It's easy to find a bedside monitor in a hospital in the developing world, but it's harder to find one in use. Western hospitals replace their electrocardiogram machines every few years and donate their used equipment. The second-hand machines work fine, with one glaring exception: They don't come with pads. The pads are disposable and often in short supply in impoverished regions.

The solution is to make ECG pads (link to E4C's how-to) from easy-to-find materials such as snap buttons and bottle caps. Robert Malkin and students at Duke University invented the trick, and our friends at Engineering World Health travel the world and demonstrate that making ECG pads and conductive gel is fun for the whole family. The materials required are bottle caps (read: beer and soft drinks) and the conductive gel is a gooey mess that kids enjoy. Incidentally, the gel is two ingredients and some changed proportions shy of homemade Playdough (another Instructable), which may also also go over well in the pediatric ward. 

Electrocardiogram (ECG, sometimes EKG for the German name) machines measure the heart rate and rhythm and indirectly assess the blood flow to the heart. They monitor electrical activity through the pads stuck to the patients' skin.

Here's how to make the the pads, and see the last step for directions for use.

Step 1: Materials

Pad materials:

1. Bottle caps
2. Nickel-plated brass sewing snap buttons, size 3
3. Flathead screwdriver
4. Utility knife (boxcutter, X-Acto or another sharp-bladed, small knife)
5. Pot, water and a stove
6. Optional: tweezers/forceps

Step 2: Boil and Peel

See that plastic lining on the inside of the cap? That's what you want. The lining is 36mm low-density polyethylene plastic. It will provide mechanical support for the electrode, which is the snap button, and help ensure that it has continuous contact with the patient's skin.

1. To get it, first boil the bottle caps in water for 30 minutes.

2. Then peel off the lining. Start the peel by prying an edge off with the screwdriver, then carefully pull the rest out with your fingers or with tweezers or forceps.

* It may become harder to separate as the cap cools. In that case, try heating the cap in the water again for a few seconds then remove it and finish peeling.
* It's okay to use plastic liners that tore a little bit when you separated them, as long as they didn't tear in the middle.

Step 3: Assemble the Pad

1. Cut an “X” in the center of the lining to make a hole, no larger than 1cm on each line.

2. Then insert a size-3 nickel-plated brass sewing snap into it.

3. Trim the tiny corners of plastic from the edge of the button nub to help expose it more.

Congratulations, you made an ECG pad. They’re washable and reusable up to 100 times or so. See the last step for directions for use.

Step 4: Conductive Gel Materials

Now, to make the conductive gel.

Conductive gel materials:

1. Water, 1 cup
2. Salt, 2 tablespoons
3. Flour, 1 cup
4. Bleach, just a drop

Step 5: Gel Recipe

1. Mix the water and salt in the glass bottle.

2. Slowly pour in the flour. It will become gelatinous. Mix it until it the consistency is even throughout.

3. Add a drop of bleach to sterilize the gel.

Note: Just use regular white flour, not fancy whole grain flour like we used in this demo (it was all we had).

Step 6: How to Use the Pads

Directions for use:

1. Cleanse and, if necessary, shave the patient's skin where the pads will attach. Use antiseptic wipes.

2. Spread the conductive gel (which you'll make) on the spot where you plan to attach the pad, then lay the pad over it with the snap button nub facing up.

3. Tape the pad to the skin with medical tape (micropore), leaving the button nub exposed.

4. Fasten the ECG leads to the nub.

5. Then, after you've set everything up, tape it all in place. Reapply the conductive gel every 24 hours or as needed.

Cleaning: The pads are washable and reusable up to 100 times. To clean them, remove the buttons from the plastic and wipe everything with alcohol pads.

Warning: Check for allergies and to see if patient's skin reacts badly to nickel, flour or high levels of salt.

[The image is a composite made from photos by Engineering World Health]
<p>Any substitution for flour in the conductive gel? I assume it is wheat flour because it is simply stated as flour. I am allergic to both ingestion and skin contact of gluten. Any work-arounds that would be just as conductive?</p>
If you're just doing a quick ECG, just use what early researchers used: cloth soaked in salt water. Or paper towels for convenience. As long as the towel is in contact with the electrode and your skin, conductivity is achieved.
You can use virtually any gel since it's just a substrate to hold the salt, which is the crucial ingredient for conductivity. Some people use aloe vera gel, which unfortunately, is somewhat expensive. A more readily available solution might be corn starch (aka corn flour), which actually has twice the thickening power of wheat flour. Depending on your application, you may need to wet the electrodes with water every few hours. If you're doing a quick ECG, it's a non-issue, but if you're doing continuous monitoring, you'll want to either wet the gel every few hours (or re-apply), or use a gel that doesn't dry out as easily. I am currently experimenting with an oil-based mixture, i.e adding in some mineral oil (or any cooking oil, including lard) or petroleum jelly to prevent evaporation. I need to see if conductivity is lessened by the oil.
here is a link to gf playdough<br>http://onecreativemommy.com/gluten-free-play-dough-recipe-review-and-tips/?m
You could try a gluten-free flour like rice, almond, taro or the others. Good luck!
<p>Xanthan Gum would be a better option (cheap to buy online). Just a tiny amount would be enough to create a gel and would be conductive with a little salt.</p>
<p>Could the conductive gel be created by adding salt to K-Y Jelly?</p>
Yes, that would be fine. You can use virtually any gel since it's just a substrate to hold the salt, which is the crucial ingredient. Depending on your application, you may need to wet the electrodes with water every few hours. If you're doing a quick ECG, it's a non-issue, but if you're doing continuous monitoring, you'll want to either wet the gel every few hours (or re-apply), or use a gel that doesn't dry out as easily. I am currently experimenting with an oil-based mixture, i.e adding in some mineral oil (or any cooking oil, including lard) or petroleum jelly to prevent evaporation. I need to see if conductivity is lessened by the oil.
<p>K-Y jelly drys out too fast </p>
Great idea
HI amigo me podrias dar tu correo, me gusto el proyecto y me gustaria hacerte varias preguntas, soy estudiante universitario.
God Bless you , man! <br>It was Amazing. Good Luck
<p>This is great!</p><p>Some of you may also find this little update on how you can repair broken shielding on ECG cables useful:</p><p><a href="http://davidkvcs.com/2015/01/11/how-to-repair-broken-shielding-on-ecg-cables/" rel="nofollow">http://davidkvcs.com/2015/01/11/how-to-repair-brok...</a></p>
<p>&quot;snap buttons, size 3&quot;, what would that mean :s</p>
This is great, and for a good cause as well! Would this also work for EMG (muscle) sensing?
I have never had reason to comment on this site, although I enjoy many of the instructables. This one tops them all. This could truly be life saving. Thank you, from the rest of the world.
Thank you, so good of you to say. We'll pass your kind words on to our friends at Engineering World Health, too, to spread the love.
if u used thermal electric generators. instead of battery's they, the instrument could be powered by the user instead of a external power source, as well. if u go to http://tegpower.com/pro4.htm if the full link doesnt or refuses tto work look at the base link then products page <br>
Could you use cotton for the pads?
Step 3, &quot;1. Cut an &ldquo;X&rdquo; in the center of the lining to make a hole, no larger than <strong>1cm</strong> on each line.&quot; Typo: this should read &quot;...no longer than <strong>1mm</strong> on each line.&quot; I'm sure everyone else read it correctly, though.
When I was learning to do ECGs as a medical student, a little over 20 years ago in Melbourne Australia, our ECG machines used washable suction cups as electrodes. Actually, I see they are still made - http://www.diytrade.com/china/4/products/7681402/Multifunction_Suction_ECG_electrodes.html<br>I bet a lot of these have been thrown out, when they might have gone with the ecg machines to better homes.<br><br>If you cook the flour water mix, you'll need a lot less flour to get the same texture.<br><br>Great work!<br><br>Jennifer
creative idea now the issue where to get some pads is well ended!!!
Hello - This is a very nice solution and well documented. I had not thought about medical equipment from this perspective. <br><br>It sound like donated equipment needs to be &quot;de-Americanized&quot; for use without disposables. <br><br>I could also see where there maybe safety and proprietary features that are useful in the developed would, but would present a significant barrier to use elsewhere. <br><br>Is there ever an opportunity to modify the equipment before it is shipped off?<br><br>I also wanted to add that if you have disposable diapers, you can make electrode gel from the water absorbing crystals by removing them from the diaper and adding salt and water. One diaper will make a cup or so of gel. It is like ultrasound gel. <br><br>A disposable diaper with salt and water should work as an ES ground pad as well.<br><br>Of course, that is if you have disposable diapers.<br><br>I like the 'play-dough' solution better.<br><br><br>
Do you use new diapers, or can you cheat and use one that already has salt and water added to it? :)
Huh, hadn't thought of diaper crystals. Interesting, thanks!
This is absolutely brilliant, and a much needed alternative to massive use of disposable supplies. Thank you for sharing this excellent idea.<br> <br> Do you think the pads and conductive gel will work well for use with a wearable TENS unit for pain management? I could try making the pads bigger like mine, which are some sort of black conductive rubbery stuff, about 40 mm across. But the best gel I've been able to buy is usually only good for a few hours before it dries out and needs to be re-applied to the pads, and new skin tape.<br> <br> A long time ago I tried some self-stick conductive pads coated with a thick conductive gel made with (I think) agar. They were marketed for people with sensitive skin. They worked well, since I have trouble with the glue on skin tapes, and they lasted for several days of application, removal, and re-application, but they were disposable and quite expensive. Any ideas on how to make your pads &amp; gel self-stick? It could radically reduce the need for all the tape needed to keep the pads in place, especially if the gel doesn't dry out too fast without needing tape around the pads.<br> <br> I'm delighted to see this excellent and important contribution on Instructables! Thank you!
Haven't heard of DIY self-stick pads, yet, but we'd be interested to see it if someone has an idea. Thanks!
Nice method.&nbsp;A few hints on ECG pad usage though since I can imagine a few people here using these in their own experiments.<br> <br> After cleaning be sure to dry the skin.&nbsp;Ironic as it might be; Don't use wipes with alcohol at all since it may cause excessive drying of the skin. And go over the skin once or twice with a fine abrasive, just be sure it's clean and doesn't cause any skin damage. Fine sandpaper generally does well. All of the above is essentially what makes those &quot;ECG Prep Pads&quot; so special (and expensive).&nbsp;Especially the latter step might seem weird, but it reduces the skin contact resistance&nbsp;significantly.<br> <br> Also be sure to not leave the wire hanging if the person the pad is applied to is able to move. Movement causes a lot of noise. Attach the wire to the skin with some extra tape.
Great, thanks. These tips are a nice complement to the Instructable. We'll pass them on to our friends at EWH.
Cornstarch might work instead of flour. It's a very interesting Instructable. Thank-you for teaching me something.
I have used a thin layer of (liquid) honey very successfully, and find that it lasts for quite a while.
Is Borax 'slime' conductive? That might make a better gel than flour, although I can see how flour would be easier to get ahold of in the developing world.
Sometimes the soft drinks have a look under the cap contest where you can peel away the liner by hand. That'd make collecting the liners much easier.<br><br>There is also an abundance of scratched prepaid phone cards that are discarded in Africa everyday. Do you think they would make a suitable substrate?
Good tips. We'll suggest the phone card idea to EWH to see if they can use it. Those cards are all over the place, right?
Have you considered using rolled up condoms in lieu of the plastic liner in the bottle caps? They are significantly larger but they may serve equally well and avoid the need to boil the caps which could be a bit of an undertaking in certain parts of the world. Just a thought.<br> <br> Great post!&nbsp;
Interesting idea, thanks. We'll pass it on to the researchers at EWH.
Great work!! I can't wait to try this out.
you could save the world with this you need to tell someone!
Thanks, we're trying! We have this project as a solution in our Solutions Library: https://www.engineeringforchange.org/solution/library/view/detail/Health/S00058<br><br>And Engineering World Health is also trying to spread the word through training courses it offers in developing countries.
now... can these be used to detec nerves, and pulses and stuff like that?
They're part of ECG machines, which can detect electrical potential on the skin to measure heart rates and, indirectly, blood flow to the heart. New applications might require new machines that they link to. Thanks for your interest!

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