ISO 17665 consists of the following parts, under the general title Sterilization of health care products — Moist heat: — Part 1: Requirements for the development, validation and routine
General attributes
Detailed attributes
The following attributes provide detail for characterizing a medical device and a sterilization process Increased resistance to steam penetration is indicated by ascending code numbers.
Manufacturers of medical devices define certain attributes essential for users to evaluate steam penetration resistance and select the appropriate processing category for sterilization It is crucial to reassess both the resistance and the category when integrating the medical device with other items in a sterile barrier or packaging system.
The sterilization process should be qualified to verify that the required lethality will be delivered to all medical devices processed together (see ISO 17665-1 and ISO/TS 17665-2).
To identify the appropriate sterilization process for reprocessing medical devices, it is essential to categorize them based on their designs as outlined in Table 2 Each design exhibits varying steam penetration resistance when air is removed and replaced by saturated steam Key considerations for developing an effective air removal process include the predictable displacement of air as temperature increases with steam introduction, which is generally unaffected by orientation Instruments may need to be positioned openly, and an active air removal process is often necessary to prevent residual air in hollows from causing delays in achieving sterilizing conditions Inadequate air removal can lead to uncertainty in sterilization efficacy, necessitating an active air removal process to mitigate issues such as condensate formation, which can hinder air removal and steam penetration Therefore, if an active air removal process is required, it is crucial to tailor the sterilization process to the specific product.
Solid, hollow 1 Bowl, jug, dish, bottle, chisel, single piece skin retractor, single component empty instrument tray
Pin and box joints 2 Scissor, forceps, needle holder
Lumen 3 Laparoscopic sheath, sucker, cannulated reamer, rigid endoscope, cannulated screws
The article discusses various components used in power tools and medical devices, including tubing, moving parts, and tortuous paths Key items mentioned are silicone tubing, dental handpieces, and ear, nose, and throat drills Additionally, it highlights the importance of a lumen surrounded by a large mass, featuring tools such as drill bits, cannulated screwdrivers, obturators, ratchet handles, and bored handles.
Medical devices are made from either metallic or non-metallic materials, or a combination of both Generally, metallic materials exhibit high thermal conductivity, while non-metallic materials tend to have low thermal conductivity.
Materials with low thermal conductivity show greater temperature variations than those with high thermal conductivity, posing challenges for the sterilization process Additionally, the moisture content of the material can affect heat transfer into the product, which must be considered during performance qualification when the material is in its most challenging state.
When compared to materials with low thermal conductivity, materials with high thermal conductivity and equal heat capacity will:
— initially generate more condensate in a given time period,
— absorb and release energy faster,
Examples of some of the materials used are shown in Table 3.
Metal Stainless steel, carbon steel copper and copper- based alloys Other metals or combinations of metal.
Non-metal Glass, cellulose, polycarbonate, PVC, PTFE, silicon
The weight of a medical device, its individual components, or a collection of devices within a single sterile barrier or packaging system must be classified according to the codes listed in Table 4 This classification is essential for evaluation purposes.
— exposure time in a mixed weight sterilizer load;
— the stability of a single or composite construction material;
— the amount of condensate and its effect on steam penetration.
4.2.4 Sterile barrier system and/or packaging system
Medical devices, unless presented aseptically right after re-processing, must be contained in a sterile barrier or packaging system before sterilization, as outlined in ISO 11607 (all parts) It is essential to understand the combined steam penetration resistance and moisture retention of these systems, as they are influenced by the materials used in their construction A list of sterile barrier and packaging systems can be found in Table 5 Additionally, it's important to note that some countries may have regulations prohibiting the sterilization of unwrapped medical devices, rendering code d1 inapplicable.
Table 5 — Sterile barrier system and/or packaging system
Double wrapped in wrapping material or pouches, double wrapped container or tray, reusable sterilization container according to manufacturers instructions
Combination of two or more systems, for example, a reusable sterilization container with an inner sterile barrier system
Manufacturers will provide information regarding the intended use of sterile barrier systems Additionally, combining multiple systems may necessitate further performance qualification, as outlined in ISO 17665-1:2006, Clause 8.
The classification of a medical device into a product family should rely on specific attributes outlined in section 4.2 Table 6 presents several potential product families that can be derived from these identified attributes.
Use Table 6 to assign a product family to a medical device and then from this assignment identify the steam penetration resistance For each medical device:
— select a level for each attribute a to d;
— establish a match to one of the product families in the table;
— note the product family and then from column ‘e’, the estimate for steam penetration resistance;
— if a match cannot be obtained, establish a new one and then by comparison with established product families and from performance qualification, estimate a steam penetration resistance.
This article presents an analysis and estimation of steam penetration resistance for three categories of medical devices, detailed in sections 5.1, 5.2, and 5.3 Users may need to create additional product families for designs that do not fit into the seven categories outlined in Table 2.
The steam penetration resistance for each product family in Table 6 is estimated based on design attributes, with adjustments made for other influencing factors A procedure set typically comprises multiple medical devices and components from different product families, each with its own steam penetration resistance The product family assigned to a procedure set should generally match the device or component with the highest steam penetration resistance, unless affected by adjacent devices or components The actual steam penetration resistance is ultimately determined by the load configuration and various factors, as illustrated in Annex B.
— operational state of the sterilizer witnessed by validation and conformity to the requirements for scheduled periodic tests;
— quality of services delivered to the equipment witnessed by test;
Example 1 — pf 1
A shallow, thin wall, metal bowl.
— sterile barrier system and/or packaging system: d1.
Steam condensation on the bowl leads to an increased concentration of air on its surfaces As steam displaces this air, sterilizing conditions are established on the surface, particularly when the sterilization temperature is assessed at the reference measurement point, such as the chamber drain.
Nominal alterations in non-condensable gases (NCG) within the steam or air infiltration into the sterilizer chamber are unlikely to negatively impact the anticipated efficiency of the sterilization process.
The estimated steam penetration resistance for this medical device is e1 (see Table 6) based on design a1 The other attributes of the device will not affect this estimation.
Example 2 — pf 24
A length of thin wall soft plastic tubing.
— sterile barrier system and/or packaging system: d3.
When selecting a sterilization process and loading configuration, it's important to note that the sterilization temperature measured at the reference point may not accurately reflect the actual sterilizing conditions within the tubing.
— an active air removal system is necessary;
— thin wall tubing is susceptible to kinking and collapse;
— occlusion caused by condensate will prevent the removal of air from within the tube and delay or prevent the presence of sterilizing conditions;
— steam condensing on adjacent items can cause an increase in NCG local to the tube and this gas can then be driven by the steam into the tubing;
Air leakage into the sterilizer chamber and the presence of increased non-condensable gases (NCG) in the steam can contribute to the existing air in the tubing, negatively impacting the expected efficiency of the sterilization process.
The estimated steam penetration resistance according to design a5 will be e5 For this medical device, the other attributes listed in Clause 4 will not affect this estimate.
When choosing a sterilization process and loading configuration, it is crucial to consider various factors to ensure that the estimated steam penetration resistance remains at e5 However, due to the numerous variables involved, it may be necessary to assess steam penetration resistance based on performance qualification, as outlined in ISO 17665-1.
Example 3 — pf 27
Cannulated screw driver with a non-metallic or metallic coated handle.
— sterile barrier system and/or packaging system: d3.
Inefficient heat transfer from the handle's surface can postpone the establishment of sterilizing conditions within the lumen, with the extent of this delay influenced by various factors as illustrated in example 2.
The estimated steam penetration resistance based on design a6 will be e6 Weight and material may affect this estimate.
MD Attribute Steam penetration resistance
(c) Sterile barrier system and/or packaging system (d)
21 x x x x x x x x a Special - sterilization process should be developed and qualified.
MD Attribute Steam penetration resistance
(c) Sterile barrier system and/or packaging system (d)
+ a Special - sterilization process should be developed and qualified.
+ New product families that may be identified by the user.
Medical devices classified under a processing category must be determined by their product family and supported by data that demonstrate the effectiveness of a particular sterilizer and its sterilization process.
The combination of diverse medical devices within the same processing category can lead to an increased predicted steam penetration resistance For the general orthopaedic set, the individual instruments are designed with a penetration resistance of e2 However, factors such as the sterile barrier system, the overall weight of the set, condensate collection, unpredictable air retention, and the potential for increased air leakage or non-condensable gases in the sterilizer chamber elevate the steam penetration resistance to an estimated e5 It is crucial to understand how these combinations and changes impact the efficiency of the sterilization process for each item in the processing category.
One example of how to designate a processing category for a number of procedure sets is illustrated in Annex D.
The safe maximum values for process parameters during moist heat sterilization of medical devices must adhere to the specifications provided by the manufacturer (refer to Annex A).
Services
The efficiency of the sterilization process can be significantly impacted by variations in service quality during delivery These variations may influence steam penetration resistance, contaminant levels, and the shelf life of medical devices undergoing sterilization It is essential that the quality of the steam service adheres to the standards outlined in ISO/TS 17665-2:2009, specifically section A.11.2 and Table A.2.
Process selection
A sterilization process involves a series of controlled stages, each defined by specific process variables and parameters that determine the medical device type, processing category, and load configuration suitable for sterilization The initial stage is crucial for ensuring that designated parts of each medical device achieve sterility after the second stage of the process Finally, the third stage facilitates the return to atmospheric conditions for safe use.
In health care facilities, medical devices are primarily sterilized using saturated steam, which involves three key stages: air removal, sterilizing, and drying The air removal stage is crucial and should be designed to effectively eliminate air from the surfaces of each device A passive air removal system relies on gravity displacement, but it is ineffective for devices with trapped air, such as those in packaging or lumens In such cases, active air removal is necessary, utilizing steam, vacuum pumps, or pressurized water to create pressure changes The specifics of these pressure changes depend on the medical device type, steam penetration resistance, and processing category Proper air removal is essential to ensure that residual air does not compromise the sterilization efficiency.
Air leakage in the sterilizer chamber and the presence of non-condensable gases in steam can significantly reduce the effectiveness of the air removal stage Additionally, including medical devices with varying conductivity and weight within the same processing category can further compromise sterilization efficacy.
Stage two begins at a designated minimum sterilizing temperature, with the required exposure time at this temperature being the minimum specified for the holding duration For high-weight medical devices, additional exposure may be necessary to ensure proper temperature equilibration during sterilization.
Stage three involves restoring the sterilizer chamber to atmospheric pressure after the drying process, typically achieved through vacuum drying The length of the drying stage varies based on the presentation and weight of each item in the sterilization load.
The essential variables for effective moist heat sterilization include temperature, time, and moisture presence, as outlined in ISO 17665-1 To design a successful sterilization process, additional parameters such as pressure, the rates of pressure and temperature changes, and dwell times must also be taken into account.
A.2 A medical device should not be exposed to process parameters that can adversely affect functional efficiency, therapeutic value and shelf life.
To ensure a minimum sterility assurance, process parameters can be established using either a parametric or biological approach, as outlined in ISO/TS 17665-2:2009, Annexes A and B Additionally, the determination of processes based on product bioburden considerations is detailed in ISO 17665-1, sections 7.3 and 8.5.
The tests outlined in ISO/TS 17665-2, Annex A, are essential for a parametric approach to verify the minimum performance of specific sterilizers These tests help establish critical process parameters and ensure that any air and non-condensable gases remaining in the test load after the air removal stage are insufficient to hinder the presence of saturated steam on all surfaces of the test piece, including concealed areas within the sterilizer chamber The test piece is designed to exhibit high steam penetration resistance, as detailed in Table 6 Additionally, Figure A.1 presents a temperature profile for the small load test, where the temperature difference between S1 and S2 serves as an indicator of saturated steam presence.
To justify the use of the identified sterilization process and parameters for a medical device with greater steam penetration resistance, it is essential to have supporting data This rationale must be thoroughly documented to ensure compliance and accountability.
T 3 maximum difference – after 60s t 1 plateau period t 2 equilibration time t 3 60s t 4 holding time
Figure A.1 — Performance requirements: Small load test
Medical devices with comparable steam penetration resistance but differing attributes may necessitate distinct processing parameters To include them in the same processing category, as outlined in sections A.1 and A.2, it is essential to verify the appropriate process parameters.
Steam condensate within a sterile barrier system can indicate a failure in the sterilization process, but it may also suggest that additives are affecting steam penetration resistance The causes may include one or a combination of several factors.
— design and materials used to manufacture the sterile barrier system;
— combination of high and low weight medical devices;
— water contained in the steam;
For certain medical devices, it is essential to implement preheating before pressure changes for heavier devices, introduce delays between pressure changes to ensure pressure and temperature equalization in narrow lumens, and establish a high vacuum (e.g., 2 kPa) prior to pressure changes to reduce water inclusion in open-ended tubing Additionally, controlling the rate of pressure changes is crucial to prevent crazing in thick-walled plastic medical devices, and modifying the load configuration can help decrease moisture retention.
Characterization of a procedure set — Examples
The following are examples and illustrate the combination of various medical devices in order to derive product families.
The assessment/extraction set includes several individual items, as shown in Figure B.1 and detailed in Table B.2, with analysis provided in Table B.3 The evaluation of this set follows the guidelines outlined in Clause 4.
The items in the set feature designs that range from simple to moderately complex Notably, Item 8, the surgical suction tip, is classified with a lumen, an a3 design classification, and boasts an estimated steam penetration resistance of e3, which is the highest among the items in the set.
The article discusses the materials utilized, highlighting that both metal and plastic are involved It specifically notes that the tray is constructed from polycarbonate, which is characterized by low thermal conductivity and presents significant challenges Additionally, polycarbonate is classified as B2 and has an estimated steam penetration resistance of E2.
— The average weight of the items is 25g The total weight is 150g and classified as c2.
— Crepe paper wrap is used for the sterile barrier system This has a classification of d3 and a steam penetration resistance of e3.
Table B.2 — Content of assessment/extraction set
Table B.3 — Analysis: assessment/extraction set
Attribute Description Code Steam penetration resistance
(estimated) General description A collection of solid instruments placed on to a liner in a plastic tray and double wrapped, OR
A similar collection of solid instru- ments placed in a paper mache tray and left unwrapped.
Perforated polycarbonate tray Lumen instrument (suction tip) a1 a2 a3 e1 e2 e3 Material Stainless steel
Sterile barrier system and/ or packaging system