Basal I-Q shuts down Extended Bolus

I have been using Dexcom G5 CGM and a Tandem t:slim X2 pump for some time. I recently started using the Dexcom G6, and I started using the Basal I-Q software on my pump. I have been very pleased with the Basal I-Q, at least until last night….

As a long time pump user, I have learned that for certain meals I do best with an extended bolus, specifically pasta. I usually take 15-25% of the insulin before the meal, and have the remainder delivered over 6-8 hours. I know the phrase your mileage may vary, but this has worked well for me for pasta meals.

So last night I started my extended bolus. Five minutes later the Basal-IQ suspended my pump. The slope was slightly downward, but my BG was at 136!! I restarted the basal, but I did not realize that the Basal-IQ suspension terminated my extended bolus. Needless to say, my BG went high overnight.

Since I now know that that a Basal-IQ suspension will terminate the extended bolus, I will be better prepared to deal with it in the future.

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Last time I had pasta, it turned off all insulin delivery at 186, including my extended bolus. (obviously I guessed my “deliver now” percentage wrong), and I hadn’t noticed in time. I hit almost 300 before I was able to swing it back down again. Ever since then I’ve learned to turn basal IQ off for Carby meals. I actually WANT to go a little below target before those meals, but basal IQ doesn’t like that. It’s just an amusement to be made, but otherwise still love it

You are correct that Basal-IQ can easily cancel your extended bolus if you have a downward trend it thinks you will go low on.
You can either take less up front, so maybe a 5-10% initial, and space out the rest.
Or you can do a really high temporary basal rate that might also do the trick.
Or you can just turn off Basal-IQ. You just have to remember to turn it back on…

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I have found this feature to be advantageous under certain circumstances. I extend an over bolus to bring down a BG quicker and let Basal IQ turn off the excess. For a high carb meal it is best to set a high temporary basal. Then you don’t have to remember to turn Basal IQ back on.

Basal-IQ will stop basal delivery when a simple linear regression predicts you will drop below 80 in 30min or less. So regardless of your starting BG, if it’s dropping fast enough, basal will be stopped.

For the issue with extended bolus, would you be able to deliver the meal bolus, then use a higher temporary basal for the 6-8 hours you normally extend your bolus? I know that will depend on the relationship between the amount you’ve called for and the limit on how high your basal rate can be increased (200% I believe), but if the math works out you could get the same impact you get from an extended bolus without concern that Basal-IQ will interfere with things. Now if Basal IQ suspends basal delivery in that period, you’ll obviously lose that portion of the increased basal while Basal-IQ is active, but it won’t kill the temp basal.

That is just genius. Won’t have to remember to turn the b-IQ back on later.

What’s the maximum temporary basal rate?

I also understand that extended bolus has a 5 hour maximum, and the IOB time is locked down at 5 hours?

250% should be the MAX temp basal rate.
IOB is only locked down on CONTROL-IQ, on Basal IQ you can change this as needed. I think the minimum allowed is 2.5 hours?

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I don’t know how people live with the Tandem thing monkeying with their insulin deliver like that.

It’s an optional feature. No one is forced to “live with” it. Personally, I’m living FOR it. Some people have an easier time living with diabetes, but I’m definitely not one of them. I’ve struggled for control every day for nearly my whole life. This is the best I’ve ever been able to maintain it. I virtually never go low anymore, no more rebound highs (I’ve lowered my total daily dose because of this), I finally get restful sleep instead of hearing the roller coaster alarms go off, and I get to bolus more aggressively to avoid post-prandial spikes.

It’s not a perfect system. Devices always require modifications for improvement. But it’s it’s pretty darned good. I’ve only been using it a few weeks, so I’m still at the beginning of the learning curve, as I believe the OP is, too. I’m excited to see how much better it gets when I learn the quirks.


Apparently with the new control IQ update, once blood sugar stops dropping the pump, will resume an extended bolus if it was shut off by auto suspend! This will be so nice for lots of us extended-bolusers.

Good news.

You sure it’s a linear regression? Based on the discussion and one cancelling a bolus with a reading at 180, it sounds to me like it may be an exponential trace.

Thanks to all for the helpful advice. I am especially pleased by Allison1’s report that the next software update should solve this.
The other night I had Pasta All’Amatriciana, which is fabulous if you have never had it. I did an extended bolus for 120g carbs, 20% now and 80% later. Following the advice here I shut off basal IQ and also set a reminder on my phone to turn it back on. At bedtime, I turned basal IQ back on and also increased my basal to 200%. It worked splendidly! No highs and no lows. The basal IQ kicked in a few times during the night, shutting off the remaining extended bolts, but the increased basal compensated.

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Just parroting what the Tadem rep told me. She had just returned from product training so I’m assuming she was up to date.

is there a way to shut off the IQ portion of the pump and take over for say 4 hours? Then you can program your extended bolus as you wish and then have pump take over later.

You have to manually turn Basal-IQ on and off.
The temp basal is easy to set for the time you want. And you don’t have to turn off Basal_IQ.
I have been doing this a lot recently and it works great!

And you can be aggressive in your temp basal because Basal IQ will turn it off if you have bolused too much.