The Importance of Use Environment and User Characteristics in Medical Device Usability Engineering

Introduction

In medical device development, usability engineering has become an essential component of ensuring device safety and effectiveness. The International Electrotechnical Commission (IEC) standard IEC 62366-1:2015+A1:2020, titled “Medical devices — Part 1: Application of usability engineering to medical devices,” along with the U.S. Food and Drug Administration (FDA) guidance “Applying Human Factors and Usability Engineering to Medical Devices” (February 2016), provide comprehensive frameworks for implementing usability engineering processes. These standards and guidelines emphasize that understanding the use environment and user characteristics is fundamental to developing safe and effective medical devices.

The field of usability engineering, also referred to as human factors engineering (particularly in the United States), focuses on analyzing, specifying, developing, and evaluating the usability of medical devices as it relates to safety. This systematic approach enables manufacturers to assess and mitigate risks associated with correct use and use errors during normal use conditions. While usability engineering can identify potential issues related to abnormal use, it is primarily designed to address use-related risks that arise during normal operating conditions.

The Critical Role of Use Environment Analysis

The use environment—the physical, social, and organizational context in which a medical device will be operated—plays a pivotal role in determining device usability and safety. IEC 62366-1:2015+A1:2020 requires manufacturers to develop a comprehensive “use specification” that includes detailed descriptions of the use environment. This specification forms the foundation for all subsequent usability engineering activities.

Physical Environment Considerations

The physical environment encompasses a wide range of factors that can significantly impact device operation and user performance. In hospital settings, for example, lighting conditions can vary dramatically from brightly lit operating rooms to dimly lit patient rooms during night shifts. Ambient noise levels in intensive care units or emergency departments can reach levels that impair auditory alarms or verbal communication between healthcare providers. Temperature and humidity variations can affect both device performance and user comfort, particularly in regions with extreme climates or in facilities with inconsistent environmental controls.

Space constraints represent another critical environmental factor. In crowded emergency departments or ambulances, medical devices must be operable in confined spaces where users may have limited freedom of movement. The device’s physical footprint, cable management requirements, and the need for clear visual access to displays all become paramount considerations in such environments. Furthermore, the presence of other equipment in close proximity can create electromagnetic interference issues or simply make it physically difficult for users to access controls or view displays clearly.

Social and Organizational Context

Beyond the physical environment, the social and organizational context profoundly influences how medical devices are actually used in practice. In many healthcare settings, devices are operated by multiple users across different shifts, with varying levels of training and experience. Communication patterns among healthcare team members, hierarchical structures, and workflow pressures all affect how devices are integrated into clinical practice.

Time pressure represents a particularly significant factor in many medical environments. In emergency situations, users must be able to operate devices quickly and accurately under extreme stress. This necessitates interfaces that support rapid task completion without sacrificing safety. Similarly, devices used in routine clinical workflows must accommodate the realities of heavy patient loads and competing priorities for healthcare providers’ attention.

The organizational culture regarding error reporting and continuous improvement also affects device safety. In environments where use errors can be openly discussed and analyzed, manufacturers can gain valuable insights for device refinement. Conversely, in settings where error reporting is discouraged, potentially dangerous usability issues may go undetected until serious adverse events occur.

Understanding User Characteristics and Capabilities

IEC 62366-1:2015+A1:2020 and FDA guidance both emphasize the critical importance of developing comprehensive user profiles that accurately represent the intended user population. These profiles must address not only the obvious characteristics such as professional training and experience, but also the full spectrum of human capabilities and limitations that can affect device use.

Physical Capabilities and Limitations

Users’ physical characteristics can vary widely and must be carefully considered in device design. Visual acuity, for instance, naturally declines with age, and many healthcare providers in senior positions may have reduced near vision even with corrective lenses. This has direct implications for display design, font sizes, color coding schemes, and the use of icons versus text labels. Similarly, color vision deficiencies affect approximately 8% of males and must be accommodated through redundant coding systems that do not rely solely on color to convey critical information.

Manual dexterity and fine motor control represent another area of significant variation among users. Conditions such as arthritis, essential tremor, or simple fatigue can impair a user’s ability to manipulate small controls or perform precise movements. Device designers must consider the size and spacing of buttons, the force required to activate controls, and whether gloved operation is necessary. For devices used in surgical settings, the need to operate controls while wearing sterile gloves adds an additional layer of complexity.

Physical strength and stamina also vary considerably among users. Devices that require repeated physical effort, such as manual resuscitation equipment or devices that must be frequently moved between patients, need to be designed with consideration for users across a range of physical capabilities. This is particularly important given the increasing recognition of gender differences in physical capabilities and the need to ensure devices can be safely operated by all intended users.

Cognitive Capabilities and Information Processing

Perhaps even more critical than physical capabilities are the cognitive demands that devices place on users. Human cognitive capabilities—including attention, memory, decision-making, and information processing speed—are subject to both individual differences and situational factors such as stress, fatigue, and cognitive load from concurrent tasks.

Attention and working memory are particularly limited resources in clinical environments. Users are frequently interrupted, must divide their attention among multiple patients and tasks, and often operate devices while simultaneously processing complex clinical information. Device interfaces that require users to remember information across multiple screens, perform mental calculations, or maintain awareness of device state across long procedures place significant demands on these limited cognitive resources.

The concept of “recognition versus recall” is particularly relevant in medical device design. Users perform much better when they can recognize the correct option from a set of choices rather than having to recall information from memory. This principle supports the use of clear menu structures, consistent iconography, and contextually appropriate default values rather than requiring users to remember specific values or sequences.

Decision-making under uncertainty is another critical cognitive challenge. Medical devices often present users with complex information that must be interpreted and acted upon quickly. The way information is displayed—including the use of trend data, predictive indicators, and alarm management systems—can either support or hinder effective clinical decision-making.

Training, Experience, and Mental Models

Users come to medical devices with varying levels of formal training, clinical experience, and familiarity with similar devices. These factors profoundly influence how users interact with devices and what types of use errors are likely to occur. Experienced users may operate largely on “autopilot,” relying on well-established procedural knowledge and mental models. While this generally enables efficient performance, it can also lead to automation bias and make experienced users more susceptible to certain types of errors when device behavior deviates from their expectations.

Mental models—users’ internal representations of how devices work and what they can expect in response to their actions—are shaped by experience with similar devices and can be either beneficial or problematic. When a new device conforms to established conventions and behaves consistently with users’ mental models, learning is facilitated and use errors are reduced. However, when devices violate established conventions or behave in unexpected ways, even experienced users may make errors.

The phenomenon of “knowledge in the world versus knowledge in the head” is particularly relevant for occasional users or for devices used in emergency situations. Devices that rely heavily on users’ memory of specific procedures or settings are inherently more error-prone than devices that provide clear guidance and constraints at the point of use.

The Integration of Risk Management and Usability Engineering

A fundamental principle emphasized in both IEC 62366-1:2015+A1:2020 and ISO 14971:2019 (Medical devices — Application of risk management to medical devices) is that usability engineering must be tightly integrated with risk management processes. These standards work in concert to ensure that use-related hazards are systematically identified, evaluated, and controlled throughout the device lifecycle.

Use-Related Risk Analysis

The risk analysis process for medical devices must explicitly address use-related hazards—potential sources of harm that arise from the interaction between users and devices. IEC 62366-1:2015+A1:2020 introduces the concept of “use-related risk analysis” (URRA) as a specific application of risk management principles focused on the device user interface.

Use-related hazards can arise from multiple sources. Devices may require physical, perceptual, or cognitive abilities that exceed users’ capabilities in certain situations. Critical information may be obscured, difficult to perceive, or presented in ways that are prone to misinterpretation. Control actions may be ambiguous, require excessive precision, or lack adequate feedback to confirm correct execution. These and many other factors can create situations where use errors become not merely possible but highly probable.

The FDA’s guidance document emphasizes that use-related hazards exist on a continuum with device failure hazards. Some hazards are purely use-related (occurring only because of how users interact with the device), while others are purely device-related (occurring regardless of user action). However, a significant category of “overlap hazards” exists where both user actions and device characteristics contribute to risk. For example, an infusion pump might have a hardware defect that causes occasional flow rate errors, but the risk is significantly exacerbated if the user interface makes it difficult for clinicians to verify that the programmed rate matches the intended rate.

Critical Tasks and Use Scenarios

A cornerstone of the usability engineering process is the identification of critical tasks—user actions or sequences of actions where use errors could result in serious harm. Not all tasks that users perform with a device carry equal risk; some errors may result in minor inconveniences or temporary delays, while others could lead to serious injury or death.

The process of identifying critical tasks requires careful analysis of the device’s intended use in the context of its actual use environment. This analysis must consider not only the obvious high-risk tasks (such as programming a therapeutic dose) but also seemingly routine tasks that could have serious consequences under certain circumstances. For example, the task of cleaning and disinfecting a device might seem routine, but if incorrect cleaning procedures could damage critical components or leave harmful residues, this becomes a critical task requiring careful design consideration.

Use scenarios—detailed descriptions of how devices will be used in realistic clinical situations—provide essential context for understanding when and how critical tasks are performed. These scenarios must reflect the realities of clinical practice, including time pressures, concurrent tasks, and the full range of patient conditions and clinical situations in which the device will be employed.

Risk Control Measures and Their Verification

When use-related risks are identified, IEC 62366-1:2015+A1:2020 establishes a clear hierarchy for risk control. The first priority is always inherent safety by design—eliminating hazards entirely or reducing risk to acceptable levels through device design. This might involve using forcing functions that make certain error sequences physically impossible, providing clear differentiation between controls, or automating tasks that are prone to human error.

When risks cannot be adequately controlled through design alone, protective measures in the device itself or in the manufacturing process represent the next line of defense. These might include software interlocks that prevent dangerous programming errors, automatic verification systems, or built-in redundancy for critical functions.

Finally, when residual risks remain after implementing design and protective measures, information for safety—including warnings, cautions, and training—must be provided. However, the standards are clear that information for safety is the least effective form of risk control and should never be relied upon as the primary means of risk reduction for serious hazards.

The effectiveness of risk control measures must be verified through formative and summative usability evaluations. Formative evaluations, conducted throughout the design process, help identify usability problems early when they are easier and less expensive to address. Summative human factors validation testing, conducted with representative users performing critical tasks in realistic use scenarios, provides essential evidence that the device can be used safely and effectively by the intended user population.

Current Regulatory Landscape and Best Practices

International Standards and Regulatory Harmonization

The landscape of usability engineering for medical devices has evolved significantly in recent years, with increased regulatory harmonization around core principles while maintaining some regional variations in implementation details. IEC 62366-1:2015+A1:2020 has emerged as the globally recognized standard, with Amendment 1 published in July 2020 providing important clarifications and updates to the original 2015 version.

The FDA recognizes IEC 62366-1:2015+A1:2020 as a consensus standard, meaning that manufacturers can use a declaration of conformity to this standard as part of demonstrating compliance with regulatory requirements. However, the FDA’s guidance document provides additional detail and clarification on specific topics, particularly regarding validation testing methods, sample size determination, and documentation requirements.

In the European Union, IEC 62366-1:2015+A1:2020 serves as a harmonized standard under both the Medical Device Regulation (MDR 2017/745) and the In Vitro Diagnostic Medical Device Regulation (IVDR 2017/746). Compliance with this harmonized standard provides a presumption of conformity with relevant essential requirements of these regulations, though manufacturers must still demonstrate that they have appropriately applied the standard to their specific device.

FDA’s Risk-Based Approach to Human Factors Information

In December 2022, the FDA released a draft guidance titled “Content of Human Factors Information in Medical Device Marketing Submissions,” which represents a significant evolution in how the agency evaluates human factors data in premarket submissions. This guidance introduces a risk-based approach that categorizes submissions into three categories based on the modification of use-related hazards and the presence or modification of critical tasks.

Category 1, representing the lowest risk level, applies to devices where there are no modifications to use-related hazards and no new or modified critical tasks. For such devices, manufacturers need only provide a brief summary and explanation of why human factors validation testing is not necessary. This might apply, for example, to software updates that fix backend bugs without affecting the user interface, or to minor manufacturing changes that do not impact device operation.

Category 2 encompasses devices where modifications to the user interface, intended users, use environments, training, or labeling have occurred, but these modifications do not introduce new critical tasks or meaningfully impact existing critical tasks. For Category 2 submissions, manufacturers must provide more comprehensive documentation of their usability engineering process, though full validation testing may not be required in all cases.

Category 3, representing the highest risk level, applies to new devices or modified devices where new critical tasks have been introduced or existing critical tasks have been significantly impacted. These submissions require full human factors validation testing with comprehensive documentation according to the eight-section report structure outlined in the FDA’s guidance.

This risk-based approach allows manufacturers to focus their resources on the areas of highest risk while reducing unnecessary burden for lower-risk changes. However, it requires careful analysis and documentation of the rationale for category assignment, and manufacturers are encouraged to engage with the FDA through the pre-submission process when there is uncertainty about appropriate categorization.

Documentation and Traceability Requirements

Both IEC 62366-1:2015+A1:2020 and FDA guidance emphasize the critical importance of comprehensive documentation of usability engineering activities. This documentation serves multiple purposes: it provides evidence of regulatory compliance, supports internal quality management processes, and creates an institutional knowledge base that informs future development efforts.

The usability engineering file (UEF), required under IEC 62366-1:2015+A1:2020, must contain records of all usability engineering activities throughout the device lifecycle. This includes the use specification, user profiles, use environment descriptions, use-related risk analysis results, descriptions of the user interface and its development, results of formative and summative evaluations, and documentation of all design changes made in response to usability findings.

Traceability is a key principle that runs throughout these documentation requirements. Manufacturers must be able to trace from identified hazards and use scenarios through risk analysis, design decisions, risk control measures, and validation testing results. This traceability ensures that all use-related risks have been adequately addressed and that the effectiveness of risk control measures has been verified.

The FDA’s guidance document provides a detailed outline for human factors engineering reports to be included in premarket submissions. This eight-section structure has become the de facto standard for organizing human factors documentation, even for devices not subject to FDA jurisdiction. The sections cover: conclusion and high-level summary; description of intended users, uses, use environments, and training; description of the device user interface; summary of known use problems; analysis of hazard-related use scenarios; details of human factors validation testing; analysis and results of validation testing; and conclusions.

Practical Implementation Strategies

Early Integration in the Design Process

One of the most important insights from decades of experience with usability engineering in medical devices is that waiting until late in development to address usability issues is both expensive and ineffective. IEC 62366-1:2015+A1:2020 emphasizes that usability engineering must be integrated throughout the entire product development lifecycle, from initial concept development through post-market monitoring.

Early-stage usability activities focus on understanding users and their needs, defining use scenarios, and establishing usability objectives. This might involve ethnographic research to observe how similar devices are currently used, interviews with potential users to understand their needs and pain points, and competitive analysis to understand market expectations and identify opportunities for differentiation.

As design concepts emerge, formative evaluations provide iterative feedback that guides design refinement. These evaluations typically employ rapid, low-fidelity methods such as paper prototypes, cognitive walkthroughs, and small-sample usability tests. The goal is to identify and resolve major usability issues before significant resources are invested in detailed design and development.

Summative Human Factors Validation Testing

Human factors validation testing represents the culminating activity in the usability engineering process, providing definitive evidence that the device can be used safely and effectively by representative users. The FDA’s guidance and IEC 62366-1:2015+A1:2020 both provide detailed requirements for the conduct of validation testing.

Test participants must represent the actual intended user population in terms of relevant characteristics such as professional training, experience with similar devices, age, physical capabilities, and other factors identified in the user profiles. Sample size determination requires careful consideration of the critical tasks being evaluated, the consequences of use errors, and statistical considerations regarding the detection of problems. While the FDA does not specify minimum sample sizes, the guidance provides methodologies for justifying sample sizes based on risk and the probability of detecting problems if they exist.

Testing must be conducted under conditions that simulate actual use as closely as possible. This includes using realistic clinical scenarios, appropriate task materials (such as actual or simulated patient cases), and environmental conditions that reflect the intended use environment. Participants should perform tasks without inappropriate levels of assistance, though the test protocol must include mechanisms to ensure participant safety and provide necessary guidance when participants become stuck on tasks unrelated to the critical use errors being evaluated.

Perhaps most importantly, validation testing must focus on the objective completion of critical tasks rather than subjective measures of user satisfaction or preference. While subjective data can provide valuable insights, the core purpose of validation testing is to verify that users can safely and effectively perform critical tasks without unacceptable use errors.

Post-Market Monitoring and Continuous Improvement

The relationship between usability engineering and risk management extends beyond initial device approval into the post-market phase. ISO 14971:2019 requires manufacturers to establish processes for collecting and reviewing production and post-production information relevant to device safety. This explicitly includes information about use errors and use problems that emerge after devices are placed on the market.

Sources of post-market usability information include complaint reports, adverse event data from regulatory databases, user feedback, field safety corrective actions, and systematic post-market surveillance studies. This information must be systematically reviewed to identify trends, emerging issues, or new use-related hazards that were not anticipated during pre-market development.

When post-market information indicates that use-related risks are higher than anticipated or that new hazards have been identified, manufacturers must evaluate whether risk control measures remain adequate or whether changes to the device, labeling, or training are needed. This creates a continuous improvement cycle where real-world experience informs ongoing device refinement.

Conclusion

The principles and practices of usability engineering for medical devices, as embodied in IEC 62366-1:2015+A1:2020 and FDA guidance, represent a mature and sophisticated approach to ensuring that medical devices can be used safely and effectively by their intended users. At the heart of this approach lies the recognition that devices do not operate in isolation but within complex sociotechnical systems involving diverse users, varied environments, and demanding clinical workflows.

Understanding the use environment—in all its physical, social, and organizational complexity—is not merely a preliminary step in device development but an ongoing responsibility that continues throughout the entire device lifecycle. Similarly, recognizing and accommodating the full spectrum of user characteristics, capabilities, and limitations is essential for creating devices that support rather than hinder clinical performance.

The integration of usability engineering with risk management provides a systematic framework for identifying use-related hazards, implementing effective controls, and verifying through rigorous testing that devices can be used safely. The regulatory landscape continues to evolve toward more sophisticated, risk-based approaches that focus resources on areas of highest concern while reducing unnecessary burden.

For medical device manufacturers, the path forward requires not merely compliance with standards and regulations but a genuine commitment to user-centered design. This means involving users early and often in the development process, conducting rigorous and realistic usability evaluations, maintaining comprehensive documentation of all usability activities, and continuously learning from post-market experience. The devices that succeed in the market are increasingly those that not only meet regulatory requirements but genuinely support healthcare providers in delivering safe, effective patient care. In this sense, excellence in usability engineering is not just a regulatory obligation but a competitive advantage and, most importantly, a moral imperative in the service of patient safety.