July 12, 2021
ISO 14971 Probability of Occurrence of Harm
When tackling the estimation of probability of occurrence of harm during medical device risk management, I think it is important to remember that there is no one-size-fits-all approach. Instead, each manufacturer’s approach needs to be derived and appropriate based on the nature and complexity of the subject device, as well as on the availability (or lack thereof) of supporting data.
The particular approach can either be quantitative or qualitative (see ISO 14971 and ISO/TR 24971). The probability can be estimated per use, per device, per hour of use, within a population, etc. (ISO/TR 24971). The particular comparator (i.e., per use, per device, per hour of use, within a population, etc.) needs to be chosen based on the nature of the device. For example, some devices’ intended use (e.g., reusable devices) will intrinsically make the “per hour of use” comparator more appropriate than per device. In contrast, single-use devices may very well be appropriate for a “per device” comparator. The “per device” comparator is where sales numbers may be utilized. As hinted at above, these are longstanding principles that have been part of the ISO 14971 risk management paradigm for many years.
When using a “per device sold” comparator, various factors (e.g., nature and complexity of the device; marketplace tenure, emergent risks or device problems, etc.) will determine whether it is appropriate to use sales per day, per week, per month, per year, cumulative all-time sales, or some other timeframe. It is up to the manufacturer. Just be sure that the chosen paradigm makes sense by giving meaningful insight toward the ultimate goal of properly managing the subject device’s risk profile with regard to public health.
Consideration of device lifetime when estimating probability of occurrence harm is also a longstanding best-practice in risk management. Indeed, seeds for this can be found more than two decades back in the year 2000 version of ISO 14971 and even in EN 1441 (1998) that was a gold standard before modern risk management really got traction via the ISO 14971 series. Moreover, the consideration of device lifetime as part of estimating probability of occurrence harm remains a modern best practice today in the latest versions (see ISO 14971:2019 and ISO/TR 24971:2020), for example where it’s stated that device lifetime is an important factor for estimating probability of occurrence of harm. Accordingly, it is wise to figure out what is meant by device “lifetime” in the context of risk management and for the estimation of probability of occurrence of harm.
On that note, my experience has been that there seems to be harmonized general agreement on the meaning of device “lifetime”. That said, I haven’t found many standardized, statutory, or legislative definitions for this. At the moment, I generally rely on, adapt, and/or expand existing explanations such as:
FDA’s 21 CFR Part 803.3: “…(f) Expected life of a device means the time that a device is expected to remain functional after it is placed into use. Certain implanted devices have specified “end of life” (EOL) dates. Other devices are not labeled as to their respective EOL, but are expected to remain operational through activities such as maintenance, repairs, or upgrades, for an estimated period of time…”
ISO/TR 24971:2020: “…What determines the lifetime of the medical device?…Factors that should be considered include battery depletion, deterioration of materials and failure of components due to ageing, wear, fatigue or repeated use. The availability of spare parts should be considered as well…” [emphasis added].
FDA’s 2016 3rd Party Servicing Workshop: “…Information about reliability is needed to…understand the expected life of the device…” [emphasis added].
ISO TC/210: “…the rationale for the determination [of medical device lifetime] should be recorded and can involve consideration of the following…shelf life of the medical device…expiry date for medical devices or components which are subject to degradation over time…number of cycles or periods of use of the medical device, based on life testing of the medical device…anticipated material degradation…stability of packaging material…for implantable devices, the residual risk that results from the entire period of residence of the medical device inside the patient’s body…for sterile medical devices, the ability to maintain sterility… organization’s ability/willingness or contractual or regulatory obligation…” [emphasis added].