Filling an X2 Insulin Cartridge

Back in the early T-Slim days the method promoted to fill a cartridge was to pierce the white dot with the syringe/needle then pull back on the plunger creating negative pressure in the bag prior to filling the syringe with insulin and injecting it into the cartridge. Somewhere along the way Tandem changed the preferred method to injecting insulin into the bag, then withdrawing it into the syringe, identifying any bubbles in the syringe and pushing them out before again refilling the cartridge. I’m a fan of the first method but am left wondering why they made this change. Any answers out there?

Where did you hear that? When I just googled “Tandem tslim cartridge change” I got this PDF from Tandem’s site. It’s also in this video (taken directly from the site) to retract the plunger.

I still do it that way. No issues.

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Yes, you are right and the video shows the current technique. But years ago they promoted a different technique as described above. Does anyone else still use the older setup instructions? I find it easier as I fill the cartridge with 300 units of insulin (4 days) and when the syringe is filled to 300 there isn’t a lot of room to pull back looking for bubbles as the new technique instructs.

I’ve been using Tandem for over 5 years and have always done it this way, so I am not sure what other way there is! :wink:

Yeah, I’m old and go back to Tandem pumping since 2014.

I’ve been pumping since 1997, but I used Medtronic for most of that. Tandem has been wonderful.

I believe the change to putting some insulin into the syringe before extracting air from the cartridge was because one can actually see the air bubbles come up through the insulin. Otherwise, with no insulin (or any other liquid) in the syringe, one cannot actually see when there are no more air bubbles being extracted.

I just switched to Tandem from Medtronic last April. The way it was explained to me was to fill the syringe, do the thing of pulling the air out, then remove the syringe, tap the barrel and push the air out, then re-insert it and fill the cartridge. There are YouTubes demonstrating it this way. But I think tapping the bubble out is redundant—not to mention a royal PITA—so I just suck the air out and then push the insulin in. I guess the point was to be sure you don’t end up pushing air back into the reservoir, but I just do it with a brightly lit background so I can see when the bubble approaches the tip and then I pull it out.

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I’m a creature of habit and the very first way I was taught has stuck. But it’s very different from what’s done now. I start by taking the empty syringe with needle in place, piercing the diaphram in the cartridge, pulling back a couple of cc’s, then removing the syringe with the vacuum in place. I then fill the syringe and inject the insulin and I’m good to go. I watch when I do the initial fill (with cartridge upright) and never see more than a microscopic bubble in the line. I’m mostly curious why they would have made this switch in technique at some point. Is creating that suction too hard on the bladder? I’ve done it both the old and new way and the old way is much easier. For me.

It’s changed at least 2 other times, too. The TLDR version is that people complained and it was their idea of a solution.

When I first started, you didn’t have to remove the bubble at all. It got pushed out when you primed the tubing. But before there was any automation, the biggest complaint about the T:slim was how different the cartridge was from other reservoirs and how long it took to prime the tubing. They added the complicated suck the bubble out step, so you weren’t spending priming time pumping more air than necessary. Your were now supposed to insert a loaded syringe into the cartridge, and then pull back on the plunger, letting the air bubble float up the top of the insulin. Give it a few flicks to make sure all the bubbles get up there. Then inject the insulin into the cartridge. You can see the bubble. You were supposed to stop pushing right before you injected the air back into the cartridge, but in all these years it’s never been an issue. That air bubble PERFECTLY fills up the empty space in the needle’s luer lock connection. Just when it’s time to stop pushing the plunger, you discover it’s fully seated and you couldn’t have injected it even if your wanted it.

It might sound complicated, but it was a tiny change from the original process. Just added a “pull back the plunger and flick” step to the original instructions. I still do it that way. I don’t know where all this hokey pokey (stick the needle in, pull the needle out, stick the needle in and push it all out) nonsense came from.



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@Robyn_H Thanks for that background. I tend to assume that any changes to medical practice follows evidence-based research. But not always, I guess. Anyhow, I’ve not had any problems that I know of with my ancient technique so I’ll stick with it for now. Thanks, all, for sharing what works for you.

I use the more recent version with a twist. I’ve noticed that after releasing the tension and the plunger and letting fluid go into the cartridge if I pull back the plunger a second time, nearly always another bubble comes out.

During decades of using syringes with my insulin and other injectibles, I learned that adding slightly less air than the fluid volume withdrawn reduced bubbles in the syringe, so using the same principle in reverse to fill a flexible reservior made sense to me.

I think when I started with the X2, it was with a DexCom G4. I started with their prescribed method, filling the syringe with insulin to 3cc after getting rid of bubbles, putting the needle into the cartridge pointing down, draw the plunger back, let the bubbles float up, then fill the cartridge.

I changed it, I don’t know how many years ago. Now I insert an empty syringe, draw the plunger all the way back and remove the syringe. Then I fill it with insulin, chase out the bubbles, and push it to 3 cc. Then I fill the cartridge, pushing the plunger all the way down.

I wasn’t aware Tandem changed the fill method. I’ll stick with what I’m doing now.

This is how I was trained 30 months ago when I got my Tandem pump. Been doing it this way with no issues.