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Hi Adrian,

The point is that the Surgeon and members of the electrosurgery "team" have to make the decisions regarding electrosurgery - no-one else can (certainly not a technologist or Engineer as far as I am aware) - it is clearly the Surgeons responsibility to look after the welfare of the patient. The surgeon will have had lots of basic training under supervision, be highly educated, should have experience in the use of, should be fully conversant with, electrosurgery equipment and more specifically with the equipment he/she uses routinely.

The surgeon is responsible for the clinical outcome RE: the outcome of the patient being operated on. It's in the surgeon's own interest and that of patients' for the Surgeon to be aware of the risks associated with electrosurgery; this includes the fundamental principles and an appreciation of what happens to RF current and voltages in the body (including safety aspects).

I think that it's a bit rich to question Surgeons' ability to make (possibly informed or not) decisions themselves. Of course these decisions must be based on current practice, guidelines, recommendations, technical advice from experts, literature or their peers - but they don't have to - the final (albeit more informed with credible, reliable, expert technical advice) decision rests with them.

Precisely because they are responsible, highly educated, intelligent people, who "make life and death decisions every day", then I would have thought that the basic concepts of electrosurgery and safety aspects are not beyond them. There is plenty of material on the subject out there - clinically biased information that describes the principles, clinical usage of electrosurgery equipment and associated risks. I would urge Surgeons to establish the validity of any advice given by any "expert" in this field since many are "practising" without the necessary education, training, experience and expertise, in my opinion.

Three questions Adrian: -

1). Is your area of expertise in Electrosurgery or RF Engineering?

2). How do you assess whether an individual is an expert in a particular field?

3). Why would you wish to take on someone elses responsibilities for "life and death" decisions, as you put it, when you are not required to do so?

Hello,

I'm sorry but I wasn't suggesting that it was up to a technologist to make the final decision on the use of equipment in Electrosurgery. Though I think we should be more supportive in finding answers about electrical safety so the Trust can come to a more informed decision.

I've had time to think about this and I'm interested to hear what other people make of some ideas knocking around in my head.

Firstly the idea of two current paths crossing, yes there would be increased power at this point, but it would only be at most the sum of the two output powers. i.e. if one surgeon was using 100W and the other 120W the maximum this could be at any point would be 220W. I've assumed that reflections would be negligible. As Richard Ling has already mentioned best practice is to keep the return paths as short as possible so to reduce tissue heating. So restricting the output powers used would seem a more practical solution.

But then I started wandering whether it was due to the interaction of the two current paths! As we all know during electrosurgery large amounts of current surges though the patient body without causing shock due to its high frequency nature. But if to two high frequency signals are mixed and there is a small difference between the frequencies, a lower beat frequency is produced. This would give rise to the potential of a macro shock! I can see that having the correct phase in a system designed with two outputs is vital, as there is only one return plate. What I am very interested to hear from other people is whether they believe that two current paths from two floating generators would interact, because I'm not convinced. And surely with this practice being widespread throughout the country there should have been patients electrocuted as a result by now.

I think the issue brought up be Double D of burning on the edge of a plate is interesting, though the same would be true with single diathermy use. As there have been no known cases I would expect that there probably isn't a problem.

I'm eager to hear other people's thoughts,

Adrian.

Mr R J Ling
What you have said in your last two postings is all very well, but in my capacity when I see a dangeous situation or am made aware of bad practice I have to act to advise the surgeons. That is I feel part of my job. It is part of my job description to advise medical staff on the safe use of electronic medical equipment. Their area of expertise is us, where ours is medical electronics. Combining the two when an issue is raised like this one, together we can get to a safer working arena for the patients' sake. As we all know through time every one can become flippant in what we do and things can be missed. Just because an incident has never happened before
does not mean it never will. That is why I will be advising the staff involved to improve the situation and in the fullness of time hopefully purchase equipment that is designed for the job in hand.
Your question "Why would you wish to take on someone elses responsibilties etc". If there was an incident and I was aware of the problem before hand but did nothing, how would I feel about myself?
Adrian raised the question "should surgeons have to make decisions on issues like this?" Not only the surgeons but all of us together should combine efforts. That might be naive of me but I must try.
Thank God its Friday.

Dave

Actually Adrian said we should "make decisions" I say "give advice", based on valid technical knowledge/clinical evidence of good/best practice and let the Surgeons make the decisions.

I do agree that technical advice is absolutely necessary but we should only work in an advisory capacity. Surgeons must not assume everyone is an "expert" just because they work in Medical Engineering/EBME/Medical Physics. Otherwise they put themselves at risk when poor advice is given.

Where do you stand if your advice is incorrect and causes an incident DD? i.e. How would you feel if the advice you gave actually harmed a patient - who would act in your defence - the Surgeon you advised? How would you demonstrate your competence to give advice?

Finally do you have the authority to take that sort of responsibility on your shoulders and that of the organsation where you work?

Adrian,

Yes, interferential currents may be generated to some extent but complex RF waveforms of varying amplitude, phase and frequency will be involved - complex analysis that goes beyond anything we would get involved with plus there are all sorts of subtle issues such as the rectification of current due to the arc at the active electrode, etc, etc.

The magnitude and frequency of the interferential current you suggest would be the issue since the magnitude of the current required to provide a patient stimulus is proportional to frequency isn't it? I doubt it's a major issue practically speaking but It'd be interesting to see if anyone has looked into it and produced some literature or whether anyone has had problems attributed to this.

As for DD's "edge of plate burning" issue - do you not think it may be a relatively simple case of the highest current density, hence heating effect, occurring at the portion of the plate with the lowest contact impedance and relatively small contact area (compared to the neutral plate area in total). The implication being that the rest of the plate may have been a relatively poor contact with the patient i.e the plate was peeling? Alternatively perhaps the shortest-edge of the plate was presented to the return-current path and contact in the rest of the plate was poor, relatively speaking.

What I wonder is whether the plate was split or not - if not then perhaps it should have been. Neutral plates should offer a low contact resistance over a relatively large surface area to reduce heating effect/return current-density. As far as I am aware; current may preferentially return to the edges under the right circumstances (plate orientation, contact area, current density, etc, etc). This is why some manufacturers, such as ERBE, use "NESSY" to overcome this and related problems I think.

Richard,

I'm sorry but I feel you are twisting some of what I am saying. If you read over my last posting, I said "I think we should be more supportive in finding answers about electrical safety so the Trust can come to a more informed decision.' What I clearly meant was, the Trust should make informed decisions from advice given by all the staff involved. I believe DD is right he should be taking an active role on matters of equipment safety. It is also in my job description to advise medical staff on the safe use of electronic medical equipment. Of course with the "Agenda for Change', this may not be apart of your description.

It seems to me that DD has come on this site to try to find answers to his diathermy problem, and he feels criticized. I came on because I'm interested on the subject and you criticized me. I feel this is only going to stifle a good interchange of views. Anyone reading who may wish to add something will think twice in case their views are also jumped on. I can see you enjoy a good jousting competition, but some of us aren't here with this motive in mind.

On a more technical note it appears you have made the whole idea for beat frequencies appear more complicated that it actually is. I could dig out my old notes on frequency mixing, but I don't see the point as I don't believe two floating generators will mix frequencies, unless someone could explain otherwise. But just for the fun of it, if we take a small percentage of say 200W, how many Watts does the patient have to sustain internally at say 20 – 100 Hz to receive a macro shock?

Adrian.

DD,

In my opinion, I believe the operation of two floating diathermies may be perfectly safe. However I certainly wouldn't stake my job on it unless a great number of others who could give detailed descriptions of the issues also agreed with me. Probably the best option is to use the safety net of the Diathermy manufactures who claim their machines are capable of this operation.

Adrian.

Hang on Adrian - you said make decisions, not advise in your previous posting - now you're saying it's your role to advise. I was only responding to the statements you made. I'm not criticising DD - I was responding to your comments not DDs. It's a fact that the responsibility for decisions in electrosurgery rest with the clinical staff - as published and expressed in guidelines by the MHRA (EBME has an advisory role, not clinical decision making), I'm not criticising, I'm expressing my disagreement and my own opinions plus trying to give you an idea of my understanding (read as: how I understand it to be - NOT "I am an expert and you are not") of the ethics as well as the technical stuff. You're perfectly entitled to critcise what I have to say.

In the analogue world the mixing of two or more complex signals depends upon the relative frequency, phases and amplitudes plus the complexity of the load of course. Take two signals of different frequency, phase amplitude and crest factors considering power waveforms (non-sinusiodal i.e. complex) and things get a tad difficult when you consider a highly complex load plus leakages (the patient) and other influences such as cables, plates, other equipment - ad infinitum if you want - please don't try to trivialise something that is actually quite complex. College notes are quite a long way from the real-world in my experience.

You said:

DD,

Valleylab do actually suggest in their manuals that two electrosurgery units (Force FX) have to be used for dual operation - CH1 and CH2 outputs on a single FX unit definitely should not be used on a patient together. The force FX has floating outputs so I guess that, generally speaking, the issues that we have been discussing are not a problem with floating devices. However you would have to refer to manufacturers recommendations.

Richard,

I'm afraid we're not going to find middle ground on this one. What I've written is on the board for everyone to read, people can make up their own minds on what I've written. I'm sorry but I'm not going to endorse your version of what I meant.

Adrian.