EBME Forums Forums Maintenance Technical Assistance microshock by ionisation in the skin

Sorry for the delayed response chaps,I've had an extended Bank Holiday break.
Thank you for the in depth responses,to answer your queries the application in question uses a commercially available enuresis device to detect a venous needle dislodgement during haemodialysis and is placed directly onto the patients skin (I believe) to detect the bloodleak hence my concern that given it is in place for perhaps 5-7 hours at a time 3 times a week there could be an effect on the tissues which was highlighted on a recent paper published in Japan :
STUDY OF LIGHT TRANSMISSION THROUGH
GAUZE PAD EFFECTED BY BLOOD OR LIQUIDS
TO DETECT NEEDLE DISLODGEMENT
Akihiro Takeuchi, MD, PhD1, Kai Ishida, MS2, Yasuo
Morohoshi, VMD, PhD3, Toshihiro Shinbo, CCE4,
Minoru Hirose, PhD4 and Noriaki Ikeda, PhD1

Which has this statement in the text:

"We attempted to sense the small amount of blood on a
small gauze pad that covers the needle site. A direct
electronic sensor such as a moisture or enuresis detector is
not suitable in Japan because the DC 5 V power supply
could cause a microshock by ionization in the skin."

PhD's or not, I don't believe they meant to say that. Perhaps something was lost in translation.

Any electrode placed on the skin could potentially become a return path for any extraneous currents lurking (leaking) about, of course. But I should imagine that they meant "ulceration" or some such thing.

Meanwhile, can't your blood leakage detector be positioned on top of a gauze pad, a sheet, clothing or similar?

Meanwhile, see here and here.

Hi Geoff,
I think the issue with the enuresis type device as shown in your link is that it would become less sensitive it they did put a pad in between the sensor and the needle exit site hence my query as to whether the statement in the paper in relation to tissue damage could be true.
Clearly in it's original intended use it wouldn't be placed directly onto skin but would just detect urine on the bed clothes.
I don't think it could become a return path if it was battery powered and therefore isolated could it, but the patient is earthed through their blood pathway via the dialyser if the dialysate pathway in the machine is earthed so is there a possibility of current flow to ground via that pathway from one electrode on a damp arm even if the 2 electrodes aren't shorted?

Can't locate the paper, but since this was a research paper perhaps they weren't using medical equipment and instead prototype test equipment. Wouldn't have thought there would be a problem with medical equipment designed for the job.

Hi Chris,
This is where it was published if it helps:
Takeuchi A, Ishida K, Morohoshi Y, Shinbo T, Hirose M, Ikeda N,
Study of light transmission through gauze pad effected by blood or
liquids to detect needle dislodgement.
J Clin Monit Comput 2010; 24:35–39

They were writing a paper about their own prototype which didn't really work.
The issue with the device in question is that it was originally designed as an enuresis alarm and is now being used to detect blood and is in direct contact with skin hence my enquiry.

Ah found it, abstract here

Looking at the paper I'm wondering if they are referring to their own equipment as the device they produced uses a 5V DC supply, LED and photo-transistor. Presumably they originally intended to use electrodes or to make a Eneuris device. Not sure why they used a DC power supply and not a 9V battery?

"A direct
electronic sensor such as a moisture or enuresis detector is
not suitable in Japan because the DC 5 V power supply
could cause a microshock by ionization in the skin."

Hi Chris,
I think their system using light from LED's was trialled purely because of their concerns with a direct current sensor being on the skin and the relative high cost of the commercial alternative.
What I'm not at all sure about is whether their concern is a valid one,i.e. is there any possibility of tissue damage from a 5v DC electrode type system sat on the arm in the same place for over 15 hours /week.