Medical device testing

Common questions

Being an engineer in the medical device profession for the past 15 years has been quite an education.  Working with a team of talented engineers has been fun and together we’ve been able to learn from each other and solve almost any problem from an engineering perspective.  Our team has worked on several first to market Class II and Class III medical devices from the ground up, these experiences have been very helpful for us in transitioning from a large medical device company to a consulting firm.  As anyone who has worked in this field knows, sometimes you learn the most when your device fails, but it is what you do after your device fails that defines your career.  To sum up in a few words, what we’re really trying to do as medical device engineers is  find balance between risk and benefit.  Engineers write standards, guidance documents, papers and books to communicate how to find the right risk balance. Even with appropriate references in place, we have several questions that come up during most device development lifecycles.

1. When do you justify and when do you test?

You can have the perfect scientific justification to not test a device, yet the 1000 words that it will take to justify often become more expensive than a simple test. Tests have their own associated risks and costs.  How do you find the balance?

2. How do you choose the right confidence and coverage for a potential failure mode?

Often times test plans are developed with 90% confidence that 90% of the population will not encounter a failure mode. How does one know that this confidence interval is good enough for patient safety? This is a tough question that when put into a FMEA procedure can become systematic.  I’m not sure this should be a systematic question when a potential failure mode is death. How do you find the balance?

3. When is the worst case model a bad enough case?

The terms worst case conditions or worst case model often come up during device development.  What is the worst case scenario and will my device survive when this scenario happens?  And if you design your device for the worst case, what happens to the rest of the population?  Questions like this are hard to answer and can slow product development to a halt. How do you find the balance?

4. How close to the acceptance criteria are too close?

What if your safety factor is right on top of the acceptance criteria?  How does one justify questions like this?  Is there uncertainty analysis incorporated and what was that acceptance criteria based upon anyway?  When pushing the limits of device design to treat a new disease, questions like this arise. How do you find the balance?

Moving a medical device from concept to clinical use is a rewarding accomplishment.  There is quite a grind along the way and many tough questions to answer.  Finding your way through these questions is difficult, but when you get it right, patients benefit.  When you do find the right balance, everyone wins!