Manufacturers of Sterilization Cases and Trays are Working Toward the Same Patient-Safety Goal
By David C. Furr
There has been a lot of discussion recently in the hospital products and service industries about sterilization cases and trays. Some of the information circulating is accurate; however, some of it misses the mark or is just out of date. If you are a user or even a manufacturer of hospital sterilization cases and trays, there are a few things you should know.
Several types of equipment can be considered under the general heading of sterilization cases and trays. All are generally used for containment of reusable medical devices and supplies during sterilization processing. They include everything from mesh baskets or flat trays used in some fl ash sterilization applications, to perforated cases with lids, intended to be enclosed in a sterile barrier wrap, to sterilization containers with a base, lid, and some sort of permeable filter mechanism. Cases and trays are constructed from various materials including metal, plastic, or a combination of these materials (hybrid cases) and they may or may not have inner trays or compartments for holding devices. Finally, they may be intended for use in one or more different sterilization environments such as steam, ethylene oxide, hydrogen peroxide plasma, or even ozone.
The regulatory status of sterilization cases and trays depends on their intended use, and has evolved over the years. The Food and Drug Administration (FDA) maintains a system of classification of devices to help manufacturers determine their regulatory status and requirements. Sterilization cases and trays are included in 21CFR§880.68501 which contains the description and classification information for sterilization wrap. Most products covered by this part are considered to be Class II medical devices, and as such, they require FDA clearance in the form of a 510(k) pre-market notification before they may be placed onto the U.S. market.
The FDA maintains that the use of a sterile barrier is the key to determining if the case or tray is covered by this part of the regulations. In the case of baskets or flat trays that may be used in a flash sterilization application, they do not fall under this rule and are generally considered to be Class I devices which do not require FDA clearance prior to marketing. Sterilization wrap and pouches are obviously included in this rule, making them Class II devices. In addition, sterilization containers which incorporate filters to maintain the sterile barrier are also Class II devices. Sterilization wrap and container manufacturers have long been aware of their products classifications and all should have 510(k) clearance from FDA for marketing in the U.S.
There has been an outstanding question about whether products that do not fall clearly into the sterilization wrap classification are actually Class I or Class II devices. Products such as sterilization cases, cassettes, and trays with perforations and lids, which are intended for use in sterilization processes, but must be wrapped to maintain sterility are considered to be accessories to sterilization wrap. Under the rule, the FDA considers these accessory products to be Class II devices, which also require pre-market approval in the form of a 510(k). Many manufacturers do not agree, and they maintain that these devices should be considered as Class I devices, not subject to FDA clearance, based on their interpretations of the original intent of the regulations. They may be right, and the subject is open to continuing debate. The FDA has made its current position on this matter clear in both a letter to manufacturers in 1998, and in a recent draft guidance document for industry released in March 2002.2 Even though there is not agreement on the Class II status of these products, some manufacturers have gone ahead and applied for, and received FDA 510(k) pre-market approvals on their products.
In order to receive FDA clearance to market cases, trays, containers, or wraps, manufacturers must submit data, which demonstrates the product is safe and effective for its intended use. This includes testing in the sterilization environment specified, biological indicator studies, evaluation of materials for biocompatibility and integrity, and device-dependent testing such as barrier properties and drying capability. Products which have not been cleared for marketing through the FDA 510(k) process may not have been evaluated in this manner.
In the development of sterilization case and tray products, several materials have been introduced. Experience has shown that not all materials are compatible with the sterilization environment. As a result, modern materials are tested extensively, and a number of robust materials are now available for use in construction of sterilization cases and trays. Some of the more common materials along with potenial advantages and disadvantages are discussed below:
Untreated aluminum was found to oxidize easily in sterilization environments and was determined to be less than satisfactory for use in sterilization cases and trays. As a result, modern cases and trays constructed from aluminum are anodized and coated to provide an attractive durable finish. Anodized aluminum is a good material, relatively lightweight, and versatile for case and tray construction. With use over time, and in some sterilization environments, the material may begin to oxidize slightly or discolor, even with an anodized surface.
High-grade stainless steel has proven to be a durable and long-lasting material for sterilization cases and trays. It is an expensive raw material and more dif. cult to work with, making for a more expensive final product. Stainless steel is heavy, contributes more unproductive mass to the sterilization load, and in large configurations, makes up a significant portion of the weight of the loaded case.
Various plastics have been used for the manufacture of sterilization cases and trays over the years. Some earlier polymers were not up to the task and did not prove to be durable with continuous use. In addition, some early designs had problems due to being drawn too thin or being made from brittle polymers, resulting in breakage. Since sterilization cases and trays are reusable devices, some of these earlier models are still around and contribute to the perception that plastic may not be a suitable material. Modern plastics used by manufacturers have been extensively tested in sterilization environments and are quite durable, providing a long useful life. Polyphenylsulfone is the principal high-performance polymer used in plastic cases and trays. The manufacturers using plastic have also improved designs, resulting in a wide variety of excellent performing configurations. Modern polymers used by FDA-cleared case and tray manufacturers are proven to be biocompatible, reusable over many loads, and resistant to the sterilization process for which they are specified. Heat-resistant plastics are commonly used; however, some polymers cannot be used in highly oxidative environments such as in ozone sterilization.
Plastic, as a material of construction, has also been criticized in the past due to concerns about drying. Laboratory and hospital testing demonstrates that when properly designed and handled, plastic cases and trays can be dried just as effectively as metal. Several factors can affect case and tray drying, irregardless of the material. These include the design of the case, loading, steam quality, and drying time.
Some modern case and tray designs take advantage of the best qualities of both metal and plastic materials. Several successful designs are now in use in configurations such as metal bodies for strength with inner plastic trays and plastic lids to reduce weight.
The Association for the Advancement of Medical Instrumentation (AAMI) is a standards organization which maintains standards for users and manufacturers of many medical products. Currently, AAMI is working on a draft document titled Containment Devices for Reusable Medical Device Sterilization.3 Collaborators on the writing of this standard include users from the hospital community, manufacturers, regulators, and independent experts in sterilization. The proposed document will be finalized into an industry standard for manufacturers. The document acknowledges and discusses the various types of containment devices, sterilization methods, and materials, as well as specifying testing requirements.
A wide variety of viewpoints and concerns has been considered in developing the standard to its current revision, and the final standard will represent a consensus document. Many manufacturers are already using the concepts embodied in the draft standard. The FDAs proposed draft guidance document for testing containment devices may be finalized or superceded once the final AAMI standard document is established.
Testing of Sterilization and Drying Cycles
Manufacturers of sterilization cases and trays subject to FDA 510(k) clearance must test and validate the performance of their products. These tests are intended to assess the design, material of construction, and configuration of the cases and trays. They are evaluated in a worst-case loading confi guration, usually with maximum loads, multiple bio-indicators, and may even be monitored with thermocouples. The testing is done in sterilization environments using cycles which match the capabilities of common hospital cycles.
Users should always follow the manufacturers instructions for use. The instructions for use are developed from the validation studies performed on the product. Exceeding the loading capacity, loading incorrectly, reducing the sterilization time, or using a different sterilization method than that described in the manufacturers instructions may result in inadequate sterilization efficacy. Users should feel free to request summaries of validation testing and manufacturers should readily provide this data.
Sterilization methods and minimum times are usually established using maximum loads and common hospital cycles. Occasionally, instruments need to be sterilized which require a longer sterilization cycle time than the case or tray. Users should always set the sterilization cycle to meet the longest sterilization time needed for any instrument or case placed in the load. Manufacturers generally try to keep their cycle recommendations consistent and within standard settings for most hospital cycles. Occasionally, there is a need to adjust the cycle time for some of these worst-case situations. In most cases, user equipment cycles can be adjusted, and users need to be aware of any specific instructional requirements for objects they are sterilizing. Unfortunately, some complex instruments or configurations for a given surgical procedure just cannot be sterilized using the standard cycle setting.
The same concept holds true for drying. Since a manufacturer cannot predict all of the variables, such as total load density, steam quality, and type of wrap in a user load, drying time is usually given as a range. Users can usually estimate a final drying setting based on experience with their equipment and loading practices.
It is generally accepted that users play as critical a role in sterilization effectiveness as do the manufacturers. The AAMI also publishes standards for users to evaluate their equipment and test various devices within their hospital environment. User equipment must periodically be calibrated, operated correctly, challenged with test packs, and maintained properly. Operators must be trained and have a good basis of understanding of sterilization methods and techniques.
Responsibilities to the End User
Members of industry, regulators, hospitals, and standards agencies are all working toward the same goal of providing safe and effective hospital sterilization capabilities for the patients in our clinics and hospitals. By working with manufacturers that comply with FDA and industry standards, using accepted materials and testing practices, users can help assure that they are offering patients the best care possible. Most manufacturers want to have open lines of communication with the users of their products so that designs and methods can continuously improve.
David C. Furr is a regulatory/quality/sterilization consultant based in Ft. Wayne, Ind.