Perfect photo!
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resurrecting this discussion as I just had a long conversation with Tandem technical support (Mariel) who told me that I should do a “wet purge” when getting my new cartridge ready to take insulin. This is as opposed to the “dry purge” that I had been taught.
The dry purge goes like this (and it was discussed further up in this post): before I put insulin in the syringe, I put the tip of the needle into the white reservoir gate hole in the cartridge and draw out any air that may have found its way into the cartridge. The problem with this, according to Mariel, is that you may over-draw the balloon, creating too much of a vacuum in the cartridge, and this can contribute to problems with filling.
The wet purge goes like this: first put insulin in the syringe. Then put the needle into the reservoir gate - this allows you to see how much air you are drawing out of the cartridge (you can still overdraw, but you have more indications not to).
Anyway, I thought of this thread and thought I’d let you all know about this, as this “wet purge” was not the way I was taught 5 years ago. I was taught the ‘dry purge,’ and I have been having occasional difficulties in getting insulin into the cartridge. Maybe this will solve those…
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This is what was taught in January. I guess Tandem has learned a better way.
Thanks @psfud123 for bringing this discussion back up. I have been wondering about a related but different question:
- How much should we care about bubbles anwyay?
Does it matter if there are a few air bubbles in your tubing?
As you probably all know by now, I am a sceptic - I’d maintain that, while of course you want to get out as many air bubbles as possible, there’s no reason to worry about bubbles in your tubing.
No one has told me this, but my evidence would be the filling of the cannula after insertion. There are about .3 ml of air that are displaced into your interstitial fluid when you fill the cannula at the end of the cartridge change process. So if that’s okay, then why should we be concerned about a few bubbles in the tubing?
It’s not that the air is harmful to you, it’s that the air isn’t insulin, but any closed-loop software will think it gave you insulin that you didn’t actually receive. Watching the tube fill process, I think I decided that 1" of bubble in the tubing was around 1u of insulin. Don’t know if that’s actually right, but it gives some idea of how much bubble would be required to matter. They say the so-called “champagne bubbles” are small enough not to matter. But the collection of bubbles in the photo in the original post might add up to some decent fraction of a unit, which could have an effect.
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