AAMI News October 2019

What Does It Mean to Design for Failure?

Human factors in design
Human factors design should consider post-design failure.

A patient undergoes surgery to relieve leg pain. During the procedure, the 2-cm tip of a catheter is sheared off and lodges in an artery while being removed from the leg. A blood clot forms around the catheter tip and begins to restrict blood flow to the leg. This goes unnoticed until the patient complains of worsening pain during a surgical follow-up appointment. The patient now needs emergency surgery to remove the catheter tip and dissolve the clot and may have permanent weakness in that leg.

This unfavorable patient outcome would not have occurred if the clinician recognized the catheter tip was missing before the patient was removed from the operating room—that is, if the device was designed with failure in mind.

Medical devices are designed for when they perform as intended. They should have the same thoughtfulness in design for when they fail.

That’s the call-to-action from Rebekah Friedrich and Jason Custer, MD, of the University of Maryland Medical Center (UMMC), who expressed their desire for more effective human factors design in a recent AAMIBlog post. A sensible design-standardization approach by manufacturers—for example, making all catheter tips a visible green color—could help prevent these types of user interface failures, they wrote.

“In my experience speaking with clinicians, they are tip for integrity. But the design makes it difficult to do so quickly and reliably,” wrote Friedrich, senior performance innovation leader at UMMC.

Failing in a safe space

Paul Sherman became an engineer after a decade working as a technician in part because he was frustrated by the lack of medical device designs that accounted for failure.

“Engineers are not taught about device failures post design,” wrote Sherman, president of Sherman Engineering, LLC.

Like Sherman, Tim Reeves is a proponent of incorporating design failure into medical device development. As the founder of Human Factors MD, Reeves sets up medical simulations for clinicians to test medical device prototypes. In this safe environment, Reeves and his colleagues can see where and why user interface failures occur with the goal to either design out user interface failures or help users detect and respond to failures should they arise.

From these usability tests, human factors experts can capture information about psychological and situational factors behind user interface failure in order to “improve the design by optimizing the fit between the user and the device,” said Reeves, who is also a lead instructor for AAMI’s Human Factors for Medical Device Design course.

Usability studies conducted by Human Factors MD help manufacturers identify where user interface failures could arise so that manufacturers can design out failures. But eliminating failures is not always possible or feasible. So user interface designs that help clinicians and other users detect when a device has not performed as expected, such as Friedrich and Custer’s green catheter tip design, could prevent serious outcomes.

Reeves stressed the value of manufacturers adhering to design principles, like the ones provided in the standard ANSI/AAMI HE75, 2009(R)2018, Human Factors Engineering—Design of Medical Devices.

“If a manufacturer is following good design principles, they are making sure their medical device designs help users detect when failures arise,” Reeves said.

AAMI offers multiple resources on human factors for medical devices, including standards and courses. To learn more about human factors training courses at AAMI, visit www.aami.org/Training.


AAMI offers a book, Writing Human Factors Plans & Reports for Medical Technology Development by Michael Wickund et al., available for purchase at the AAMI Store.