Filling a T:slim Cartridge: The Idiot’s Guide
I must say that one of my ongoing issues with the t:slim has been filling those little pesky black insulin cartridges.
The empty cartridges still have some residual air trapped in them, which needs to be drawn out with your syringe prior to filling with insulin. I know from experience that when I haven’t properly drawn air out of the cartridge, my blood sugars run high and insulin delivery from my pump has been compromised.
I’ve had several moments over the past few months where correction after correction hasn’t been able to tame my blood sugars. There have even been some moments where I wake up high at 3am and in a ‘lightbulb’ moment realise that my cartridge needs to be replaced. Of course, I know I that I won’t be able to lay still until the problem has been fixed.
To my understanding, the empty black cartridges have two components: the chamber at the top of the cartridge which you can see, and an invisible plastic bag inside the cartridge where insulin is stored. When I caught up with the friendly team at AMSL Diabetes in March, I was shown a demo cartridge where I could see that the plastic bag inside was vacuum sealed. So no air in there. Which meant that the air that needed to be released was actually trapped inside the chamber at the top of the cartridge.
With credit to the T:slim Users Australia and New Zealand Facebook group, I’ve learned to fill my syringe with 50-100 units of insulin, draw the air out of the cartridge and then top up the syringe with additional insulin as desired. It’s far easier to withdraw air with an emptier syringe than a full one. I’ve also tried drawing air using a completely empty syringe, but I’m a bit paranoid and prefer to actually see the air bubbles come out.
Which brings me to my next dilemma. Last week I must have wasted at least half an hour drawing seemingly endless air bubbles from my syringe, leaving me feeling downright paranoid and wondering what I was doing wrong.
After a chat with the team at AMSL Diabetes, I’ve been told that it’s not possible to draw all of the air out of the cartridge, and that one pull of the syringe and a few big air bubbles is sufficient. I’d also add, with credit again to the t:slim Facebook group, to make sure that the needle on your syringe is screwed on tightly enough.
If you look closely at the cartridge on the right, you’ll see a fair few air bubbles in the chamber at the top. I replaced that cartridge at around 3am a couple of weeks ago after it was causing untame-able high blood sugars. Perhaps this is also a result of me over-drawing air from the cartridge. Sometimes I like to settle my paranoia by simply popping off a loaded cartridge just to confirm that there’s no signs of air.
I don’t like having to babysit my diabetes devices, when I already have my blood sugars to babysit all day every day. So I’m crossing my fingers and toes that this is the last of my issues with filling these cartridges. Because I really do love this pump.
Updated 7/10/19: One pull has been working perfectly. Overdrawing air from the cartridge only compromises insulin delivery from the pump. Same goes for refilling cartridges with insulin more than once or twice. As I’m filling my tubing, I also like to keep an eye on the nobbly bit for any air bubbles that sometimes get trapped there. Holding the knobbly bit upright while I’m filling my tubing, I sometimes give it a few little taps so that any air bubbles rise to the top and pass through the knobbly bit and out through my pump line.