Chapter 15: Low-Temperature Sterilization PDF

# Chapter 15: Low-Temperature Sterilization ## Learning Objectives As a result of successfully completing this chapter, the reader will be able to: - Discuss basic requirements for low-temperature sterilization systems - Explain different types of low-temperature sterilization - Review parameters...

# Chapter 15: Low-Temperature Sterilization ## Learning Objectives As a result of successfully completing this chapter, the reader will be able to: - Discuss basic requirements for low-temperature sterilization systems - Explain different types of low-temperature sterilization - Review parameters of low-temperature sterilization methods ## Introduction Low-temperature sterilization is important due to the development and growing use of heat- and moisture-sensitive medical devices. Common methods used to sterilize instruments are *ethylene oxide (EO)* and *hydrogen peroxide (H₂O₂)*. Chemicals used to sterilize instruments have toxic properties, so Sterile Processing (SP) technicians must be trained on how to use them safely and effectively. This chapter reviews common low-temperature systems and basic requirements for their use. ## Basic Requirements for Low-Temperature Sterilization Eight basic requirements are important for any type of low-temperature sterilization system: - **Efficacy (effectiveness)**: Has the capability of providing the minimum-required *sterility assurance level (SAL)*. - **Sterility assurance level (SAL)**: The probability of a viable microorganism being present on a device after sterilization. - **Safety**: There should be no toxic residuals remaining on the packaging or device after completion of the sterilization cycle. - **Exposure monitoring**: Ability to monitor the sterilization process to ensure concentrations of sterilants in the work area remain within any required exposure limits. - **Sterilization performance monitoring**: Must be capable of being reliably monitored using physical, chemical indicators (CIs) and biological indicators (BIs). - **Penetration**: Must be able to penetrate through packaging materials and into lumens and other the devices other hard-to-reach areas. - **Material compatibility**: There should be no changes in the device's functionality. - **Adaptability**: Should be compatible with existing healthcare practices. - **Approval**: Must be cleared by or registered with the appropriate regulatory agencies. To be effective in the healthcare environment, a sterilization system must satisfy all requirements. Failure to meet even one requirement may pose a significant risk to patients and healthcare workers. ## Efficacy To be legally marketed in the U.S., the U.S. Food and Drug Administration (FDA) requires each sterilant and sterilization technology to be rigorously tested against a broad range of microorganisms. The low-temperature sterilization technologies addressed in this chapter use different sterilization agents and have different processing methods. When used according to the sterilizer's instructions for use (IFU), each sterilization method meets the required minimum SAL, as outlined by the regulations, standards and guidelines. ## Safety Chemicals used as sterilants are designed to destroy a wide range of pathogens. In sterilization methods, such as EO, significant toxic residues can build up in medical devices and packaging. To ensure a safe work environment, low-temperature sterilization systems should be used according to the manufacturers' instructions, and appropriate work practices, engineering controls, personal protective equipment (PPE), and monitoring should be followed. ## Exposure Monitoring EO has been widely used as a low-temperature sterilant since the 1950s. It has potential health risks that require monitoring, in addition to long aeration times and other precautions. While safer for healthcare workers, newer low-temperature sterilization technologies also can pose health risks. To ensure the safety of healthcare workers, the Occupational Safety and Health Administration (OSHA) has established permissible exposure limits (PELs) for all low-temperature sterilants. - **Permissible exposure limit (PEL)**: The maximum amount or concentration of a chemical that a worker may be exposed to under OSHA regulations. - **Time-weighted average (TWA)**: The amount of a substance employees can be exposed to over an eight-hour day. The National Institute for Occupational Safety and Health (NIOSH) also has developed standards for immediately dangerous to life or health (IDLH) concentrations for low-temperature sterilants. ## Sterilizer Performance Monitoring Monitoring sterilizer performance is essential to ensure the successful sterilization of medical instruments and devices. No single monitoring method provides all of the information necessary to ensure effective sterilization. Recommended practices state that available information from physical, chemical and biological monitors should be used to assess the effectiveness of a process before releasing a load. It is essential that SP technicians understand how to handle and use CIs and BIs and also know how to read and interpret their results. ### Penetration Many devices are significantly more complex than their counterparts of just a few years ago. Not only must the sterilant penetrate packaging material (in some cases, multiple layers), it must also reach narrow lumens. The properties of a chemical sterilant impact its ability to penetrate effectively. For example, EO inactivates microbes by a process called *alkylation*. This allows EO to penetrate packaging and materials to reach remote surfaces where microbes may be located. *Hydrogen peroxide* destroys microbes through *oxidation*. - **Alkylation**: A chemical reaction where hydrogen is replaced with an alkyl group; this renders the cell unable to normally metabolize or reproduce or both. - **Oxidation**: Involves the act or process of oxidizing, which is the addition of oxygen to a compound with a loss of electrons. ### Materials Compatibility Medical devices are composed of a variety of materials that may be affected by sterilant ingredients. Sterilizers must be tested to establish compatibility with a wide range of materials. Medical device manufacturers test the compatibility of their devices with one or more of the available sterilization technologies. Compatibility information can be found in the IFU. The manufacturer's IFU should be carefully followed to help ensure successful sterilization and prevent damage that may increase costs and limit instrument availability. ### Adaptability The low-temperature sterilization process should be compatible with existing device processing practices. ### Approval The sterilization system must be cleared and registered with the appropriate regulatory agencies. ## Ethylene Oxide ### Background For more than 60 years, EO gas has been an effective sterilization technology for heat- and moisture-sensitive medical devices. ### Efficacy EO has excellent microbicidal activity. During the *alkylation* process, EO destroys the cell's ability to metabolize or reproduce, which leads to the organism's death. ### Penetration EO is a small molecule that vaporizes easily and can permeate throughout a wide range of materials to reach recessed areas. Due to its high vapor pressure and low boiling point, EO is easily maintained in the gas phase. ### Sterilization Cycle and Process Parameters In healthcare EO systems, the gas is provided in individual dose cartridges that are placed inside the chamber. If a leak develops after the cartridge is punctured, the ventilation system will pull room air into the chamber rather than allow EO to be released. The basic EO sterilization cycle consists of five stages: *preconditioning and humidification*, *gas introduction*, *exposure*, *evacuation and air washes*. The cycle takes approximately 2 ½ to 3 ½ hours, excluding aeration time. Upon completion of the sterilization cycle, the items must go through an aeration process to remove all residual EO before the sterilizer can be unlocked and the items can be removed. - **Aeration**: A process in which sterilized packages are subjected to moving air to facilitate removal of toxic residuals after exposure to a sterilizing agent such as EO. - **Residual EO**: Amount of EO that remains inside materials after they are sterilized. Operators should demonstrate competency in all parameters of EO sterilization. To minimize the safety risks associated with the use of EO, employees should be instructed about: - EO hazards - Sterilizer manufacturer and EO supplier IFU - Processing procedures - Storage and handling of EO cartridges - Procedures to reduce employee exposure to EO - Use of PPE - Principles of EO monitoring and interpretation of results - Handling canceled cycles - Applicable OSHA regulations - EO emergency plans - Safety data sheets (SDS) **Safety Data Sheet (SDS)**: A written statement providing detailed information about a chemical or toxic substance, including potential hazards and appropriate handling methods. An SDS is provided by the product manufacturer to the buyer and must be available in a place that is easily accessible to those who will use the product. ### Exposure Monitoring Personal monitoring involves the use of devices affixed directly to the employee's clothing in the breathing zone (within one foot of the person's nose). One limitation of personal monitoring devices is that sampling results are not available until after the actual sampling period has ended. OSHA requires that facilities using EO sterilization have a system or procedure to immediately alert affected employees in case of a leak, spill or equipment failure. ## Hydrogen Peroxide Systems Several types of low-temperature systems use H₂O₂ as the sterilant. While the systems operate similarly, there are some key differences. ### Hydrogen Peroxide Gas Plasma #### Background The more recent low-temperature sterilization technologies includes H₂O₂ gas plasma for the inactivation of microorganisms. This method is popular due to its safety, relative to EO, and its cycle times that allow faster turnaround of medical devices. The byproducts of the cycle (water vapor and oxygen) are nontoxic, eliminating the need for an aeration phase. H₂O₂ is a highly effective sterilant that sterilizes by *oxidation* of key cellular components. *Plasma* is a state of matter distinguishable from a solid, liquid or gas. #### Efficacy H₂O₂ gas plasma-using a hydrogen peroxide solution ranging from 59% to 95% for the sterilization cycle-has been proven effective for killing microorganisms. #### Penetration H₂O₂ gas plasma sterilizers use deep vacuums, multiple pulse additions of the sterilant, and increased concentrations. These systems can sterilize a wide range of devices. Guidelines have been developed for lumen diameter and length to ensure adequate penetration and efficacy for various cycle parameters. Newer generations of H₂O₂ gas plasma sterilizers utilize a higher concentration of hydrogen peroxide (up to 95%) to shorten exposure time and lessen lumen restrictions. There are still some restrictions involving the size, length, and number of lumens, and the type of material and number of devices per cycle. As always, users should closely follow the instrument and sterilizer manufacturers' instructions and recommendations. #### Types of H₂O₂ Gas Plasma Systems There are several types of H₂O₂ gas plasma sterilizers available, ranging from compact systems with 28- to 38-minute processing times to large-capacity systems with 75-minute cycle times. Different models have different cycle times, load capacities and capabilities for processing instruments. The phases of H₂O₂ gas plasma include: - **Vacuum**: The load is heated while the vacuum system removes air from the chamber and packages until the pressure is reduced to below atmospheric pressure. - **Injection**: Once the correct pressure has been reached, a pre-measured amount of concentrated H₂O₂ is pumped into the chamber. - **Diffusion**: This phase drives hydrogen peroxide vapor into the small crevices and lumens of devices. - **Plasma**: A vacuum decreases the pressure, and radio frequency (RF) energy is radiated within the chamber from an electrode screen. The RF energy creates H₂O₂ gas plasma. The injection and plasma phases are repeated a second time. - **Vent**: At the end of the second plasma sequence, air is vented into the chamber through bacterial high-efficiency particulate air (HEPA) filters, returning the chamber to atmospheric pressure. The process byproducts are water vapor and oxygen. Aeration is not required, and instruments can be used immediately after cooling. Operators should demonstrate competency in all parameters of hydrogen peroxide (H₂O₂) gas plasma sterilization. #### Safety Concentrated H₂O₂ liquid can irritate skin and is damaging to eyes if direct contact occurs. A number of safeguards built into H₂O₂ sterilizers are designed to minimize the likelihood of personnel contacting H₂O₂. The H₂O₂ is packaged in sealed containers, with a chemical leak indicator on the outside of the package. These indicators change color when exposed to liquid or vapor H₂O₂. To minimize the likelihood of exposure to H₂O₂ when removing items from a canceled cycle, SP technicians should always wear the recommended PPE. As with any chemical used for sterilization, healthcare workers should consult the SDS and follow all manufacturer recommendations and departmental procedures. To minimize H₂O₂ risks, employees should be instructed about: - Hazards of H₂O₂ - Storage, handling and disposal of H₂O₂ - Handling canceled cycles - Applicable OSHA regulations - Use of PPE - SDS #### Exposure Monitoring Monitoring the area around the system during operation should be conducted according to the manufacturer's IFU and established guidelines. #### Materials Compatibility H₂O₂ gas plasma sterilization is compatible with a wide variety of materials found in medical devices; H₂O₂ gas plasma is not compatible with: - Liquids and powders - Any material that absorbs liquids - Items that contain cellulose, such as cotton, paper or cardboard, textiles or any item containing wood pulp #### Packaging Packaging materials can affect the penetration of H₂O₂. Packaging materials used in the sterilizers should be designed to optimize diffusion of the H₂O₂ and not interfere with the RF energy or absorb H₂O₂. Approved trays and container systems, polypropylene wrap and Tyvek pouches are compatible with H₂O₂ sterilization. Cellulose-containing packaging materials, such as paper/plastic pouches, cellulose-based disposable wrappers, and muslin wraps, should not be used with H₂O₂ gas plasma sterilizers because they absorb the peroxide and inhibit effective penetration. Excess moisture remaining on devices can cause the cycle to abort. Consult the manufacturer's IFU for suggested drying methods. #### Loading H₂O₂ Gas Plasma Sterilizers As with other low-temperature sterilization technologies, H₂O₂ gas plasma sterilizers must be properly loaded for effective sterilization. If the available amount of H₂O₂ is reduced because it reacts or is absorbed before reaching all surfaces, a sterilization failure could occur; therefore, the chamber should not be overloaded. #### Sterilizer Performance Monitors H₂O₂ gas plasma sterilizers should be monitored with physical indicators, CIs and BIs. Sterilizer performance monitors include: - **Physical monitoring**: H₂O₂ gas plasma sterilizers operate on a fixed automatic cycle controlled by a microprocessor. All critical parameters are monitored during the operation of the cycle, and a printed record documenting the process parameters is provided at the end of each cycle. All physical monitors must be carefully examined to ensure the correct parameters were met before devices are removed from the sterilizer. - **Chemical monitoring**: External CIs should be used on the outside of every package to demonstrate exposure to H₂O₂ gas plasma. Internal CIs should also be used to demonstrate exposure to H₂O₂. Internal CIs should be placed at challenging locations inside each pack. - **Biological monitoring**: The microorganism of choice for H₂O₂ gas plasma BIs is the *Geobacillus stearothermophilus* spore. Biological monitoring should be performed at least daily, but preferably with each load. Follow the sterilizer manufacturer's IFU for proper BI use. ## Vaporized Hydrogen Peroxide ### Background Low-temperature sterilization technology utilizing vaporized hydrogen peroxide (VHP) has been available to hospitals in the U.S. since 2007. As with H₂O₂ gas plasma, VHP systems utilize an oxidative process and provide a cycle time that improves the throughput of medical devices. ### Efficacy VHP sterilization uses a 59% H₂O₂ solution that is shown to be effective against a broad spectrum of microorganisms. ### Penetration VHP is injected four times during each sterilization cycle. Upon completion of the fourth injection hold period, the load is automatically aerated in the sterilizer. The VHP is exhausted from the chamber through a catalytic converter that converts the VHP to water and oxygen. ### Types of VHP Systems There are different types of VHP sterilizers. One system has a single, pre-programmed, 55-minute sterilization cycle for use with both lumened and non-lumened instruments and devices. Another system offers two pre-programmed cycles: a 28-minute cycle for non-lumened instruments and a 55-minute cycle used to sterilize instruments with lumens and non-stainless steel mated surfaces. These sterilizers use different technologies, and the cycles have different sterilant injection numbers, sterilant exposure times, H₂O₂ concentration levels, and cycle pressure profiles. VHP sterilization processes are based on a fixed amount of sterilant for each cycle type and for every load placed in the chamber. This fixed amount of sterilant is delivered in different manners such as an ampule contained in a cassette, or cup, depending upon the type of sterilizer used. It is important to note that by having a specific fixed amount of sterilant there is little room for error since no additional sterilant is added during the sterilant exposure phase; therefore, a small load (or a very large load) is exposed to the same amount of sterilant during the sterilization exposure phase. Always follow the manufacturer's IFU for sterilizer operation. ### Sterilization Cycle and Process Parameters The sterilization cycle of many types of VHP systems operate at low pressure and temperature and is suitable for processing heat- and moisture-sensitive medical devices. VHP is generated by injecting a fixed amount of aqueous H₂O₂ into a vaporization chamber where the solution is heated and converted to a vapor and then introduced into the sterilizer chamber under negative pressure. The phases of VHP systems include: - **Conditioning**: To remove air and excess moisture from the chamber and packaging, the chamber is evacuated and then recharged with dry, filtered air. - **Leak test**: Vacuum is held to ensure a leak-tight chamber. - **Sterilization**: Enhances penetration by injecting VHP into the chamber with a series of pulses, each followed by a hold period. - **Aeration**: Upon completion of the last VHP injection hold period, the load is automatically aerated in the sterilizer. The chamber VHP is exhausted through a catalytic converter that changes the VHP to water and oxygen. No special venting is required. As with all methods of sterilization, operators must demonstrate competency in all parameters of VHP sterilization. ### Safety Concentrated H₂O₂ is corrosive to skin, eyes, nose, throat, lungs and the gastrointestinal tract. Under normal conditions of use, the VHP sterilizer operator is not exposed to the contents of the sterilant container. The sterilizer automatically dispenses and injects liquid hydrogen peroxide (LHP) into the chamber. After each sterilization pulse, VHP is removed from the chamber and converted to water and oxygen. An aeration phase facilitates the removal of H₂O₂ residuals from devices and packaging. To avoid exposure to H₂O₂ when removing items from a canceled cycle, SP technicians should always wear the appropriate PPE. To minimize risks, employees should be instructed about: - H₂O₂ hazards - Applicable SDS - Handling canceled loads - Applicable OSHA regulations - PPE use - Storage, handling and disposal of H₂O₂ cartridges ### Exposure Monitoring No personal or area monitors are required. Testing to check for H₂O₂ vapors in the environment around the sterilizer has shown acceptable VHP levels during typical sterilization cycle conditions. ### Materials Compatibility VHP sterilization is compatible with a wide range of medical devices being processed. The VHP system is not intended to process liquids, linens, powders or any cellulose materials. ### Packaging Packaging materials can affect the penetrating capability of VHP. Packaging materials approved for use with VHP sterilization include polypropylene. Tyvek and some sterilization containers are also validated for H₂O₂ sterilization. ### Loading VHP Sterilizers VHP sterilizers must be loaded properly for effective sterilization. Sterilizers are cleared by the FDA, with a maximum weight limit for individual loads for each cycle type. Always refer to the sterilizer's IFU for specific restrictions on devices for each cycle type. During the loading process of a low-temperature H₂O₂ sterilizer, the following details should be taken into consideration: - Ensure the devices are approved for a specific VHP sterilizer model and cycle type. - Ensure the total load weight is below the stated weight limit. - Select the packaging type acceptable for use in the VHP sterilizer. Always follow the sterilizer IFU for lumen size, length, and quantity. ## Advantages & Disadvantages of Low-Temperature Sterilization Technologies | Sterilization Method | Advantages | Disadvantages | |---|---|---| | 100% ethylene oxide (EO) | - Penetrates medical packaging, many plastics and device lumens - Compatible with most medical materials - Simple to operate and monitor - Single-dose cartridge and negative-pressure chamber minimizes the potential for EO exposure | - EO is toxic, flammable, a carcinogen and a mutagen - Requires lengthy aeration time to remove EO residue - Requires personal and area monitoring - EO emission regulated by states - EO cartridges should be stored in a flammable liquid storage cabinet | | Hydrogen peroxide (H₂O₂) gas plasma | - Safe for the environment - Leaves negligible toxic residuals - No aeration required - Compatible with most medical devices - Cycle times vary with model type - Used for heat- and moisture-sensitive items - Sterilant contained in a multi-use cassette to prevent user contact with H₂O₂ | - H₂O₂ may be toxic at levels greater than 1 ppm time-weighted average (TWA) - PPE should be worn when removing items from a canceled load - Cellulose (paper), textiles, liquids and powders cannot be processed | | Vaporized Hydrogen Peroxide (VHP) | - Safe for environment - Leaves negligible toxic residuals - Compatible with most medical devices - Used for heat- and moisture sensitive items - Cycle times vary with model type- Sterilant contained to prevent user contact with hydrogen peroxide - Simple to operate and monitor | - H₂O₂ may be harmful at levels greater than 1 ppm TWA - PPE should be worn when removing items from a canceled load - Cellulose (paper), textiles, liquids and powders cannot be processed | ## Sterile Processing Terms - Sterility assurance level (SAL) - Permissible exposure level (PEL) - Time-weighted average (TWA) - Alkylation - Oxidation - Aeration - Residual ethylene oxide (EO) - Safety data sheet (SDS)