The past couple days have been a BUMPY ride…night before last, 4 lows (and 2 juice boxes later). Last night, 2 lows (and 1 juice box later), and yesterday he skyrocketed up to over 400 for about an hour before finally coming back down. Today has been great…but wow, those days you can’t explain are just…I can’t even put the feeling into words honestly…
I call those days “Can’t win for losing” days. Or “WTF’s with this?” days.
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I find the remaining insulin to underestimate by 7-15U most of the time. The longer a pod is delivering small sips at the lower end of the fill, the worse this gets in my experience.
The main problem here is the pod really doesn’t have a precise mechanism for measuring how much you put in to start with. It only know its more than around 80U (otherwise the pod wouldn’t activate). It estimates when around 50U is left by the end of the plunger shaft making electrical contact with small spring, at which point it begins counting full turns of the plunger screw to estimate how much is left.
All of this is incredibly imprecise. As a result, the system deliberately underestimates remaining insulin, most of the time being off 7-15U (i.e. when it goes from 1U left to LOW, you still get another 7-15U out of it before it dies completely).
35U definitely sounds like a lot, but I’d put my money more on an outlier flakiness with the approximate remaining insulin mechanism rather than a leak.
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You do good work, Dave26 !! 
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There still has to be a ‘prime’ after insertion. Once the needle+cannula is pushed in, and needle retracts, there is ‘space’ left in the cannula. Assume that ‘prime’ takes place after insertion, without any notification to user. For MM pumps, the user had to initiate the prime to fill after actual insertion.
Ok, I will check it out next time I put on a pod. For every 0.05 units of insulin the pod delivers you hear a faint “click”. So I’ll count clicks after the cannula stab and see. I do recall there are a few clicks after the stab, maybe 4 or something like that. I just always thought that was the needle retracting.
I have experienced a rare situation where either insulin is pooling just under the skin (not being absorbed), or the cannula is kinked. Either way, the effect was BG continuously going up–me correcting–then at some threshold, a quick drop of BG. Maybe pressure built up enough to “push” a large amount of insulin through a kinked cannula or the insulin eventually did absorb–only it happened all at once.
I am still not entirely sure what happened. The result was several stressful hours of trying to raise up the BG.
I know that horrifying feeling! That hit me last week.
https://forum.tudiabetes.org/t/am-i-sitting-on-a-time-bomb-now/
I agree the way they implemented it is not optimal, but overall reservoir content could be estimated like the other pump companies do, and base it on the prime turns. But they are keeping the cost down, so I cannot complain too loudly about it. I like the Omnipod a lot.
I got the “errant” pod back and it had roughly 40 units left in it. That isn’t an underestimate - that is a bad pod. My bigger complaint is the “leak” theory the support rep gave me, while refusing to replace the pod because I “obviously did something wrong.” I called back this week and got a different rep. She quickly and cheerfully said “it must be a bad pod” and replaced it within 1 day. She also apologized that the other rep had not dealt with my call the first time.
Still a fine company in my eyes.
@kmichel, the main reason for imprecision is two-fold: No information on how much insulin was loaded (all they “know” is at least approx 80U is in it, and the mechanism that detects fill past 80 is the same as the 50U remaining detection), and the imprecise nature of the shaft/spring contact.
The fact that this contact estimates that you’ve put at least 80U in when it makes contact, and then when it loses contact later estimates this occurs at around 50U should give you an idea of just how imprecise it is.
The pump is capable of very precise delivery accounting, which it must be, of course. The problem is, when it knows there is about 50U left, it can accurately count down from there, it’s just that the 50 is a gross estimate, so we don’t know if we’re counting down from 50, 55, 65.
So counting pulses won’t make any difference in terms of estimating actual remaining insulin. The only way to make this work is 1) design in an accurate measuring mechanism (very expensive), 2) require user to enter insulin put in pod into PDM (too error-prone), 3) require a precision fill so the same precise (to the unit) amount is required to activate the pod (too inflexible).
What we have is the best compromise, I think.
I have actually primed several PODs off the body with saline to see that-- sometimes saline comes out–sometimes it doesn’t (actually taking up to 1-1.5 units before visually seeing saline). Air bubbles being a likely reason.
I have nothing to add but my own explanation of the unexplainable. “My diabetes is acting weird because I’m diabetic” 
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Keep in mind that the pod “over-primes” to ensure the cannula is completely filled; it’s not a problem since this extra insulin is discarded when the sealing tab is removed from the cannula port. That’s why the little silicone “claw” on the tab that holds the cannula firmly during priming is always wet.
So, if you instead apply the pod before priming, this insulin will instead absorb through your skin. It’s a fair amount for many people, and could cause an oddball hypo.
Yep, that makes sense. For a young one that could be make a difference.