Determining a device’s potential use errors, a mini-series. Part 4: Normal use versus abnormal use of your device

PUBLISHED 5th March 2018

Medical Device Usability has decided to post a mini-series in relation to understanding different areas of research that feed in to the ‘risk management file’ or the usability failure modes and effects analysis (uFMEA). In part 4 of this mini-series, we will discuss what is meant by ‘normal use’ and what is meant by ‘abnormal use’ and how they relate to determining use errors. In the previous installments, we discussed;

The intended user (Click here for Part 1)

The intended use environment (Click here for Part 2)

Investigating ‘known use problems’ (Click here for Part 3)

The terms ‘normal use’ and ‘abnormal use’ relate to the context of use of a medical device. Standard 62366-1:2015 outlines that the usability engineering process ‘permits the manufacturer to assess and mitigate risks associated with correct use and use errors, i.e., normal use.’ It then goes on to state that the process ‘can be used to identify but does not assess or mitigate risk associated with abnormal use.’ When determining an appropriate extent of depth of analysis of risk for the usability FMEA, the concept of ‘normal use’ and ‘abnormal use’ are core principles in determining the cut-off point.

Once initial analysis and research into the intended user, intended use environments and known use problems has been done, the manufacturer may start to put into context the use of the device. This may be in the form of a task analysis, or function analysis or designing use scenarios for the device. These documents outlining use of the device contribute to what could be described as the device’s ‘normal use’.

Normal use

Normal use is defined as;

“Operation, including routine inspection and adjustments by any user, and stand-by, according to the instructions for use or in accordance with generally accepted practice for those medical devices provided without instructions for use”

  • 62366-1:2015 Medical devices – Part 1: Application of usability engineering to medical devices

This can be considered anything that is intended as use by the manufacturer. Here I will use an aerosol inhaler as the example device; hypothetically speaking, the manufacturer intends the user reads the instructions, and then the task analysis may go something like this;

Shake inhaler
Remove cap
Inhale slowly and steadily
Press actuator
Continue with same inhalation technique
Hold breath
Exhale
Replace cap

The use errors should be associated with these tasks, and those use errors should come from ‘normal use’ – i.e. use intended by the manufacturer. An example of a use error within normal use would be;

“Users try to remove the cap as instructed (normal use), however the cap was too difficult to remove, therefore user fails to remove the cap, assume it does not come off and proceeds with the remaining tasks without removing the cap (use error).”

Abnormal use

Abnormal use is defined as (1);

“Conscious, intentional act or intentional omission of an act that is counter to or violates normal use and is also beyond any further reasonable means of user interface-related risk control by the manufacturer”

  • 62366-1:2015 Medical devices – Part 1: Application of usability engineering to medical devices

And also as the following (2);

“An 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 design of the user interface”

  • UCM259760: Applying Human Factors and Usability Engineering to Medical Devices

Abnormal use is generally outside of the scope of the usability engineering process, as actions considered abnormal use are largely outside the control of the manufacturer. FDA UCM259760 does not provide any more information on the context of abnormal use, however 62366 defines sub categories of what can be considered abnormal use in Annex A, ‘General guidance and rationale’ where it categorises abnormal use as the following;

  • Exceptional violation (e.g. using the medical device as a hammer)
  • Conscious disregard for the contraindications (disregarding information for safety)
  • Reckless use (i.e. unconcerned with danger such as users making their own risk benefit decision) and
  • Sabotage

Abnormal use can be observed in a study and then determined as such during a post-test interview. Abnormal use errors should not be included in the uFMEA. Following with the hypothetical aerosol inhaler, here is an example of an observed ‘abnormal use’ use error;

“During a study, a participant was observed to omit the step of holding their breath. When during the post-test interview the moderator asked the participant to discuss this, they stated that based on their experience they know that whether they hold their breath or not it makes no difference to how effective the medication is so they choose to omit the act.”

In this instance, the participant consciously omitted the task, and therefore acted abnormally. The use error was caused by a participant’s choice to ‘ignore the instruction to hold breath’, however as this is abnormal use, it would be outside the scope of the manufacturer’s responsibility. Including the potential use error ‘does not hold breath’ with the cause ‘chooses not to hold breath’  is the same as the manufacturer agreeing that they can mitigate it with the design of their device or accompanying labelling. An individual’s decision to skip a step is outside of the control of another person. Taking on this use error would potentially result in failure of critical tasks that on re-evaluation could be considered as abnormal use and should not have been included in the uFMEA to begin with (this is of course, under the assumption that the designed inhaler cannot somehow ensure users hold their breath after inhaling).

This example cause could be determined ‘abnormal use’, however the use error can be caused by other means. An example of where the use error falls within the manufacturer’s scope, would be if the post-test interview revealed that something to do with the design of the IFU meant the user did not notice the instruction, or did not understand that they were required to hold their breath. This use error would be caused by a miscommunication between the user interface (instructions) and the user.

If the user shows that they realised they were not doing what the manufacture is recommending, then your user interface has done its job – it has communicated intended use to the user.

In conclusion

‘Normal use’ use errors are used to populate a uFMEA, whilst ‘Abnormal use errors’ can be uncovered during studies, can be considered in the actions taken after a formative study but should not be used to populate a uFMEA in relation to validating a device. Understanding the difference between normal use and abnormal use is a core requirement in populating and amending a uFMEA during the usability engineering process of medical devices.

For more information, please don’t hesitate to contact us! The next instalment will be titled; ‘Designing the uFMEA and how to populate it, a brief introduction’.

References

2015. International Electrotechnical Commission 62366-1:2015, Medical devices – Part 1: Application of usability engineering to medical devices.

2016. Food and Drug Administration, Center for Devices and Radiological Health UCM259760, Applying Human Factors and Usability Engineering to Medical Devices.