Application of 60601-1 and 60601-2-2 to a hand-held laparoscopic unstrument with motorisation in the handle

[PhilTK]

Hi guys,

as the name of the thread already states, I am trying to figure out how to apply the IEC 60601-1 and IEC 60601-2-2 to the device I'm developing.
The device is a laparoscopic instrument which has some low voltage motorized parts inside of the handle unit. The handle unit has a cable which splits up into two connectors: One for a external power source for the motors and one which attaches to an ESU.

kolorado22 already addressed this a bit in this post: HF surgery device accessory insulation requirements
Hi William:
The answer you received about no creepage and clearance requirements for HF Surgical Accessories is correct ONLY for that part of your accessory that is transmitting HF energy to the patient. If your Accessory is POWERED by anything other that the HF surgical current from the ESU then the IEC 60601-1 clauses 8.8.1 and 8.5.1.2 apply. Further if there is any protective or functional earth present in the accessory, that earth connection must be protected from the HF circuits according to 201.8.8.3.101. An example would be an accessory within a robot arm or with a camera built in.

My theory is that the part of the device that is motorized and isolated from the HF circuit can be seen as a F-TYPE APPLIED PART of my power source (60601-1, 8.5.2.1):
F - TYPE ISOLATED ( FLOATING ) APPLIED PART (herein F - TYPE APPLIED PART )
APPLIED PART in which the PATIENT CONNECTIONS are isolated from other parts of the ME EQUIPMENT to such a degree that no current higher than the allowable PATIENT LEAKAGE CURRENT flows if an unintended voltage originating from an external source is connected to the PATIENT , and thereby applied between the PATIENT CONNECTION and earth NOTE F- TYPE APPLIED PARTS are either TYPE BF APPLIED PARTS or TYPE CF APPLIED PARTS .

It doesn't technically make contact with the patients body during normal use however because the instrument shaft wouldn't be considered part of it. That makes me unsure...
APPLIED PART
part of ME EQUIPMENT that in NORMAL USE necessarily comes into physical contact with the PATIENT for ME EQUIPMENT or an ME SYSTEM to perform its function

If however - as kolorado22 said - the part of the device that is transmitting the HF energy from the ESU to the patient can be considered an ACTIVE ACCESSORY (60601-2-2) of the ESU I wonder which quote from the standards gives the possibility to split up the device.

I also wonder what quote from the standards this ("Further if there is any protective or functional earth present in the accessory, that earth connection must be protected from the HF circuits according to 201.8.8.3.101.") is based on. More precisely I would like to know how the two parts of the device need to be insulated from each other and what tests need to be performed regarding this.

I would really appreciate it if anyone could help!

 

[Peter Selvey]

With respect to 201.8.8.3.101, this clause is really about testing the insulation quality, not so much why the insulation is there.

Normally, we have 2 MOP (two means of protection) between dangerous stuff and accessible stuff. So the starting point is to identify both of these parts (live stuff, accessible), also there are various options on how to assemble the intervening 2MOP, which can include earthing and other clever stuff.

But for HF insulation, there is a more simple approach: assume the insulation will be on the active electrode, i.e. a tube or wire that is coated with an insulating material. Then test that material according to 201.8.8.3.101. There's no clear identification of accessible parts or any complicated considerations such as being near earth.

In reality, this simple approach doesn't always work, especially with complex systems like endoscopes, trocars, catheters, robotics and so on. In particular the potential for high currents to flow with capacitive coupling, and worse if that coupling can somehow concentrate the current to a small area of patient/operator tissue. Consider for example a system with internal insulated active electrode with articulation cables running along side. The insulation on the active electrode might comply with all of 201.8.8.3.101, but due to the length there is still some good capacitive coupling with the other cables. Say these cables are floating, but in a reasonably foreseeable condition could end up with small point of contact with the patient or operator. Then the coupled HF current (which can be in the order of 100mA or more) gets funneled into that spot creating high current density and ... well ... burns.

Thus, at least for the HF side of things, it's good to look at the individual construction carefully and make sure the design is safe independent of the standard.

With respect to F-Type insulation, this is for a hypothetical case of assuming the patient is raised to mains potential and making sure the medical device does not provide a path back to earth. It's a different focus. You can think about that independently of the HF insulation.

 

[PhilTK]

Hello Peter,

Thanks for the detailed reply, it has made some things clearer for me. The only thing I still don't quite understand is your example with the articulation cables. Wouldn't such a system fail the 201.8.8.3.101 tests?

 

[Peter Selvey]

Not necessarily, but it could. If you study the rationale it's based on the assumption that the tissue contacts the insulating material directly, i.e. three concentric layers:

<METAL> (active electrode)
<INSULATION>
<TISSUE> (Patient or operator)

In this case all the math in the rationale makes sense. However, if the insulation couples with intermediate parts then all bets are off, since the current density of the final part that contacts the tissue cannot be known, at least from the point of view of the standard. It might be known or predicable for an individual construction.

 

[PhilTK]

Yes, that makes sense! Thank you so much, you really helped me a lot.