Lifecycle / Expected Service Life of Steel Parts

[ga2qa23]

Greetings! this is a bit of a brain-teaser. I was looking for guidance on whether I need to actually assign an Expected Service Life (ESL) or Lifecycle for steel parts/assemblies of a medical device? I was hoping someone could please point me in the direction of a guidance / regulation / standard I could read through. I feel like this is a common problem and the answer would benefit anyone getting certification to IEC 60601-1.

Here is some background:

• I am getting a low-risk Class 2 medical device certified to the standard IEC 60601-1 for electrical safety. The device is a simple plastic shell with electronics/software inside.
• Now per IEC 60601-1, I am defining an ESL (Expected Service Life) for my electrical medical device as a certain number of uses (e.g. 200 uses). But it will not have a public “lifecycle”. The ESL is a number internal to my risk management file, whereas the public “lifecycle” number is optional and is more a matter of product warranty.
• The IFU that the customer reads will not mention any lifecycle and will just state to keep using the device until it breaks. The IFU will have some basic maintenance “checks” (visual/functional) that the customer must do periodically to make sure that the device is still functional. So as long as they do the maintenance “checks” every week, they can keep using the device, even after it passes its ESL (Expected Service Life) of 200 uses.
• But now my medical device will also connect with a steel piece as well. It can connect with a variety of steel pieces in different shapes/sizes. The steel piece isn't a sensor or anything, it's basically just a rod made of 316L stainless steel but it has a strictly-controlled orientation with the plastic shell.

So now the question arises: do you also need to also assign an internal ESL or a public “lifecycle” for the steel parts? The steel parts are now considered part of the “finished” medical device but will last much longer than the electrical medical device.

I am incredibly tempted to not even mention any ESL nor public “lifecycle” of the steel parts, but these steel parts have to maintain the correct orientation when connected, so I’m not even sure. I could possibly do a verification test where I connect a steel part 200 times to the electrical medical device (to match its own ESL) and confirm it still works. Then would I have to throw out the steel parts as well after 200 uses? Man, this is confusing!!

Or I instead do a verification test where I connect/disconnect a steel part 4000 times (something extreme) to prove that the steel parts last an extremely long time. I may need to use a lot of different electrical medical devices to connect it with, but it could be worth it. Then I never need to perform a maintenance “check” on the steel parts or throw them out ever. I just state the risk is incredibly low for a steel part to ever be used that much.

 

[yodon]

I don't think I've ever seen a breakdown of service life per component. The service life for the SYSTEM needs to be defined and, often, that's driven by some specific components.

Stating "use the device until it breaks" is a bit concerning. Is there no risk if it actually breaks?

It doesn't sound like the steel is your device(?) so the connector your device uses would be your focus. I don't think your assertion of the steel being part of the 'finished' device is accurate. 13485 recognizes that devices can be connected and so there are clauses in both verification and validation testing to demonstrate that your device works when so connected. I think you will want to demonstrate (maybe considering worst case / largest and/or smallest steel rods?) that you can connect 200 times (with a safety margin). Maybe you run those tests until your plastic breaks to establish a safety margin?

 

[ga2qa23]

That's the tricky part. Both the steel part and my electrical part (plastic shell) must be combined to form the medical device for use on patients. The two parts cannot be used independently for treatment. So I suppose the ESL will be driven by the shorter-living part (the electrical part).

If it breaks, then it won't result in injury to the patient. It's a therapeutic medical device but it's not treating an urgent patient condition/illness.

I get what you're saying, thank you. The steel part must maintain a specific shape and tight fit (no play) with the electrical part. Sure, I can do repeated testing for how the steel part connects with the electrical part. However, even if I validate a certain number of connections, won't I need to have some kind of verification check between uses in the field, to make sure that the device hasn't deformed under misuse or something?

Also I'm pretty sure that it's common practice in industry for a medical device to not a defined lifecycle for the customer, but still has an internal ESL for the manufacturer. So we'd need to implement some kind of verification check between uses for the customer regardless. And if the customer uses the device past its ESL, then that's OK and the customer would just keep using the device until it does break.

At least, these are my understandings after discussing briefly with a certification laboratory to IEC 60601-1. I'd be happy to read/purchase a guidance/webinar that states otherwise. Thank you!

 

[yodon]

won't I need to have some kind of verification check between uses in the field, to make sure that the device hasn't deformed under misuse or something?

You should absolutely consider misuse cases but I wouldn't necessarily count those towards your service life.

after discussing briefly with a certification laboratory to IEC 60601-1

My philosophy is just do whatever it takes to get through 60601-1 testing.

 

[ga2qa23]

Haha I agree! Have you encountered a similar situation before? (no public lifecycle but the customer has to perform periodic verification checks)?

I understand that orthopedic companies that manufacture sets of reusable surgical instruments will ask the distributor to complete an inspection checklist between surgeries, to make sure the instruments still work properly. But that's not really relevant here.

 

[yodon]

No, in everything I've worked on, there's always been a (I guess what you would call public) defined service life.