Simulated use is defined as “use that mimics the intended use of the medical device”[1]. In guidance documents such as the AAMI TIR12:2020[2] or AAMI TIR30:2011[3] simulated use testing often refers to test soil selection, specifying that “the test soil selected should be that which closely simulates the contamination in actual clinical use”2. FDA guidance for reprocessing medical devices in health care settings[4] has a broader definition of simulated use and states that “validation studies should incorporate multiple full use cycles and should be designed to assess the accumulation of soil over time”, using devices “that have undergone some simulated use”. Hence, simulated use testing refers to selecting test soils that mimic in-use conditions as well as to repeated full use cycles designed to assess the accumulation of soil over time. Given that simulated use testing is linked to soil selection and soil accumulation, it is always part of a cleaning validation. For other validations, such as disinfection or sterilization validations, soil (accumulation) is not part of the validation and simulated use testing is therefore not required.
In addition to selecting a test soil that closely simulates contamination in actual clinical use, simulated use testing with regards to soil selection implies that the methods of soiling will also simulate clinical use. This could mean articulating, actuating, or heating the device whenever applicable to mimic ingress of soil in different locations of the device which may occur during clinical use.
With regards to simulated use testing to evaluate soil accumulation, FDA states that “The number of simulated use cycles that you use should be scientifically justified”4, which can be tricky to pinpoint. Nelson Labs has historically used six full use cycles of soiling, cleaning and disinfection, and/or sterilization to perform simulated use testing. This number is deemed sufficient to detect soil accumulation that may occur over time. However, it may be appropriate to use fewer or more cycles depending on the device design or intended use. Rather than performing simulated use testing for soil accumulation in the lab, manufacturers may decide to submit devices to perform cleaning validations that have been clinically used and therefore have undergone multiple full use cycles. However, the choice to use devices that have been subjected to full use and reprocessing steps rather than performing simulated use cycles should be scientifically justified. FDA recommends using worst-case simulated use protocols throughout the validation of the cleaning process4 and prefers to have the simulated use tests performed during the validation to ensure the validity and reproducibly of the data. Consequently, submitting used devices for cleaning validations without performing simulated use testing should be thoroughly justified and these devices should have a clear record of their previous use.
[1] ST98 Cleaning validation of health care products – Requirements for development and validation of a cleaning process for medical devices, which is currently in draft and is intended to replace AAMI TIR30:2011
[2] AAMI TIR12:2020 Designing, testing, and labeling medical devices intended for processing by health care facilities: A guide for device manufacturers
[3] AAMI TIR30:2011 A compendium of processes, materials, test methods, and acceptance criteria for cleaning reusable medical devices
[4] FDA 2015 Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling. Guidance for Industry and Food and Drug Administration Staff.
