Redefining "Normal Use" for Medical Devices

Here at UserWise, we rely heavily on IEC 62366:2007 and IEC 62366-1:2015 to ensure that our work, and our clients’ medical products, meet all the appropriate regulatory requirements. In particular, when we plan and analyze data from summative usability validation studies for medical devices, the concept of Normal Use is central to our discussions.

In the documents mentioned above, Normal Use is defined as the “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.”

In our view, the current definition of Normal Use does not adequately capture how real-life users interact with instructions for use (IFU) nor how an IFU should be presented to users in usability validation testing. Addressing these issues would result in more studies that better model how IFUs are referenced in the context of real-world situations.

Below, we address each of these issues in greater detail, and provide our own suggested definition of Normal Use.

Real-Life Interactions with the IFUs

The phrase “according to the instructions for use” in the definition above does not capture the way all users would “normally” use a product. Some users regularly do not consult the IFU of a new medical device. These users may use the device in the manner indicated by the IFU without actually reading it, and so phrasing this concept as “according to the instructions for use” is misleading. The definition suggests that it is not “normal” to skip reading the IFU.

Additionally, there are ways to correctly use a system that do not explicitly match what is presented in the IFU. For example, a user of a reconstitution device might spike the vials out of order compared to the instructions. This is foreseeable (i.e. “normal”) and has no impact on safety or effectiveness, and so should be considered Normal Use (and in this case, Correct Use).

Presenting the IFU in Summative Usability Validation Testing of Medical Devices

The phrase “according to the instructions for use” also does not map to state-of-the-art usability study methods for evaluating medical devices. The current definition of Normal Use implies that a user is responsible for referring to the IFU in order for their behavior to be considered “normal.” As mentioned above, users do not always read the IFU. Thus, the current state-of-the-art practice for usability validation testing is for study personnel to wait for users to consult the IFU on their own, rather than asking them to use the IFU outright.

UserWise has additionally observed that medical device manufacturers tend to put much effort into developing comprehensive training for device users, to account for those users who do not read the IFU. This demonstrates that manufacturers are not considering their IFUs as the only source for understanding how one should use a medical device.

Proposed New Definition of “Normal Use”

For these reasons, we propose to remove any mention of the IFU and rephrase the sentence to clarify what types of user actions are considered “normal.”

Normal Use should instead be defined as “the correct use and use with use errors or difficulties that occur during operation, including routine inspection and adjustments by any USER, and during stand-by actions.”

Next Steps

If you are looking for help in evaluating the usability of your medical device or medical product, UserWise stands ready to help. Our competent team of consultants has years of experience providing expert Human Factors reviews of medical devices and products, as well as risk management consulting specifically tailored to FDA and international regulations. Contact us today to learn more about how we can assist in getting your medical product to market.

1. IEC 62366:2007 “Application of usability engineering to medical devices.”
2. IEC 62366-1:2015 “Part 1: Application of usability engineering to medical devices.”

︎ Ali Decker | July 29, 2019

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