Insulin on board algorithms in pumps

Hi...

I have a question about bolus advice when there is active insulin involved. I use a Medtronic pump.

Here's a scenario...

My carb ratio is 1u:10g, my correction factor is 1u:3mmol/L, BG target 6.5mmol/L

My BG is 6.5 and I eat 60g food and take 6u of insulin. In the next 2 hours I do a little exercise but nothing too dramatic. I then decide to have 30g (3u insulin) of food which is 2 hours after the 6u I took. I test my BG and they are 7.0mmol/L. Clearly I have insulin still working (approx 2.3 units). My pump will still suggest that I take the full 3u even though it will show that there is insulin on board. Why? Should it not take my lower than expected BG levels into account and suggest something like a 0.9 U dose?

It appears that most calculators use an algorithm similar to this but I don't see the reasoning behind this as in this scenario that is not unusual, I will clearly have a hypo if the full dose is taken.

Thanks

Hi Jim, I use a ACCU-CHEK COMBO.
Active Insulin means there has been a correction, so that's gone don't worry. The 6 units of insulin you had is at it's peak 2 hours after. Therefore, if I was you I wouldn't have any insulin with the 30g carbs, to do so causes what's called STACKING and will probably cause an hypo. Remember that no insulin with the 30g will increase your BG level, better that than an hypo. It will be corrected the next time you test and take on carbs.
Ultimately you have to do what you're comfortable with. GOOD LUCK!

I am also on a Medtronic pump, the paradigm 754........

your pump should only recommend you take the full 3.0 units if the correction of the 7.0mmol equals that of the remaining insulin....I think..........

I would love to confirm but I have no more insulin left and I am 4.2......

Does your pump not subtract the active insulin and then add a correction (which can also be negative)...?

Thanks for the responses guys....

Davey38 - your comment 'Active Insulin means there has been a correction' is only applicable to the roche pump as roche only count correction insulin as active insulin. Medtronic and every other company count any insulin taken as active insulin.

novorapidboi26 - Medtronic will only subtract the active insulin from the correction part of a dose if the correction is greater than the IOB. So if no correction is needed the pump will not subract the IOB from the bolus suggestion, which personally I think is wrong as it could lead to a hypo in the scenario explained above.

If no correction is suggested when you test mid meal, this means that the IOB is sufficient..........

Maybe if the difference between the correction is less than 1 it might just suggest the food insulin only.......

I need to set up the above scenario for myself.......its very rare for me to be lower than I thought mid meal, unless there is alcohol in my system......

Thanks for the reply novorapidboi26. I agree about the scenario being fairly uncommon, but possible if you were to do some light/unexpected exercise or unknowingly overestimate your insulin etc between the 2 meals. I am just not sure why the pump wouldn't take the IOB into account for every dose instead of just when a greater correction dose is needed.

Have you tried rapid calc app for iphones? I think this has better algorithms set within it.

I am on android so haven't looked, I used to use apps now but my pump takes care of everything to my satisfaction now..........

I just tested my BG there and it was 5.4 and I planned to have 22g of carbs just over half way through my insulin action, I have 1.5 units remaining.

BG: 5.4
Carbs: 22
Food Bolus: 2.7 {8:1 ratio}
Correction: -0.1
IOB: 1.5

So the pump suggested 2.6 , which is food bolus - minus the correction, so yeah, I can confirm that happens, but why?

If the correction was more than the IOB, then there has been a miscalculation and there is not enough insulin to get you back on target. So the pump would offer the correction and also consider what is still on board.

The reason it doesn't remove IOB from a correction less than the IOB is likely because the pump is assuming the IOB is still present to process the remaining carbs on board.

So for my scenario above, the pump made the assumption that the 1.5 IOB was still there working on the breakfast carbs, and so all of that 1.5 is still required. Theoretically this 1.5 would still be required even if I had ran to work and was low when I tested. And so it uses the negative correction instead to drop down the final bolus.

Reading this back sounds quite confusing...........lol....

I think extra activity uses glucose stores from your muscles directly, and so the carbs you had eaten previously are still there, the drop in BG is down to the muscles absorbing back from the blood stream.

I think that is the logic behind the algorithm.....

Hi novorapidboi26,

Thank you for the reply and good reply on perhaps the logic behind the algorithm.

It would be good to get a reply or comment from someone who is an HCP dealing in pumps or from a pump company wouldn't it?

Thanks

The pump company for sure............its likely we as pump users know more than the HCP's...

It happened again for me this afternoon, correction was less than the IOB........only by a few decimals right enough....