Trials and Tribulations with Medtronic 670G AutoMode


#1

I was so excited to get started on AutoMode on the Medtronic 670G that I finally received about three weeks ago, I could hardly wait. I got started on the pump and Guardian sensors a week before I was able to schedule the 670G training session and waited impatiently for my AutoMode training which finally occurred yesterday. At that training session, I put the pump into AutoMode following the trainer’s instructions and after a discussion about whether or not I should change my Active Insulin Time (AIT) to 3 hours from 4. I am hypoglycemic unaware and also experience rapidly crashing blood sugars. We decided that it would be best to leave the AIT at 4 to start with even though the recommended value is 3. Left the training with a song in my heart and a skip in my step because I’ve been anxiously awaiting AutoMode technology for at least 5 years now. After about 5 hours of watching my glucose readings steadily rise and hitting almost 400 mg/dl, I switched the pump back to Manual Mode and called my trainer. Her suggestion was to change my infusion site and reservoir, manually inject insulin to correct the high blood sugar, and try to go back into AutoMode in the morning. Sure, I can do all that. But I need to know why AutoMode wasn’t working and what I should change to get it to work. So I called the Medtronic help line. No answers there. Same suggestions as the trainer gave me. Searching the Internet (and especially this site - thank you all) I discovered just how important it was to adjust the AIT. So this morning I restarted AutoMode after adjusting my AIT to 3. Same problem. An hour of reasonable glucose levels and then a sharp rise in the readings. This time I switched the pump back into Manual Mode when the glucose levels reached 250. Decided maybe I needed to adjust the AiT even lower. Tried AutoMode again this afternoon with an AIT of 2 hours and 45 minutes. Again, an hour of reasonable readings and then sharp rise.

Anyone else have a similar experience getting started in AutoMode on the 670G? Any suggestions on actions I can take? Should I just keep tweaking the AIT value down in 15 minute increments? Would appreciate any information or insight you could provide.


670G just tried to kill me tonight!
#2

@DrBB may be able to help you. He is using it.

Paging @DrBB


#3

I sense the Bat Signal has been received…


#4

When you think about it, AIT is a different critter under Auto Mode than in a standard pump because of the microbolus thing. Each one of those little blips is subject to an AIT estimate. Every five minutes it’s looking to see how long the last little blip still has on its clock and adjust the current blip accordingly. So if you tell it 4hrs it’s going to be v-e-e-e-e-r-r-r-r-y conservative about how much it’s going to give you no matter what the SBG is saying. Similarly, if you take it all the way down to 2hrs–which is probably a lot shorter than what you entered in your standard pump–you’re telling it to discount the effect of the previous blip a lot more, while in reality what you’re doing is making the effect curves overlap a lot more. If that sounds like you’re treating these parameters not so much as hard-and-fast scientific facts but more like a story you’re telling it to coerce the thing into doing what you want it to, you’d be right. Mine is currently set at 2hrs.

Similarly with CR, which I suspect you’re going to need to start adjusting too. In a standard pump it really only applies to meal bolusing and the bolus calculator. With auto mode… well, no one seems to know, officially, but in practice it seems to make a difference to microbolus rate as well. I’ve got six different rates going now, all of them low enough that the pump gave me an “Are you sure you really mean this???” alert, and it’s finally starting to be more aggressive about correction doses and post-prandials, so it seems like I’m moving in the right direction. Dawn Phenomenon is still being a problem, but there’s progress.

If you’re on Facebook there are two groups I’d recommend: 670G Users, which has a couple of hoops they want you to jump through before joining (they really only want people who have the sensors and are using–or at least have used–Auto Mode), and 670G Support, which isn’t quite as closed. I think the level of expertise and experience on the Users group is a bit higher, so it’s worth going through the rigmarole, but they’ve both been helpful to me.

I also have two other threads on this that may be of interest:


#5

Thanks, DrBB. Not on FaceBook but this definitely would be a good reason to be there. Really appreciate the information. I’ve only got two CR going at the moment in Manual - one in the morning and one for the evening. Did you find you had to adjust your Insulin Sensitivity in any way.

Thanks again!


#6

That was one of the first things I tweaked, yes. Only to be informed by my trainer that Sensitivity is another one of those settings that are null in auto mode. Same with Max and Minimum Basal–the algorithm has its own version of those that it determines all by itself and isn’t affected by the ones you can tweak in your settings.

It’s really a different beast this thing, and the continuity of terms carried over from standard pump therapy, which are actually carried over from basal-bolus MDI before that, tend to obscure as much as explain what’s actually going on. As someone on the FB User group pointed out, “insulin is just insulin.” Well, not so much In MDI of course: then you actually had two separate insulins doing separate things, so “basal” and “bolus” were quite distinct. That distinction gets a little more permeable in a standard pump, where it really is just one insulin doing everything, but you still needed that conceptual distinction because “basal” was just a more nuanced way of doing what Lantus did. In place of one big 24-hour square wave you could now have several different ones, but they were still pre-set, programmed-in rates.

But microbolusing is very different, and it’s actually significant that they call it micro bolusing. With a standard pump, “Target” is only used in the meal bolus calculation. “Basal” doesn’t take any account of your target setting because it’s a fixed rate you’ve programmed in; it isn’t taking any other input. But in auto mode even your “basal” insulin is being targeted, just the way your “bolus” insulin is. It’s more like a real pancreas in this regard. A real pancreas doesn’t keep administering “basal” insulin at the same time that it’s responding to signals that you’ve just eaten a cupcake; it’s just ramping up production for that cupcake. Same thing here: the “microbolus” is subsumed in the larger meal bolus because the whole system is just based on doing whatever’s called for to bring you back to the set point. I infer that this is why “Carb Ratio” figures into microbolus rate even during fasting times, though exactly how it does so is locked away in the blackbox of the algorithm.

In any case, my larger point is that a) the only parameters you can control in Auto are AIT and CR, and b) it’s probably most useful to think of them as “dials I can turn to force this gadget to give me the results I want,” and not worry too much about how concretely they map to the specific physiological entities they seem to imply. Is my insulin really clearing in just 2 hours? Funny how that changed the minute I switched to Auto when 4 hours was working just fine on my old pump…


#7

Can you clarify something for me? When you eat a meal, does it give you a large bolus for that, or does it just start micro-bolusing like crazy?

As an example, if your IC was 1:15, and you ate 30 grams, would it just give you the 2.0 units right away? Or spit it out in little bits for x minutes?


#8

It behaves like a normal meal bolus. MdT has always had a thing about not just zapping you with the whole amount but delivering it gradually at a pre-set rate. Supposed to help with absorption or something. But there is a setting for Bolus Speed and you can choose Standard (1.5u/min) vs Quick (15u/min) delivery. Don’t think we had that in their earlier pumps.


#9

We found the Tandem t:slim delivers the bolus slower than the Animas Ping did. But bolus over period of minutes. Or 5 minutes or 10 minutes or whatever. Certainly not hrs - that would be specific if you extend the bolus.

But it was obvious when moving to the Tandem from the Animas in terms of the speed with which the bolus was delivered.

I have wondered the impact that has on absorption.


#10

I have also wondered the same thing. We know that the healthy tissue surrounding an insulin pump cannula does have absorption limits. For most of us those limits are two to three days.

Yet we can leave a Dexcom continuous glucose monitor subcutaneous sensor in place usually with relatively little consequence. I’m thinking that the kinetic action of the flow of insulin contributes to site injury. I suspect that the total volume and speed of insulin delivery also contribute to tissue damage.


#11

Again, thanks so much! It’s so nice to finally get some useful information as to how to make this beast work. The trainers in my area don’t seem to have a whole lot of practical knowledge about the Auto Mode functionality.

As for the CR values, maybe I’ve jumped to a conclusion that is not necessarily so, but in Auto Mode, is the CR analogous to the Basal rates in Manual mode? I’ve currently got 7 basal rates set for a 24 hour period. Can I use those as a template for when I need more aggressive CR values?


#12

Well, it’s still a bit of a mystery to me, too, so I don’t want to sound like I know more than I do. I think it is kind of similar but I don’t think there’s any direct way to convert one to the other. In Manual I had evolved a pretty aggressive basal rate from 3am-10:30am because of DP. My first tweak to CR in auto mode was to see what would happen if I took my CR way down at that time. It seems to have helped, but it’s a gradual kind of thing. The algorithm doesn’t immediately take account of those changes but integrates them with other factors. I’ve read that there’s a 6-day cycle for this stuff as well. It all makes it kind of hard to tell what is the effect of a given change.

Most frustrating thing to me now is that my fasting SBGs are great, but while the sensor is impressively accurate most of the time, it just doesn’t want pick up on the DP trend. At 6 a.m. today SBG was 119–yay!–but my finger stick was 158. Boo. I actually had gotten up at 4am and did a finger stick then, and both SBG and meter BG were ~110. So somewhere in there my DP took off and the sensor lagged too far behind to rein it in. There’s nothing I can do to force the sensor to be more responsive, and the pump can’t react to what it doesn’t see no matter what my settings are. So it may be my only option is to take it out of Auto overnight—I’ve read of other people doing that—though it bugs the part of me that wants to make the thing work the way it’s supposed to.


#13

Great! I’m back to feeling optimistic about this pump again, DrBB. And I think I’ve got a path forward. I’m going to crank that AIT down and also look at setting more CR’s (cranking those down as well). And try Auto Mode once again. Thanks for sharing all this important information.


#14

what is AIT?


#15


#16

Found this topic and just joined. It’s so nice to see others have adopted similar strategies to mine.

I’ve been on the 670G for about 8 months now. It took me about 2-3 months to decide to take things into my own hands with the only 2 variables still available in auto mode - AIT and carb ratios.

Lowered my AIT from 5.5 to 4. And CRs from ~14 to ~10. While results improved, I must admit I am now on my 4th day happily back in manual mode with BGs back where they used to be in the low 100s. OK, MOST of the time. :slight_smile:

After finding this great info, I will try again with AIT of 2. And with 2 concerns:

1 - no fix for DP. I want to throw my pump out the window every time I wake to a 160 BG. I’ll keep manual for nights.

2- when I DO need manual mode, my AIT and CRs are too low which can be risky. Be careful.


#17

I have been on the 670G for seven months now. My A1c has come down to 7.0 (from 7.5-8.0), but I suspect that a large part of that change was finally using CGM - that was a life changer. I cannot get the auto-mode to handle dawn phenomenon. Interestingly, I seem to have had a honeymoon period where I woke up right at 120, both CGM and BG. Now, my CGM is usually ~30 points behind my BG at 6:30AM. My CGM says 120 and my meter says 150. Sometimes it’s worse than that. If I wait until 7AM, my BG is higher; auto-mode does not bring it down. It drives me nuts that it won’t administer more insulin. My graph trend is clear - at 4:30AM, the line starts going up, and keeps going up. Has anyone succesfully dealt with dawn phenomenon in auto-mode? Please share!