Stupid Pump Tricks Vol MLXVIII - Extended Bolus Rollovers

On the Vibe you can only have one Combo ("wave"/"extended") bolus running at once. This is a pain if you eat something else that requires an extended bolus, while the first extended bolus is still running.

As an approximation, what you can do is cancel the running extended bolus, after taking a note of the amount remaining. You then start a new extended bolus, calculate the new amount required, then add on the amount remaining from the previous extended bolus. In theory you can repeat this "rollover" process indefinitely. OK it's not pinpoint accurate but it's close enough for horseshoes and glucose meters. (Note - so far we are not at the "Stupid Pump Trick" stage).

In the Vibe you can get the amount of extended bolus remaining by going to the Combo Bolus menu screen. If an extended bolus is running, instead of getting an option to bolus, you get a status display on the currently running extended bolus.

The status screen looks something like this:


Crystal clear right? Not really. The left hand number is the amount delivered, but is the right hand number the amount remaining or the total amount that was to be delivered? To me the colon says "remaining", somehow, where a slash (/), or the word "of", would say "of". Anyway turns out I got it wrong and the amount on the right is not the amount remaining, it is the total original amount ("of"). Hence the Stupid Pump Trick - you can see that this type of rollover, using the wrong quantity, is NOT repeatable indefinitely, and builds up a bigger and bigger extended bolus dose with every rollover. I did this three times in a row and I got a hypo for my troubles.

Incidentally there is another way to check the extended bolus quantity remaining on the Vibe, which is to go to the History menu. This is a few more steps and doesn't allow you to proceed directly to Cancel and then enter the new extended bolus, but it does quite clearly say "of". What a difference one or two characters can make eh? Luckily we had teams of FDA assessors teeming over every screen for years in order to declare the Vibe safe as a consumer medical appliance... :-/

I tend to just use TBR for illness or exercise, that's an interesting idea to use it for protein. It seems like it would be more fiddly to calculate though, especially as my basal varies every couple of hours. It would be easier if my pump had "+ X units/hour" type of TBR but it only has "+ X%" type of TBR.

masonbason63 said:

I got very confused with the word Combo " an Accu-CHEK pump" and also Rollover "the National Lottery". Is this your first pump Spiker I can't remember? It's enough to put someone off.

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This is the Animas Vibe, my first and only pump, on which the extended bolus feature is called "Combo Bolus".

Well apparently the pump manufacturers all have to use different names for every feature otherwise they will sue each other for $BILLIONS in patent infringement and the whole industry will go into a death spiral.

Apologies if you thought you had won The Big One, Mason Bason. ;-)

noblehead said:

Yeah that's true but that's where the old adage 'trial & error' comes into play.

I've been using a TBR of 60% for a high-fat meals set for 6 hours which has had a very good effect, as when you use the Extended Bolus feature it doesn't take into account fat and protein and only carbs, unless of course you add this in your calculation and add it to the carb value of your meal (if that makes sense ).

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What I do is I do a normal bolus for the carbs and an extended bolus for the protein (2 hrs extended, dosing for one third of the protein, in my case). That way I get to use the bolus calculator for both operations and don't have to do both ratios in my head, let alone have to account for my basal rates varying every two hours. But, that said, I'm not accounting for fat at all, and I think I might need to do that. The most economical way might be for me to override the carb ratio in the bolus screen, which (on the Vibe) you can modify at the time of bolusing without having to go to the setup screen.

By the way I believe the newer pumps on the market allow stacking of multiple extended boluses, not just running one at a time. It's not exactly rocket science after all. So pumps with that feature won't ever need us to attempt to do this kind of rollover trick.

noblehead said:

I get what you mean, but the TBR deals with the fat content of the meal as we can become insulin resistant many hours later.

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Interesting. I'll have to reread that. I can see how it could be good to have a "third arm" - TBR to deal with fat, extended bolus for protein, normal bolus for carbs. (Maybe in a few years we will have pumps or dose calculators that will just let us explicitly enter the three values.)

I still worry that the TBR doesn't have any way of corresponding to the amount of fat or carbs or protein ingested. The TBR isn't the inverse of insulin resistance, after all. So I can see how an increased TBR could compensate for an increase in basal requirements caused by transient insulin resistance, which is useful, but how could it also compensate for increased insulin resistance vs the carb and protein bolus?

Anyway thanks, and I may give it a try, because what I am doing now ain't working.

Well, just had another hypo so I don't think I want to be increasing the TBR. I am not sure what is going on to be honest. Maybe what I am seeing is the fat delaying the effect of the insulin, rather than reducing the effect of the insulin?

Gary is a little hand wavy on what happens with fat causing insulin resistance in TLAP. I don't have Walsh so I am going to check what Prof Taylor says about the fat to insulin resistance relationship.

Spiker said:

Gary is a little hand wavy on what happens with fat causing insulin resistance in TLAP. I don't have Walsh so I am going to check what Prof Taylor says about the fat to insulin resistance relationship.

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Prof Taylor says

http://www.ncl.ac.uk/magres/research/diabetes/documents/BantingDiabeticMed.pdf

Well everything he says about the effect of dietary fat on BG sounds like it only applies to T2, at least in the short term. He says two things:

1. circulating trigs suppress insulin production in beta cells. (I don't got none)
2. excess trigs cause fatty liver which makes the liver resist insulin's suppressing effect on basal glycogen output. In effect, basal requirements go up. Again, I don't think this affects me (a T1), certainly not in the course of just a few days.

So Prof Taylor has nothing to say on the effects of increased dietary fat on the BG of a T1. Gary Scheiner (Ch 8 of T.L.A.P) is all hand wavy and says "we don't understand why but" and then gives a very vague explanation that sounds like a simplified version of Prof Taylor's. Does anyone else have anything to say about the effects of dietary fat in T1s?

donnellysdogs said:

Don't use extended or multiwave. Just whack on a high tbr if needed.
Went out with parents n hubby tonight. Just the pudding had 110g in it. The dinner 59g and the starter guestimated at 40g. So over 200g in one meal!!!!!

So bolused for that and then stuck on a tbr of 250% for 4 hours.

As this is actually 4 times the qty of my whole days food then even this 200% tbr is not going to cope with the inbalance between of my 50/50 basal/bolus ratio. So at end of 4 hours will do another tbr probably of another 4 hours, depending on levels though.

The pudding of millionaires shortbread sundae wasn't worth 110g carbs though!!

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DD I don't understand your reason for doing a massive TBR on top of bolusing for the carbs. Is the TBR just for the fat in the food?

Hmm it might be time to move this to a new thread.

http://care.diabetesjournals.org/content/36/4/810.full
Wolpert 2012 - free fatty acids cause acute rise in glucose concentrations and insulin requirements in T1s

http://jn.nutrition.org/content/136/10/2506.full
Wolever 2006 - protein and fat cause linear dose dependent delays in processing of carbs in nondiabetics (kind of the reverse effect)