Dexcom insight

The past few days have been rough going with Samson’s sensor. Last night he read 109, finger prick showed 167 and 177. Then, throughout the night he was hovering in the 50s… and finger prick showed 80 or 75. Before that, the sensor was really noisy for a few days and the calibrations were also off. Yesterday evening, he was drifting slowly down when all of a sudden he went from 91 to Low one arrow down, then jumping up to 72, then down to 67, then up to 80, etc.


Well, it’s just a hypothesis of course, but we think we have an explanation. We do what we call the hot swap for his sensor – we insert a sensor about a day before, but don’t switch the transmitter. This allows us to avoid the noisy, jittery readings of the first 24 hours usually. But that means there is a 12 to 24 hour period where the new sensor is attached to his body but bare, with no transmitter on it.

Normally we just swap it without a bath, but this time Samson took a bath prior to the swap…and it’s been noisy since. Mitch looked and found moisture underneath. He dried it and the noisiness improved. But the amount it’s off is still pretty bad. The other time we had an abject sensor failure on startup, we had done a sensor insertion, hadn’t put in the transmitter, and then Samson went swimming at the beach. So we think the bare sensor connection just doesn’t like water, and that the transmitter acts like a seal to keep it out.

So, my tentative suggestion: Keep the bare sensor away from moisture if you want to get good readings.

My possible solution is to hang onto the dead transmitters and then just plug one of the dead ones into the new sensor sites until you’re reading to swap in the functioning transmitter. They may not send bluetooth but presumably they’re just as watertight after 6 months or a year.


@TiaG, nice sleuthing job!

When we “hot swap,” we do just what you describe: we keep all of our dead transmitters anyway (in case we want to swap batteries later), and use one on the new sensor until ready for the swap.

We do still occasionally get noisy sensors. Where there is the least amount of fat is often where we get the noisiest sensors (although that is not always true: we have a belly sensor right now that started its life a bit noisy, for instance).

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A couple questions since haven’t “hot swapped” yet.

  1. What is the advantage of the hot swap? You mentioned “noise” for the first 24 hours, but I’m unsure what noise you’re referring too because, once we change Liams sensor/Transmitter out, the readings don’t skip readings or anything like that for usually around 14 days.

  2. I’ve heard of something like this being done while also eliminating the “2 hour” warm up period? How does that work?

  3. Does the sensor ever get hung or snagged? The inside of that sensor has a small jiggly part that moves around…I’d be afraid of that getting stuck or snagged?

  4. Our readings are off quite often but I’ve got a feeling it’s the Skin-Tac that we use that I plan on NOT USING for an upcoming change-out (at least where the cannula gets inserted) to test the accuracy difference.

Great insights! I may try hot-swaps in the future if it makes sense. I’m just trying to rationalize the “upside” to doing it.

  1. We do the hot swap because the first day of readings are typically off by about 60 to 70 points sometimes. And even when calibrations are relatively accurate, the readings are “noisy.” So for instance, in the first 24 hours the readings will wander up and down: 67, 72, 95, 78, 82. You’ll see what I call “triplets” where one of the readings is way higher or lower than the two on either side, then the sensor will randomly drop back into the overall trend line. Sometimes the directional arrows may not show up (it may be the sideways arrow with cross-hatching).
    I’ve attached a picture so you can see what I mean. You’ll see the triplets: the st of three dots where one is occasionally way out of line, and then the next reading will be close to the overall trend. That lowest yellow dot, for instance, is likely some sensor reading glitch:

Our artificial pancreas is continually dosing insulin off Dexcom and the teachers at school also treat lows off Dexcom’s directional arrows and don’t see every reading, so eliminating this kind of uncertainty is important. Also, our son goes to school. To ride the sensors till their last days means an increasing risk we’ll get the dreaded ??? when he’s at school. That means I have to take him home, he’ll likely have no readings for several hours, and my work day is finished. If we do the hot swap once we start seeing either noisy data, data that wanders, or ???, we know that if the sensor fails at school, I can just swap out the transmitter, start the two hour warm-up period and check him once an hour until the restart. So it reduces the risk of my workday being totally wiped out.

If you’re not dosing off Dexcom and if you don’t rely as much on the directional arrows, but rather the absolute numerical change, or if you’re swapping the sensors out the moment they’re a little wonky, I think it’s less of an advantage.

  1. With normal operation, you can get the warmup readings but only when the 2-hour warmup period coincides with when you’re going to replace the transmitter…so the old transmitter hasn’t expired yet but you activate the new one and you’re using both on both arms. I think you also need two separate phones for pairing, although I can’t remember as it’s been 3 months since we last did it. It’s not really useful for the weekly or biweekly change out though. I think xdrip+ does allow you to read the warmup readings though anytime…not sure if you ever successfully got it set up?

  2. yes, it’s possible Skin-Tac is throwing off your readings if you’re putting it on Liam’s arm before doing the sensor insertion. If you’re going to put adhesive on, I’d put it on over the secondary patch you put on— so if you use a GrifGrip, put the skin tac liquid over that, just around the edges, not near the sensor insertion site.

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I actually HAVE seen these bogus readings myself. In fact, just last night he was heading downward from 100 very slowly, he hit 80, then suddenly a 45 reading! I was like wt…!!! So I checked his sugars quickly and he was 77. The next tick on the Dex read 75…and then it followed the correct trajectory after that. I hadn’t really connected the dots here, but we DID just change his out the day before yesterday so it makes sense. These bogus readings do clear up the longer it’s on his arm.

So just to be sure I understand the benefit of hot-swapping…by installing the sensor the day before you plan on changing out the transmitter it does what? Eliminates that noise? And if so, how? Does this have something to do with the cannula inserted under the skin getting situated or something?

@ClaudnDaye, yes it’s precisely that the cannula when inserted causes local, transient damage in the tissue, and so the interstitial milieu needs time to settle and heal to get optimal readings. At least, that’s my understanding. So the first 24 hours of readings are jumpy because of that local inflammation or damage, and then it gradually dissipates. By the time you’re actually using the sensor’s readings, the sensor should have had plenty of time to get well settled. It also helps if you get a “bleeder” – those do work and are actually quite accurate eventually (IME), but they need a few days for the wound to heal. The other obvious downside – apart from having to wear two sensors at once – is that you are reducing the life of one of the sensors because the first day of readings you’re not using.

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Yes it does. With xDrip+ I let the new sensor “soak” for a few hours (what you call hot swap I think). Then when I place the transmitter on the new sensor it is already warmed up, and xDrip+ will ask for a double finger stick in about ten minutes.

In that 10 minute window I get readings on my watch, which is used as the collector, or receiver. The first reading is always >300, but it settles down immediately. Obviously, you can’t get these readings on the phone that’s in warm-up, you need another device to receive the transmitter signals.

@TiaG I Also recall somewhere in the Dexcom documentation that the sensor by itself is not waterproof. I think that was in the Dexcom 7 or 7+ documentation, when the sensor-transmitter was first claimed to be waterproof.

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Have you had any issues with my #3 question? With the sensor getting snagged w/o the transmitter being there?

yes, but we remove the tab and then it’s not a problem. You can still insert the transmitter without the tab.

perfect, thanks! That’s the info I was looking for.

TBC – you are not supposed to have the sensor exposed without a dead transmitter on it. It is looking for trouble. Everyone I know inserts a dead transmitter when they hot swap.

Are you sure it wasn’t a compression low? It happens often with my son at night.[quote=“ClaudnDaye, post:3, topic:946”]
I’ve got a feeling it’s the Skin-Tac that we use that I plan on NOT USING for an upcoming change-out (at least where the cannula gets inserted)
Harold, we use SkinTac all the time, but never where the sensor gets inserted. After we have cleaned the skin with alcohol and the alcohol is dry, we make a little circle, about 1/2" diameter, with a pen, then coat the skin around the circle with SkinTac multiple times. Having SkinTac at the insertion point is not recommended (although I did not do any testing to prove that, but that’s what Dexcom says).

@TiaG So you put on a new sensor while the old one is still on in anticipation of a site change? Also, what about the loose part of the sensor with the two little rubber nubs that the transmitter locks into place? I would assume the dead transmitter is used for that reason plus the waterproof piece?

I have a couple dead transmitters if you want me to send them to you for hot swapping.

Okay, I don’t think @TiaG does it for Samson that’s why I was asking. We have dead transmitters so it wouldn’t be an issue! [quote=“Michel, post:12, topic:946”]
Are you sure it wasn’t a compression low? It happens often with my son at night.

No, I’m not sure what it was. I don’t recall which side he was sleeping on. I guess it could have been either, but strange that it corrected itself without him re-positioning his body, though.

Yes, I remember you saying this in an earlier thread. We tried this also, but my circle I guess was too small, and my eyes were too bad because, after we took off the CGM, we noticed I “missed the mark” and it was still inserted outside the circle. I guess I need to just make my circle a bit bigger. Will do that with the POD and the CGM for future changeouts to see the difference. Since I have NEVER had issues with using Skin-Tac right on the insertion spot, I’ve just always done it. However, if NOT putting skin-tac on the insertion spot yields even better results then it’s a win-win.

Just thought about something…how the heck can you use a “dead transmitter” as a placeholder on a new sensor pod??? To do this you have to use the ONE USE lever to snap it down…or is this just a false assumption on my part? Is that lever NOT a one use lever? I’ve always just turned and pulled it off after making sure the transmitter was snapped into place. Do you just not remove that lever and pull it back when you want to remove the old transmitter and install the new one?

Getting the old transmitter off wouldn’t be an issue (using the tool that comes with the Sensor pod), it’s getting the GOOD transmitter snapped back on after removing the dead one that I would think would be an issue? Unless that lever arm is supposed to stay on…and if that’s the case, I would think that lever arm would cause snag issues?

This sounds like a great area for a tutorial, or walk-through guide including do’s and don’t do’s! :smiley:

Yes, so I think basically what we were doing was exposing the sensor in a way we weren’t supposed to. It always seemed to work pretty well in the past so we did it. But to clarify, what @Michel is saying is absolutely right; we should have been using a dead transmitter as a placeholder the entire time. We just never did and mostly got away with it.

@mikep, thanks for the offer! I’ll check with my husband to see if we have any dead transmitters still. I think we have at least one but I’m not positive.

Anyone able to answer this for me?

You can snap them in place with no lever. You just sort of shimmy it into place and push down till you hear the soft click. Wish I could describe the process better… But, you can snap a transmitter on and off as much as you want even after the initial placement(well, I haven’t tried doing it like 100 times, but Samson has certainly accidentally snagged his active transmitter on his shirt and dislodged it, which required it being snapped back on. When that happens you have to restart the 2-hour warmup period but otherwise it all works fine).

There is quite a bit of pressure required to get it to snap into place…even with the lever. I’m not sure how comfortable this would be (or how much it would hurt him, or even cause a disruption to the cannula) for the amount of force required to get the transmitter to snap back down onto the sensor pod. Am I just overthinking? I just don’t recall a single instance of pushing the transmitter down onto the sensor base that it was didn’t require quite a bit of pressure (from the lever pressing it downward).