The BXM method relates to performing decomposition of the medical device system, followed by risk analysis on the parts of the system and finalised with an integration of the underlying reports into the system-level analysis.
This method is in compliance with ISO 14971 and brings with itself several benefits, such as:
- A complex system can be easily decomposed into several simpler parts which, thus, can be understood easily;
- It reduces the probability of errors of omission or commission during the risk analysis;
- It allows parallel work streams, i.e. different teams can simultaneously analyse different system elements;
- The method permits the reuse of the analysis of components used in multiple systems or different generations of the same system.
As said above, the first step, when using this method, is the system decomposition, which follows the system structure. A visual representation of how a decomposed system looks like is presented in the picture below.
Two criteria need to be taken into consideration during the process of decomposition:
- the novelty of the medical device system
- the degree of the desired reusability.
These two criteria determine how far to go in the process. For example, the decomposition of a novel system should continue to the lowest level, but if a component is being reused in other systems, then the process of decomposition should proceed to a level where the reusable component gets analysed.
Integration is the corollary to decomposition, and it is based on the hierarchical multilevel FMEA (Failure Modes and Effects Analysis). What does this mean? It means that the architectural design of the medical system is used as a road map and each structural element is examined for failure modes. During the integration, there is strict adherence to the scope and boundaries of the analysis set within the FMEA.
Quantitative risk estimation
The BXM method uses a mathematical approach due to which it allows any identified risk to be measured quantitatively. This, consequently, enables a simple way of evaluating the acceptability of residual risk. In the end, it is all brought down to a simple comparison of two numbers: the amount of residual risk and the acceptable risk level.
The BXM method is highly suitable for implementation in software tools, as the use of software tools in risk management has the following benefits:
- the risk acceptability can be objectively and automatically determined
- there is an up-to-date risk assessment
- avoidance of error-prone manual computation/assessment of risk
- Evaluation of the safety impact of proposed design changes
- Estimations of harm probabilities can be reused across multiple projects
- The overall residual risks of the medical device system can be computed.