To insert or to applicate?

Here’s today’s CGM Primer: “Does it hurt[to put in a CGM sensor]? Hmmm . . . sometimes. I guess it depends on your pain threshold. It’s not like having bamboo shoots shoved under your fingernails . . . well, actually I don’t know that because, lucky for me, I’ve never had bamboo shoots shoved under my fingernails. But I don’t think that putting in a CGM sensor is torture by any means, and it only happens about once per week in any event. Also, any insertion pain you may experience dissolves after the guide needle is removed (seconds after insertion). The actual wearing of a properly placed sensor is absolutely painless.”

---- Excerpted from Beyond Fingersticks: The Art of Control with Continuous Glucose Monitoring, with permission of the author.

The change is there is no change. Not to the naked eye, anyway. I’m sure if you had an electron microscope and a mass spectrometer you could see the difference. But to look at them, you can’t tell the difference between the Dexcom Seven Plus sensor and applicator and the Dexcom G4 sensor and applicator. Look for yourself. Can you tell the difference?

The only difference is under the hood. They are the same car, but the G4 is turbo charged in the accuracy department. At least that’s what Dex claims. I’ll need to experience that for myself to “certify” it. And you’ve got a front-row seat to the process.

But backing up, just what the hell is a sensor applicator in the first place, you ask? Personally, I don’t like the word applicator. It sounds too much like a feminine hygiene product for my chromosomal comfort. To me it’s an insertion device… But come to think of it, that sounds vaguely like something that belongs in an S&M dungeon—so clearly we need a better name for these things that are the tools to help you place a sensor under your skin.

Until I come up with something better, we’ll call it: The sensor thingy. And why do we need a sensor thingy at all?

Well, sensors are just high-tech fish line soaked in enzymes. They require a firm guide needle to help slip them through the skin and get where they belong: In the fat layer between your skin and your muscle, the same place insulin goes. Sensors don’t actually read the sugar in blood, they estimate blood sugar by proxy, looking instead to interstitial fluid. We’ll talk more about that on another day.

Anyway, the guide needle is removed as soon as it places the sensor, and only the flexible sensor stays behind. For any of you pumpers out there, it’s the same process as putting in an insulin pump infusion set, except the needle is bigger.

The Dex sensor thingy looks like the dental tool from hell. Or a high-tech space age torture device. I bet if Darth Vader had come into Princess Leia’s cell with a Dexcom sensor applicator she would’a spilled the beans on the location of the hidden rebel base in two seconds.

But appearances are deceiving in this case. Because while it looks frightening, and while the Dex thingy won’t win any awards for ease of use (I once heard that using it takes eleven steps, but I haven’t counted them), it does its job pretty well. Once you get the hang of it, it’s simple and generally painless. I remember I spent a lot of time trying to make sense of the first one I ever did. I pored over the manual for hours, studying the pictures and trying to figure out how the hell to use it. Once I did it, it made sense. But if you’ve never done one, I urge you to search for a YouTube video first.

If you’ve been using the current Dex sensors, nothing changes. The thingy looks, works and acts the same as the ones you’ve been using. You just need to keep your shit together so you don’t confuse your old stock with your new stock. The two look so much alike that you could. Reminder: Seven Plus sensors won’t work on a G4.

My receiver hasn’t been plugged in for the full five hours yet, but I’ve got a big, fat, battery icon glowing solid green, so I decide it’s time to get this show on the road. I slip the receiver into my pants pocket, fish a new G4 sensor out of the box, and head into the main clinic.

I swing past the nurse’s station and into the lab. I grab an alcohol pad, and sensor in hand, slip into the unisex bathroom (the one my boss mistakenly called a “bi-sexual” bathroom when the men’s room was converted into an office for the I.T. guy—we are rather short on space—and the women’s room became a staff bathroom).

I pull off my shirt and drape it over the paper towel holder, rip open the alcohol pad, and swab my arm down. An email yesterday gave me a head’s up that the G-4 was on its way, so this morning in the shower I ran a Quarto over the top of my upper arm to clear off any hair that might get in the way.

While the alcohol evaporates (and for God’s sake don’t blow on it—it defeats the purpose to blow germs all over skin you just cleaned), I open the sensor sack. You pull the two halves apart, just like opening a snack-sized bag of Nacho Cheese Doritos. A $75 bag of Doritos.

I pull the sensor thingy out. At the base of the sensor is a sticky pad that holds the transmitter cradle (“sensor pod” in Dexspeak) on your skin. It’s covered with two pieces of slick paper backing that never want to come off. They stress me out every week because one week, years ago, the sticky pad folded over and stuck to itself like super glue. I was not able to untangle it successfully and I lost a sensor. Talk about being kicked in the checkbook.

With slightly shaking hands, and with a limited number of new sensors adding to the stress, I pull one half of the backing slightly loose, then the other half partly off. Finally I strip both off, being careful not to fold the pad, steady the applicator above my arm, then plant it firmly downward onto my skin.

I let go of the applicator and smooth the sticky pad onto my skin with my fingertip. The handle of the applicator rocks back and forth like a dog wagging its tail. I pull the safety lever out and chuck it in the trash (you are supposed to save it to help you remove the transmitter later, but I have a different trick for that I’ll teach you another day). The bomb is armed.

Now, I’ve got skinny arms. I could ask one of the nurses to help me, but being half-naked in the “bisexual” bathroom with a nurse will make people talk, and my life is already complicated enough as it is. Gripping the applicator like a cigar, with my fingers upstream from the collar and my thumb on the white button at the top, I lean against the towel holder mounted on the wall next to the sink, squeezing my bicep between my chest and the cold plastic to “pinch up” some skin. I ram the inserter button down. It stings. A little. Keeping my thumb on the base of the handle, I slip my index and middle fingers over the collar and pull it back towards my thumb. The guide needle retracts back out of my body, leaving only the sensor behind. The stinging drops in volume.

Next I squeeze the clips at the base of the handle (“applicator barrel” in Dexspeak) to remove it. It comes out easily. Excalibur from the stone. I chuck it across the room at the trash can and miss. It ricochets off the wall and falls to the floor with a clatter.

I take the grey transmitter, smooth and aerodynamic, unlike its oddly angular predecessor, and click its nose into the top of the sensor hub, then using the tab at the base as a lever, force the transmitter down into its carriage with a satisfying Click-Click. I twist the handle to break it off. Done and ready. Now that the new transmitter is on my body, I can see that it rises quite a ways higher off of the skin than the old one did. Like maybe twice as high. It’s noticeable to me, although I can’t say yet if it will be annoying.

The new transmitter’s shelf life, at six months, is only half that of the original, but it’s bigger. That seems ass-backwards to me. Or should I say bass-ackwards? Hmmmm… could this be for future capabilities? Dex has stated that they hope move the “brains” of the CGM system from the receiver to the transmitter in the future. What’s the benefit of a thinking transmitter? Well, if all the FDA-approved mathematics happens right on your skin, the data could be transmitted to just about anything. Like a smart phone.

Oh. Wait. Never mind. I bet I know what it is. The old Dex had a very limited transmission range, even line-of-site on a clear, calm day, much less in the real world. It wasn’t as bad as the Other Guys, but I always made sure to wear my Dex receiver on the same side of my body as the sensor and transmitter. Now we’re supposed to have a range of something like 20 feet or more. No doubt the beefier transmitter is what had to be done to boost the signal. I’ll have to design a clever science experiment to test the real-world range.

A project for another day.

I flex my arm and rub it gently. Still achy. Bad luck no doubt. Some insertions hurt more than others. I don’t think the new sensors will necessarily be more painful just because this one was.

Hey, why the arm, you ask? Not in the tummy, like you are “supposed” to? Well, I’ve been wearing CGMs for 8 years. And looking at downloads of other people’s for 6 years—more and more over the last few years. And I’ve noticed that stomach sets have more jagged sensor trace lines. In fact, I can look at a sensor trace and predict with pretty good accuracy where on the body the sensor is worn. My personal theory to explain this is that sensors in the midriff get “jostled” around more as we move through our days, standing, sitting, turning, getting in and out of cars. I think this creates “static” that shows up like little earth-quake lines on the CGM traces. Arm and leg sets give smoother downloads. It’s that simple to me.

I pull the receiver from my pocket, navigate to the “start sensor” screen and boot up the new sensor. On the home screen, a little slice of green pie shows up. The countdown has begun.

Now I have to wait two hours. The sensor needs to soak in my tissues. The insertion site needs to settle down. It’s called the warm up period. I call it the fear factor period. Yeah, it’s only two hours once per week, but I’m naked in a swamp full of alligators during this time. Being totally hypo unaware, this is my most vulnerable time. I usually burn through more than a few test strips during new sensor warm up. But today Old Dex is still watching over me. I can relax. I’m bristling with sensors. Well, OK. I guess two sensors doesn’t qualify for a bristle…

As the countdown nears its end, the pie is supposed to become two pieces, then three, then four, then six. When it’s a full green circle, it’ll be time to rock and roll.

But in the meantime, I have work to do… my next patient is waiting…