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
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]