Oh it’s site-changing time down on the old T1 Ranch and it’s one of those days when I’ve got too much left in the old vial to just toss it but not nearly enough to fill m’dang reservoir. Which means going through the whole rigamarole of charging two vials with enough air to suck out the insulin I need without it gets sucked right back in again, while trying to avoid ending up with something that looks an insulin milkshake. So this is by way of reminding myself the best way of doing it because it only comes up like every 4th or 5th site change and I always end up wondering how in the heck did I do this last time. I’ve tried various methods, but this one seems to work the best of a bad bunch. This is with a Medtronic pump but may apply to other tethered machines as well.
Start with the old vial. Pull enough air into the reservoir to offset what’s left in the vial, attach reservoir to vial (reservoir on top) and push the air in. Holding the plunger down, remove reservoir without filling it.
Pull enough air into the reservoir to equal the amount you’re going to draw from the fresh vial: total amount less your eyeball guestimate of how much is left in the old vial (best to err on the side of underestimating it since leaving a bit in the vial is less of a hassle than coming up short). Proceed as above only this time you do fill the reservoir, to the total level less the guesstimate.
Go back to the old vial, reattach the reservoir and with the vial on top draw off the remainder, filling the reservoir to the full amount you need.
I’ve tried doing it the other way around but if you start with the fresh vial the amount of overpressure causes it to squirt insulin out the teeny hole you’ve made in the rubber stopper when you pull the reservoir and adapter off. You want to start with the old one because there’s already plenty of air in there so it’s more forgiving and won’t pull back very hard even if you underestimate how much air you need to add. If the level is low enough you may be able to skip step one above entirely. I’ve also tried to do it where you charge one, pull the insulin, then try to charge the other and do the same, but no matter how you do it the fact you’ve already got insulin in the reservoir means you’re squirting the stuff back and forth, churning it up and doing it no good.
My process is to skip your step 1. Then modify your step 2. After filling estimated insulin from New bottle into reservoir, I detach, and then pull air into the reservoir. So now reservoir is filled to line for total amount, but includes air and insulin.
Then I push entire reservoir amount into old bottle, mixing with what remained in old bottle. Then fill as normal from old bottle, usually leaving a small amount that is thrown out.
Other times I keep the old bottle, to take with me as backup, with syringes, for example on overnight or short trips if they are planned within the next week or so.
I’m going to file this information for future use, but remain thankful that I have been able to get and fill from pens. To me, this is just so much of a simpler process…
I wonder if the difficulty is due to the type of pump? Or am I doing something wrong that could cause me trouble down the road?
I use a t:slim, and fill my cartridge using a plain old syringe. So I just pull out the last bit from the old vial, inject it into the cartridge, then pull out the rest that I need from the new vial and inject it in.
People tell me to push air into my vial equal to the amount of insulin I’m taking out, and I do, but don’t really understand why.
T:Slim uses a different reservoir technology, so there’s that. But regarding the reason for pushing air in, I think it’s the same. Basically if you don’t do it the back pressure as you fill the syringe fights with you to suck the insulin back into the vial. I find this is much more a problem with a fresh vial and becomes less so as you get through more of what’s in there. WIth a Medtronic you’re pulling it directly into the reservoir, which you then insert into the pump, but the principle’s the same with a syringe. When you’ve got two vials to draw from it gets awkward because you either have to do the pressure-balance thing with some insulin already in your reservoir/syringe, which inevitably seems to involve sucking the stuff in and squirting it out again and sucking it in again, or figure out a way to do the pressure thing first for both vials and then pull the insulin. To me the squirting-back-and-forth seems like it could be not so great for the insulin and hard to do without getting at least one of the vials all foamed up, but that may just be my ineptitude with mechanical devices.
If you take the reservoir off and leave the needle connector on the vial (do this with the vial facing up) you’ll get pressure equalization as air rushes into the vial. This helps if you didn’t inject enough air in the first place. Though as a nurse, you get so used to drawing off of vials you never injected air into in the first place you don’t even notice a little resistance!
Like @Thas, I fill my cartridges from penfill cartridges (I use a refillable insulin pen as pump backup). I never have to worry about injecting or equalizing air or anything like that. I just stick the pump cartridge needle into the penfill and pull back the amount of insulin I want. It also seems I get far fewer bubbles with penfills than I do with vials (judging from the couple times I’ve used vials).
Ha! I thought it was just me! I read DrBB’s post & thought, “Whoa, i’m doing something wrong!” But if you look at the part where he says something about attaching the reservoir to the vial, it makes us t:slim folks grateful for an ol’ syringe & lickety split cartridge fills!
As someone pumping for just three short months, i’m thankful i was able to get the hang of an easy (for me) to use system. Thank you, Tandem!!
DrBB, thanks for taking the time to identify new processes & tips & for sharing
This is with a Medtronic pump but may apply to other tethered machines as well.
–but yeah, definitely not a universal problem.
The thing about putting air into the vial in general is that if you don’t, especially the first time or two you draw insulin from it, there’s a lot of back-pressure that wants to pull the plunger back in. So even with a syringe it makes things more difficult: having to hold the plunger against the back pressure so you get the right amount and don’t squirt some back in etc. When the vial isn’t as full it’s less of a problem, and as a few people have pointed out, for an almost-used-up vial you may not need to: just start with the new one, putting the air in as usual and leaving enough space for what’s left in the old one, then pull the remainder from the old one and don’t worry about putting any air in. Works ok as long as the old one is pretty close to empty. Estimating those amounts by eye can be tricky, especially when the old one isn’t quite enough, but still has a significant amount in it.
I’m sure I’m repeating what others do…this is what I do (Medtronic reservoirs):
Note: I lubricate the reservoir barrel O-rings before filling it with insulin. Move the plunger in a new reservoir by pushing it fully into the reservoir, turning the plunger inside the barrel twice to coat the O-rings with lubricant, and pulling the plunger to the back of the reservoir.
Fill reservoir with air up to where I want to fill it to. In my case about 110 units.
Place reservoir on old vial, push air into vial, pull back to 110 unit line.
Remove reservoir from old vial with reservoir facing up so I don’t get spill out from insulin in the reservoir from the old vial.
Insert the reservoir (which is still facing up) into the new vial and slowly (to avoid creating too many bubbles I need to remove later) push the air still in the reservoir into the new vial.
Draw back insulin into the reservoir up to the 110 unit mark, and tap and remove all air bubbles before attaching the reservoir to the infusion set.
I just had to do this today. What a complicated lot you all are. Here’s what I did.
Draw back plunger and inject air into old vial. Fill cartridge with as much insulin as is in the vial.
Remove cartridge, point needle upwards and draw back plunger again.
With needle still pointed upwards, push into new vial and push the plunger back just enough to inject all the air back.
4.Withdraw plunger again to fill the cartridge to the full mark.
When I’ve done it that way the insulin in the new vial ends up all frothy at the top from blowing all that air through it. Seemed like something to avoid, but maybe it doesn’t matter, dunno.
I read DrBB’s post & thought, “Whoa, i’m doing something wrong!” But if you look at the part where he says something about attaching the reservoir to the vial, it makes us t:slim folks grateful for an ol’ syringe & lickety split cartridge fills! 
