Question about pre-filling the Tandem reservoir

I travel - a lot. Just got back from Antarctica. Great trip. Here’s my question: Is there any problem with pre-filling several reservoirs ahead of time? It is much easier to fill them in the comfort of my home than when on the road. At home I normally fill 2-3 at one time and keep them available for changing them out, as needed, with no issues at all. When I have previously traveled (a lot, up to 2 weeks at one time) I have not had any issues. I have been on the Tandem system for almost 2 years. Since this trip was for 2 weeks in Antarctica, I took 3 times the supplies I might need, instead of just 2x, and that included (many) multiple filled reservoirs. It also included several plane flights (insulin ALWAYS stays on my person - never, ever in baggage of course), and of course, cruising the Drake Passage in high waves. Because this was surely the most active vacation I will ever take, I knew my BS would require high vigilance, which I gave it. And I knew it would rocket all over the place, which it did. But even with that, I had many unexplained highs and lows, that made absolutely no sense. I wonder if this kind of travel - or just the length of time the insulin was in the reservoirs (I know they will lose a small amount of effectiveness over time and I allowed for that) added to the crazy ups and downs.

Does anyone else pre-fill their reservoirs? Has anyone had an experience with this?

FYI: I am 63 years old, TI for 53 years, on a Dexcom sensor and CIQ Tandem pump.

PS- I know that Tandem does not recommend pre-filling, but there are a lot of things that are not necessarily recommended that we choose to do anyway.

I would really like to hear about your personal experiences.


My first pump was a Minimed 504, and I was told I could pre-fill; so I filled them and kept them on my fridge. I continued when I switched to Tandem - although at some point I did learn it was not recommended I never noticed any issues that I associated with doing so…It’s possible some of the “sweet mysteries of life” we deal with were due to it, but who knows.
I wonder if some of the foods, spices and cooking methods may be too blame for some odd your unexpected readings.
Welcome back!

Terri @TJC, I understand wanting to fill extra cartridges while you are relaxed - and not bouncing around on stormy waves. I only fill one to have ready when the one in my pump gets down to a day’s supply; although one time when traveling I did put enough insulin for two weeks in a cartridge.

The caution you might want to follow is what appears on the flyer packed with each vial of insulin, “, insulin in a cartridge / reservoir should be discarded after seven (7) days”. I presume this may be because of reaction with plastic.

First off- that is so cool that you got to go to Antarctica!!
For context I’m a 16 year old gal, T1D for 3 years, using Tandem for almost 2 years, and using about 40 u of insulin a day.
I pre fill my cartridges to the max (300u) and then when I get down to about 20 u I prefill the next cartridge, stick it in a baggie, and put it in my purse/backpack so I can easily swap them out when it’s time. It’s handy and saves time, $$, plastic, math, and annoyance. Often times my cartridge runs out at really unhelpful times, and I can never seem to figure out how much insulin will last me exactly 3 days without running out or wasting a bunch of insulin.

This summer when my family was traveling I’d fill several cartridges at a time and stick them in the fridge until I needed them. I noticed some more insulin resistance towards the 5-7 days out of the fridge, 10-14 days in the cartridge mark, but I was never quite sure if it was due to insulin degradation from the cartridge, heat, something I ate/did, stress, if my basals needed to be adjusted, or hormones. I’m guessing it was a combo of multiple factors. At home it usually lasts 7-10 days in the cartridge (out of the fridge) before I really notice any negative effects on my BG.

Good luck :slight_smile:

Dear Lise,

Thanks for your reply. Very much to what I experience.

Quick question for you: Why do you fill the cartridge with the full 300 units? I usually only use about 20 units per day, and I change out my insulin about 4 days (5 days max). I use less than 150 units in that time, so I only fill the cartridge to about +/- 200 units, otherwise I would be throwing away a lot of insulin. At 40 units/day, do you keep using the cartridge until it’s empty? More than 5 days? I have found the heat of wearing the pump on my body (I wear it in a front pants pocket or side yoga pant pocket) wears down the effectiveness. Just curious…

Thanks as always Dennis for your advise. I just wondered if some of the really unexplained crazy BS’s were due to the filled cartridges and not just the trip’s unique routine.

Thanks for your thoughts Dorie. I see others do some pre-filling as well. I always appreciate your advice and guidance.

Terri @TJC, you are welcome. If I had been on that adventure and used pre-filled cartridges, I probably would “blame” the adventure - the excitement and sampling different foods for which I need to guess at carbohydrates.

Like you, I also use about 20 units a day and follow the User Manual advice to always begin a new cartridge with at least 100 units [I put in 110 - 120 after purging air bubbles] and usually use the cartridge until empty or at least less than 4 units. I hate the thought of wasting insulin. I do change the infusion portion every three days and fill the cannula.

There isn’t any “rule” that says infusion set AND cartridge need be changed at the same time. It is interesting that Medtronic is currently on an advertising campaign marketing their new 10-day infusion and telling potential users that there isn’t any need to change the cartridge and infusion set together.

So this is very interesting. I also tend to change out the cartridge and infusion set separately as well. I do each when needed. Coming off Medtronic 2 years ago, where the cartridge is very easy to fill, I find the Tandems very un-user friendly. One, if I remove one and refill another - don’t get them mixed up! Can’t tell which is filled. Learned after one mistake of not knowing which was which and needing to throw both away. Two, the method for removing air and filling is very awkward! I can NEVER get all the air out of the syringe. This is why I fill the syringe with about 200 units, fill the cartridge with about +/- 180 units and stop when I get near the bottom of the syringe insulin. I probably waste about 20 units there, but want to be sure I don’t get any air in the cartridge. For a pump that is spectacular in so many way, this filling method is a head scratcher.

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Hi @TJC Terri,
I fill my cartridge with 250-300 units and then use it until there’s no more insulin- at 40 u per day that is about 6-8 days according to the calculator. I sometimes notice the insulin degrades around the 6-7day mark, but usually I run out of insulin around the same time so I haven’t really worried about it. I do notice that in the summer/when it’s above 75 degrees the insulin in my cartridge degrades a lot faster. I live in Washington state and it’s January so heat isn’t really an issue at the moment. I usually clip my pump to my waistband or stick it in a sweatshirt pocket so I haven’t noticed any degradation because of my body heat.
I guess I started filling it with 300 u partly because it’s the max my tandem cartridges will hold and because when I first started prefilling I was using humalog insulin pens, which come prefilled with 300 units. I didn’t like leaving 20-50 units in the pen and having to switch between pens each time I filled a cartridge (the little things that bug me :woman_facepalming:t3:) so I just started using all of the insulin in the pen when filling my cartridges. Now I use the standard 10 mL vials of humalog and that’s obviously different.
I still change my infusion set/tubing every 3 days so that also takes an extra 10-15 u off.

Ps- I’m not a very precise or detail-oriented person. Can you tell? :roll_eyes:

Haha yes tandem needs an easier way to fill cartridges. They’re really awkward! I usually end up with some air bubbles in my cartridge and occasionally have to pump a long thread of air bubbles out of my tubing. I’m trying to figure out how to eliminate that.

Before you start, make sure the needle is screwed firmly into the fill syringe “finger tight” but not excessive. When I started doing that it helped get rid of a lot of the air I was drawing in, although not necessarily all. For the rest, I intentionally draw some more air into the syringe, hold it upward so the air is at the top, and then tap the syringe so the little bubbles mix with the air, then push the plunger to send the air into the air or back in the bottle. When I was first trained in a pump my trainer said not to worry about tiny little “champagne bubbles.”
A session with your trainer or educator may help.

Thanks for the tips. I’ll try that the next time I fill a cartridge!
Haha I seem to have an extraordinary amount of champagne bubbles sometimes, especially on roadtrips when the elevation messes with my cartridge.

The champagne bubbles they referred to in training were little tiny ones - not large enough to take up space in the tubing.

Lise @6yGodsGr, a couple of tips to avoid champagne bubbles.

  • Never shake a vial of insulin - something I was told in the 1950s even with "suspension-style [NPH] insulin. If mixing is needed, roll the vial between hands.
  • Always push insulin into a vial when the vial is upright - never squirt air into insulin.
  • Follow the Tanden instructions and put the needle snugly onto the syringe and, then give another quarter turn.
  • As Dorie said, point the needle up, tap the syringe a couple of times and expel all air bubbles.
  • Hope for the best.

Lise, I like the way you think and find your own solutions, not afraid to find the nest diabetes management style for you.

Thanks for the tips and for the encouragement Dennis @Dennis and Dorie @wadawabbit. I’m still learning how to do all of the stuff that comes along with T1D.
I really admire you for your experience and determination to keep living life to the fullest with T1D. Thanks for setting a great example for me and the other younger members of “the club no one wants to be in”!

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I found that procedure so strange…and after a while I wondered…why not pull air out BEFORE filling with insulin to avoid getting air into the insulin filled syringe? So…i switched to pulling air out of the cartridge, then fill the syringe with insulin and inject the cartridge.
I have no idea what Tandem would say about it…but havent noticed any issues.

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Karen @T1Dx2, I have tried this method a couple of times and it appears to work - although I did have a couple of unexplained “highs”. The highs could have been because of my miscalculations for bolus so, I’m ready to do some more testing of this method.

Dennis…I would love to hear your feedback. I, admittedly, don’t spend as much thought on sugar variances as I should. So, maybe there are issues to this method, and I haven’t paid attn.

But, my logic doesnt see how it should matter. Why should it matter if air is taken out before putting insulin in the syringe? And, why would it be good to add air to a filled syringe, just to have to flick it back out?

Follow up with me! Would love to hear from you on this.

Katren @T1Dx2, I use the same logic as you just expressed. And it is one fewer steps.
I’ll do this next week and share what I learn.