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December 1, 2021

Closed Loop, Hypoglycemia

Question from Virginia, U.S.A. :

My 19 year old daughter uses the t:slim and Dexcom with Control IQ. She has noticed that if her blood sugar starts to drop, it keeps dropping and Control IQ doesn’t prevent it. Even if her blood sugar starts in range or high, any steep drop means she will go low. She eats to try to prevent the eventual low but her sugar keeps dropping and it takes forever to come back up. Then, she goes high from over treating the low and the cycle starts all over again. We brought it up at her last endo appointment but they weren’t sure what settings to change to help. Is the problem that she gets too much correction or not enough basal? Does the insulin-to-carbohydrate ratio need adjusting? Or, is there a setting in the pump that would help? She’s tried sleep mode and exercise mode but no luck yet. Any suggestions?


From: Marissa Town, BSN, RN, CDCES

For the t:slim with Control-IQ, the settings that are best to change are the insulin-to-carb ratio and the correction factor. The active insulin time and targets are determined by the algorithm and cannot be modified. Are her lows usually happening after a mealtime bolus? I’m wondering if what is happening is that she takes a bolus for the meal, her blood sugar goes high and then she takes a correction, perhaps even a manual correction, meaning she has so much insulin on board that it causes these big crashes. If this is what’s happening, it would mean that her mealtime insulin is not matched with the meal properly. This could mean that her ratio needs to be made more aggressive, that she needs to take the bolus ahead of the mealtime more such as 15 to 20 minutes before she eats as opposed to right when she eats, or that she is under counting her carbohydrates. (No judgment – I do this sometimes, too, as a person with diabetes!) If you need to make the carb ratio more aggressive, you would want to lower the number for the carb ratio by 10% and try that for a few days to see if it works. For example, if it’s 1 unit for 10 grams of carbs, try 1 unit for 9 grams and see how it goes.

If the correction is only being given by the algorithm, and not added manual boluses by her, the correction factor may be too aggressive. So for example if it is 1 unit drops her 40 mg/dl, you may want to try increasing it to 45 mg/dl which would make it less insulin for corrections.

The other possibilities are that she has scar tissue or the infusion sites need to be rotated more effectively, Sometimes, what can happen is that when insulin is infused into scar tissue the insulin will absorb very randomly, and it can be difficult to figure this out. I found that I ,personally, was trying to do too much on my own Control-IQ and it seems to work better iwith more of a “hands off” approach. This is why I asked if she’s doing manual boluses or multiple corrections, etc., because I found myself doing that, and in reality, I just needed to time my boluses better. Another thing that I am doing that has helped me personally is using sleep mode 24/7. I have found that this eliminates the roller-coaster effect you mentioned which has been really beneficial for me physically and emotionally. The roller coaster stuff is stressful and unpleasant. So, perhaps try this to see if it works, and pre-bolus ahead of meals.

There’s a really great website from the Barbara Davis Center in Colorado called the Panther Program (https://www.bdcpantherdiabetes.org/) that has more information in case it is helpful. Feel free to write back if you want to clarify what you think is happening – there are a couple of other things that could be happening if none of these sound right or work for her.