I am a new pumper just starting Tandem t:Slim pump with AutoSoft 90 Infusion Set recently. Notice about 30% chance of high post-meal BGs after a new infusion set at a new site. Finally realized a bent Cannula is the main reason for unsuccessful insulin delivery. The Tandem pump did not display any notification in this event. I have the following observations and speculations:
A bent Cannula should cause a partial blockage of insulin subcutaneous delivery. If insulin is not delivered successfully, where does the insulin flow to, i.e. leaking out or else? If external leaking is not observed, where is it? Since the insulin pump did not notify user, we can assume that pump doesn’t recognize the un-successful delivery. Pump manufacturer should consider build in a suitable sensor. So far, the only way to know a bent Cannula is high BGs after a meal beyond 2 hours. Is there any way to know a bent Cannula in a shorter period of time, say immediately after the completion of a bolus delivery? I haven’t find any answer yet.
Recently, I notice an unsuccessful bolus insulin delivery 3-4 hours after a meal with a new AutoSoft 90 infusion set installation just before the meal. Decide to change the infusion set anyway. While removing the old infusion set, my wife notices that there are liquid droplets (insulin) inside the dome of the infusion set. See the picture below. It is likely that insulin droplets leaked from the Cannula to the dome due to a blockage in the passage. Does anyone observe the same when a Cannula is bent during insertion or a Cannula is clogged with blood?
We now check any droplet appearance in the Cannula dome after each bolus insulin injection, so that we don’t need to wait for 2 to 3 hours of high BGs. It may appear in Day 2 or Day 3. So far, this procedure works. If anyone has different way of knowing a bent Cannula, please share.
Possible problems in the design of the AutoSoft 90 launching device:
a) un-even force during user pulling the spring resulting in adhesive pad surface not in parallel to the casing, i.e. causing a slightly offset angle during insertion. Is it possible to have a design without the need of pulling spring, such as, the Dexcom G6 launcher design, i.e. the spring is loaded in factory? The tubing may be disconnected at the infusion set end, just like at the cartridge end for easy priming purpose.
b) highest reflective force resulted from a 90 degree insertion, the strength of a non-metal Cannula material may not be adequate. A better non-metal cannula material is required. There are reports that metal Cannula does not bend.
c) some type of muscle or blood vessels beneath the infusion site may cause bending or plugging in Cannula
d) no observation window is available for verification of the integrity of the Cannula after insertion. In this respect, VariSoft may be a better choice.