Medtronic 670G Automode Correction Bolus


(Jess) #1

I found something a little disturbing last week with the 670G automode feature.

After using automode for a few weeks, I happened to notice the correction boluses for high blood glucose were really REALLY SMALL. One afternoon, I ate a large lunch, and didn’t estimate the carbs very well. Around 3PM, by blood-sugar had climbed to over 300 mg/dL. I had issued a few correction boluses when my high-alarm went off, and it didn’t seem to be doing anything. Then I noticed the bolus calculator inside auto-mode gives you a ridiculously low correction bolus, and to compound matters, backs off the microbolusing after you issue a bolus while in auto-mode. According to my insulin sensitivity I needed about 14U to correct my high blood sugar; Automode said I needed 1.3U (That’s about 10%) This was at 3PM, and only had a few units of active insulin remaining in my system, and no infusion set issues.

So, watch out for this. This really tripped me up because I was expecting auto-mode to calculate high-blood-glucose correction boluses using my insulin-sensitivity; IT DOES NOT. The bolus menus in auto-mode and manual-mode (which correctly calculates a correction bolus) look very similar, and the pump does not warn you about how little insulin you will be getting.

The effect is that it takes auto-mode about 12 hours to come down from a high blood glucose value, compared to about 2.5 hours to be back to normal while in manual mode.

The take-away for me, is if you need to do a correction bolus, get out of auto-mode first, because it won’t give you enough insulin to correct your high in a reasonable amount of time.


(Kathy) #2

Hi Jess. I have noticed the mini micro corrections too, and have on occasion used manual mode to get a reasonably sized correction. If you do this you need to be careful though. What happened to me, apparently due to the manual corrections, was auto mode decided to recalculate my “personal max basal rate” to something ridiculously small. Thus, not enough basal at night or when meal boluses wore off. It got to the point where I was frequently dealing with the “you have been at max basal for 4 hours do a BG” situation. Thus, my trainer, on advice from the local Medtronic rep, has me out of auto for a week so everything can reset itself and my “personal max basal rate” can be recalculated to what I need. The algorithm that auto uses is extremely complicated and very counter intuitive for some things. In this case you can end up getting into a vicious circle. More manual corrections, even lower basal provided by auto.

Something to consider…


(Jess) #3

Thanks Kathy,

That is good to know. I cranked up my max basal setting to about 8U/hr, before starting auto-mode, because I had concerns about auto-mode maxing out on basal delivery when trying to bring down a high BG. But I don’t even know if auto-mode looks at this max basal setting. I get super frustrated with all the auto-mode “proprietary secrets” that Medtronics will not share with it’s users. We need this information about how the system works to set it up properly and be able to effectively troubleshoot the issues we are having. But no, Medtronics has chosen to make things more (unnecessarily) difficult for it’s customers.


(Ryan) #4

The growing pains are many on this pump. The correction bolus in automode starts with a target of 150. The theory there is to keep micro-boluses flowing to get you all the way to 120 in too distant near-future.

In addition to the typical onboard bolus/active insulin, it also accounts for the micro-bolus insulin in your system. When you are high, it’s pushing more micro-bolus out than normal. This leads to corrections being extremely conservative. In response, I have made my settings more aggressive. Automode seems to only take account of two settings: insulin to carb ratio and active insulin time.

Both settings must be approached much differently than our previous experiences. If I used my old settings in automode, micro-boluses would never catch up and my A1c would skyrocket.

I give myself way more insulin for each bolus than before. I set my active insulin time to 2 hours not because that’s true (it’s really more like 3 or 4 hours), but because my glucose will go way too high due to hours without any insulin delivery. Shorter active insulin times allow micro-boluses to start in time to cover my needs more like the dual boluses I used to run on my old pump.


(Jess) #5

rpm3313,

I think it really stinks that you have to readjust (increase) your carb-ratios because auto-mode dials back your “micro-bolusing” after a large meal bolus. There is only one set of carb-ratios that can be stored in the pump at any given time. So if you get kicked out of automode or switch back to manual mode, your carb-ratios are too agressive for manual-mode. THAT SUCKS.

There is no reason Medtronic couldn’t have designed their microbolusing algorithm to maintain carb-ratio equivalance between manual-mode and auto-mode.


(Maggie) #6

This issue has me really confused. Inhave only been using auto mode for about 2.5 weeks and just this week, I started turning auto mode off for corrections.
Now reading that it is going to negatively affect my microbolusing, I’m not sure what to do. It seems like every solution has a negative consequence. It’s this kind of stuff that makes me think that I’ll quit using auto mode.


(Kirsten) #7

I’m having the opposite problem. The correcton boluses calculated in Auto mode are higher than the ones in regular mode. I started crashing in Auto mode about 2 weeks ago & I figured out that one reason is this calculation discrepancy. I also crash even without a correction or carb bolus & have no idea why, so I’m really confused.

I have lots of other complaints about the 670G but those are for another thread…


(Kathy) #8

Hi Kirsten. There are other groups out there that only focus on 670g issues. The one that I use a lot and have found a lot of techniques that work for me is the “Medtronic 670g support group” on facebook (it isn’t sponsored by Medtronic by the way). Its a very supportive group and they have a lot of experience with the 670g. While I haven’t seen this particular issue out there, I expect that someone has.