I have been using my T-slim since around October. It is my first pump. I have noticed something recently that I can't figure out. When I fill my cartridge, I have noticed that some of the insulin goes "missing". For example, if I draw up 260 units to put into my pump, insert it, and then fill tubing (which is 22" and should be ABOUT 20 units), my pump shows that I only have 160-190 units available. I have no idea what this means or where it is going. I use the syringes that were included with the cartridges for the pump. Can anyone answer this? Or explain what is happening here?
Anna, yours is a question that bothered me at first, too. Here is a response from Tandem that was posted on the t:slim users facebook page:
"Tandem Diabetes Care provides a therapeutic syringe and needle [manufactured by Becton Dickinson (BD)] with each cartridge. One could use these syringes and needles to inject insulin from a vial if they needed to in case of an emergency. The markings on the syringe are calibrated to be accurate since the syringe is intended for therapy.
The other insulin pump companies use custom syringes that are not calibrated for injection but for the devices they are intended to be used with.
For example, a syringe calibrated for another pump may read 300 units, but actually contains more than 300 units. Those syringes are calibrated to indicate useable insulin, not the total amount of insulin they hold. Just like with a tube of toothpaste, one cannot extract all the insulin from the syringes due to the dead space in the syringe and needle.
While other companies compensate by shifting the markings on their reservoirs to account for the amount that cannot be delivered, Tandem adjusts the volume of insulin that cannot be delivered in the insulin estimation algorithm of the t:slim Pump. Our adjustment is for 20 units of insulin. We do this to ensure customer safety. You would not want your insulin gauge to read 20 units when your reservoir is empty.
In conclusion, our insulin gauge displays only usable insulin. I hope this helps clarify some of the differences seen between the amount filled in the syringe and the amount displayed on the pump gauge. As usual, if anyone is experiencing anything out of the ordinary they should contact our 24/7 Customer Technical Support team at 1-877-801-6901."
Thanks for your responses! I actually ended up calling tandem because I couldn't sit with the idea of all the insulin wasted after i started calculating what was getting thrown away. tandem is replacing my pump--I should have a new one by Thursday. The team I spoke to was super nice and understanding. they gave me some troubleshooting steps to try during my next fill-which was yesterday morning. Even after the steps I was down to 80 units missing.
Like GrandmaKissy said, they allow for approximately 20 units as a cushion which is considered "unusable", as well as small amount for filling tubing. My fill tubing takes approximately 16-17 units. So the variation should be approximately 36-40 units depending on the length of tubing. I hope this new pump works! I will post an update once I know.
One thing I've noticed with mine is that if I fill with 200u, after priming and resuming insulin, my pump said 150. This happened whether I had to prime with 15u or 25u or 28u, but NOT 29u (the pump would read 145 then). So, now, since it takes so much to get bubbles out, I always fill it with 50u more than what I need for 3 days, and let it prime 28u (usually gets rid of all the bubbles), and then it's reading the amount I need. It's still hiding that 20u, but I don't think about it that much because, as stated, my Animas "hid" that much too.
I noticed this too, and on the tslim FB page I read that you should clean that little metal base on the pump with an alcohol swab on every change because that is the sensor! Several people claim this has helped immensely. I have not had a cartridge change since reading this, but am going to try it on the next go round.
There is usually a cushion built in....when I change cartridges, I often pump air into the old when and draw out whats left. I store it in an empty vial and use for an occassional syringe bolus when I am nearly at the end of my next cartridge if I am not in a convenient place to change it out.
