© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
Understanding Key Factors In Steam Sterilization Donna Swenson
About the Author Donna Swenson, BS, CRCST, CHL, CSPDM, works for Synergy Health, PLC, as the onsite clinical operations manager of the Sterile Processing Department at Mount Sinai Hospital in Chicago. She is co-chair of AAMI’s committee for the ANSI/AAMI/ISO 17665 series and PB70. E-mail: [email protected].
Many factors influence whether a sterilization process will, in fact, result in a sterile medical device, starting with how the device is used and the level of contamination. It is important to understand that the cleaning of a device—removing as much bioburden as possible— is crucial to effective sterilization. But even if a device has been adequately cleaned, it may not be sterile at the end of the sterilization process. Why? There could be several reasons. The design and configuration of a device could impede penetration by the sterilant, the device could be loaded into the sterilizer in a way that hinders contact between all surfaces and the sterilant, the concentration or exposure time of the sterilant could be inadequate, or a wet pack at the end of the cycle could result in recontamination. This article examines crucial factors in effective steam sterilization: conditioning, steam penetration, “wet packs,” and understanding the difference between verification and validation.
It is important to understand that the cleaning of a device—removing as much bioburden as possible— is crucial to effective sterilization. But even if a device has been adequately cleaned, it may not be sterile at the end of the sterilization process.
106
Biomedical Instrumentation & Technology March/April 2014
Conditioning The conditioning phase of the sterilization cycle refers to the process of eliminating all air from the chamber, which houses the device or equipment to be sterilized. The chamber must be cleared of all air to ensure that the steam contacts all of the device surfaces to be sterilized. The process for conditioning depends on the type of steam sterilizer being used. As the name suggests, a gravity displacement sterilizer relies on gravity to remove air from the chamber. Steam is injected into the chamber. As it builds, the colder air, which is heavier, is pushed down and out through a drain. Device and load configuration can have a major impact on the ability of the sterilizer to remove air from the chamber. Dynamic processes are faster at removing air and allowing the steam to quickly come into contact with the device surfaces. Dynamic air removal involves either a steam flush pressure pulse (SFPP) or a pre-vacuum method. With SFPP, steam is injected into the chamber through a series of steam flushes, which also push air out. In the pre-vacuum method, air is removed via a vacuum pump, followed by injecting steam into the chamber, which helps to push out any remaining small amounts of air. This is usually done three to four times. Once the final vacuum is pulled, steam is injected to fill the chamber. Since all of the air has been removed from the chamber, the dispersion
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
contact of the steam is usually very rapid. However, some device configurations can require additional exposure time to allow the steam to reach all surfaces. This has resulted in extended cycles being approved for the sterilization of some devices. The U.S. Food and Drug Administration (FDA) approves standard steam sterilization cycles for healthcare applications and does not allow the conditioning phase of the cycle to be changed.
Steam Contact If the steam cannot reach all of the surfaces, sterilization of the device will fail. A variety of steam penetration tests are available to help with this challenge. Different tests are designed for specific product families. Steam penetration tests check the amount of noncondensable gas (NCG) present in the sterilizer chamber. Too much NCG will prevent steam from contacting the surfaces to be sterilized. Quality assurance testing is performed on products that are routinely sterilized to ensure that there is adequate steam contact. Process challenge devices are designed to simulate a product to be sterilized, offering a challenge to the sterilization process that is equal to or greater than the actual device.
Leak Test Many dynamic air removal steam sterilizers have a leak test built into the machine. This test measures the leakage of air into the chamber. It is complementary to the airremoval test, known as Bowie-Dick or DART (daily air removal test). The maximum rate of air leakage should be 1.0mm Hg/minute.1 The presence of NCG in larger quantities could affect the ability of steam to contact all surfaces to be sterilized. According to ANSI/ AAMI/ISO TIR 17665-2:2009, the leak test should be performed quarterly. Some experts recommend running this test weekly, and others prefer to run it daily. Individual facility preferences and manufacturer recommendations influence test frequency.
Bowie-Dick Test Intended to be run at the same time each day, the Bowie-Dick test is used to evaluate the efficacy of air removal and steam penetration. The test involves a chemical
indicator test sheet inside a pack that meets the criteria specified in the ANSI/AAMI/ ISO 11140 series of standards. A specified cycle is run, and the test sheet must show a uniform color change. Results that are not uniform are considered a failure.
Extended Cycles One solution to steam penetration issues might be an extended cycle. The time needed at the point of exposure does not change. But if it takes longer for the steam to reach a given point, then an extended sterilization exposure time might be needed. If that is not possible (e.g., in healthcare facilities in the United States), then the device needs to be redesigned or the exposure time needs to be increased to compensate for the extra time needed for the steam to reach all contact points.
Wet Packs A wet pack refers to moisture remaining after completion of the sterilization and cooling cycles. Such packs may lose their barrier properties, which could allow bacteria to migrate to the inside of the package and contaminate the contents or shorten the shelf life of the package. When steam encounters an object with a lower temperature, the steam gives up energy to the object that it condenses upon. For the condensation to be re-evaporated, the same amount of energy must be applied to the condensed water. At the end of the sterilization cycle a vacuum is used to remove the steam from the sterilization chamber. The condensed water produced during the exposure phase must either be drained away or re-evaporated. Under ideal conditions this is not a problem since the energy needed for revaporization is exactly the same amount of energy that was produced during condensation! In a properly working system, wet packs should never be a problem. Unfortunately wet packs do occur. For the condensate to be re-vaporized the condensate must be kept in contact with its energy. This energy was given up to the product upon which the steam condensed. If the condensate gets separated from the product then there is no energy to be used for re-vaporization. This condensate must instead be drained away. If the condensate is not re-vaporized or drained away a wet pack occurs.
If the steam cannot reach all of the surfaces, sterilization of the device will fail.
Biomedical Instrumentation & Technology March/April 2014
107
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
Additional Resources • Association for the Advancement of Medical Instrumentation. Sterilization of Health Care Products— Moist Heat—Part 1: Requirements for the Development, Validation and Routine Control of a Sterilization Process for Medical Devices. ANSI/AAMI/ ISO 17665-1:2006. • Association for the Advancement of Medical Instrumentation. Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities. ANSI/ AAMI ST79:2010, A.1:2010, A.2:2011, A.3:2012, A.4:2013. • International Association of Healthcare Central Service Materiel Management. Central Service Technical Manual Workbook. 7th ed. • Lewis PE, and Raymond G. Practical Guide to Autoclave Validation. Pharmaceutical Engineering. July/August 2002. • Pflug I, Holcomb R, Gómez M. Principles of the Thermal Destruction of Microorganisms. In: Block SS, ed. Disinfection, Sterilization and Preservation. 5th ed. • U. S. Food and Drug Administration. Guidance for Industry. Process Validation: General Principles and Practices. Revision 1. • U.S. Food and Drug Administration. Draft Guidance for Industry and FDA Staff – Processing/Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling.
108
A number of things can cause the condensate to eliminate the conditions which will cause to become separated from its energy. the wet pack. Poor steam quality may cause wet pack Most of these problems can be prevented problems. Steam might condense in the pipes by configuring the device and the load to leading to the sterilizer. Sometimes this minimize the accumulation of condensate condensate can find its way into the sterilizer and the separation of the condensate and its chamber. Since the energy that produced the energy. Textile and peel packs should be condensate is in the pipes and not the champlaced above trays. Place wrapped trays above ber or product there is no energy available for sterilization containers. Provide adequate revaporizing the condensate. This condensate space between packs and trays. Do not stack must be drained away. Steam quality also can containers or packages. A water separator be affected if the demand for steam is higher will help to prevent carryover of water from than the steam generator or boiler’s capacity. the steam pipes. Ensuring that the steam In this situation the steam pressure will drop generator or boiler has enough capacity to causing a boil, and some water will be carried accommodate peak load periods will help along with the steam into the sterilizer prevent carryover of water. chamber. This water never evaporated to become steam and therefore did not conVerification vs. Validation dense, and thus it does not have any energy to Verification is “the confirmation by examinause for re-evaporation at the end of the tion and provision of objective evidence that sterilizer cycle. specified requirements have been fulfilled.”2 Anything that causes a large amount of Whereas, validation is “a documented condensation to occur might procedure for obtaining, result in a wet pack. If a recording, and interpreting The best way to sterilizer door is allowed to the results required to eliminate wet packs stay open between cycles it establish that a process will might cool off, which can consistently yield product is to eliminate the cause a large amount of complying with predeterconditions which will condensation to occur at the mined specification.3 cause the wet pack. beginning of the sterilization Processes that can be cycle. This condensate can confirmed with objective be blown onto the load evidence only need to be during the turbulence which occurs in the verified each time that they are run. However, cycle. Again, the source of the energy and the processes that do not provide objective condensate has been separated. Large evidence that the process has been accomamounts of metal in the load also can cause plished need to be validated. This is the case large amounts of condensation to occur. This with sterilization processes. For many condensation will drip off the product and reasons, it is impossible to prove that an item can cause revaporization problems for that has been sterilized is sterile. Once the products that the condensate drips upon. process used to sterilize a particular device Products that absorb the condensate will not has been validated by the manufacturer, then dry at the end of the cycle because there is no verification is conducted by the user each energy available to re-vaporize the condentime that the process is run. Verification sate. The following conditions may also ensures that the parameters of the validated separate the condensate from its energy process were achieved and provides a strong source: support devices, multiple tray layers, probability that the process achieved its goal, stacking of trays, dented or deformed trays. i.e., a sterile device. Most steam sterilizers dry the load under Product quality assurance testing as vacuum conditions. If no energy is available described in ANSI/AAMI ST79 is used to for revaporization the vacuum will insulate confirm that the manufacturer’s validated the load. For this reason, increasing the dry processes being used at a particular facility time will have little effect on eliminating wet works in the particular sterilizers and for the packs. The best way to eliminate wet packs is particular devices that the facility sterilizes. Biomedical Instrumentation & Technology March/April 2014
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
This testing, like process validation, is specific to a particular machine. Product quality assurance testing is performed by developing product families and designating a master product for each product family. The master product which represents all members of the product family is then used for all testing. Results of testing apply to all members of the product family which the master product represents. Facilities might need to develop more than one product family.
Conclusion Steam sterilization has a long history of use; the mechanism of kill is well understood and the process seems straightforward. However, the process is more complicated than it seems at first. Many factors have an impact on whether a sterile product will actually be produced. n
References 1. AAMI. Sterilization of Health Care Products— Moist Heat—Part 2: Guidance on the application of ANSI/AAMI/ISO 17665-1. ANSI/AAMI/ISO TIR 17665-2:2009. Arlington, VA: Association for the Advancement of Medical Instrumentation; 2009. 2. FDA. Quality System Regulation. Code of Federal Regulations, Title 21, Part 820, Section 820.3 (aa) Definitions. Silver Spring, MD: U.S. Food and Drug Administration. 3. AAMI. Sterilization of Health Care Products— Vocabulary. ANSI/AAMI/ISO 11139:2006. Arlington, VA: Association for the Advancement of Medical Instrumentation; 2006.
Human Factors Guidance Standards on CD – Human Factors Recently expanded, this CD is your single source for Human Factors standards and guidance documents. Searchable and easy to use, the CD contains • ANSI/AAMI HE75:2009, Human factors engineering - Design of medical devices • ANSI/AAMI/IEC 62366:2007/(R)2013, Medical devices - Application of usability engineering to medical devices • AAMI TIR49:2013, Design of training and instructional materials for medical devices used in non-clinical environments • AAMI TIR50:2014, Post-market surveillance of use error management • Human Factors & IT Horizons articles • Human Factors articles from BI&T, AAMI’s peer reviewed journal • FDA guidance documents and much more Order Code: HFCOL-CD List $390 / AAMI member $195
SOURCE CODE: PB
Order Your Copy Today! Call +1-877-249-8226 or visit http://my.aami.org/store
Biomedical Instrumentation & Technology March/April 2014
109
Features
Understanding Key Factors In Steam Sterilization Donna Swenson
About the Author Donna Swenson, BS, CRCST, CHL, CSPDM, works for Synergy Health, PLC, as the onsite clinical operations manager of the Sterile Processing Department at Mount Sinai Hospital in Chicago. She is co-chair of AAMI’s committee for the ANSI/AAMI/ISO 17665 series and PB70. E-mail: [email protected].
Many factors influence whether a sterilization process will, in fact, result in a sterile medical device, starting with how the device is used and the level of contamination. It is important to understand that the cleaning of a device—removing as much bioburden as possible— is crucial to effective sterilization. But even if a device has been adequately cleaned, it may not be sterile at the end of the sterilization process. Why? There could be several reasons. The design and configuration of a device could impede penetration by the sterilant, the device could be loaded into the sterilizer in a way that hinders contact between all surfaces and the sterilant, the concentration or exposure time of the sterilant could be inadequate, or a wet pack at the end of the cycle could result in recontamination. This article examines crucial factors in effective steam sterilization: conditioning, steam penetration, “wet packs,” and understanding the difference between verification and validation.
It is important to understand that the cleaning of a device—removing as much bioburden as possible— is crucial to effective sterilization. But even if a device has been adequately cleaned, it may not be sterile at the end of the sterilization process.
106
Biomedical Instrumentation & Technology March/April 2014
Conditioning The conditioning phase of the sterilization cycle refers to the process of eliminating all air from the chamber, which houses the device or equipment to be sterilized. The chamber must be cleared of all air to ensure that the steam contacts all of the device surfaces to be sterilized. The process for conditioning depends on the type of steam sterilizer being used. As the name suggests, a gravity displacement sterilizer relies on gravity to remove air from the chamber. Steam is injected into the chamber. As it builds, the colder air, which is heavier, is pushed down and out through a drain. Device and load configuration can have a major impact on the ability of the sterilizer to remove air from the chamber. Dynamic processes are faster at removing air and allowing the steam to quickly come into contact with the device surfaces. Dynamic air removal involves either a steam flush pressure pulse (SFPP) or a pre-vacuum method. With SFPP, steam is injected into the chamber through a series of steam flushes, which also push air out. In the pre-vacuum method, air is removed via a vacuum pump, followed by injecting steam into the chamber, which helps to push out any remaining small amounts of air. This is usually done three to four times. Once the final vacuum is pulled, steam is injected to fill the chamber. Since all of the air has been removed from the chamber, the dispersion
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
contact of the steam is usually very rapid. However, some device configurations can require additional exposure time to allow the steam to reach all surfaces. This has resulted in extended cycles being approved for the sterilization of some devices. The U.S. Food and Drug Administration (FDA) approves standard steam sterilization cycles for healthcare applications and does not allow the conditioning phase of the cycle to be changed.
Steam Contact If the steam cannot reach all of the surfaces, sterilization of the device will fail. A variety of steam penetration tests are available to help with this challenge. Different tests are designed for specific product families. Steam penetration tests check the amount of noncondensable gas (NCG) present in the sterilizer chamber. Too much NCG will prevent steam from contacting the surfaces to be sterilized. Quality assurance testing is performed on products that are routinely sterilized to ensure that there is adequate steam contact. Process challenge devices are designed to simulate a product to be sterilized, offering a challenge to the sterilization process that is equal to or greater than the actual device.
Leak Test Many dynamic air removal steam sterilizers have a leak test built into the machine. This test measures the leakage of air into the chamber. It is complementary to the airremoval test, known as Bowie-Dick or DART (daily air removal test). The maximum rate of air leakage should be 1.0mm Hg/minute.1 The presence of NCG in larger quantities could affect the ability of steam to contact all surfaces to be sterilized. According to ANSI/ AAMI/ISO TIR 17665-2:2009, the leak test should be performed quarterly. Some experts recommend running this test weekly, and others prefer to run it daily. Individual facility preferences and manufacturer recommendations influence test frequency.
Bowie-Dick Test Intended to be run at the same time each day, the Bowie-Dick test is used to evaluate the efficacy of air removal and steam penetration. The test involves a chemical
indicator test sheet inside a pack that meets the criteria specified in the ANSI/AAMI/ ISO 11140 series of standards. A specified cycle is run, and the test sheet must show a uniform color change. Results that are not uniform are considered a failure.
Extended Cycles One solution to steam penetration issues might be an extended cycle. The time needed at the point of exposure does not change. But if it takes longer for the steam to reach a given point, then an extended sterilization exposure time might be needed. If that is not possible (e.g., in healthcare facilities in the United States), then the device needs to be redesigned or the exposure time needs to be increased to compensate for the extra time needed for the steam to reach all contact points.
Wet Packs A wet pack refers to moisture remaining after completion of the sterilization and cooling cycles. Such packs may lose their barrier properties, which could allow bacteria to migrate to the inside of the package and contaminate the contents or shorten the shelf life of the package. When steam encounters an object with a lower temperature, the steam gives up energy to the object that it condenses upon. For the condensation to be re-evaporated, the same amount of energy must be applied to the condensed water. At the end of the sterilization cycle a vacuum is used to remove the steam from the sterilization chamber. The condensed water produced during the exposure phase must either be drained away or re-evaporated. Under ideal conditions this is not a problem since the energy needed for revaporization is exactly the same amount of energy that was produced during condensation! In a properly working system, wet packs should never be a problem. Unfortunately wet packs do occur. For the condensate to be re-vaporized the condensate must be kept in contact with its energy. This energy was given up to the product upon which the steam condensed. If the condensate gets separated from the product then there is no energy to be used for re-vaporization. This condensate must instead be drained away. If the condensate is not re-vaporized or drained away a wet pack occurs.
If the steam cannot reach all of the surfaces, sterilization of the device will fail.
Biomedical Instrumentation & Technology March/April 2014
107
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
Additional Resources • Association for the Advancement of Medical Instrumentation. Sterilization of Health Care Products— Moist Heat—Part 1: Requirements for the Development, Validation and Routine Control of a Sterilization Process for Medical Devices. ANSI/AAMI/ ISO 17665-1:2006. • Association for the Advancement of Medical Instrumentation. Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities. ANSI/ AAMI ST79:2010, A.1:2010, A.2:2011, A.3:2012, A.4:2013. • International Association of Healthcare Central Service Materiel Management. Central Service Technical Manual Workbook. 7th ed. • Lewis PE, and Raymond G. Practical Guide to Autoclave Validation. Pharmaceutical Engineering. July/August 2002. • Pflug I, Holcomb R, Gómez M. Principles of the Thermal Destruction of Microorganisms. In: Block SS, ed. Disinfection, Sterilization and Preservation. 5th ed. • U. S. Food and Drug Administration. Guidance for Industry. Process Validation: General Principles and Practices. Revision 1. • U.S. Food and Drug Administration. Draft Guidance for Industry and FDA Staff – Processing/Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling.
108
A number of things can cause the condensate to eliminate the conditions which will cause to become separated from its energy. the wet pack. Poor steam quality may cause wet pack Most of these problems can be prevented problems. Steam might condense in the pipes by configuring the device and the load to leading to the sterilizer. Sometimes this minimize the accumulation of condensate condensate can find its way into the sterilizer and the separation of the condensate and its chamber. Since the energy that produced the energy. Textile and peel packs should be condensate is in the pipes and not the champlaced above trays. Place wrapped trays above ber or product there is no energy available for sterilization containers. Provide adequate revaporizing the condensate. This condensate space between packs and trays. Do not stack must be drained away. Steam quality also can containers or packages. A water separator be affected if the demand for steam is higher will help to prevent carryover of water from than the steam generator or boiler’s capacity. the steam pipes. Ensuring that the steam In this situation the steam pressure will drop generator or boiler has enough capacity to causing a boil, and some water will be carried accommodate peak load periods will help along with the steam into the sterilizer prevent carryover of water. chamber. This water never evaporated to become steam and therefore did not conVerification vs. Validation dense, and thus it does not have any energy to Verification is “the confirmation by examinause for re-evaporation at the end of the tion and provision of objective evidence that sterilizer cycle. specified requirements have been fulfilled.”2 Anything that causes a large amount of Whereas, validation is “a documented condensation to occur might procedure for obtaining, result in a wet pack. If a recording, and interpreting The best way to sterilizer door is allowed to the results required to eliminate wet packs stay open between cycles it establish that a process will might cool off, which can consistently yield product is to eliminate the cause a large amount of complying with predeterconditions which will condensation to occur at the mined specification.3 cause the wet pack. beginning of the sterilization Processes that can be cycle. This condensate can confirmed with objective be blown onto the load evidence only need to be during the turbulence which occurs in the verified each time that they are run. However, cycle. Again, the source of the energy and the processes that do not provide objective condensate has been separated. Large evidence that the process has been accomamounts of metal in the load also can cause plished need to be validated. This is the case large amounts of condensation to occur. This with sterilization processes. For many condensation will drip off the product and reasons, it is impossible to prove that an item can cause revaporization problems for that has been sterilized is sterile. Once the products that the condensate drips upon. process used to sterilize a particular device Products that absorb the condensate will not has been validated by the manufacturer, then dry at the end of the cycle because there is no verification is conducted by the user each energy available to re-vaporize the condentime that the process is run. Verification sate. The following conditions may also ensures that the parameters of the validated separate the condensate from its energy process were achieved and provides a strong source: support devices, multiple tray layers, probability that the process achieved its goal, stacking of trays, dented or deformed trays. i.e., a sterile device. Most steam sterilizers dry the load under Product quality assurance testing as vacuum conditions. If no energy is available described in ANSI/AAMI ST79 is used to for revaporization the vacuum will insulate confirm that the manufacturer’s validated the load. For this reason, increasing the dry processes being used at a particular facility time will have little effect on eliminating wet works in the particular sterilizers and for the packs. The best way to eliminate wet packs is particular devices that the facility sterilizes. Biomedical Instrumentation & Technology March/April 2014
© Copyright AAMI 2014. Single user license only. Copying, networking, and distribution prohibited.
Features
This testing, like process validation, is specific to a particular machine. Product quality assurance testing is performed by developing product families and designating a master product for each product family. The master product which represents all members of the product family is then used for all testing. Results of testing apply to all members of the product family which the master product represents. Facilities might need to develop more than one product family.
Conclusion Steam sterilization has a long history of use; the mechanism of kill is well understood and the process seems straightforward. However, the process is more complicated than it seems at first. Many factors have an impact on whether a sterile product will actually be produced. n
References 1. AAMI. Sterilization of Health Care Products— Moist Heat—Part 2: Guidance on the application of ANSI/AAMI/ISO 17665-1. ANSI/AAMI/ISO TIR 17665-2:2009. Arlington, VA: Association for the Advancement of Medical Instrumentation; 2009. 2. FDA. Quality System Regulation. Code of Federal Regulations, Title 21, Part 820, Section 820.3 (aa) Definitions. Silver Spring, MD: U.S. Food and Drug Administration. 3. AAMI. Sterilization of Health Care Products— Vocabulary. ANSI/AAMI/ISO 11139:2006. Arlington, VA: Association for the Advancement of Medical Instrumentation; 2006.
Human Factors Guidance Standards on CD – Human Factors Recently expanded, this CD is your single source for Human Factors standards and guidance documents. Searchable and easy to use, the CD contains • ANSI/AAMI HE75:2009, Human factors engineering - Design of medical devices • ANSI/AAMI/IEC 62366:2007/(R)2013, Medical devices - Application of usability engineering to medical devices • AAMI TIR49:2013, Design of training and instructional materials for medical devices used in non-clinical environments • AAMI TIR50:2014, Post-market surveillance of use error management • Human Factors & IT Horizons articles • Human Factors articles from BI&T, AAMI’s peer reviewed journal • FDA guidance documents and much more Order Code: HFCOL-CD List $390 / AAMI member $195
SOURCE CODE: PB
Order Your Copy Today! Call +1-877-249-8226 or visit http://my.aami.org/store
Biomedical Instrumentation & Technology March/April 2014
109
