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Reverse-engineering the Omnipod Bubble

Discussion in 'Parents of Children with Type 1' started by Darryl, Feb 14, 2010.

  1. Darryl

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    For those involved in the discussion of bubbles in the Omnipod...

    I took apart a pod and examined it, and found the following. Before you read on, my
    conclusion is: There is no reason to worry about bubbles in the pod as long as you
    keep the pod in any orientation other than pointing "straight down".

    Referring to photos below:

    1) The insulin port on the bottom goes has a rubber membrane where you inject the insulin.
    After that the insulin enters the pod chamber directly (see label "Fill Port" in the photo).
    There is nothing to prevent you from injecting bubbles into the pod's insulin chamber as far
    as I can see. So you'd want to be careful to keep bubbles out of the syringe when filling the pod.

    2) During priming or actual use, a bubble could theoretically exit the insulin chamber (see "outlet"
    in the photo). For this to happen, the bubble would have to be present exactly at the "outlet",
    meaning that the pod would have to be pointing "straight down."

    3) I tried this, by inducing an air bubble, then orienting the pod so that the bubble was exactly at the
    "outlet". Then I spun the gear, and saw the bubble move through the clear tube, through the "coupling",
    through the metal tube, and out the cannula. After the bubble was fully compressed out of the chamber,
    insulin filled the clear tube and continued out through the cannula. This means that there is nothing in
    the path from the insulin chamber to the cannula that would prevent air from making its way through.

    4) There is no evidence of any kind of bubble detector in the path to the cannula. Just a clear tube,
    a coupling, and metal tube that lies within the plastic cannula (the metal tube also serves as the insertion
    needle). None of these components had any electrical connection to the circuit board.

    So what does this mean?

    There is nothing I can see that inherently prevents a bubble from entering the chamber, and nothing
    could happen during priming as far as I can see that would froce out a bubble. If there was a bubble,
    and if it was flloating precisely at the outlet of the insulin chamber, it could make it's way to the cannula.

    However, the risk of this happening seems remote. For a bubble to exit the chamber, the pod's cannula
    would have to be pointing straight down, and held at a very specific angle in two dimensions. Even if
    the pod was in this position for a short time, only the "clicks" that occur during that time would expel
    air from the chamber. In any position other than "straight down", a bubble would rise to other parts
    of the chamber where it could not be expelled.

    My recommendation: First, prime the pod in any position other than straight down, and don't install
    the pod with the cannula pointing down. Either sideways or pointing up is best (We've only applied
    them sideways or facing up, dd prefers it that way for comfort anyway). Secondly, I would change
    a pod with <20u of insulin. If there was a bubble, the risk of the bubble entering the cannula would
    become significant if the bubble's volume approached the volume of the remaining insulin.

    Our experience in almost 3 years of pod use has been that we've not seen anything that would
    indicate bubbles are getting into the cannula.

    If anyone from Insulet is reading this, any comments or corrections would be appreciated.

    Fig. 1: Whole OmniPod

    [​IMG]

    Figure 2: Closeup of fill port, outlet, compression disk, and coupling.
    Note small bubble under "fill port" and how it floats to the top of the chamber.

    [​IMG]
     
    Last edited: Feb 14, 2010
  2. funnygrl

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    So what about Omnipod's advertising that it forces bubbles out automatically?
     
  3. Flutterby

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    Wouldn't the pod have the same chances of a traditions tubed set of having airbubbles reach the cannula? and maybe less of a chance as there is the long tube with traditional pumps so the bubble may be seen?

    The only way to prevent any bubble entering the pod or any other pump is if the reseveroirs were filled in a factory with a vacuum to pull the bubbles out.
     
  4. bbirdnuts@aol.com

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    This is great Darryl!!! I usually apply the Pod's sideways on the stomach or a little downward. Now when I will apply the Pod's I will make sure they are sideways or pointed a little upward.
     
  5. saxmaniac

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    Thanks, nice pics. How far did you fill the reservoir in this case? Is that 100u?
     
  6. Darryl

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    It was a used pod with around 60-70u left at deactivation. That's why I rotated the gears manually to force the insulin out.
     
  7. Darryl

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    I don't know... never seen a traditional pump up close.
     
  8. Darryl

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    I didn't know that. Where did you see it?
     
  9. etringali

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    How'd you get the darn thing open? I've tried and never had any success.
     
  10. Toni

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    Nice to have an engineer on the board, LOL. I kind of wish your DD was using one of the tubed pumps so you could analyze that one for us.
     
  11. saxmaniac

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    You do know the pods are disposable, right? I'd rather take apart a $30 pod than a $6000 pump.

    Taking things apart is easy. It's putting them back together which is hard.
     
  12. danismom79

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    That's good to know. We've gotten down to 9u, but I don't remember what kind of experience we had. The only time we have problems that I can't attribute to bolus or basal issues is when we change the pod.
     
  13. Darryl

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    Use a table knife - not a sharp knife, a dull knife, and using the edge, pry the cap off. It is held in place only with a rubber seal and will open if you pry it.
     
  14. Heather(CA)

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    Cool Darryl, Thanks for the info:D
     
  15. Flutterby

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    its not the pump that you would need to look at but the reseveroir. In traditional pumps the reseveroir comes out, unlike the omnipod, and then locked into place. If I can find my camera I'll take a picture of a filled reseveroir and the tubing.. If you look in the Pumping insulin book there is a picture of a MM reseveroir with bubbles inbetween the O-ring.


    The other thing I wonder is that with traditional reseveroirs there is a lube in the reserveroir to keep the insulin from leaking out, and keeping the O-rings sealed tight, if they are not sealed and insulin leaks out you loose pressure and the proper amount of insulin won't be administered. Before you fill a reseveroir you have to move the plunger back and forth to make sure the lube fully coats the inside of the reseveroir and isn't stuck in one spot, causing the O-rings to be leak prood.. So for Omnipod, how do they do this in the omnipod since you can't move the pludger around.. how to they make sure the lube isn't pooled in one spot (storage makes the lube college to one stop..)
     
  16. Toni

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    I wonder if placement of the cannula in the body (up, down or sideways) effects absorption or if placing the pump upside down in a pump pack (like we were told) prevents bubbles?
     
  17. danismom79

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    We use the pod, and I have no idea really, but regardless of the direction of the cannula at insertion, it will face all directions at some point. If she sleeps on her side, the cannula will be facing down, even though the pod is placed sideways on her stomach.
     
  18. buggle

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    Before pod change last night, my hubby removed the old pod and left it running. He injected 10 units of air into it. He told it to bolus 3 units, which it did without a problem in all sorts of orientations.

    Then he told it to bolus 4 more units, trying to get the bubble to go directly over the outlet. It still worked fine. While running, he took the back off the pod so we could see exactly where the bubble was. He filled the tank with about 50% air. Then he turned the pod over so that the air covered the outlet and it didn't work. :D

    It does seem possible with enough air to get the bubble in exactly in the right place to prevent it delivering insulin properly. But it would be difficult. My husband was surprised it did as well as it did with the big air bubble in it.

    Conclusion: Darryl is right. ;)
     
  19. Darryl

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    Well at least the fill port is underneath the pod, so there's no way to try this experiment with the pod still on the body!
     
  20. Lorraine

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    Pliers, for one, will work. But I was able to pry two open with my hands. I attribute it to determination. Caleb and I were out of town and two Pods failed upon priming. This meant the endless BEEEEEP. At home, I put those in the garage and forget about them. I could not do this in a hotel room. So I just pulled them apart with brute force.

    PS - the two Pods that failed were expired. I hadn't paid any attention to expiration dates until this happened.
     

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