Usability Engineering of Non-Active Medical Devices in Light of the MDR

Abstract

Usability engineering is one of the key elements of the medical device design process, the aim of which is to reduce the risk of use errors resulting from the interaction between the user and the device. Although this issue is most often associated with active medical devices and software, the requirements arising from Regulation (EU) 2017/745 (MDR) also apply to non-active devices. In the practice of conformity assessment, it is precisely with regard to this group of devices that an incomplete understanding of the role of the usability engineering process and its connection with risk management is often observed. The aim of this article is to present a practical interpretation of the MDR requirements and to indicate the elements of documentation that make it possible to demonstrate compliance with the requirements concerning safety of use.

Introduction

The conformity assessment process for medical devices in accordance with Regulation (EU) 2017/745 of the European Parliament and of the Council (MDR) requires manufacturers to demonstrate that the design of the device ensures an appropriate level of safety and performance throughout its entire intended lifecycle. In practice, this means the need to document not only the safety of materials, technical parameters or clinical properties, but also the manner in which the user will use the device.

One of the areas that still raises numerous questions during the assessment of technical documentation is usability engineering (Usability Engineering) with regard to non-active devices. Many manufacturers assume that the requirements of standard EN 62366-1 primarily concern active medical devices equipped with a control panel, display or software. However, safety of use is a requirement that applies to all medical devices, regardless of their class, design or power source.

This does not mean, however, that the manufacturer of a simple single-use device should carry out the usability engineering process to the same extent as the manufacturer of a surgical robot or an infusion pump. Both the MDR and harmonised standards are based on the principle of proportionality and a risk-based approach. What is crucial is demonstrating that the manufacturer has analysed the manner of use of the device, identified possible user errors and implemented appropriate solutions to minimise risk.

The aim of this article is to present a practical approach to preparing usability engineering documentation for non-active devices in accordance with the requirements of the MDR and standard EN 62366-1. It will also discuss the most commonly encountered difficulties and the elements of documentation to which particular attention is paid during conformity assessment.

Regulatory Basis

MDR requirements concerning safety of use

Regulation (EU) 2017/745 does not impose on manufacturers the obligation to apply a specific standard concerning usability. It does, however, impose an obligation to demonstrate that the device has been designed in a manner ensuring the safety of the user during its intended use. In practice, this means the need to meet the relevant General Safety and Performance Requirements (GSPR) set out in Annex I to the MDR.

Already the first requirements of Annex I indicate that devices should achieve their intended performance while limiting risk to an acceptable level, taking into account the current state of the art. The risk associated with the use of the device is an integral part of this assessment and cannot be considered separately from the design process.

Requirements of particular significance for the usability engineering process concern:

● eliminating or reducing risk through safe design of the device;

● taking into account ergonomics as well as the technical knowledge, experience and working environment of the user;

● reducing the risk arising from foreseeable user errors;

● ensuring appropriate information and instructions enabling the safe use of the device.

It is worth noting that the MDR does not use the term “active device” in relation to the above requirements. This means that the manufacturer of every medical device should analyse the usability of the device, even if the scope of such analysis will be considerably smaller than in the case of more complex devices.

EN 62366-1 as a tool for demonstrating compliance

In practice, manufacturers often ask the question: Is the application of standard EN 62366-1:2015+A1:2020 Medical devices — Application of usability engineering to medical devices mandatory?

The answer is: no. As with other harmonised standards, a manufacturer may apply an alternative solution, provided that it is able to demonstrate fulfilment of the relevant MDR requirements. In practice, however, EN 62366-1 constitutes a recognised method of systematic design taking into account safety of use, and is therefore the most commonly chosen approach.

The standard describes the process of identifying hazards arising from the use of the device, the analysis of possible user errors, and the assessment of the effectiveness of the risk-reducing measures applied. This does not mean that extensive studies involving users must be carried out for every device. The scope of activities should be adapted to the level of risk, the complexity of the device and the characteristics of its users. What is essential is an appropriate justification of the approach adopted and demonstrating that design decisions were made consciously and on the basis of risk analysis.

Usability engineering and risk management — two separate processes or one system?

One of the most frequently observed problems during the assessment of technical documentation is treating the usability engineering process as independent of risk management. In practice, this leads to the creation of two separate sets of documents that describe the same issues but are not linked to one another. However, the requirements of EN ISO 14971 and EN 62366-1 complement one another.

The risk management process answers the question: What hazards may occur and what will their consequences be?

The usability engineering process, on the other hand, answers the question: In what way can the user bring about the occurrence of these hazards, and how can this be prevented through the design of the device?

For example, risk analysis may indicate the possibility of using an incorrect size of surgical instrument. The usability engineering process, on the other hand, makes it possible to determine why the user might make such an error and what solutions — for example, colour coding, clearer labelling or a change in packaging design — will reduce the likelihood of its occurrence.

This approach makes it possible not only to meet the MDR requirements, but above all to demonstrate that safety of use was taken into account already at the device design stage, and not only when developing the instructions for use.

Why Does Usability Also Concern Non-Active Devices?

The purpose of the usability engineering process is not to assess the degree of complexity of the device, but to analyse the interaction between the user and the device. Every medical device — regardless of whether it is active or non-active — is used by a human being. It is precisely the manner of use that may constitute a source of hazards affecting the safety of the patient or user. The basis here is the appropriate design of the user interface, which comprises all the means by which the user and the medical device interact, including the physical aspects of the device as well as visual, audible and tactile displays, and is not limited to the software interface. Examples of a user interface include all kinds of displays, control panels, audible and visual signals, but also — of particular importance for non-active devices — the labelling of the device (the label) and the instructions for use.

The MDR requires that the medium, format, content, legibility and placement of the label and instructions for use be adapted to the particular devices, their intended purpose, and the technical knowledge, experience, education or training of the intended user. In particular, the instructions for use should be drawn up in such a way that they can be easily understood by the intended user and — where appropriate — should also include drawings and diagrams.

An example of a non-active medical device may be a simple surgical instrument. Although its construction does not include any electronic components, incorrect size marking, the possibility of reverse assembly of parts, a non-ergonomic handle, or difficulty in distinguishing the working position may lead to use errors. In certain circumstances, such errors may result in a prolonged procedure, tissue damage or the need to apply additional medical procedures.

A similar situation applies in the case of catheters, infusion sets, tubing or implants equipped with application tools. The risk does not always result from the construction of the device itself — it is often a consequence of the manner in which it is prepared, assembled or used.

The most commonly encountered hazards associated with the use of non-active devices include:

● the use of an incorrect size of device/equipment,

● use inconsistent with the intended purpose,

● misinterpretation of labelling,

● an incorrect sequence of actions,

● improper preparation of the device for use,

● omission of information concerning limitations of use.

In each of these cases, the source of risk is not a material or construction defect, but the manner in which the user interacts with the device.

For this reason, the usability engineering process should be viewed as an element of designing a safe device, and not as a requirement reserved for a specific group of products.

How to Prepare Usability Engineering Documentation for a Non-Active Device?

The usability engineering process should be proportionate to the risk and, at the same time, sufficiently documented to demonstrate how design decisions were made. This is not about preparing extensive documentation, but about presenting a logical process showing that the manufacturer consciously analysed the interaction between the user and the device.

Regardless of the type of device, the documentation should make it possible to answer the following questions:

● Who will be the user of the device?

● Under what conditions will it be used?

● What activities will the user perform?

● What errors may be made?

● Can these errors lead to a hazard?

● How has the manufacturer reduced the possibility of their occurrence?

● How has the effectiveness of the solutions applied been confirmed?

Stages of the Usability Engineering Process

Step 1: Developing the specification of use.

The usability engineering process should begin with determining who will use the device and under what conditions this will take place.

Although this information is usually also found in the design documentation and the instructions for use, it is worth gathering it in one place as a starting point for further analysis.

The description should include, among others:

● medical indications (e.g. conditions or diseases to be imaged, monitored, treated, diagnosed),

● indication of the patient population (e.g. age, weight, sex, health condition)

● indication of the body part or type of organ with which the device comes into contact

● indication of the user profile (e.g. physician, nurse, layperson, service personnel)

● indication of the intended environment of use (e.g. home, operating theatre, doctor's office)

● indication of the principles of operation of the device and limitations of use.

In practice, very general formulations are often encountered, such as: “User: medical personnel.”

Such a description usually does not provide sufficient information.

It will be much more useful to indicate that the device is intended for orthopaedic surgeons performing surgical procedures, scrub nurses preparing the surgical set, and personnel responsible for washing and sterilising the instruments. Each of these groups performs different activities and may make different errors.

The environment of use should be described in a similar manner.

For example, an operating theatre is characterised by limited working space, the need to maintain sterility, intense lighting and time pressure. All of these elements may influence the manner in which the device is used.

Step 2. Identification of user interface characteristics related to safety and indication of potential use errors.

The next stage involves determining the characteristics of the device that may affect safety of use.

Characteristics affecting safety may include, among others:

● the shape of the handle,

● the manner of locking the mechanism,

● size marking,

● legibility of the scale,

● the colouring of components,

● the manner of opening the packaging,

● the arrangement of information on the label,

● the font size of the instructions for use.

In order to identify interface characteristics that may contribute to the occurrence of use errors, various techniques can be applied, the most common of which is the method indicated by standard EN ISO 14971. The Technical Report to the standard, ISO/TR 24971, contains in Annex A a list of questions supporting the identification of interface characteristics affecting safety and supporting the identification of use errors.

Risk is not yet assessed at this stage.

Based on the identified user interface characteristics and the specification of use, potential use errors should be indicated (e.g. the user's selection of inappropriate equipment when using the device, performing an incorrect action, or incorrectly omitting an action).

Factors leading to a use error should be considered (e.g. insufficient experience with the device, insufficient training, impairments of users).

In practice, user errors do not mean only failure to follow instructions.

Standard EN 62366-1 focuses on foreseeable errors that may occur even among appropriately trained users.

Examples may include:

● the use of an incorrect size of device,

● reverse assembly of a component,

● omission of the locking step,

● improper preparation of the device before use,

● the use of an inappropriate accessory.

It should be noted that the analysis should not be limited to answering the question of whether the user may make an error, but also why they may make it.

The cause may include, among others:

● similar appearance of components,

● illegible labelling,

● insufficient colour contrast,

● working while wearing gloves,

● the need to perform multiple activities simultaneously.

It is precisely the identification of causes that makes it possible to design effective risk-reducing measures.

Step 3. Identification of known and foreseeable hazards and hazardous situations.

At this stage, the usability assessment process is closely linked to risk analysis. For all identified use errors, the manufacturer analyses what hazards they entail.

This is one of the areas that most often raises doubts during the assessment of technical documentation.

Situations are encountered in which the usability analysis indicates the possibility of, for example, incorrect assembly of a component, while this hazard has not been included in the risk analysis. Such discrepancies make it difficult to demonstrate the consistency of the documentation.

It is good practice to establish a link between:

● the usage scenario,

● the foreseeable user error,

● the hazard,

● the hazardous situation,

● the possible harm,

● the risk control measure,

● the method of verifying effectiveness.

Such a compilation makes it possible to trace the entire process of making design decisions.

Step 4. Identification and description of hazard scenarios, and selection of hazard scenarios for summative evaluation.

The purpose of this step is to indicate the possible usage scenarios that may lead to a hazardous situation. For this purpose, for each identified hazard, the sequence of events that may lead to the occurrence of the hazard should be determined, taking into account the user's interaction with the interface, in order to identify possible use errors.

A usage scenario is a specifically described situation containing the context of use, interaction with the interface, a potential use error, and a possible hazardous situation.

Example:

Medical device: Hospital bed.

Use error: incorrect locking of the hospital bed rail

Hazard: Patient falling to the floor

Usage scenario related to the hazard: The mechanism locking the hospital bed rail is difficult to lock. The nurse does not notice that the rail is not completely locked. The rail is not properly engaged. The patient rolls onto their side, pressing against the rail. The rail lowers and the patient falls to the floor.

Harm: hip fracture

User interface risk control measure: An easy-to-use protective rail mechanism. A clear indication of the absence of locking.

Step 5. Development of the user interface specification.

At this stage, the requirements for the user interface should be specified, and its characteristics that will help avoid use errors should be determined. For this purpose, the specification of use, the identified use errors and the described hazard scenarios should be taken into account.

The user interface specification should define the following interface characteristics necessary to reduce the risk of use errors:

● Visual and physical requirements for the interface (e.g. colour, display, font size, arrangement of control elements)

● Information on whether the use of alarms/warning messages is necessary,

● Determination of whether accompanying documentation (IFU) for the device is required

● Indication of whether training of users in the operation of the device is required

Step 6. Development of the User Interface Evaluation Plan.

The user interface evaluation plan should specify the manner of formative evaluation of the user interface at the design stage, as well as the methods for carrying out validation of the usability engineering process, i.e. the summative evaluation.

Formative evaluation is carried out at the design stage in order to:

● Identify problems at the interface design stage,

● Optimise the interface

● Increase the likelihood that the final summative evaluation — usability validation — will be successfully carried out

The purpose of summative evaluation is to simulate actual use by the intended users.

Step 7. Preparation of the user interface design, implementation, and conducting the formative evaluation.

The manufacturer designs and implements the user interface, including the accompanying documentation and, where required, user training, in accordance with the user interface specification and the risk analysis of potential use errors carried out.

During the design of individual user interface elements, appropriate formative evaluation methods, as defined in the Plan, are applied to evaluate the interfaces at particular design stages, in order to:

● Identify usability problems at the design stage

● Identify new potential use errors

● Introduce any necessary corrections before usability validation.

Step 8. Conducting the summative evaluation of user interface usability — validation of the usability engineering process.

The final stage of the process is confirming that the measures applied actually reduce the risk. For this purpose, after completing the design and implementation of the user interface, the manufacturer carries out an evaluation for each identified hazard scenario, applying an appropriate method.

The justification for the choice of an appropriate method is of key importance.

If the manufacturer considers that full usability validation is not necessary, it should demonstrate why the measures adopted are sufficient in relation to the level of risk and the characteristics of the device.

Questions Worth Asking Before Submitting the Documentation for Assessment

Before beginning the conformity assessment process, it is worth verifying whether the documentation makes it possible to answer the following questions:

● Have the intended users been clearly defined?

● Have all relevant usage scenarios been identified?

● Have possible user errors been analysed?

● Has this analysis been taken into account in the risk management process?

● Do the risk-reducing measures applied correspond to the hierarchy set out in the MDR and ISO 14971?

● Do the instructions for use support the safe use of the device?

● Does the documentation contain a justification for the scope of the usability engineering process?

● Do the PMS data confirm the design assumptions adopted?

Summary

With regard to non-active medical devices, usability engineering is sometimes perceived as an issue of limited regulatory significance. However, the practice of assessing technical documentation shows that safety of use remains an integral element of the requirements set out in the MDR, regardless of the degree of complexity of the device.

For demonstrating compliance, the consistency of the documents prepared is of key importance. The manufacturer should demonstrate that the intended manner of use has been analysed, that potential user errors have been taken into account in the risk management process, and that the design solutions applied, together with the information supplied with the device, effectively reduce risk to an acceptable level.

A properly documented usability engineering process is not merely an element of fulfilling regulatory requirements. It is, above all, evidence that user safety was taken into account as an integral part of the design process, in accordance with the current state of the art and the principles set out in Regulation (EU) 2017/745.

Bibliography:

1. Regulation (EU) 2017/745 of the European Parliament and of the Council of 5 April 2017 on medical devices.

2. EN 62366-1:2015+A1:2020 Medical devices — Part 1: Application of usability engineering to medical devices.

3. EN ISO 14971:2019+A11:2021 Medical devices — Application of risk management to medical devices.

4. EN ISO 20417:2021 Medical devices — Information to be supplied by the manufacturer.

5. EN ISO 15223-1:2021 Medical devices — Symbols to be used with information to be supplied by the manufacturer.