Hazard Probability of Occurrence Definition

Nash27

Involved In Discussions
#1
Dear All,

We have used attached template (below the forum question) for our Class IIb medical device that was approved by the regulators 5 years ago. For new medical device, which is, class IIa medical device we used same matrix however regulator made following comments for the definition stating it is unacceptable.

?In the hazard-probability table , the ?probability range? and ?definition? columns are inconsistent (e.g. P1 improbable is stated as <10-6 in the probability range column but only < 1 in 10000 in the definition column)

According to the hazard acceptability matrix , an A5 (catastrophic) event which results in patient death is considered by the manufacturer to be ?acceptable? provided it is improbable (up to 1 in 10000 chance). For manufacturers device, it is not clear how a 1 in 10000 chance of killing a patient can be justified as acceptable.?


Before submitting the application we have evaluated that the matrix and ensured definitions are correct.

The matrix is in reference to the ISO 14971: 2007 Appendix D example figure D5

We have evaluated hazard severity and highest hazard severity is A4, which is critical. Based on risk evaluation none of the risk severity was adjudged as A5

Can someone explain whether;

1. The definitions we put are correct or incorrect,
2. We should not use hazard acceptability as acceptable for catastrophic event


Your comments will help me a lot
 

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sagai

Quite Involved in Discussions
#3
So, coming back to your question let me have one ...

How do you justify the quantitative probabilities?
With other words, based on what calculation have you come into a conclusion that for example P5 for your particular device is >=10-3?

My side-note is that we actually do not use at all acceptability threshold and I am more or less certain that for EU legislation it is recently also advocated with one of the mentioned deviation among the sevenish for ISO14971.

Cheers!
 

yodon

Staff member
Super Moderator
#4
I've never been a big fan of trying to assign numbers to probability but it would certainly need to be consistent. The manufacturer is responsible for the definitions so as long as your math is correct, the definitions are fine.

I wouldn't want to try to defend a catastrophic (leading to death) failure as acceptable.

Bear in mind that the harmonized 14971 requires all risks to be mitigated to the greatest extent possible (irrespective of economic consideration). Further (if you comply with the harmonized standard), you'll (still) need to conduct a risk-benefit analysis (for all risks as well as an overall analysis).
 
M

MIREGMGR

#5
"...it is not clear how a 1 in 10000 chance of killing a patient can be justified as acceptable.”
The literal response to this would be: via the risk benefit analysis.

I'm surprised that a medical device QMS auditor would ask that question.

Risk analysis of many kinds of medical devices cannot be done in a vacuum. As Yodon notes, their non-zero risks, sometimes of very severe outcomes, are justified by their benefits.

Chemotherapy, for instance, in the case of a hypothetical cancer context can increase the odds of five year survival from 1 in 10,000 to 5 in 10. The chemo itself imposes a death risk of maybe 5 in 100. It's conceivable that a person who might have beaten the cancer untreated would instead be killed by the chemo. That outcome however is very unlikely, and the opposite (beating the cancer, surviving the chemo) is much more likely...and as a matter of medical-technical fact, most of the chemo deaths are in parallel with cancer death, and probably not subtractions from the chemo remission rate. So, on a risk-benefit basis, the use of this very toxic therapy (with a severity of death) is justified.
 

sagai

Quite Involved in Discussions
#6
I think it was more about the justification for the risk acceptability threshold they have set rather than the lack of risk benefit analysis.
Recently for EU more or less risk acceptability threshold is banned and companies accommodated such threshold ( including ALARP concept) are a wee struggling to adapt this change.
 

Nash27

Involved In Discussions
#7
Thanks Yodon, MIREGMGR, Sagai,

Sorry i wasn't clear enough, it is not the QMS auditor, it is a Device assessor, we are trying to register our new device.

Residual risk was evaluated and then the risk benefit analysis was performed prior to approval of the design for its safety and efficacy. Attached is general outline of the risk management process of the concerned device, as well as snapshot of the hazard identification along with determination of residual risk.

We are in bizarre situation when assessor commented on the risk matrix. Our logic is use of device unlikely going to result in patient death, based on this logic probability of occurrence of catastrophic event is unlikely, and termed this hazard as acceptable. In the risk analysis none of the hazards analysed are/will be causing any catastrophic event.

Plus, risk benefit analysis determined overall risk of the device and is acceptable.

The definitions we used are for guideline purpose, to determine risk acceptability. But now with assessor point of view it states that we are accepting 1 patient death for every 10,000 incidences (in that case my entry to the heaven is permanently forbidden).

I agree with 'hypothetical cancer context' example of MIREGMGR, but how I am going to explain that definition are correct and are for guideline purpose only, besides risk benefit analysis.

Any suggestions?
 

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medwise

Involved In Discussions
#8
Nash,

This sounds like that the TGA Assessor is just being picky on the wordings in your risk management documentation. I'm assuming that your risk management report would have cross-referenced the clinical evidence which can support your claim that your device may not be catastrophic. However, as a manufacturer, it is your responsibility to explain them this (direct them to clinical evaluation report in your response). Your main source of information from which you determine the severity and probability is the post market data. If any of the predicate devices in the past have not had any catastrophic history you can highlight that in your response.

I agree with all the comments provided by sagai, yodon and MIREGMGR.

Hope this helps you going back to the assessor.

Regards
Romit:tg:
 

sagai

Quite Involved in Discussions
#9
The thing I would consider actually to remove the risk acceptability matrix from the list of principles you accommodate and assess on a sensible way the risk-benefit of each individual risks (it seems to me you do so based on your attachment) as well whereas you still assess the overall risk-benefit of the cumulative effects (I am not sure if it was indicated based on the pfds you have provided).
I do not think if there is a way forward with the risk acceptability matrix in EU.
One more mentioning about the diagram you have provided would be I do not really know why the Risk benefit analysis segregated from residual risk evaluation, for me the assessment of the residual risk is an input for risk benefit analysis.
Cheers!
 
M

MIREGMGR

#10
I think part of the problem is in thinking of, and describing, the risk structure as "hypothetical". The reviewer appears to want it to be reality-based, related to your real devices. I would agree in general that that's how risk should be analyzed. Anything that's "hypothetical" has less meaning than it should. I don't really care what the hypothetical risk of any of my employer's devices may be, as long as I can show that their real risks are acceptable.

That of course requires a fundamental change of viewpoint in regard to how one thinks of risk management. ISO 14971 doesn't do a good job of communicating how risk quantification scales should be constructed and interpreted, in my view.
 
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