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[IP] Avoiding Bubbles

Hi, Curtis.

>There is another source of bubbles in the set.  It from dissolved air.

I didn't account for this because I don't use cold insulin. But it's 
certainly true. The next question is _how much_ air will there be?

I got out my old Physical Chemistry texts and checked.

Using Henry's Constants for nitrogen and oxygen in water at 0 deg C and 25 
deg C, the "air" liberated by warming from the fridge to room temperature 
can be calculated. After correcting for volumetric expansion per the 
Universal Gas Law...

...it can be determined that in a full 3 ml (300 unit) reservoir filled 
with cold insulin that's saturated with air, approximately 0.030 ml of air 
will be released by warming to room temperature. That's enough space to 
hold 3 units of U-100 insulin. This space isn't likely to be a single 
bubble, but many fine bubbles scattered around the reservoir. Still, that's 
a fair amount of air trapped inside the reservoir with no way to escape 
except through the catheter.

(It's easy to test this. Fill a reservoir with cold insulin, get rid of the 
bubbles and prime the infusion set. Let it sit for a couple of hours. Then 
look. What do the bubbles look like? Where are they?)

I'll amend my text as follows:

First of all, bubbles aren't magic. ** If the reservoir is filled with 
insulin already at room temperature, ** they're present because either they 
were _pushed_ into the tubing (from trapped air) or _pulled_ into the 
tubing (from a loose fitting).

Curtis -- Thanks for pointing this out!

regards, Andy

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