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.