I am a bit hesitant to share my thoughts on the first publicly available closed-loop pump because I know how excited people are about the prospects for this. But from what I have heard, some of the aspects of how they are implementing it are deeply troubling to me.
First off, I have never used the Medtronic pump. But I have discussed it with an Endo that is a big-shot with Medtronic. He does a lot of their clinical trials, he is an advisor to them, he is a big Medtronic proponent (has nothing but Medtronic stuff on the walls of his exam rooms).
I went to see him, not as a normal Endo visit, but just to glean information from him. I met with him a few weeks ago. I didn’t tell him anything about my regimen, just asked him all about his pump and insulin recommendations.
So this is what he told me for the new 670g:
When you are in closed-loop mode, you can’t bolus. You have to let the pump make all the decisions for you. The only thing you can do is tell the pump how many carbs you are eating. If you want insulin, the only thing you can do is enter carbs. That is all.
I asked the Endo, how do you correct? He said, in closed-loop mode you can’t!
[starting to feel troubled]…
So you enter your carbs for a meal, but later after you have eaten, you want to add some more insulin. Maybe the plate was bigger than you thought, or the food was a bit sweeter. Maybe you just think you will need more than originally estimated. Maybe you snuck a few bites off your date’s plate. Maybe you are starting to spike. You can’t simply add insulin or correct!
Here are your options. You can either:
a) Wait until you go above your BG target and let the pump correct automatically for you (and I don’t know how much control you have over how aggressive you can set those type of corrections).
b) Enter more carbs, “pretending” you are eating more, just to get more insulin. Kind of tricking the pump.
c) Exit out of closed-loop mode and do a manual bolus.
So option c) sounds like the easiest way to go, right? Just exit out of closed-loop mode, enter your bolus, and then go back into closed-loop. Easy right? No. From what he told me, it takes about 12 button pushes to exit out of closed-loop and do a manual bolus. And then I am not sure how many button pushes to get back into closed-loop mode.
To me, this sounds crazy. I can’t take a 0.15 unit bolus? I can’t add just a little bit of insuln? If I see myself starting to rise, I can’t correct that?
A couple other things.
The only BG target values are 120 or 150. So if I am 90 and going up, I have to wait until it gets to at least 120 for the pump to do anything. And even then, I have no guarantee of how aggressively it will correct.
All this is based on CGM interstitial readings, which can have a big lag. If I test and see a BG number I want to correct, I can’t. I have to wait for the CGM to catch up with my BG meter test. Argh!!!
Keep in mind, I have never used it, this is just what the Endo told me. It’s possible he is totally wrong about all this. After all, the pump is not out yet, so maybe he is basing all of this information he told me simply on his discussions with them during the design phase. I don’t know for sure.
But if what he said is true, I am troubled. Not that I have to use the pump, but I know how these companies work. If one company does it a certain way, a good chance all of them will follow the same path. 
What would you think of such a design? I know for some people it makes sense, they don’t need to ever do anything except enter carbs, that is all. But for people who like to manage things a bit more tightly, it seems like a bad setup. Plus the limited options of 120 or 150… Another “Argh!!”.
I learned of all these things a few weeks ago, but didn’t know if I should share it publicly because it just seemed bad to me and I know how excited people are about the prospects of closed-loop and AP.
I don’t want to talk anyone out of it, but some of these things just bothered me.
Anyway, would love to hear your thoughts, and I apologize for not being all happy about it.
You can quickly attach, bolus, and disconnect. Also, you wouldn’t need to stay disconnected for 2 hours, if you have breaks between the periods. I know most pro games the periods are less than an hour, so I think you’d only need to be disconnected for that much at a time. I wouldn’t want to go the entire game with no basal, that is almost a guaranteed spike! I have never used this pump, but most of the tubed ones use a luer lock connector that lets you disconnect and reconnect the tube super easy (like for a shower). The Medtronic has their own proprietary connection, but it is basically the same as a luer lock.