Animas 2020 IoB question (yes, another one!)

[Gary_W]

Hello everyone,

Loving the pump so far, and using it live shows far more than playing on a desk ever will.

After lunch today, I spiked quite badly (my own fault for eating an unholy amount of white bread). Anyway, I needed a smallish correction at hour 2. No problem.

When I came to eat my next meal, I was down at a very nice 4.5 (81) pre meal. My target pre-meal is 4.8 +/- 0.3 so this was peachy. According to the pump, I still had 0.95u of bolus on board.

My meal was going to consist of 65g of carbs. I popped this in to the bolus wizard and it calculated that I needed 4.3u of insulin. My ratio for dinner is 1:15. In essence, it hadn't bothered to knock off the 0.95u for IoB. I thought this was crazy and went with my instincts; it helpfully tells you on the calcs screen how much IoB you have, so I knocked it off myself and popped in 3.35u. I did a combo bolus (aren't I flash inside 48 hours :D ) as there was lots of fat and protein going on there too.

I was 5.2 (94) after 2 hours and have been between 4 and 5 ever since. In other words perfect, tight control. Which is fantastic news, but what confused me is why the IoB didn't recommend it being subtracted. I then looked at my .pdf user manual and p64 shows this as intentional. I cannot for the life of me think why you would not wish to subtract it; if you trust the IoB settings on the pump (and as you can program them, you should) then why on earth is this helpful? It can only but cause you to go hypo.... Can someone please explain why they do it like this? Now I'm aware of it, no problem as it's easy to overide, but surely this is a hypo waiting to happen if you're not aware of it?

Gary

[HollyB]

Hi Gary,

You need to input your current BG as well as your carbs for the pump to subtract your IOB from your carb bolus.

[JediSkipdogg]

IOB is ONLY taken into calculations if you put in a BG value as well. If you only do carbs then there is no point for IOB since you need the full bolus to cover the carbs you are about to eat. So I'm not sure what you think might be wrong.

[Gary_W]

Thanks for the replies; I'll try and explain myself a little better.

On the occasions where this happens, I AM putting in the BG value. My point is that if you BG value is in range, it DOES NOT knock it off the total. I will give an example. I'll use UK BG values if that's OK.. Multiply by 18 if you need US.

Patient X....

Patient X has a I:C ratio of 1:10 all day. He has a a BG target of 5.0 +/- 0.5 all day plumbed into his pump. One unit of insulin drops him by 2.5mmol

He ate 2 hours ago and bolused for it. He still has active insulin on board, as he has told the pump that his insulin lasts for 4 hours.

He tests his BG and finds it to be 4.5. He has a look at IoB in the pump and it says he still has 1.00 units on IoB from his previous meal. The bad news for Patient X is that he is going to drop from 4.5 down to a BG value of 2.0 over the course of the next couple of hours due to that extra unit of insulin that is sloshing around the old body.

He decides to eat a meal consisting of 50g of carbs. He fires up the ezCarb wizard and dials in 50. He then adds his BG value of 4.5.

He then sees the following screen

Bolus Total

Carb 5.00u
BG + 0.00u
IoB 1.00u

Total = 5.00u

THIS is my beef. IF your BG that you enter is WITHIN your target range, it does not take IoB into consideration with the calcs; it DISPLAYS it, but it DOES NOT subtract it from the total bolus that it recommends. If your BG value you enter is either ABOVE range or BELOW range, it does indeed knock the IoB off the total! In the above example, patient X will go hypo due to the extra unit of insulin that he does not need. If patient X had a BG of 15.0, it would still recommend allowing for the IoB. When you are within your nice low range that we all set, it recommends ignoring it.

Please try this on your pumps. It is clearly not a bug as it says that it does this plain as day on P 62 of the manual. Can ANYONE explain why this would be of any benefit whatsoever to a patient because I just cannot see why you would do this. You could have 10u active IoB, be at a BG of 5.0 and eat 10g of carbs. The pump would still recommend that you bolus a unit for it! I know you shouldn't use a pump if you don't understand it, but surely it's giving very dodgy advice in these cases where you have IoB AND are in your target range. What you you all think?

For now, I will set my range +/- 0 and, if the BG reading I put in matches my range exactly I will lie to the tune of 0.1. In this manner, my pump will correctly do the maths for me.

Don't get me wrong, I love this thing already. I just need to fully understand everything about it and this little 'feature' could get someone out there into trouble!

Gary

[Subby]

Gary, here's my take. I'm thinking the issue that's happening here is that you are allowing for an expected BG curve through the life of the bolus, while the pump is not. I'm not saying one or other is right, my opinion is that ideally the pump would be able to track carbs and requirements and trends far more thoroughly than it does, but at present it doesn't have the sophistication. Nor is the question of how to inform it of carb longevity a simple one, see below.

To put it another way, based on your experience, you assume that because the person is already in the target range and two hours have passed from the last meal, having IOB will have a downward effect on BG, rather like what most MDIers are used to, nice big curves. (And of course pumpers see curves too, its true that insulin action just doesn't match food action in most cases).

The pump does assume that the insulin action should match the carb action, so things should remain stable. So, no correction should be made... it runs on the principle that the IOB belongs to the carbs that may still be in your system and that the two are nicely fighting it out and keeping things even. You are absolutely right this probably doesn't match reality often. But then again, maybe your theoretical pumper in the scenario ate pizza or porridge. I know if it were me there would still be maybe 1/3 or more of carb life remaining, thus requiring that remaining IOB for those carbs.

If you step back and look at it, it's not really possible to see at the moment how the pump could assess the presence or lack of carbs from a previous bolus and therefore predict future BG. It can apply the knowledge of IOB to current boluses, but has no real knowledge of COB (Carbs on board). After all, it really matters what type of carbs you ate, how you personally react to carbs, etc etc. Action can vary from 30 min to 4 hours or more or less, depending on what "carbs" are.

Two ways I could see it possibly working: If we could enter the expected action for the particular carbs we eat, informed the pump of the carb action. (Obvious problem occur in trying to quantify carb action, it's such an individual things between carbs and between people, and between life situations, and difficult for us to find out a meaningful "number" in the first place. I'm not saying this to dismiss it, though, maybe this could be workable.)

Another way, is if the pump could take into account the recent blood sugar trend (eg, seeing a rapid trend down via CGMS) and have some kind of protocol to adjust doses to deal with BG "vertical velocity" if you will.

For the moment though, if you feel this is a problem, you will need to decide for yourself if that IOB is likely to send you down further or not, and adjust it out manually.

[Subby]

Looking over that I'm not sure I got to the point very clearly. I suppose in a nutshell, the pump is blind to what carbs are in your system from before the current event. You can explicitly TELL it that you've gone low, thus it knows it should under-correct, but it will not predict that you are going to go low, as far as it knows you still need that IOB for previous carbs. Perhaps it should predict carb action in some general way, at this stage I'm really not sure how you'd come up with a useful setting.

And I can see the point of not automatically allowing for a BG curve, there have been times when my BG was rock steady for the 6 hours surrounding a high carb meal/bolus and I thought "this is awesome, it's the theoretical aim of pumping and sometimes it works". I hope to get more of that happening. So there can be virtually insignificant curves when it's working at it's best.

[Gary_W]

Hi Subby,

The problem is if you are 0.1 OVER target or 0.1 UNDER target, it takes off the IoB... it's just if you're in target it doesn't. If you are correct in them trying to account for carbs on board then why does it account for IoB when higher OR lower, but not just right?

I agree with what you are saying about the carbs and insulin still fighting it out, but that is where judgement comes in; if I test as a 5.0 at the 2 hour point and I know all the stuff I ate was high GI, I'm confident that I'll be going hypo and will have an apple or similar to soak up the excess. If my meal was nice and brown and had fats etc to slow it down, I'd leave well alone and see where things were going by testing again 1/2 hour later. Equally, when I'm high at the two hour point it is possibly that I've spiked due to eating the wrong stuff, and that the remaining IoB will bring me down to range without intervention. Again, a judgement call. When you've made that call, it would be helpful if the pump did the maths in a consistant manner! Maybe the 'carb battle' is something to do with the reasoning behind it. I've emailed the pump rep and will try to get an 'official' answer as to why it does it like this.

Gary

[Subby]

If you are correct in them trying to account for carbs on board then why does it account for IoB when higher OR lower, but not just right?

Not my point at all, sorry if I was unclear, I was trying to say the opposite. The pump DOESN'T try to account for carbs from previous boluses (just the current one). It assumes the previous bolus was correct and that your BG is in range... unless you put in a BG that contradicts this. So if you put in a BG that is in range, it doesn't see the need for a correction. Implicit in this is a blanket assumption that the previous bolus was indeed correct for the carbs you had, thus the IOB is fine and dandy. Which is of course possibly untrue.

That's it in a nutshell. It is always correcting to get back to the target range. If it is higher or lower, it has work to do. If it is already there, it simply has nothing to do, mission accomplished.

You are saying "why doesn't it predict you will go low". It can't because it doesn't have a tracking or predictive ability with carbs and whether the previous bolus has correctly covered the previous carbs. It can only work with BG and insulin parameters to keep calculating back to the target.

You say it's an inconsistency in the maths, I don't think it is because the equation revolves around the parameter of how far away from your target you are. If the result returned from that is 0, then there is no calculation to be had - and no result.

Your general point that this is a pretty limited system that in situations could require user intervention, I agree with you 100%. But I don't think it can be considered some kind of error or inconsistency, it just isn't sophisticated enough for the kind of predictive function you are talking about.

If I'm just confusing things more I'll leave it up to someone else to explain it :)

[milfordj]

Gary, I agree totally with Subby's replies. When I first read your inquiry I wondered the same thing, but after reading Subby's reply I did understand why the pump does not adjust for IOB. Your comment, "The problem is if you are 0.1 OVER target or 0.1 UNDER target, it takes off the IoB... it's just if you're in target it doesn't. If you are correct in them trying to account for carbs on board then why does it account for IoB when higher OR lower, but not just right?" I think is wrong. I do NOT think the ANIMAS 2020 makes any adjustment in insulin dose based on wheter IOB is Under or Over target range because that is a separate issue. I used to look up my IOB before treating a hypo to determine the amount of carbs I needed to injest and would consume MORE carbs if I still had a good bit of IOB. I then invariably overate because, as Subby said, my IOB was still treating my yet-to-be digested carbs. I no longer check my IOB. One other consideration in this matter (not that we need ANOTHER), is determining the correct IOB for the insulin you are using. I use Humalog, and have varied the IOB Basal setting from 3 - 4 hrs, but have no way of knowing exactly how to set it, as this cannot (to my knowledge) be "tested". This is another reason I tend to disregard anything my pump shows for IOB. I asked an Animas rep whether the pump varies the insulin dose for different IOB settings, and was told that the pump did not vary the dose if set higher or lower. So why have an IOB "setting"? Very Confusing.

[Coppernob]

Gary, I think you are doing a great job and so soon after becoming a pumper.
The question you are asking is one that I struggled with for ages (before I saw the light and joined DF) - I think that Subby's explanation is spot on. If I feel I might go low, then I adjust for the IoB but at other times I let it be as I know that the carbs are still working their way in. When I am going to bed I am especially vigilant of IoB - there are times when my BG is low normal and there's 1+ units of insulin around. Then I'll have a small amount of carb to soak it up.
Keep asking those questions as it helps to refresh my memory! :)

[JediSkipdogg]

I think there was a topic on this a while back where Cyborg and I tried to figure out the IOB. I think we came to the conclusion that it is flawed. Unfortunately, Animas won't give out the magic formula that they use. I wonder if this is only an Animas problem or if other pumps do weird calculations as well.

I may have to do a bunch of test entries to see what happens in different instances.

[Gary_W]

Thanks for all the replies, folks.

Jedi - The calcs aren't weird; I will post the table later showing all the IoB remaining for settings from 3 hours through to 5. That's how it does the maths. It then recommends subtracting this IoB from a bolus IF you are outside your BG range at that moment in time. High or low, it matters not.

Milford - Again, look out for the table I'll post; it may help to explain how it does its calcs.

Coppernob - I see where you're coming from.

Subby, I can see what you mean now and thanks for taking the time to explain it again. It is something that I can agree with the logic of in certain situations, but not in others.

In all, this part of it makes my brain hurt at the moment. I just looked at my copy of 'Pumping Insulin' and it effectively says in there that the different pumps all give slightly different results as far as taking 'bolus on board' into account; the upshot of his advice was summed up on P.49

'As long as the user knows how their pump works, they can select appropriate boluses for each situation'.

He goes on to give an example where the Animas would not recommend a bolus, but one is clearly needed... I'll paraphrase slightly.

You have the pump set to a duration of insulin action of 4 hours. Say you have eaten 100g of carbs for your main course meal. You cover with 10u of insulin. At the two hour point, you blood test and you are just slightly above your range at a BG of 5.9. Not a problem as you have 3.80 units of insulin left (I know this due to the experiments I did). That 3.8u would potentially drop you through the floor, but, applying Subby's thinking above you should not panic as you carb counted correctly and the 3.8u will be counteracted by the slower acting bits of your meal. All is well with the world.

The problem comes when you then decide to eat desert. It's fairly low carb for a desert, with 35g of carbs. You put this number into the pump and it tells you that you need 3.5u of insulin to cover the carbs. It then notes that you are 'out of range', albeit high, and it decides that you should knock off 3.8u due to Insulin on Board. So it tells you that you need no insulin. You take the pump's word for it, eat the desert and then spend hours recovering from a raging high because you HAD carb counted your original meal correctly and the 3.8u 'on board' was already spoken for by the chick peas cooked in lard that are taking an age to digest. The icing on the cake you just ate is the icing on the cake of your BG...

Sorry to labour the point here. I think that it's potentially a great feature and it is certainly useful compared with the wonders of MDI... I think it is very badly explained in the manual (as in it's glossed over completely) and has the potential to get you into trouble if you take it as red that it knows what it's talking about. It gives you useful information, but it depends entirely upon the situation as to how that information should be used. As a feature, it is obviously fairly poorly understood; I consider myself to be reasonably switched on, and I'm having great difficulty getting my head around it. Subby's point about it not being able to predict a low is, of course, completely true. The pump cannot possibly know everything that is going on with you and as such, a healthy dose of common sense is needed with any of the recommendations that a pump gives. I just think they should be a little more open about how useful the feature is and also give examples (like above) where it would not be helpful...

IMO it would be better to always show IoB on the bolus wizard screen but to never recommend what to do with it, as 'what to do with it' depends COMPLETELY on the situation. As it's algorithm to decide whether to count it or not depends upon your BG being 'in range' or 'out of range', it is making a recommendation when it only knows 10% of the facts. Few people will realise why it is recommending the dose it does, and it can clearly get you into a world of hurt if you blindly follow it. And, in the absence of clear guidance in the manual, blindly following it is something that some folks will do.

Gary

[Coppernob]

13 years of MDI
And then a little pump floats by
And now my pants are filled with tubes
That tangle all around my.... er .... knees

The hours I'm hooked up? All twenty four
And that's it for now until evermore
But I disconnect for up to an hour
For wonderful fun (and sometimes a shower)

And when I 'suspend' it, it plays Barry White
And my wife knows she's in for one heck of a night
But only an hour of that night is with me
As an hour is all I'm allowed now, you see...

You are just too funny :rofl:

[Subby]

All this talk is very worthwhile Gary, it helps me work things out myself and I am reminded again not follow the recommendations too closely at times.

I'm not sure if either there is a difference in the way that pumps calculate their corrections boluses or if you might not have completely tested it, but in the scenario you described in your last post my MM would always still bolus for the food, so the 3.5 would remain.

The IOB is only taken into account with the correction component, not the food bolus component. This avoids the problem you are talking about. Here is my year 10 maths level of describing the equation. At the 2 hour mark bolus you described:

Variables:
(from BG input) Correction bolus = >3.8 (any number will do)
IOB = 3.8
Carb bolus = 3.5

Calculations:
A). Correction bolus minus the IOB equals the actual correction, with 0 being the lowest correction
B). Actual correction plus carb bolus = TOTAL

A). 3.8 (or greater) - 3.8 = 0
B). 0 + 3.5 = 3.5

Therefore the pump would still cover the carbs with a bolus of 3.5. And again "in a perfect world" you end up wonderfully in range a few hours later. (hehe... from the sounds of your BG thats a decent chance. I generally count myself lucky if I don't hit double figures. My nick should be Mr Brittle).

Again, perhaps there is a difference on the pump calculations between models, give it a go on yours when you can. If the example is instead "flawed" let me say I've only stuffed up about 5 times today dealing with complicated things like this... and counting. It all really hurts my head too. I agree things should be explained better and that the adjustment corrections should be monitored carefully.

If however your pump does in fact keep your carb bolus intact like mine, you can relax a bit about the correction problems!

[Subby]

Oops, I stuffed up, as if it wasn't already confusing enough. Here's what the pseudo maths bit should have looked like:

Variables:
(from BG input) Correction bolus = 3.8 (or any smaller number will do)
IOB = 3.8
Carb bolus = 3.5

Calculations:
A). Correction bolus minus the IOB equals the actual correction, with 0 being the lowest correction
B). Actual correction plus carb bolus = TOTAL

A). 3.8 (or lesser) - 3.8 = 0
B). 0 + 3.5 = 3.5


If the correction number happens to be bigger, of course the IOB will be subtracted from it, but again the carb bolus will remain the same. None of this feels intuitive at all, but that particular problem is mine, not my pumps :)

[Gary_W]

Hi Subby,

The pumps DO do calculate these things differently; the 'Pumping Insulin' book states this. On the Animas it recommends subtracting 'insulin on board' from either a carb bolus OR a correction bolus if the BG value you put in is OUTSIDE your target range. In light of the changes, we all just need to be aware of the spirit of the advice on the pump we own which may or may not be appropriate.

On the Animas, it seems to be opting for patient safety in the short term (i.e. hypo avoidance) at the expense of not always being correct and I can see where they are coming from here. I've given this a great deal of thought and have come up with the following. Please point out flaws in my logic, folks, or agree with me if you do :)

Examples of all the possible situations...

2 hours ago, you injected 10u to cover 100g of carbs. The possible scenarios are as follows:

Scenario 1: You blood test at hour 2 and find your BG is 15.0. Your target is 6.0. The pump makes the assumption that the 3.8u of insulin left 'on board' will still eventually work and so it knocks this off the correction bolus. It is also assuming at this point that NO MORE CARBS are being absorbed in your system. This is reasonable behaviour to do if you are high and I would take the pump's recommendations. I might give a bit extra due to corrections being pants at that kind of BG, but that's another story and you can't go blaming the pump for that :D

Scenario 2: You blood test at hour 2 and find your BG is 3.8. If you are anal enough to check your pump at that point rather than treating the hypo, it will tell you not to bolus. It will also tell you how much IoB you have still going and you can make a judgement call as to how much food you've still got absorbing.

Scenario 3: You blood test at hour 2. Your BG is in range. The pump recommends no action, but still displays IoB for your information. As with Scene 2, you have to decide 'do I really want to be 'in range' at hour 2? Will I drop before the insulin is used or is their still food in there fighting the good fight?

Scenario 4: You blood test at hour 2. Your BG is high (9.0) but you decide you're going to eat that 50g desert anyway. Bring it on! The pump recommends taking the IoB figure AWAY from the carb bolus. Dodgy advice IMO. The way I feel about it is this; if you are OVER target range and decide to eat, the Animas will recommend that you under-bolus. It is making the assumption that there is NO MORE FOOD in your system to use the IoB. This is a different assumption it makes than if you are 'in range'. It is the worst bit of advice of the six IMO as it will almost certainly result in a high BG reading. As stated earlier in the thread, if you are only just over your target range it can even make out that your desert can be freely eaten without a bolus.

Scenario 5: You blood test at hour 2. Your BG is low (3.9). You decide that the 50g desert is a great idea compared with glucose tablets but realise you'll need to cover part of it. The pump will already take a bit off the bolus for the fact that your BG is low (which is good). It will also knock off the IoB as you are out of range. Again, this could be dodgy advice; you may be low because you stuffed up the carb counting earlier. Equally, you could be low due to low GI food, Pizza effect etc etc. Again, the pump is making the assumption that there is no more food left in your system. It is a safe assumption to avoid further hypos but could result in highs later.

Scenario 6: You blood test at hour 2. Your BG is in range, and you go for the desert. The pump will give you the full bolus for the carbs and will disregard the IoB.

So in summary....

If you are 'in range' when you blood test, the pump assumes you got the carb counting right; any IoB left is fine, as it will be soaked up by (as yet) undigested carbs. If you are 'out of range' (be it low or high) it assumes you stuffed up the carb counting and that you have NO MORE active food. It therefore knocks the IoB off any bolus required (be it correction or carb) for the sake of hypo avoidance.

It's a dodgy decision if you're eating when JUST above your target range. This is very possible for me and others, as (after discussions in the other thread about setting 2 hour targets higher) it came out that many of us seem to set an all day long target which is fairly low. If I go back to setting a higher target at hour 2 after I typically eat (hard, as mealtimes vary) then it will give better advice re IoB as I am a bit more forgiving of my 2 hour post prandials than I am of my pre-meal. I'm not going to do this, as it will then give dodgy advice on correction shots.

Best to leave the targets alone and be aware of all the above, although I may widen them a little; if you have a narrow target, the IoB will ALWAYS assume you have no carbs left on board becuase you must have 'got it wrong'. Depending on when you blood test, this may or may not be correct... It has helped me a great deal to write this down as it was doing my head in. For those that have stuck with this, well done and thank you! I hope my logic above isn't flawed, as I finally feel like I understand it. Please don't disappoint me ;)

Gary

[Subby]

Hey Gary, I've had a horrible day and I just don't have the ability to work with these things right now... but it's great you are working out exactly how your pump works and thinking about those scenarios. At a glance the pump logic seems right, but as I say I can't concentrate. Hopefully the behaviour of removing the IOB from the carb bolus can be gotten around without too much heartache, I agree it's not a good default behaviour!