High Blood Sugars

Filling a T:slim Cartridge: The Idiot’s Guide

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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.

Lesson Learned: Don’t Overfill Your t:slim Cartridges

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Update: If you are having insulin delivery issues with your t:slim, please refer to this more recent post which I hope may help. 

Yesterday morning after breakfast, after I could no longer ignore the vibrations coming from the needy insulin pump in my pocket, I swapped out the cartridge on my t:slim.

I slowly drew insulin from my penfill cartridge into the syringe, filling it all the way up to its 3ml capacity. After tapping and priming the air bubbles from my syringe, I stuck the needle into my black t:slim cartridge and began to slowly inject the insulin in.

As I tried to continue pushing that last bit of insulin from my syringe into the cartridge, I was met with a little resistance. The cartridge must have been nearing full.

I knew I should have stopped then and there. Except that I didn’t.

After pushing a little more in, I pulled the syringe out and slid the cartridge into place on my pump. I was feeling a little hesitant, but figured I’d be able to pick up on anything weird soon enough.

I had lunch a little later on, and found myself at 10.6 when I checked my blood sugar afterwards. Which felt plausible, given that I had also eaten ice cream with my lunch. I can never seem to bolus for ice cream quite right.

After some correction insulin, a walk and nothing more than a coffee that afternoon, I was still lingering around the 10 mark.

After loads of corrections that evening, I don’t know why I didn’t just replace my insulin cartridge before I went to bed.

I guess a part of me was seeing the 200+ units of insulin in the pump, and didn’t want to be wasteful by throwing it away if there was actually nothing wrong.

After a full correction at bedtime that had little effect by the time I woke up at 5.30am this morning, I hauled myself out of bed and made a dash to the fridge. I swapped out my cartridge for a fresh one, this time only filling to around the 2ml mark on my syringe.

Yes, Frank was told to put less insulin into his cartridges when he got set up on his t:slim a few weeks ago. But Frank also didn’t like to be wasteful and wanted to get his money’s worth from the cartridges that he paid for with his hard earned money. Frank also doesn’t like not being able to reuse these cartridges like could with his Animas pump.

Anyhow, lesson learned.

Don’t overfill your t:slim cartridges. It just feels like your insulin isn’t working.