Verification of Expected Service Life: Max # Reprocessing Cycles

[ga2qa23]

Hi All, I please had an interesting question about “Expected Service Life” (ESL) per the standard IEC 60601-1. There are several semi-related forum threads about this topic but none of them cover this particular question, so please don’t move/delete this thread. The regulations, guidances, and standards are super clear for devices that are provided sterile, but there’s nothing for reusable medical devices.

Per IEC 60601-1, you need to define an Expected Service Life (ESL). My own device, for example, is a Class 2 reusable device that is not provides sterile and must be reprocessed (cleaning & autoclave sterilization) for intended use in the sterile field of an operating room. The ESL is the starting point and can be a business decision (i.e. device ESL is 5 reprocessing cycles).

If you have a device with an ESL of 5 reprocessing cycles, then sure it would make sense to just pay a laboratory to clean & sterilize the device 5 times, and then do visual/functional testing on it to confirm it will works. But what do you do if your ESL is instead 50 reprocessing cycles (or an even higher number)? It can easily cost tens of thousands of dollars to pay a test lab to run 50 cycles on even 1 device, let alone multiple devices for a statistical sample size for testing.

In an IEC 60601-1 test lab, they only ask for the device to be cleaned & sterilized only 1 time, to do their testing.

But on the other hand, you need to address risks of “ESL” by implementing “risk controls”, which feed into your “Design Inputs”, and each Design Input thus requires a “Design Verification” (either an analysis review or a formal test with acceptance criteria). So now are you actually forced you to run the device for 50 reprocessing cycles?

Am I also forced to write a specific product requirement (“Design Input”) stating that my device must remain functional after 50 reprocessing cycles?

Is this all governed by industry best practices or is there an actual standard/regulation that helps? Do different rules apply if your reusable medical device has a lot of plastic components? (More effects from cleaning & autoclave sterilization).

 

[Peter Selvey]

This question is all about testing, whereas the answer lies entirely within the design.

In a good quality design, the testing is a formality, whether it is 1 time or 50 times.

IEC 60601-1 skips over this by only requiring tests on one sample. The hidden assumption behind a single sample test is that the design is sufficiently robust that a single sample test is representative. That's true for roughly 99.9% of design issues. Most engineers know that successful designs are the result of overengineering the crap out of it so there are no questions about whether 1, 50 or 1000 samples are needed.

Sometimes, not very often, there is no choice, and the design needs to walk a fine line. It could be cost; sometimes technology limits; more often it is two or three conflicting parameters, where trying to fix one means giving ground on the other: whack a mole design. And sometimes it is just lazy design.

In those marginal cases, we need to take care about whether a "test" is really representative, and if necessary, think carefully about the number of samples and tests that may be required to give confidence that requirements are met, not just for the samples tested, but for the objects that actually get used on real patients in real world clinical situations.

If it is "overkill", one-sample-is-enough kind of design, a good engineer should be able to point to the parameter(s) that make it a robust design.

If not, then yes, tests on many samples may be required.

 

[ga2qa23]

Thanks for your input, I really appreciate it. You're talking about number of tests, but I'm also asking about # of reprocessing cycles required for a test. If my ESL is 50 reprocessing cycles, and I don't already have the full data to back it up, then am I pretty much forced to subject at least 1 test device to 50 reprocessing cycles, then do functional testing on it?

 

[Peter Selvey]

Sorry for the late night rant!

Yes, a functional and safety test after 50 re-pro cycles is reasonable (not only clean and sterilise, but simulated use as well). If 50 is claimed, and there is any known weak point (as discussed in the rant), you also need enough samples to be statistically confident of the 50 claim, for example testing 10 samples to failure, and they all fail in the range of 80 - 100 cycles (a good margin) that's probably good enough to make a 50 claim. A test on a single sample for exactly 50 cycles would only be reasonable if design is so obviously OK that the test is a formality (as in the rant).

However, normally a test lab does not get involved in this kind of testing. In these situations the standard usually says "compliance is checked by inspection of the risk management file" or similar, which means the test lab only needs to check the manufacturer's documents. The risk management table should link to a report which can be your own internal report. The test lab as a minimum should verify there is a traceable link to the report, i.e. they should be able to see at least the report number, and the test lab may request a copy of that report, but not do the actual tests. A normal IEC 60601-1 would not have the competence for this kind of thing.

 

[planB]

For re-usable device, depending on its criticality, you might also want to have a look into ISO 17664-1:2021 or ISO 17664-2:2021.