EC.710 | Spring 2010 | Undergraduate

D-Lab: Medical Technologies for the Developing World

Projects

Swiss Army Electrocautery

A combination scalpel and extendable electrocautery tip for rural surgical procedures

Team: Sonya Makhni, Victoria Lee, and anonymous MIT students [AK] and [SG]

This content is presented courtesy of the students and used with permission.

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Post 1

Our project will address some of the problems the rehab center in Nicaragua faces with their electrosurgery machine. Right now, the machine runs a huge risk of burning the patients because there is a faulty circuit between the return pad and the machine’s generator. They used to have a means for checking that the circuit is functioning properly, but this no longer works. As a result, several patients experience severe burns during surgical procedures.

Our first idea was to develop a low cost, easy to use electrocautery device that would have rechargeable batteries. The electrocautery machine would be able to function when plugged in to a power source and if it were simply using the batteries. Another idea we had was to develop a censor-based system that would be used with their existing electrosurgery machine itself. This system would contain an auto-shutoff mechanism that would detect if the circuit between the pad and generator was broken. In addition, this system would contain a series of indicators that would alert the user as to which portion of the circuit was not functioning properly (probably via series of on/off lights).

After a couple weeks of discussions, meetings, and research, our team has decided to shift our project’s focus. We first learned that chargeable electrocautery pens could be purchased for $15, a very inexpensive price. This made us rethink our first idea of creating a cheap pen, as they already exist. We also decided to not focus on the electrosurgery idea, for this would involve hacking a system we do not have access to. We are on the road to coming up with a more innovative solution…

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Pricing for Electrocautery

by [AK]

The cheap ($30-45) electrocautery pens were just the pen unit (no tips or one complementary tip included); typically this can be autoclaved for a certain number of times (40 times was what the representative said). On these, a box of tips (blade or needle type) can be bought for about $50 dollars as Sonya said. The tips must be disposed after each surgery because they cannot be autoclaved (we need to find out why).

The expensive pens (around $80-$125) are actually a box of ten Sterile pens with the pen attached to the tip. Each of these is disposed completely after thesurgery because it cannot be autoclaved. The low temp (which Sonya found out can only coagulate not cut) is a bit cheaper than the high temp (which apparently can cut as well, we need to confirm this).

To do some math:

For 10 surgeries: 1 autoclavable pen + 10 disposable tips = approx $90-$100 (after 40 surgeries a new pen must be bought because it can only be autoclaved 40 times)

For 10 surgeries: 10 nonautoclavable (Sterile) pen+tip units = approx $100

Basically, tips cannot be autoclaved, ever….?

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Company Contacts for Electrosurgery

Response from Future Health Concepts 
Rob Gorgas 
List of Contacts 
Production Engineering - Medical Equipment Division 
6035 E. 38th Avenue, Denver, Colorado 80207 USA (303) 393-7800 FAX (303) 393-1482

Valleylab - Covidien 
Tel: 1-800-722-8772

Conmed Electrosurgery 
Telephone: 800.448.6506 
5088135544 Erica McLaughlin 
Denver

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Talk with Ailis…

by Sonya Makhni

Hey Guys,

I just got off the phone with Ailis (pronounced like alyse–whoops, I totally mispronounced her name when I called her). But I got a lot of good info, so here is a recap of the conversation:

  • She really likes our idea (the autoclavable tip + way to modify cheap cautery pens to cut AND coagulate)…She had actually been thinking about something like this before, so she is really excited about this!

Electrocautery vs. Electrosurgery

Both electrosurgery (they call it a bipolar machine) and electrocautery are used. Electrocautery is used more often. They use elctrosurgery for procedures that involve really important structures that they don’t want to damage (i.e. big vessels). It’s used for a more focused area and you can dial up the intensity. Electrocautery is more general and used for a broader number of surgeries. Because its more general, you run the risk of injuring neighboring structures because you essentially have less control than with a bipolar device.

Cutting and Coagulating: Settings

The electrocautery pens have two buttons–blue for coagulate, yellow for cut (or something like that). The surgeon presses the desired button and can immediately perform either function. Sometimes the surgeon uses a foot pedal instead of a button so that he doesn’t have to touch it.

Cut vs. Coagulate

We know that they operate off of different temperatures, but we (before) were wondering why you can’t coagulate with the higher temperature setting typically used for cutting. This is because cutting causes much more damage to neighboring tissue and coagulating uses the minimum temperature needed to get that job done. In other words, the high temperature used for cutting is excessive for the purposes of coagulation and would cause unnecessary damage to neighboring structures/ tissues.

What MGH Does

From what it sounds like, the elctrocautery MGH uses is the kind that runs off of AC current that is attached to a giant machine. She was interested in knowing more about the fancy cautery pens that run off of batteries and can do cutting/coagulation, but I forget exactly where I saw this. Help if you know what I’m talking about on this one please.

They throw away the entire pen. Because it is normal for the tips to get a little bit charred during a surgical procedure (from the vaporized tissue), it seems useful to have replaceable tips. The surgeons have a scratching pad to remove the char, but if it gets to be too much they’ll just replace the tip altogether.

After a surgery they get rid of the whole pen.

The pen they use is from ConMed Corp.

What She Will Do:

She will also get in touch with Yaffe to see if we can visit his OR

She’ll try to get in touch with a medical device representative (the people who come and give demos of their products).

She knows another surgeon that is really into technology for the developing world and will try to help us meet him.

And, she said she could probably get her hands on an electrocautery pen/ tips for us.

What WE Need to Do:

  1. She said she sees no reason why we can’t make these tips out of stainless steel. But, we still need to talk to somebody to make sure there is no reason behind not doing this. This should be our first task to complete.
  2. Find out the mechanism behind how one cautery pen can immediately switch temperature settings. We need to find out how to achieve this same duality on a cheaper, single-purpose coagulation cautery pen.
  3. We also need to let her know of our availability to come in and meet her/ see a surgery. She isn’t free this week, but she will be next week.
  4. Continue to talk to the engineers at these companies to prod them for information.

K, that’s all I think. Let me know if you have any questions, and please respond with comments about your ideas.

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Focusing on Tips

by [AK]

  1. URLs of products of interest:

Electrocautery pens and pencils (corded - cutting)

Cordless low and high temp

Tips of interest:

  1. Possible Materials:

From customer service rep -

silicone and rubber (?)

stainless steel

tungsten

copper

stainless steel

  1. Company contact - Bovie Medical

Vice President of Regulatory Affairs

I just emailed him. If he does not respond in a couple of days, I will call customer service again and other companies.

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Questions that Need to be Answered…

by Sonya Makhni

Hey guys, these are the big questions that we need to get answered (we’ve discussed these all before, but I just thought I would post as complete list as I have on our blog)

  1. Are cordless cautery pens that can switch between high and low temperatures used? Can cordless pens cut and coagulate?
  2. Or, is it more common to use the cautery pens that are attached to a generator that runs off of AC current? Why?
  3. What are the tips most commonly made of?
  4. Can they be made of stainless steel? According to one company, stainless steel tips are not used because they aren’t “approved” in hospitals…
  5. How does a cautery pen switch instantaneously between high and low temp with the push of a button (mechanistically)? Is there different wiring for the two settings or does the same system accommodate both temperatures?
  6. We understand that it is common practice to use a cautery tip once…is it possible to autoclave them? Or is there something inherent in the material that does not make this ideal? We cannot figure out if they are disposed of out of convenience, cost (for hospitals), or because the company says they should be…
  7. How exactly are the tips heated? (Does a current pass directly through them, or is heat conducted from the base of the tip?)

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Questions for Anna…

by Sonya Makhni

Hey Anna, here are a couple questions on the materials side that we said we would post. Please let us know if you have any suggestions/ ideas/ answers! Also, I don’t know if the picture will go through via this email, but I’m also attaching the picture and link of a sample cordless electrocautery pen. This particular one is only high temp, another one is low temp. The company hasn’t gotten back to me about the questions I asked them, but they said they would tomorrow or so.

http://www.medexsupply.com/products/pid-32662/AaronMedicalFineCauteryHighTem.htm?zmam=34602484&zmas=1&zmac=22&zmap=32662

  1. What are some autoclavable materials?
  2. Heat conductivity of stainless steel vs. other materials
  3. Why coat tips with silicon? Does this affect how tips can be autoclaved?

Thanks!

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Material Science Contact

I will be speaking with Professor Kimerling and Anu Agarwal (Principal Research Scientist in the medical area) about some of our materials. I’m planning on asking

  1. What are some materials that can 

    a) withstand temperatures up to 2000 F 

    b) heat up/cool down quickly (from 1000 F to 2000 F) 

    c) be autoclaved

  2. Why coat tips with silicon?

From the initial conversation I had with Professor Kimerling, he said:

“My guess, at this point, is that silicon is i) stable at the temperatures you mention, ii) has a low thermal expansion coefficient, iii) and grows a surface oxide during sterilization that is hard, protective and relatively chemically inert.”

I have to clarify why the last 2 are desirable qualities, but if there are any other questions you think I should ask, let me know.

Answers from Ailis (Correspondence 2)

by Sonya Makhni

Hey, these are some Q&A’s we were wondering about from Ailis.

  1. MGH does use a grounding pad for their electrocautery machine…they place it on the patient’s thigh.
  2. She’s never seen anyone with a cordless Bovie/ an autoclavable tip…we should still continue to look into this, though.
  3. She can give us the exact model of the instrument when we meet with her

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Bovie Electrocautery Tip Material

Just got a response from Bovie Medical, the manufacturers of the Change-A-Tip electrocautery pens.

I asked about the tip material:

“For Bovie’s cautery replacement tips, the body material is ABS with brass post.”

ABS is a plastic (Acrylonitrile Butadiene Styrene) that is a common thermoplastic. It is good for impact resistance, it is tough, light, and a good electrical insulator"

I also asked about the two different temperature settings:

“When referring to the H100 (low temperature) and H101 (high temperature) there are no design differences. This was placed into Bovie’s catalog as quick references for the end user using low/high temp cauteries.”

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Tip Ideas

We were discussing different variations of tips and came up with the following:

  • An extending (antennae-like) tip
  • Instead of a wire tip, make a plate for a larger heated area
  • A curved or bendable tip to reach into crevices
  • A hybrid scalpel/coagulating tip (a sharp edge to cut, but heated to coagulate)
  • Use some sort of non-stick coating to get less char stuck to tip

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Cautery Post Material

Got a response from Bovie about why they use brass posts instead of stainless steel:

“The brass was chosen because of its electrical resistance properties over stainless steel, even though stainless steel would be preferred over brass because of its corrosion properties and cosmetic cleaner look. The stainless steel has more resistance; this causes problems to the batteries and mold material (the ABS) around the post. I experimented with stainless steel before, preliminary testing of brass versus stainless steel indicated something like 10 times more resistance in the steel. With stainless steel posts, the batteries would drain much faster and the heat build-up could cause damage to the surrounding post material.”

So, it sounds like brass is a great option, especially if we are planning to make tips that will be used in this pen for now (so the ABS doesn’t melt). Extended battery life would be good in developing countries or areas with limited resources. The problem I see is that they might not be able to autoclave their stainless steel instruments with these tips because there might be electroplating.

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Material Data Sheet from Bovie

[Material Data Sheet from Bovie Medical Corporation has been removed due to copyright restrictions.]

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Talk with Dennis
by [SG]

I talked to Dennis today about making our prototype this weekend and any insight he has into the materials that we are going to use.

There are a few problems that we’ll have to look into:

  1. We can’t use brass for the wire at the tips because it will melt at the temperatures necessary for surgery. This is because the wire is much thinner than the posts, so since resistance is roughly inversely proportional to the cross section, the smaller the cross section the higher the resistance. Dennis recommended sticking with the material they use now, which is predominantly nichrome (the tips we found have an alloy of nichrome, iron, cr, al, etc.). Nichrome can withstand the heat of surgery and Dennis thinks that it can withstand autoclaving too.
  2. We also can’t use brass for the posts. This is because brass will corrode upon autoclaving. We can use stainless steel, but it is not a good conductor and thus may take a longer time to heat up the wire at the tip. Or, I was thinking that we could use a brass post but plate it with stainless steel. Dennis said that this wouldn’t work because the steel would separate upon plating because it is an alloy, and if we melt it to coat the brass, the brass would melt as well. Our option is to use chrome or nichrome plating, or make the posts out of chrome themselves. Plating the brass will be tricky, so we might have to “play” with a chemistry lab.
  3. Connecting the posts with the wire: This is tricky because we can’t solder the pieces, since the solder would melt at the temperatures necessary for cautery. Apparently, we have to weld the pieces, but we can’t use the one in the lab because that is too big and powerful. Dennis said we’d have to build our own mini-spot welder, which apparently isn’t too hard, actually “pretty simple with a transformer.” Or–I thought we could drill a tiny hole into the post and kind of cinch the wire inside/insert it in so that it would be tight enough. Dennis thought this might not be practical, because we’d need a 8/1000th drill, but he said we could get the necessary drill bit if we really thought this was the method to do it with. I guess another option is to get a hollow post, and cinch the wire inside, but we don’t know what making the post hollow will do. If we do make it hollow, perhaps using stainless steel isn’t a bad idea, because it would significantly reduce the time to heat up.
  4. White disc: Polypropylene is apparently fine, autoclavable, since it is a plastic solid. He said this was pretty cheap, all we would need was a cylinder of this stuff which we would slice for our prototype.

So I guess the next steps that we will need to do are:

  • Mini-spot welder or cinching by hollow post or drilling hole?

Look into what making the post hollow would do.

  • Stainless steel or nichrome post or nichrome plated over brass?

If we go by nichrome plated, we need to look into electroplating techniques.

Good news: We can get all materials we want in 24 hours, so we could definitely make our prototype this weekend.

Actually, Dennis has nichrome in the lab, but not medical grade, so we might want to order that. Polypropylene is in the lab as well, as is brass.

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Call to Ailis and Response to Meeting with Dennis
by Sonya Makhni

Hmm, looks like we have some thinking to do…

I spoke to Ailis (briefly) and she like the idea of a retractable, antenna like tip. If we do end up using the same materials, maybe we could look in to the spring-loaded system we were talking about earlier…

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Bovie Med Equipment is HERE!

Great news. The Bovie free samples are here!

What’s in the box:

  1. 2 AA01-S Cautery High Temp Fine Tip

    These are two of use-and-throw pens. Sadly, they weren’t able to send me the reusable pens, probably because they are more expensive. But, these are good enough to test our tips on, and we can take one apart.

  2. 2 H101-S Replacement Tips

    The one-use tips you would use on the reusable pens. We can’t test them on anything since we don’t have the pen that goes along with them, but we can see the morphology. An interesting thing I noticed: The tubes are actually slightly hollow, and the ends are actually cinched where the wire goes in! So it looks like the real company that makes these things uses the cinching method.

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Properties of Materials
by [SG]

Hey guys, I found the specs on the materials we were looking for. Also, I’m trying to find a place that sells really tiny pieces of brass, but have not yet had much luck. I emailed a professor who has an electronics lab, though.

Polypropylene

melting point of polypropylene = 160 C

“Polypropylene (PP) is the material used for the autoclave bags and is suitable for steam autoclaving. However, it is not suitable for dry heat sterilization and this is why bags must be removed from the chamber as soon as the cycle finishes since the hot jacket walls produce a dry heat environment inside the chamber and the bag may melt if left inside overnight.”

  • Maximum Temperature: 275°F 135°C
  • Minimum Temperature: 32°F 0°C
  • Autoclavable: Yes

ABS

melting point of ABS = 221°F = 105°C

  • Maximum Temperature: 176°F 80°C
  • Minimum Temperature: -4°F -20°C
  • Autoclavable: No
  • Melting Point: 221°F 105°C"

Brass

melting point brass = 900 C

autoclavable: yes

“Autoclave dissimilar metals (aluminum, brass, steel) in different loads as electroplating may occur which will permanently stain the tool.”

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Group Chat with Dennis; Next Steps
by [SG]

A quick summary of what happened today:

Talk with Dennis:

We got a few things cleared up with the materials again. It turns out that

a) Brass does not corrode when autoclaved, at least not significantly. It will wear away with lots of use however.

b) Polypropylene is autoclavable too? According to our outside research. At this point we don’t know why an electrocautery tip can’t be autoclaved, since nichrome 80 (the wire material), the white disc, and posts are ALL autoclavable. We should find an autoclave and put one of our tips in there and see what happens.

Measurements:

  • The brass posts are 0.062 inches with 17th/1000 in hole. The hole can be smaller, because the nichrome 80 wire diameter is 11/1000th inches.

What to do next:

  1. Focus on the retractable tip idea. Make them antenna-like or use braided wire and attach it to the end of the posts. This means that we need to track down brass tubing that is 0.062 inches in diameter, and polypropylene. Also, we need to find braided wire of that size (smaller than 17th/1000 in) to fit into the hollow. Maybe our prototype can even have plastic extendable regions, with a wire running through, if we cannot get these materials in time.
  2. Find an autoclave, and put our tips in and see what happens. We tried calling Bovie again, and it seems like someone from the engineering department should be e-mailing us about this. Hopefully, this will clear up whether the tips cannot physically be autoclavable or if it’s a regulatory/company issue.
  3. Find out from the chem lab if we can chrome-coat brass using electroplating, so that the posts will be longer lasting.

First Priority: finding the braided wire, brass tubing.

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Final Design Plan
by [SG]

Final design plans for the “retractable antenna” model and the scalpel tip

The final design plan for the project will be to make two different varieties of tips: a retractable antenna model that will allow the tips to be extended to the desired 5" during surgery, and the scalpel tip model that will have a scalpel tip on the end instead of the current wire.

Also:

  • Ordered multiple brass tubing today, of sizes 1/16", 3/32", 1/8", and 5/32" to build the retractable antenna model.
  • Will get the scalpels from Ailis.

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Dennis Meeting

We met with Dennis to see if our design would be feasible. He said we could try making some things tomorrow. He will be in D-lab starting at 10:30 am, so as soon as we get the materials, we should head over.

As for the retractable antenna model, he said if this were to be used in a medical setting, the junction between the larger and smaller rods would have to be sealed really well so that tissue and other contamination does not get in or can be cleaned out easily if it does.

He also said that we might have trouble with the plug into the pen if we use the larger tubes at the junction. We tried to buy solid brass rods so that we could drill a hole in them, but it would have been $30 to ship them in time. We are instead going to check out Economy Hardware and see if they have anything. If not, we will try to fill in the extra space with solder or something else.

The third thing we talked about was the design of the scalpel tip. We thought about changing the design from one where the scalpel itself heats up to one where it’s a combination of a scalpel and a wire that heats up. The issue with both is that the scalpel will get in the way when the user wants to cauterize. We therefore need to think of a design that will avoid this interference. [SG] and I started thinking of a design that would have 2 retractable tips so that if the scalpel is out, the cauterizing wire is in, if the cauterizing wire is out, the scalpel is in. We need to think about this more though.

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Response to Dennis Meeting
by Sonya Makhni

Hey, so about the scalpel tip…will it definitely not be feasible to just directly heat up the scalpel, itself? We briefly discussed this in class, but I can’t remember why we decided that this wouldn’t work. Because, if the scalpel was thing and small enough, it still might be able reach high enough temperatures….or at least moderately high so that it can be a start. Did Dennis have anything to say about this particular idea?

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Google Doc
by Sonya Makhni

Hey guys, I created a Google doc with some of the info we’ll need for the poster. I started it, but it probably could benefit from some revisions.

Please also add to the Pugh Chart part–I am missing some of our previous ideas. And, if there is anything missing at all–from any of the sections (existing or not)–please add!

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Autoclaving Info

This is some info I got from Gary at Bovie about autoclaving the tips:

“It is not recommended to autoclave the tips. Even though Acrylonitrile Butadiene Styrene (ABS) melts at approx 450F it can become pliable or soften. I believe the deflection and service temperatures are something like 215F. However manufacturer specs can differ from one to the next. Bovie has only validated the tips through Eto sterilization.”

In a later email, he said, “The best thing to do is to autoclave the tips and see what happens. But again Bovie has only validated sterilization through Eto because this is a disposable device and is not meet to be re-sterilized. However we have non-sterile product and I believe these are only for non-invasive procedures only, not 100% sure on this if you need to know I will pass along your request to somebody that can give you a more definitive answer.”

Sounds like if we want to know if these tips can be autoclaved, we need to just throw them in an autoclave and see what happens. Maybe if we have tips after we’ve made our prototypes with the different tips, we can try this out.

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More Autoclavable Materials Info

“Medical devices have a wide range of materials used depending on applications. For example in disposable devices I would typical use ABS or PVC. In reusable I would use Polycarbonate or Radel. However I have used Polycarbonate in disposable as well, again depending on the application and cost.

If you are looking for reusable devices for autoclave maybe you should look into Radel. I use Radel for its ability to withstand standard and flash autoclaves (has very high temperature withstand). For example Bovie’s A901 ES pencil, its body is made of Radel and the cable is silicone.”

I went to the Radel Polyphenylsulfone site and it said: “For the most challenging applications – requiring repeated sterilization or uncompromising toughness – choose Radel polyphenylsulfone (PPSU). With a high heat deflection temperature of 405°F (207°C), it can withstand continuous exposure to heat and still absorb tremendous impact without cracking or breaking” and that it was “Steam sterilizable with better retention of impact properties”

Looking into pricing though and why the silicone is used.

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=)
by Sonya Makhni

After a long waiting period of getting our supplies and materials in, we finally have some good news! We built a retractable tip that extends to 5’’. This took a while to arrive at, but it is (for the most part) functioning. It functions like an antenna; there are three layers of brass rods connected by springs. The rods are of different diameters so that the tubes can fit over one another and compress down to a length of about 2’’ or so. Big thanks to Bernard!

We now need to try to modulate this tip with a scalpel. We are still waiting for our Bovie pen to come in, so testing to see if these tips can cauterize will still need to wait. This prototype is with [SG]!

yay for some good news =)

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Another good day! =)
by Sonya Makhni

So we met with Dennis today and he helped us implement our scalpel idea. We explained to him our design idea, what we wanted the overall function to be, and how we thought our design could be carried out. He was extremely helpful in helping us drill a hole through the tip as well as providing us with an optimally sized screw + washer.

So now, we have a real Swiss army cautery tip!

We still need to do a few more things, however:

  1. Score the brass tubing so that it doesn’t come loose when we try to extend it.
  2. Use insulating material to prevent short circuiting
  3. Use a tab so that the user can more easily position the blade
  4. Implement a mechanism such that the blade is sturdy when the user is cutting through the tissue

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Progress
by [AK]

On Monday we added an “untelescoping” feature to the tip to enable it to fit into our pen. We also tested our device in the Course 6 lab with the power source.

Results:

Our tip glowed red-hot after 2 sec at 2.8 A and 1.5 V, identical to the Bovie tip. This confirms that the electrical and heating properties are comparable to the original Bovie tip.

We were able to burn paper with the low temp cautery after fitting in out tip, indicating good interfacing. We conducted tests by passing current through a thin scalpel. It became warm after 30 sec at 3.6 A and 0.5 V. To heat it up faster we would use a smaller surface area or other materials (looking into that now).

Overall, a successful day.

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Other Materials for the Scalpel
by [AK]

Current:

Stainless steel: heat capacity - 500 J/kg-°C

Alternatives:

Copper (not autoclavable so must be coated with Nichrome or gold which is actually not very expensive):

heat capacity 385 L/kg-C

Silicon: heat capacity 556.9 J/kg-C

Heat capacities are at approx. 200 degrees C

Other metals such as gold, silver, and platinum have lower heat capacities than stainless steel and are electrically conductive, but for cost reasons I have not included them.

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Tip Designs We Emailed to Ailis
by [AK]

Possible tip designs

Apparently 2 is not very feasible but we have accomplished 1 and 4 in its preliminary stages. 3 and 5 are still further possible design ideas.

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Final Pugh Chart

This Pugh Chart indicates that our design is quite useful. The only design that ranks higher is the one in which the scalpel heats up (something we have been looking into and testing).

I’m also uploading the old one so we can compare and see how our ideas have changed/how we got to where we are with the project.

Final Pugh Chart (PDF)

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Spring 2010
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Design Assignments with Examples
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