropylene wrap
Tyvek pouches
- NON-Compatible:
Liquid
Powder
Linen
Cellulose-containing materials (e.g. paper)
Reason: H₂O₂ is effective with materials that don't absorb it and allow for its diffusion.
Monitoring:
- Biological indicator monitoring with Geobacillus Stearothermophilus spore.
- Biological monitoring is required each day the sterilizer is used but is recommended for every cycle.
VAPORIZED HYDROGEN PEROXIDE (VHP):
Background:
- VHP has been available in the U.S. since 2007. It uses an Oxidative process same as Gas Plasma sterilizers and is faster than EO as well.
- Operates at low pressure and temperature. VHP is generated by heating H₂O₂ and then introducing it into the sterilizer chamber.
Sterilization Cycle Phases:
Consists of 4 phases.
Conditioning: Remove air and excess moisture from the chamber and packaging by evacuating the chamber and recharging it with dry, filtered air.
Leak Test: Maintain a vacuum to ensure the chamber is leak-tight.
Sterilization: Enhance penetration by injecting VHP into the chamber in a series of pulses, with each pulse followed by a hold period.
-
Aeration: After the last VHP injection, the load is automatically aerated in the sterilizer. The VHP is exhausted through a catalytic converter, converting VHP to water and oxygen. No special venting is required.
The rest is the same as Gas Plasma.
Sterility Assurance Level (SAL):
The probability of a viable microorganism surviving on a device after it has been sterilized.