There are three types of errors related to human interface with the medical device:

Use Error (or User Error)

Use error is an action (or lack of action) that was different from that expected by the manufacturer and caused a result that was different from the result expected by the user.  Use error is not caused solely by device failure and may result in harm.  These errors are not intentional.  These are the most common types of user-related medical device errors and often can be prevented through the application of human factors engineering or usability engineering during design.   

An example of user error would be dialing in the wrong medication dose on a dose-adjustable auto-injector due to the inability to easily read the dose indicator or failure to allow an injection pen to deliver the full dose by prematurely removing the injection pen from the injection site. 

“Reasonably” Foreseeable Misuse

Reasonably foreseeable misuse of the device is when the device is used or applied in a manner not intended by the manufacturer, but which can be readily predictable human behavior. It may be intentional (such as off label-use) or unintentional.

Abnormal Use

Abnormal use is the intentional act or intentional omission of an act that reflects violative or reckless use or sabotage beyond reasonable means of risk mitigation or control through the design of the user interface.

Both use errors and reasonably foreseeable misuse need to be considered when performing risk analysis.   A systemic process should be applied to the identification of potential user errors and the application of risk controls to eliminate these or reduce their probability.  

Key elements of useability engineering that support the management of medical device risk due to user error include the following:

1. Understand and document User population and characteristics of population, User environment, and points of User interface.

Consider the ages of the intended users and their literacy level. It is important to consider how a lay user (non-clinical user in a home environment) differs from a clinical user (health care practitioner in a clinical environment). Determine if the user is likely to have concomitant disease states or health conditions or physical conditions that may impact their ability to use the device. Understand potential challenges that may result from the environment (e.g., poor lighting). Determine if the user is likely to have used similar devices before.

2. Conduct a Task Analysis

This is a documented and detailed list of each chronological step a user is required to follow to use the device.  Tasks analysis establishes discrete tasks required of the user from the point that the device is received, stored, removed from packaging, prepared for use, used, and disposed of.

3. Perform formative study with prototypes during design verification.

At the point the initial design prototypes are available, a formative study of the user and device interface can help identify potential points where user errors may occur or abnormal use may occur.  These can then be mitigated by further design improvement.   During a formative study, example persons representative of the use population would be given some instruction and then observed as they go through the tasks necessary to use the device.   Difficulties or errors are noted and typically feedback is provided by the user via some type of survey or questionnaire.   Note that both the formative and summative studies (described below) should be conducted in accordance with a pre-approved protocol that establishes methodology, statistical sample size, data analysis methods, and acceptance criteria.

4. Identify user error based on formative study and review of clinical data, adverse event databases, etc.

Collate a complete list of historically documented user errors and reasonably foreseeable errors.  This will be the basis for documenting a Usability Failure Modes Effects Analysis (uFMEA.)  Search public adverse event databases such as MAUDE for events involving similar product codes.  Also, perform literature searches of published articles and studies involving similar product types.

5. Based on defined tasks and subtasks, execute a uFMEA.

Organize the user errors within the FMEA template based on the order in which tasks occur.  It may be helpful to break down the FMEA by type of task:  Storage, Unpackaging, Preparation, etc.  For each error specify the hazardous condition and associated hazard.

6. Map User Failure Modes to the Hazard Analysis (ref. Haz ID#).

Once the hazard is identified it can be linked to or mapped to the hazard in the hazard analysis documentation.  This provides linkage to the severity assigned in the original Master Harms list or Harms/Hazards documentation that should be established within the Risk Management File.  Estimate probability based on historical data with similar devices or experience gained during the formative study of device use.

7. Based on the severity assigned – classify “critical tasks”

It is helpful to understand which risks are considered critical as priority can be placed on considering ways to mitigate the risk posed by critical tasks.

8. Implement risk control measures, translate risk control measures into design requirements, and provide traceability between risk control and the design requirements.

Risk control measures must be considered in a specific order or priority and preference.

• First – Design/redesign so that the design is inherently safe.
• Second – Add protective measures in the device or production process.
• Third – Information to users such as warnings in labeling.

All risk control measures should be translated into design requirements.  Typically design requirements are assigned a unique number to facilitate the ability to reference them.  The uFMEA should provide the Design Requirement ID number following the description of the risk control measure. This helps ensure that the risk control measure identified is actually implemented and traceable to design requirements, which should, in turn, be traceable to design verification/design validation that demonstrate the control has been effectively implemented.

9. Perform a summative study with final design and labeling to validate the efficacy of user-related risk controls.

The summative study (or usability validation study) tests the ability of the user population to use the device correctly and safely as it was intended to be used.   This is very similar to the formative study but is typically done with a larger population sample and is done with the final device design and the final labeling and device packaging.   Users are observed and all difficulties or errors in use are documented.  The users often take a survey to provide feedback on usability.   Analysis of this data will determine if risk controls are effective and acceptance criteria are met.

The amount of effort put toward usability risk analysis and risk control should be commensurate with the risk associated with the medical device itself.  Devices that have technology or an intended use that makes them high risk (such as radiation emitting devices) warrant substantial effort in applying human factors in design.

FDA provides detailed information on their expectations for applying human factors in design to minimize user-related medical device risk.  Refer to “Applying Human Factors and Usability Engineering to Medical Devices Guidance for Industry and Food and Drug Administration Staff,” February 3, 2016.  

Additionally, IEC 62366-1:2015, “Medical devices — Part 1: Application of usability engineering to medical devices,” should be applied in device design.  This standard has two parts, the second being additional guidance to implementing the first part.

QualityHub provides professional Quality Engineering resources that can help establish and document risk analysis, including usability risk analysis.  Our resources have 10-20 years of experience in medical device development and usability engineering.   Contact QualityHub at  407-896-3386 or drop us an email at info@qualityhub.com.