Human Factors

Human Factors Engineering (HFE), also known as Usability Engineering, is the systematic application of knowledge about human behavior, abilities, limitations, and other characteristics to the design of medical devices. The goal is to create devices that can be used safely and effectively by the intended users in the intended use environments, minimizing use errors that could lead to patient harm.

Regulatory basis and standards:

IEC 62366-1:2015 - Medical Devices — Part 1: Application of Usability Engineering to Medical Devices:
The primary international standard for human factors engineering in medical devices. IEC 62366-1 establishes a usability engineering process that must be integrated throughout the device lifecycle, from concept through post-market surveillance.

Key standard requirements:
- Identify user interface characteristics related to safety
- Identify known or foreseeable hazards and use errors
- Conduct formative and summative usability evaluations
- Validate that user interface is safe for intended users
- Document usability engineering activities in a Usability Engineering File

FDA Human Factors Guidance:
The FDA's guidance "Applying Human Factors and Usability Engineering to Medical Devices" (2016) provides specific recommendations for device manufacturers submitting premarket applications (510(k), PMA, De Novo). FDA requires human factors validation testing for devices with user interfaces that could contribute to use errors resulting in serious harm.

EU MDR Annex I General Safety and Performance Requirements:
EU Medical Device Regulation explicitly requires devices to be designed and manufactured considering human factors principles, minimizing risks arising from ergonomic features and use environments.

Core concepts in human factors:

Use error:
An act or omission of an act by a user that results in a different outcome than intended by the manufacturer or expected by the user. Use errors can arise from:
- Confusing user interface design
- Inadequate instructions or training
- Poorly designed controls or displays
- Environmental factors (lighting, noise, distractions)
- User fatigue, stress, or cognitive overload

Use-related hazard:
A hazard resulting from usability problems, user error, or interaction between the user and the device that could lead to harm.

Critical task:
A user task that, if performed incorrectly or not performed at all, could result in serious harm to the patient or user.

User interface:
All points of interaction between the user and the device, including:
- Physical controls (buttons, knobs, touchscreens)
- Visual displays (screens, indicators, labels)
- Auditory alarms and feedback
- Software menus and navigation
- Instructions for use and labeling
- Training materials

Human factors engineering process (IEC 62366):

Step 1 - Prepare use specification:

Identify intended users:
- Primary users (e.g., clinicians, patients, caregivers)
- User characteristics (training, experience, age, physical/cognitive abilities)
- Use environments (hospital, home, emergency, etc.)
- Frequency and duration of use

Define intended use and operational context:
- Clinical purpose and indications
- Patient population
- Use scenarios and workflows
- Environmental conditions (lighting, temperature, noise)

Step 2 - Identify use-related hazards:

Risk analysis integration:
Human factors must be integrated with risk management per ISO 14971:
- Identify potential use errors during task analysis
- Estimate severity of harm from use errors
- Evaluate likelihood of use errors occurring
- Determine which hazards require risk control measures

Known use errors:
Review literature, competitor device issues, incident databases (MAUDE, EUDAMED), and complaint data to identify known use errors for similar devices.

Step 3 - Identify and describe user interface:

User interface analysis:
Document all user interface elements:
- Physical device controls and displays
- Software interface components
- Labeling, symbols, and instructions
- Packaging and accessories
- Training and educational materials

User tasks and task analysis:
Break down device use into specific tasks:
- Setup and preparation
- Operation during normal use
- Error recovery and troubleshooting
- Maintenance and cleaning
- Storage and disposal

Step 4 - Conduct formative evaluations:

Formative usability testing:
Iterative testing during design development to:
- Identify usability problems early
- Evaluate design concepts and alternatives
- Optimize user interface before finalizing design
- Assess effectiveness of risk control measures

Formative methods:
- Cognitive walkthroughs with subject matter experts
- Heuristic evaluations using usability principles
- Simulated use testing with representative users
- Focus groups and user interviews

Results inform design iterations: Formative findings lead to design improvements, which are then re-tested until usability goals are met.

Step 5 - Conduct summative (validation) evaluation:

Summative usability testing:
Final validation testing with the production-equivalent device to:
- Demonstrate user interface is safe and effective
- Verify critical tasks can be completed successfully
- Confirm use errors have been mitigated to acceptable levels
- Support regulatory submissions

Test requirements:
- Representative users: Participants matching intended user population characteristics
- Realistic use scenarios: Simulated clinical environments and tasks
- Sufficient sample size: Typically 15+ users per user group (FDA guidance)
- Critical tasks included: All tasks that could result in serious harm
- Use errors documented: All use errors, close calls, and difficulties recorded

Pass/fail criteria:
Pre-defined acceptance criteria for critical tasks:
- Task success rates
- Allowable use error frequencies
- Time to complete tasks
- User satisfaction scores

Step 6 - Document usability engineering activities:

Usability Engineering File:
Comprehensive documentation required by IEC 62366, including:
- Use specification and user profiles
- User interface description and task analysis
- Hazard analysis related to use
- Formative evaluation plans, data, and results
- Summative evaluation protocol and report
- Risk management linkage and traceability
- Design changes based on usability findings

Regulatory submission requirements:
FDA and other authorities require submission of human factors validation reports demonstrating:
- Usability testing was conducted per IEC 62366 and FDA guidance
- Representative users successfully completed critical tasks
- Residual use-related risks are acceptable
- Instructions for use are adequate

Common use errors to prevent:

Selection errors:
- Choosing wrong drug, dose, or therapy setting
- Selecting incorrect patient or procedure
- Activating wrong mode or function

Sequence errors:
- Skipping critical setup steps
- Performing tasks out of order
- Incomplete procedures

Time errors:
- Delayed response to alarms
- Premature termination of therapy
- Incorrect timing of medication delivery

Magnitude errors:
- Entering incorrect dose or parameter values
- Misreading displayed values (decimal point errors)
- Over- or under-estimation of quantities

Cognitive errors:
- Misinterpreting device status or feedback
- Incorrect mental model of device operation
- Forgetting critical steps or information

Design principles for reducing use errors:

1. User-centered design:
Involve actual users throughout design process:
- Conduct user research and needs assessment
- Observe users in real-world environments
- Iterate designs based on user feedback
- Test with diverse user populations

2. Simplify and standardize:
- Minimize complexity and number of steps
- Use familiar conventions and standards
- Maintain consistency across device family
- Follow industry best practices (e.g., IEC 60601-1-6 for alarms)

3. Error prevention:
- Use constraints and forcing functions
- Provide clear affordances and feedback
- Design for error tolerance (reversible actions)
- Implement confirmations for critical actions

4. Clear communication:
- Use plain language in labels and instructions
- Employ universal symbols when possible
- Ensure adequate contrast and readability
- Provide multi-modal feedback (visual, auditory, tactile)

5. Account for use environment:
- Consider lighting, noise, space constraints
- Design for multitasking and interruptions
- Accommodate emergency use scenarios
- Plan for maintenance and cleaning requirements

Relationship to risk management:

Integrated approach:
Human factors and risk management (ISO 14971) must be tightly integrated:
- Use errors identified during task analysis feed into hazard identification
- Usability testing validates effectiveness of risk control measures
- Residual use-related risks evaluated for acceptability
- Post-market surveillance monitors real-world use errors

Risk control hierarchy:
Apply risk controls to mitigate use errors:
1. Inherent safety by design - Eliminate hazard through design (best option)
2. Protective measures in device - Add safeguards (alarms, interlocks, confirmations)
3. Information for safety - Warnings, training, instructions (least effective alone)

Post-market human factors:

Vigilance and surveillance:
Monitor post-market data for use error trends:
- Medical Device Reports (MDR) and complaints
- Field safety corrective actions (FSCA)
- User feedback and social media
- Competitive device issues

Continuous improvement:
Use post-market findings to:
- Update instructions for use
- Issue safety communications
- Modify device design in next generation
- Enhance training programs

Human factors for specific device types:

Home-use devices:
Consider lay user capabilities:
- Limited medical training
- Varied literacy and language skills
- Age-related physical/cognitive changes
- Self-care and unsupervised use

Combination products:
Address drug-device interface:
- Drug preparation and loading
- Dose selection and verification
- Compatibility and stability
- Administration technique

Software and digital health:
Unique challenges:
- Complex navigation and workflows
- Alert fatigue and alarm overload
- Cybersecurity and authentication
- Connectivity and data transfer

Implantable devices:
Programmer and patient interface:
- Parameter adjustment and programming
- Interrogation and data review
- Patient activators and controllers
- Emergency override functions

Emerging trends:

AI and machine learning devices:
New human factors considerations:
- Transparency and explainability of AI decisions
- User trust and over-reliance on automation
- Alert fatigue from false positives
- Interface for reviewing AI recommendations

Virtual and augmented reality:
Novel interaction paradigms:
- Spatial navigation and gesture controls
- Visual fatigue and motion sickness
- Situational awareness during use
- Training effectiveness

Human Factors Engineering is essential for ensuring medical devices are designed for real-world users in real-world conditions. By systematically applying HFE principles throughout device development, manufacturers can prevent use errors, enhance patient safety, and achieve regulatory approval across global markets.