Usability Engineering (ISO 62366): The Key to a Safe and Compliant Medical Device
Usability Engineering (ISO 62366): The Key to a Safe and Compliant Medical Device
Introduction
A technically perfect medical device can become dangerous if its interface is confusing. Poorly positioned buttons, ambiguous alarms, incomprehensible instructions: these design flaws are the source of many preventable incidents.
It is precisely to prevent these risks that Usability Engineering (UE) exists. Defined by IEC 62366-1:2015, this approach is a fundamental regulatory requirement of the MDR (EU 2017/745).
For electromedical devices—electrical equipment with an applied part on the patient or energy transfer—IEC 60601-1-6 directly integrates UE into basic safety and essential performance requirements.
The objective?
To design devices that can be used safely and effectively by intended users, in their real environments, to minimize the risk of errors.
UE at the Heart of Risk Management (ISO 14971)🎯
UE is not an isolated process. It is the extension of ISO 14971 to aspects related to human interaction, centered on the user interface (UI).
User Interface: Beyond the Screen
The UI encompasses all means of interaction:
- Hardware: Buttons, levers, light or sound signals.
- Software: Screens, menus, alarm messages, navigation logic.
- Documentation: Instructions for Use (IFU), labeling, and even training materials.
If a clinical risk arises due to misunderstanding of the instructions, it is a usability risk.
Critical Distinction: Use Error vs. Abnormal Use
| Error type | Definition | Responsibility | UE Action |
|---|---|---|---|
| User error | Action/omission resulting from a poorly designed interface | Manufacturer | Prevent by design (e.g., single connector) |
| Normal error | Correct use but accidental error despite good design | Manufacturer | Minimize probability (color codes, confirmations) |
| Abnormal use | Intentional misuse, negligence | User | Outside the UE scope (training, organizational procedures) |
➡️ Golden rule: If your device can be misused by mistake, it is up to you to make it safer.
Hierarchy of control measures
The MDR and ISO 14971 impose a strict hierarchy for reducing risks:
- Intrinsic safety by design (UE)
- Protective measures (alarms, locks)
- Information for safety (instructions, warnings)
⚠️ Fundamental principle : Safety must be ensured primarily through design, not just through instructions or warnings. A well-designed interface makes errors difficult, if not impossible.
Example
❌ Insufficient : "CAUTION: Do not plug connector A into socket B"
✅ Best practice : Designing physically incompatible connectors
The Usability Engineering Process: The Iterative Imperative 🔄
UE must be an iterative process integrated into development. A single evaluation at the end of the project is never sufficient.
Define the Context of Use
Specification of Use :
- Define the medical indication
- The patient population
- The environment (e.g., home, operating room, ambulance)
- The user profile (training, experience, physical/cognitive abilities).
Task Analysis
Break down usage into elementary tasks: turn on, configure, confirm, monitor, shut down...
Identification of Risks Related to Use
For each task, identify possible misuse scenarios and link them to hazardous situations and clinical harm (in accordance with ISO 14971).
Critical Scenario Selection
After completing the risk analysis, select the critical scenarios that require summative validation:
- Errors that could cause serious damage (death or serious injury)
- Primary operating functions: functions whose loss or deterioration compromises the medical purpose of the device
This selection must be justified and documented in your UE file.
Iterative Design and Evaluation
Interface development is a constant dialogue with users.
Type of Assessment
| Type | Objective | When | Sample |
|---|---|---|---|
| Formative | Identify and correct problems early on. | During development, on prototypes. | 5–8 users |
| Summative | Formally prove that users can safely perform critical tasks. | Before placing on the market, on the final device (or equivalent). | Variable depending on risk (minimum 5, recommended ≥15/group) |
⚠️ Critical clarification regarding the summative sample : IEC 62366-1 does not specify a precise number but requires justification of the sample size. In practice:
- Absolute minimum : 5 participants per user group
- IEC 62366-2 and FDA recommendation : ≥15 participants per group
- If several distinct user groups : multiply by the number of groups
The most common pitfall is to postpone the UE until the end. If the summative assessment reveals a critical error (failure to meet the acceptance criteria), the process must be repeated and the system modified, resulting in costly delays.
Specific applications of UE
All medical devices are affected.
UE applies to all medical devices, regardless of their type:
- Passive devices : syringes, catheters, dressings (ergonomics, instructions)
- Mechanical devices : wheelchairs, medical beds (controls, adjustments)
- Implantable devices : prostheses (surgical instruments for fitting)
- Electromedical devices : monitors, defibrillators (IEC 60601-1-6)
- Medical software : decision support applications (IEC 62304)
Focus on Medical Software: Cognitive Errors
Each user-device interaction can generate errors: handling, assembly, information interpretation, maintenance.
Software processes complex data. Use errors are often cognitive:
- Misinterpretation of a graph
- Cognitive overload: too much information simultaneously
- Omission: critical information misplaced
- Alert fatigue: critical alert buried in 15 minor alerts
➡️ UE must ensure clear, hierarchical display adapted to urgency.
For medical software, IEC 62304 requires complete traceability between requirements, design and testing. UE integrates by transforming usability requirements into traceable software requirements.
Mandatory traceability flow:
Identified risk (ISO 14971) → Usability requirement (IEC 62366-1) → Software requirement (IEC 62304) → Implementation + Verification test → UE summative test
This bidirectional traceability proves that each usability-related control measure has been properly specified, implemented in code, technically verified and validated with end users.
Electromedical Devices and IEC 60601-1-6
For electromedical devices (electrical equipment with applied part on the patient or energy transfer), IEC 60601-1-6 is a collateral safety standard that explicitly refers to IEC 62366-1 for the usability engineering process.
Scope: infusion pumps, defibrillators, patient monitors, electric operating tables, surgical robots...
IEC 60601-1-6 integrates UE into the overall safety assessment by requiring that:
- The UE process (according to IEC 62366-1) be applied
- Usability be linked to basic safety and essential performance
- Residual use risks be assessed in the risk management file
The Usability Engineering File 📁
Traceability and Evidence
The UE file must provide complete bidirectional traceability:
- Risk (ISO 14971) → Critical Scenario → Control Measure (UI Specification).
- Control Measure → Summative Test Plan → Test Results → Acceptability Conclusion.
Each critical use-related risk must be linked to evidence that the design has controlled it.
The Importance of IFU (Instructions For Use)
The IFU must be validated. The manufacturer cannot simply write the IFU; they must test whether intended users are able to understand and apply safety-critical instructions for use.
A comprehension test of the instructions is often part of summative testing to ensure that the information provided is truly effective.
Post-Market Surveillance (PMS)
UE is a lifecycle process. Market feedback (PMS) must include:
- Analysis of incidents and complaints: This data is often the best source of information on actual use errors.
- Trend analysis: Identify recurring errors due to the interface.
If PMS reveals a usability problem, the manufacturer must resume their UE process, modify the interface or documentation, and potentially redo summative evaluation. The UE file is thus updated to prove post-market risk management.
Conclusion: UE as a Lever for Sustainable Innovation
UE is not a luxury: it is a regulatory necessity and a success factor.
Benefits:
- ✅ Fast certification
- ✅ Fewer incidents/recalls
- ✅ Customer satisfaction
- ✅ Savings (fixing in design = 10× cheaper)
The 3 golden rules:
- Start early
- Test often
- Document everything
➡️ This is the key to successful certification and devices that truly improve patients' lives.
Ready to Transform UE into a Competitive Advantage?
At Certeafiles, we support you:
- Personalized support by our experts
- Adapted practical training
- Internal audits
👉 Contact us for a free initial consultation and discover how Certeafiles can accelerate your UE process.