Prevent insulin pump cartridge bubbles


Bubbles form when the dissolved air comes out of the insulin solution (outgasses). That will happen if the air pressure above the insulin decreases, or the insulin temperature increases.

When you fill a cartridge you’re instructed to let the vial reach room temperature before starting the filling process. The extra dissolved gas in the insulin will come out in the vial as the insulin warms. If you fill a cartridge with insulin below room temperature the dissolved gas will come out in the cartridge as the insulin warms up.

The remaining issue is any pressure changes in the air above the insulin. When you inject air into the vial before pulling the insulin out, the pressure above the insulin increases and more air will dissolve. When you withdraw the insulin the pressure will decrease and the dissolved air will come out of solution.

The temperature is the most important. As a practical matter injecting the air doesn’t result in a big pressure change and if you withdraw the insulin immediately after injecting the air, there’s not much time for the air to dissolve and diffuse through all the insulin.

Bubbles can also form via leaks in the system and the pump designs vary from one manufacturer to another so this might not be universal. My experience is with Disetronic (Roche) and Animas pumps. I just starting using a Tslim:x2 and it may have it’s own issues because the pumping system is so different.

I don’t think there’s anything wrong with what’s shown in the video. If it works for you - keep going!! But I would pay attention to the temperature first. I suspect during the time spent removing air from the vial the temperature equilibrates as well so it may be killing two birds with one stone. Also, degassing the insulin as they do in this video will probably make bubble formation due to any temerature increases as you wear the pump less likely (a very hot day or wearing the pump very close to your body).

If I sound like a geek it’s because I designed micro pumps for analytical chemistry instruments. Not the same as some insulin pumps, but the principles and problems with bubbles are the same.


Thanks for this, @Paytone. What you write makes sense. I filled my second cartridge using the degassing technique and haven’t had any bubbles in either cartridge.

I was aware of the importance of using a room-temperature insulin vial to fill the cartridge and that’s been my standard practice.

It’s just strange to me that I’ve gone a long time without bubbles and all of a sudden they occur in 2-3 consecutive fills. I also have experience with cartridge cracks leaking air; that’s only happened to me a couple of times in 32 years.

Thanks for bringing your helpful expertise to comment in this thread!


I only have my experience but I am convinced that the bubbles started for me after Medtronic switched to a different company to make the cartridges. I never had bubbles from 2000 until 2+ years ago whenever the switch occurred.
It is, in my view, the black rubber band inside that is not snug inside the plastic cartridge. I see bubbles entering there all the time as I adjust the plunger. And I do know how to do the procedure. I can have a totally bubble free cartridge and tubing to start, with effort, but have lots of bubbles by day two and many more at finish. It is a poor quality cartridge. It did not used to allow air bubbles of some size to enter… Again, my two cents.


Hmmm… I can’t tell when my current 1.8 ml reservoirs were manufactured, but the expiration is 9/30/21. I’ve had no issues with them being any different than what I’ve used for many years. The best way to reduce air entering is to take at least 13 seconds to draw back the plunger. Before I draw back, I push the plunger really HARD against it’s stop, so there is the least amount of air possible. Then I draw back SLOWLY until it’s full, tap a few times and gently push maybe 20u back into the vial (usually I’ll see tiny “champagne” bubble go into the vial), and then slowly refill the amount that I’d injected into the vial, so that the reservoir is once again full. Works for me. I get no bubble in the tubing during my 3-day wear. there are other “tricks” that I do but that’s a description of how I fill the reservoir.


There is a thread on another forum (could not recall if this one or the other one but probably the other) about the change in tubing and cartridge. And, as a veteran user, I do pull back slowly when filling. Champaigne bubbles, yes. But I see bigger bubbles form & enter from the rubber band area. This should not happen.
I make sure the plunger is as tight as it can be and still operate. And am as slow as possible. It also happens during the days of use, not just at insertion. As noted, I get the cartridge and tubing clear of bubbles finally, before insertion, a crazy long process, but at the next change time, there are ridiculous numbers of medium sized bubbles accumulated near the end. Sorry, but there really is, in my view, something not quite snug enough in the last couple years. Your mileage may vary!
I use Quick-set and current supply good till 1/21 also.


I spend about 2-1/2 minutes for my set changes, so I don’t think it’s “crazy long” here. If I do switch to the Tandem pump I have a feeling set changes are going to be far, far longer.


I always use pencils to fill out the reservoirs. Then only the air in the needle will be pulled down in the reservoir and will be pulled back when I emptied the penfill.
This is in my opinion the easiest way to fill the reservoirs, nothing to do with air in vials and pulling back.

Because with the penfiles I push with a pencil the rubber down, so the insulin automatically will go into the reservoir (with the plunger completely on “empty” ).

I also think the insulin in the vials will last too long and insulin will work not that good anymore in the last bit of insulin in the vial.

With pencils you always have fresh insulin.

Maybe this helps?


I’ve never worried to much about air bubbles, only occasionally see any in tubing, I do take my time and fill back and forth a couple of times. Do notice that if I don’t pull plunger perfectly strait I get champagne bubbles. I also draw the insulin back into the resivor from the tubing when I change out reservoirs and use to fill new before installing new reservoir. I see people talking about fresh insulin, from mid days I could keep insulin out once opened for 30+ days. Don’t get but 4-5 out of 300ml cartridge so I feel that’s a non issue. But probably wrong on all counts. And oh yea am using medtronics.


Say whaaat? What do you mean vials “last too long”? Even if I had my working vial of insulin at room temp for 2 months, it would be FINE. But a working vial for me lasts a few weeks, in general. People have a misconception about the reality of insulin longevity vs the very conservative info put out by the manufacturers to cover their butts. Don’t get sucked in by the literature included with insulin–it’s just for legal purposes.