We ran into a weird problem yesterday involving a sequence of bad sites. It puzzled me so much that I thought the story might be helpful to others.
We had an occlusion very early morning, and changed to a new pod. The pod worked fine, but reaction to insulin activation was a bit sluggish. Then, at dinner time, we programmed a bolus and waited for activation. But we never turned the corner. My son’s BG remained nice and even, and never went down. After 1 hour and 40 minutes, we programmed a second bolus for dinner still, and the same thing happened. So we changed the pod and tried again. The same thing happened to the third bolus. By then I was gobsmacked. I was starting to question everything: could it be the insulin? What if the PDM was only able to program basals but no bolus? Do we have a bad lot of pods?
I was concerned, since I felt that we had no control over BG right then. I spent time on the phone with Omnipod. They encouraged me to switch to a pod with a different lot number. By that time it had been close to 5 hours: my son was really tired, and had not been able to eat any carbs. His BG was still steady, trending very slightly down after having taken 3 consecutive dinner boluses with no carbs ingested.
So I decided to first test the insulin alone, to rule that out, and to call the big guns. We injected 2 units of insulin from a pen, and waited it out. I also called @Eric (the big gun) I asked him what he thought. Eric believed that it was unlikely to be the pods, the PDM or the insulin. He felt it had to be a site issue. He suggested that, in my pod change, I look carefully at the canula when removing the pod, then test the old pod once it was out to validate that it was working.
In the meantime, the pen insulin activated and my son was able to finally eat something. Then we removed the pod carefully (without deactivating it), pulling it off the back to be able to have a good look at the canula still in the flesh. The canula looked good but there was some blood right around it. Once the pod was totally off, we programmed a bolus. We hear the old pod click and saw the insulin come out. So we knew the pod was good—and yet my son was not getting insulin. It had to be a site problem.
So we set up a new pod (from the same lot number) and my son turned in for the night. He was reacting well to basal overnight, then, when breakfast came, his insulin activated fine.
So, in the end, what happened? It seems to me that all three pods had a site problem. The first one may have had a slightly bent canula: when I looked at it through the window, it was in, but did not look 100% symmetrical. The second one seemed perfect, but there may have been some mysterious positioning issue. The third one had some blood right around the canula, which may have caused absorption problems. Either way, all three are likely to have been site issues, as @Eric suspected (although, for the second one, it really really be any other cause, including a weird pod failure).
As a data point, we have only have one site issue every since we started on the Omnipod about 6.5 months ago. So, to me, the lesson of the story is that, of all problems we are likely to encounter, site problems are the most likely: it is clearly possible to have multiple site failures in sequence, even though you change the site every time. I still find it hard to believe that we could get 3 site failures on a row—yet it is most likely what happened.