[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

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!