Understanding the BXM Method

bxm method, risk management of medical devices

I. What is the BXM method?

Compliant with ISO 14971, the BXM method helps you decompose a medical device system, perform risk analysis on the parts of the system and then integrate the underlying studies into the primary system-level analysis.

System decomposition

The decomposition should follow the system architecture. For instance, you can use the BXM method to decompose a system into two main parts. Then each of the parts you can further decompose into multiple components and so on. Refer to the figure below.

bxm method, risk management of medical devices

In addition, there are two criteria for system decomposition you need to consider:

  • the novelty of the medical device system
  • the degree of reusability that you want

When using the BXM method on a novel system, decompose the system to a lower level. If a part is reused in another system, continue decomposing to a level where the reusable component needs analysing. By doing so, the analysis of the part will become available for reuse elsewhere.


The BXM method uses the architectural design of the medical device system as a road map. Then, it looks for the failure modes of each architectural element by performing the Failure Modes and Effects Analysis (FMEA).

A critical principle in this method is the strict adherence to the boundary and scope of the analysis within the FMEA. That means that the principle allows the performance of FMEA of a given part agnostic of the system in which it’s used. Additionally, this principle has its benefits. For instance, the analyses of the different system parts can be integrated in the same way that the physical parts are integrated per the device system architecture.

II. What are the main benefits of using the BXM method?

The BXM method associates with several benefits. Namely:

  • It allows you to decompose a complex system into several parts. Each of these parts is simple, easy to understand, and less prone to errors of omission or commission during the risk analysis.
  • It allows different teams to analyse different system components simultaneously.
  • The BXM method enables the company management to assign only people with relevant skills to each team.
  • It allows modularity and reuse of risk analysis. If a specific part is used in several systems or different generations of the same system, the risk analysis of the part can be reused.  
ce marking medical devices

III. Estimating risk with the BXM method

The BXM method is a quantitative risk computation method that calculates risk in five harm severity classes: catastrophic, critical, serious, minor and negligible (see the figure below). Thus, it considers the entire spectrum of harm severities and detects the highest risk possible regardless of the harm severity.

bxm method for risk estimation

The BXM method allows you to evaluate the acceptability of residual risk by comparing two numbers: the residual risk and the acceptable risk level. To do so, you need to use a Boolean algebra to compute the residual risk of a medical device system: per hazard, per hazardous situation, and overall (check the medical device risk management glossary if you don’t know the meaning of a specific term).

Furthermore, due to its mathematical approach, the BXM method helps you:

  • Assess the safety impact of proposed design changes
  • Provide up-to-date risk assessment
  • Reuse estimations of harm probabilities across different projects
  • Compute the overall residual risks of the medical device system.

Lastly, the method is also associated with objective and automatic determination of risk acceptability and avoidance of error-prone manual risk assessment.

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