Conflicting Requirements in a Medical Device Update
A hospital’s infusion pump controller is being updated. The new version must support a new drug library, but the existing safety interlock logic (which prevents free-flow) must remain unchanged. The product manager wants to add a feature that automatically adjusts the flow rate based on patient weight, but the clinical team insists that any automatic adjustment must be reviewed by a nurse before taking effect. The development team estimates the automatic adjustment feature will take 6 weeks, while the safety interlock change (which is actually a bug fix for a rare edge case) will take 2 weeks. The project deadline is in 8 weeks. The regulatory submission requires that all changes be thoroughly tested and documented. The team has 5 developers, 2 testers, and 1 part-time regulatory specialist.
1. Identify the key conflicting requirements and propose a resolution strategy that balances stakeholder needs and project constraints.
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Key conflicts: (1) Product manager wants automatic weight-based adjustment (6 weeks) vs. clinical team requires nurse review before any automatic change (adds workflow and UI complexity); (2) safety interlock bug fix (2 weeks) is critical but competes for resources; (3) 8-week deadline with regulatory testing. Resolution: Prioritize the safety interlock fix as mandatory and non-negotiable for patient safety. For the automatic adjustment, propose a phased approach: implement the calculation and display of recommended rate (without automatic application) in the first release, requiring nurse confirmation. This satisfies clinical oversight while delivering partial functionality. Defer full automation to a later release. Reallocate testers to focus on safety-critical paths. Document the decision and rationale for regulatory submission. This balances safety, stakeholder needs, and timeline.
2. What requirements engineering techniques would you use to ensure the new feature does not compromise safety and is traceable?
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Use hazard analysis (e.g., FMEA) to identify risks of automatic adjustment. Derive safety requirements from the hazard analysis and link them to design and test cases via a requirements traceability matrix. Employ formal specification for the interlock logic (e.g., state machines) to verify no regression. Conduct joint requirements workshops with clinical team to define nurse review workflow. Use prototyping to validate the UI for nurse confirmation. Ensure all requirements are version-controlled and changes impact analysis performed. Maintain traceability from regulatory requirements to test evidence.