Reservoirs

Updated: 31 May 2013

The instructions with the pump indicate that the insulin reservoir should be replaced when changing the infusion set. I typically put in enough insulin for around three days, but only change it when it gets low. I do it like this because I'd rather do two quick operations than one long one. It probably doesn't matter as long as the insulin doesn't last too long and become old.

Standard disclaimer

Please read the disclaimer on the introduction page.

The procedure

We dilute the insulin with saline, allowing us to give 0.05 units at a time with our 0.1 unit pump. This has worked really well for us for over a year. I'll detail the procedure we follow below. Make sure you follow the first step: disconnect the pump from the set.

We start with a normal Minimed reservoir. Remember that there are alternatives, see the introduction page.

I dilute the insulin with the saline sold in pharmacies for cleaning contact lenses. The smaller and cheaper the better, since I need a new vial every three days and I have to discard any remaining saline. The best deal I have seen is at a hospital pharmacy, where I got 2ml vials specifically used for injecting.

Next, I bend three of the plastic flanges on top of the reservoir that act as guides for a syringe vial. This is the hardest part: the pieces are quite strong and you have to be careful not to impale your fingers on the needle. Look at the picture to see the result.

Now I rotate the plunger a little to spread the lubricant inside the reservoir, and empty it completely. Note that when empty, the top measuring line sits in the middle of the top rubber ring. To measure correctly we need to move the top rubber ring a certain number of gaps between measuring lines.

Next I put the insulin vial on the needle. You can see I am using a penfill since we had insulin pens at the beginning and always used the same prescription. A proper injection vial will work just as well, the important thing is to draw up the insulin before the saline so there's no chance of getting saline into the insulin vial.

Here you can see the insulin is done. Jenna needs about 60 units of undiluted insulin for three days. That means we have to move the top rubber ring over three gaps of 20 units each, letting it come to rest with the line in the middle of the ring. You can also see a tiny bubble under my finger - that one is too small to worry about.

Now we open the top of the saline vial (for air) and force the needle through the bottom, preferably where the plastic is thin. Sometimes the plastic from the vial gets lodged in the needle, and in this case it will become almost impossible to draw any saline. I normally start over with another reservoir when this happens because it doesn't happen very often.

Here you can see the saline is done. I have moved the top rubber ring of the plunger over another three measurement gaps, since we are diluting 50/50. Now there are 120 units of diluted insulin in the reservoir. I usually roll the reservoir a bit to mix the insulin well.

And there you have it. Connect the tube and prime out any air, making sure that the pump is disconnected first of course.