Reusable devices face significant design challenges that single-use devices do not. A design engineer must think about how the device will perform not only during the first use, but for every subsequent use. Many medical devices need to be able to function safely after hundreds of cleaning and disinfection or sterilization cycles; these devices must therefore be designed to comfortably withstand the stresses of the reuse procedure. Additionally, reusable devices need to be designed so that they may effectively be rendered safe for reuse by either health-care staff or patients at home. If the process is too difficult or complex, there is a possibility that the device will not be fully rendered safe for reuse.
A thorough understanding of device cleaning, disinfection, and sterilization issues is therefore essential in the design phase of any reusable medical device. Devices that are designed with the eventual reuse parameters in mind generally have a quicker and easier path through the validation process. Conversely, devices that prove very difficult to clean or disinfect often must be redesigned, resulting in delays and/or cost overruns. Thus, reusable medical devices should be designed not only to facilitate the use of the device, but to facilitate the eventual reuse as well. A contract laboratory with experience in the reusable device validation process, such as Pacific BioLabs (Hercules, CA), can assist you in the development of a reuse validation plan and can provide advice on design choices to help facilitate the process.
This article will present an overview of the validation process and what to consider during the design process, and these concepts will be demonstrated in three case studies. Also, while the term “reprocessing” can have many meanings, for the purposes of this article the term will refer strictly to the cleaning and disinfection or sterilization necessary to render a medical device safe for reuse.
The Reuse Validation Process
The ultimate goal of device reprocessing is to render a medical device safe for further human use. Typically, two steps are involved in device reprocessing: cleaning and either disinfection or sterilization. The validation process begins with the creation of a reprocessing procedure based on the intended clinical use and design of the device. Next, the device is purposefully contaminated and challenged with a worst-case level of soil, then run through the reprocessing step that is being validated. Soil residues include organic soil such as proteins, hemoglobin, and endotoxins, inorganic soil, and biological soil in the form of suspensions of microorganisms.
If the reuse procedure adequately removes the soil and all reprocessing criteria are passed, then that procedure is validated for use. Appropriate documentation must then be created for the end user, describing in detail how to reprocess the device.
Cleaning is always the first step in reprocessing and is defined by the FDA as removal of soil residues and is a necessary step prior to reuse of any medical device. To validate the cleaning process, the device is inoculated with soil, cleaned using the recommended cleaning procedure, and then residuals (any soil remaining on the device) are recovered and measured. The acceptance criteria to validate the procedure are: a visually clean device; 3-log reduction in microorganisms; protein levels 2; hemoglobin 2; carbohydrate 2; endotoxin 2.
Disinfection is defined as using physical or chemical means to kill microorganisms. This is frequently accomplished through the use of chemical disinfectants, or via thermal disinfection (the application of high temperature water). A disinfection process is considered to be validated if the device is visually clean and a 6-log reduction in microorganisms can be shown.
Sterilization is a process that renders a device free from viable microorganisms. The level of sterilization is defined by Sterility Assurance Level, or SAL, which is the probability that a device is not sterile. For example, an SAL of 10-6 indicates a 1 in 1 million possibility that the device is non-sterile. Sterilization can be achieved in a number of ways, but the most common methods of sterilization are steam, dry heat, hydrogen peroxide, ethylene oxide, and radiation. The acceptance criteria for sterilization of non-critical devices (those that do not penetrate the body) is 10-3, and the acceptance criteria for critical devices is an SAL of 10-6.
To validate a disinfection or sterilization process, a device is inoculated with a known count of microorganisms and then treated with the recommended procedure. Following treatment, any remaining viable (live) microorganisms are recovered, cultured, and colonies are counted. If there is an adequate reduction in microorganisms (or if the required SAL is achieved), then the disinfection or sterilization procedure is validated.
To understand the requirements for cleaning, disinfection, and sterilization validations, it is also necessary to be aware of the different classifications of reusable medical devices. The more invasive the device, the more stringent the reprocessing procedures must be. Noncritical devices, which only make contact with intact skin, require cleaning and low or intermediate-level disinfection. Semicritical devices contact mucous membranes but not the bloodstream, and require cleaning and high-level disinfection. Critical devices are those which contact the bloodstream or other sterile areas of the body. Given the high possibility of infection if any microorganisms are introduced into these areas, critical devices must be cleaned and then sterilized to an SAL of 10-6.
There are three main design aspects that must be considered: material selection, physical design, and total system design. The materials selected for use in a device must be biocompatible; material selection must take into account the use of the device and the potential of the material to leach toxic substances. Additionally, some materials may release toxic byproducts when exposed to cleaners or disinfectants. Semi-critical or critical devices that will most likely be exposed to strong cleaning or disinfecting agents should take this into account during material selection.
Porous materials are often prone to retaining high levels of soil residuals and can be difficult to clean thoroughly. A highly porous material may also retain residual amounts of a cleaning or disinfecting agent that can then harm patients during use. It is also important to consider the limitations of both metal and polymer materials. Metals may be scratched by brushes, leading to a greater retention of residuals. Polymeric coatings over metals can be adversely affected by ultrasonic or mechanical cleaning, potentially resulting in leaching of coating material. Polymer materials also react to some chemicals, and can become distorted or easily scratched. Finally, consider limiting the use of adhesives or lubricants, as these may become toxic when exposed to cleaning, disinfecting, or sterilization agents.
The physical design of a device can put additional constraints on the cleaning process and is one of the most important considerations in device engineering. The size and shape of components can have a large effect on the ease of reprocessing. Long interior channels, lumens, or small openings can be difficult to clean, as a brush often needs to be able to pass through openings to reach and clean interior spaces. To facilitate cleaning of small interior spaces, some device designers create custom brushes or cleaning tools. If the interior of the device may become exposed to blood or other bodily fluids, consider adding an open port that facilitates flushing the device’s interior.
Rough or discontinuous surfaces can be difficult to clean, as can sharp angles. This can result in an increased capacity to collect microorganisms. If the device must be disassembled and reassembled, small detachable pieces may be misplaced easily. The process of disassembly and reassembly should be fairly intuitive; if it is too difficult or complex, health care practitioners or patients will be reluctant to perform the necessary steps.
Total System Design Considerations
Once materials and the physical design are planned, the device as a total system must still be examined. If the device will be composed of multiple materials, the question of whether these materials will interact must be considered. For instance, stainless steel parts combined with aluminum, brass, copper or chrome can create an electrochemical reaction.
Additionally, consider whether electronic parts are adequately protected from potential reprocessing agents (such as liquids.) Finally, examine the potential long-term effects of reprocessing. If the cleaning and disinfection or sterilization cycle is repeated, will the device eventually be rendered unusable, unsafe for patient use, or incapable of further reprocessing?
To help aid in understanding how device design and use constrain and affect what reprocessing methods may be used, we present three different medical devices and their reprocessing procedures: a surgical forceps, a blood glucose meter, and a colonoscope.
Surgical forceps are simple devices, but because they will encounter sterile areas of the body, they must be cleaned and sterilized after every use. Although they are made of metal, they are limited by some potential chemical incompatibilities, as certain harsh chemicals can pit the forceps surface, reducing device effectiveness during surgeries. It is also important to ensure that any residues from the cleaning process are thoroughly removed from the device, as even a small amount of a harsh cleaner introduced into a patient’s bloodstream could have serious negative health effects.
To clean the forceps, it was determined that using an enzymatic cleaner (in this case, Alconox) combined with sponge cleaning would be effective. Enzymatic detergents are highly effective at removing the organic soil that can be the result of surgery. Following the cleaning process, the forceps were then thoroughly rinsed in water to remove all traces of the detergent.
Sterilization was achieved through the use of an autoclave, which uses steam to sterilize devices. The method was chosen for two reasons: first, it is a relatively quick and inexpensive method well suited to metals, and second, every hospital can be assumed to have an autoclave, making this a very practical sterilization method.
Blood Glucose Meter
The second device we will examine is a blood glucose meter. Compared to forceps, this device requires a very different reprocessing procedure. Although it is a semi-critical rather than critical device, it contains electronics, complex parts, and is composed of multiple materials. All of these factors introduce complexities into reprocessing. Certain disinfection methods (such as liquid immersion) or sterilization (high heat or steam) cannot be used because they would damage the device.
Consequently, care must be used in the selection of the cleaning and disinfection tools and overall process. For this blood glucose meter, Sani Cloth Plus wipes were chosen to both clean and disinfect the device. These premoistened disinfectant wipes eliminate many strains of bacteria and viruses including HIV-1, E-coli, and influenza. Most commonly, Sani Cloth wipes are used to clean and disinfect nonporous hard surfaces, making them ideal for the plastic outer shell of a blood glucose meter. They are also commonly available in hospitals and other healthcare facilities.
Cleaning of the device (as measured by removal of all visual soil) was achieved using a combination of wipes to clean the major portions of the device, as well as swabs soaked in the Sani Cloth disinfectant fluid. The swabs aided in cleaning hard-to-reach areas such as crevices and screw housings. Following cleaning, disinfection was achieved by once again wiping down the device with the Sani Cloth Plus wipes. However, to achieve adequate disinfection, the device was kept wet for 5 minutes. The longer exposure to disinfectant significantly reduced any microbial contamination, resulting in the required log reduction in microorganisms.
The final device we will examine, a colonoscope, is an example of a very common family of devices: endoscopes. Endoscopes can be very complex devices because most contain internal lighting systems, fiber optics, a lens, an eyepiece, and an internal channel to accommodate a surgical instrument. Reprocessing can be very challenging - often an endoscope may have knobs, buttons, and screws that are difficult to effectively clean and rinse. Endoscopes may also be composed of softer materials (to aid flexibility) that may become easily scratched or deformed if repeatedly cleaned using mechanical methods or brushes. Additionally, potential interaction of harsh chemicals with the material of the device can limit the choice of disinfectants.
The colonoscope is a semi-critical device because it contacts the mucous membrane of the colon. Therefore, it must be thoroughly cleaned and disinfected using a high level disinfectant. However, full liquid immersion or high temperatures can harm the device and the fragile camera lens. Given these constraints, it was determined that manual cleaning and disinfection using CIDEX would be appropriate. CIDEX is no longer commonly used, but at the time of this validation it was one of the most commonly used methods for endoscope cleaning. CIDEX provides high-level disinfection without corroding delicate device parts.
The device was first cleaned with water by partially immersing the device and using a soft sponge and water to clean the non-immersible parts. Next, the device was partially immersed in CIDEX OPA to enhance the cleaning. To disinfect the colonoscope, CIDEX Activated Dialdehyde Solution was used. The colonoscope was again partially immersed and was soaked for 12 minutes. A sponge was used to thoroughly apply CIDEX to the nonimmersible areas of the device. This combination of soaking and sponge application of disinfectant achieved the required microbial reduction while protecting the delicate instrumentation of the colonoscope.
A great deal of thought goes into the design of any medical device, and engineers should be encouraged to thoroughly examine the ways in which the design of their device can facilitate or hinder reprocessing. The best device design facilitates the use of the device, and also facilitates the reuse of the device. However, some devices, in the initial design, prove so difficult to reprocess that the design must be altered to facilitate cleaning and reuse. By understanding the choices made in creating a reprocessing methodology and how device design and use puts constraints on the reprocessing method, engineers can save significant amounts of time and speed device approval, thereby ensuring that their devices get to market as quickly as possible.
This article was written by Maria Lilibeth Samillano, M.D., Microbiologist and Device Team Leader; Diana Louie, Microbiologist; and Aaron Burke, Director of Business Development for Pacific BioLabs, Hercules, CA. For more information, Click Here .