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Re: [IP] Will the true canula volume please stand up?
John Neale wrote:
> Then I found another variable... Remove the cartridge from the pump, but
> with the primed tubing connected, and draw the plunger back a tiny bit,
> so there's a bit of air showing at the cannula end of the tubing. Raise
> the pump high in the air, keeping the free tube end at waist level, and
> hold you finger where the air bubble is. Then lower the pump right down
> to the floor, again with the tubing at waist level, and see how far the
> air bubble moves. It does move. But the amount varies. It depends on how
> many of those little air bubbles are up in the cartridge. The head of
> water (24", 48" or whatever) is enough to expand and compress the air
> bubbles. This can sometimes amount to 0.5 units or even 1 unit if
> there's a big bubble stuck in the cartridge.
Maybe that's why we're supposed to clear all bubbles out first? Of course that
doesn't mean it's absolutely going to happen!
I had a message back when I mentioned that I park the connector on
top of my medicine cabinet mirror when disconnecting for a shower.
Bob Burnett said he did the opposite, leaves it hanging down. I
do it because it seems as though it will refill the connector when
I take it down, but leaving it hang may drip some out leaving air in the
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> So when you prime the pump and tubing, it may be important to keep
> everything at the same level that you normally wear it, to prevent
> insulin being pushed or sucked up and down the tubing.
Actually I hold the canula end between 2 fingers of the same hand I
hold the hub with when I connect it, at least when refilling. That way
I don't drain any out of the hose on either end while juggling it all.
Similarly, if you keep your pump high up in your
Gee, I never had THAT problem..... :^}
then when you go to bed, the pump is lowered to roughly the same
> level as the canula, the resulting compression of the air bubbles may
> cause a back pressure, which will deny you your next hour's basal.
I never considered it as being caused by entrained air, but you're
probably right. I just thought it was more a difference in head pressure
affecting the amount that comes out of the canula, but that is flawed
thinking, isn't it.
> Sorry if this sounds a bit technical or confusing! I'm just trying to
> logically describe what I've observed.
> This might partly explain why some go high after set changing, while
> others go low. It all depends on how much air is accidently trapped in
> the system, and the relative levels of your pump and infusion site.
Also what is the effect when the pump stays on your belt and you lower
it's relative level when spending time sitting in the "necessary" room <G>.
Guess it will just return to normal when you get it back to normal position.
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