Omnipod IOB Calculations

Need some help figuring out how the pod calculates the IOB. Here is a little example:

@ 3:50 bolused 2.3 units as correction for high BS
@ 4:10 bolused 5 units to pump out air bubbles

checked bs at 5:00 and, using the bolus calculator, the PDM says I have 1.3 units on board. My active time for insulin is 3 hours. I'm no math genuis, but shouldn't it have said at least 1/3 of my bolus from 4:10 was on board (thus 3.5 units)?

I know stacking insulin isn't ideal. I was dealing with high unresponsive numbers yesterday for over 6 hours and, after checking to make sure the cannula was still inserted and knowing I hadn't changed my diet and wasn't ill, decided to give a big bolus to get any air bubbles out. Found out this morning that my cannula was bent (fabulous!), but I'm still confused about the pods math skills. Can anyone explain it or tell me where I'm wrong. Thanks in advance!

I've never heard of bolusing to pump out air bubbles. There shouldn't be any air bubbles. Were you advised to do that, or did you come up with it on your own?

In the IOB calculation, the pod is different from the other pumps. The pod only uses boluses that were given for high blood sugar to calculate IOB, not boluses given for food/carbs. So in your example if the 2.3 units were given to correct a high BS at 3:50, then at 5pm, between a third to a half of this dose should still be on board and acting (i.e. the 1.3 units). The pod does not consider insulin given for carbs as IOB because it's there to counteract the food you ate. So in your example, if the 5 units at 4:10 were given as a meal bolus, none of it would ever factor into the IOB. Does this make sense?

That makes perfect sense! Thank you so much!!

Advised by my pod rep (who is also on the pod).

I've never heard of "pumping out air bubbles" from a pod. There's only something like 11 mm of tubing inside the pump, and those cannot be seen at all, so I'm having trouble understanding how you knew there were air bubbles and how you knew to bolus such a large amount (5 u) for this occurrence (5 u is much larger than the 11 mm distance of tubing). Can you give more details about what, exactly, the rep said?

Also it looks like Allie has already answered the question, but I'll add that any bolus you give that is not a correction and is not for carbs (for example hit "bolus" from home screen, then hit "no" to BG and hit "no" to carbs, and you can still dial up units of insulin and confirm that for a bolus) will also NOT be counted in IOB. So in either case of you giving those 5 additional units (whether you somehow calculated a carb amount or whether you did what I mentioned above and bolused w/o BG o carb input), it wouldn't be counted in any future calculations.

I wouldn't do that if it were me. If there are bubbles, it's not as easy as just "pumping them out". I say that because bubbles that small don't float around, but just stick to the sides of the resevoir. Extra pumping won't do anything at all to those bubbles. Best solution is to work really hard to not get them in there at first. I noticed that you almost always have some bubbles in the syringe, and can't get them out. But, if you don't put too much pressure on filling the pod they usually don't transfer to the pod. I fill my pod rather slowly, in that I'm barely 1/2 way down by the time the pod beeps. My trick to get as few bubbles as possible is while filling the syringe, pull insulin a little way, then wait a second and push some back into the vial. That allows the big bubbles to get to the top, and be pushed back into the vial. I do that as many times as it takes until the push back in no longer produces bubbles. A tap/flick of the syringe a few times between these helps too.

As far as math skills, the pod is made that you really don't need any. You're supposed to just put in the carbs, and your take your BG often and the pod does all the math for you. If you keep your diet steady and solid, the only thing that will get the BG numbers off then is the rare occurance like you had with the canula, or if you have bad spots where the insulin does absorb well from the pump into your body.

One thing I do hate, is that the PDM doesn't carry "on-board insulin" between pod changes, so you do have to do some math there if you eat soon after you've switched pods and if you've bolused for correctly recently.

Sure Bradford! The rep told me that she often experiences differenct absorption/bubble issues and registers bs in the 200s. She experimented and found the right amount to bolus to correct for these (which is different for every person based on her/his current basal needs). If she has a bs over 200 after a previous correction (and all other factors are constant) than she figures there is something causing absorption issues (unresponsive tissue, bubbles, etc.) and will bolus accordingly. She never advised me to bolus 5 units. There were many circumstances that lead me to bolus that much (5 units is 1/2 of my total daily basal-I know it was a lot). It was my first pod using humalog and I was worried that it had stopped working properly. I had been running over 350 for 6 hours-but it had remained fixed. From prior experience I knew that my bs spikes much higher if I am receiving no insulin. So, after checking the cannula through the window and finding it still inserted I decided to do a huge bolus and see if my bs moved at all. If there was little/no movement I would know that I needed to change my pod due to poor insulin/kinked cannula. If my bs responded than I would chalk it up to absorption issues. Hope that explains it and thanks for explaining the IOB!

This picutre is awesome!

You made 2 boluses within 20 minutes.
In 20 minutes the first bolus was just starting to act and bring down your BG, you can't expect a correction bolus to show in your BG readings in such a short time.
I think it's very very dangerous your "correction method" , and never heard of.
If you have steady high readings, try instead putting a higher temporal basal, or just change pod (you can't see if it's kinked).
Bubles to little or nothing to your high BG readings, it's wrong basal, fat or protein rich meals you are not used too (ex.: pizza or only meat meal), or occlusions.

Thanks for your concern garidan! I agree-the first bolus wouldn't have shown in my bs readings w/in 20 minutes. I explained in my response to Bradford that this was my 3rd correction bolus. I had experienced 6 hours of over 350 readings that were holding constant. When I checked 20 minutes after my 3:50 correction, although I couldn't tell if it had started working yet, I was certain that my previous 2 correction boluses had been delivered and were out of my system. I decided that I would do a huge bolus and if my numbers didn't move I would change my pod.
As for the bubbles-I frequently register over 200 readings 12 hours after changing a pod or on the third day. I've only been on the pod for 3 months (after 11 years on MM) but I've come to 2 conclusions: if my bs is high 12 hours after a pod change I know that I can bring it down with a little extra bolus (or a temp. basal). My pod rep explained to me that, in her experience, this is due to abnormal absorption. Whether that is tissue related/some air being forced through the cannula the outcome is the same for me-I need to increase my insulin intake to bring down my bs and get my body/the pod used to the new site. If my bs is high on the 3rd day I know that my site has started to lose compatibility with the pod and I need to increase my insulin intake. I am still figuring out what temp. basal to use based on pod location (arms, legs, etc.) to offset the numbers in the 200s.
Thank you for suggesting wrong basal or high fat meals-all good advice. However, I have recently run basal testing and know that my current settings are right (at least for now). Also, I am on a strict low carb diet and add very little variation to what I eat. Very little-really none at all. It was the only way for me to achieve stable bs. It removed one more variable. That only leaves occlusions. This was my first pod that had a bent cannula. Now I know what those bs numbers look like vs. poor site selection/absorption resistance vs. no insulin delivery numbers. If it happens again, I will act quicker to change the site.

Did you take it as a meal bolus ? Why ?