Difficulty extracting fluid from balloon via syringe

[blah2222]

Hello,

New to the forum, so apologies if this is not the correct sub-category.

I am testing compliances of materials by filling balloons with different fluids. I do this by filling up a 30 mL syringe with fluid and placing it into an infusion pump set to infuse at a rate of 0.1 mL/min. The syringe is attached to a serial pressure transducer which is then attached to a 23 gauge needle inserted into a PE-50 catheter (350 mm long). The free end of the catheter is then implanted into the balloon. To secure the implantation, the end of the catheter is flared with a lighter to make a small lip, then it is placed into the balloon via a small hole and sealed using a purse-string suture.

Following infusion I disconnect the catheter from the transducer and attach it to a 1 mL syringe and recollect the fluid.

One thing that I noticed is that in a lot of cases I cannot extract the fluid and there is resistance while pulling the 1 mL syringe. I have checked that the end of the catheter is in the middle of the balloon and not sucking the wall of the balloon. I can understand that if the balloon is being emptied, the catheter tip might not be in the remaining fluid, but I see this issue when the balloon is full.

I was curious to see if others might know what be happening and possible solutions to get around this issue.

What I can think of:
- flared catheter tip opening causing issues
- air?
- length of catheter
- equilibration of air pressure when transferring to 1 mL syringe?

Attached a pic of setup (green rectangle is pressure transducer):

Any help is much appreciated!

 

[berkeman]

Hello,

New to the forum, so apologies if this is not the correct sub-category.

I am testing compliances of materials by filling balloons with different fluids. I do this by filling up a 30 mL syringe with fluid and placing it into an infusion pump set to infuse at a rate of 0.1 mL/min. The syringe is attached to a serial pressure transducer which is then attached to a 23 gauge needle inserted into a PE-50 catheter (350 mm long). The free end of the catheter is then implanted into the balloon. To secure the implantation, the end of the catheter is flared with a lighter to make a small lip, then it is placed into the balloon via a small hole and sealed using a purse-string suture.

Following infusion I disconnect the catheter from the transducer and attach it to a 1 mL syringe and recollect the fluid.

One thing that I noticed is that in a lot of cases I cannot extract the fluid and there is resistance while pulling the 1 mL syringe. I have checked that the end of the catheter is in the middle of the balloon and not sucking the wall of the balloon. I can understand that if the balloon is being emptied, the catheter tip might not be in the remaining fluid, but I see this issue when the balloon is full.

I was curious to see if others might know what be happening and possible solutions to get around this issue.

What I can think of:
- flared catheter tip opening causing issues
- air?
- length of catheter
- equilibration of air pressure when transferring to 1 mL syringe?

Attached a pic of setup (green rectangle is pressure transducer):
View attachment 203701

Any help is much appreciated!

Welcome to the PF.

I'm guessing there is an issue with the flare that you are making by hand with the lighter. Something that would let you still fill through it, but would resist suction back through the tubing.

Have you inspected the flange after you had problems with it? If you cut the flange off, does it work then? Maybe you can come up with a different way to do the flange that doesn't involve melting the tubing -- maybe some sort of attachment you place on the end of the tubing instead?

 

[berkeman]

maybe some sort of attachment you place on the end of the tubing instead?

Some little plastic widget with the right ID, something like this:

https://www.industrialspec.com/shop/media/catalog/category/cfltfa_lxl.jpg

 

[blah2222]

Hi berkeman, thank you for the reply and suggestions.

I was thinking of making an adapter, but it is a pretty small catheter that I am using and I cannot changing the size of it.

The flared end of the tube is patent and not obstructed. It is usually the first try or so of the extraction that doesn't work but after moving the catheter around inside the balloon and wiggling it, I can eventually start the extraction.

Somehow I feel as though the issue is pressure related w.r.t. ambient air getting into the catheter when I am transferring between the infusion and extraction periods.

 

[berkeman]

Hi berkeman, thank you for the reply and suggestions.

I was thinking of making an adapter, but it is a pretty small catheter that I am using and I cannot changing the size of it.

The flared end of the tube is patent and not obstructed. It is usually the first try or so of the extraction that doesn't work but after moving the catheter around inside the balloon and wiggling it, I can eventually start the extraction.

Somehow I feel as though the issue is pressure related w.r.t. ambient air getting into the catheter when I am transferring between the infusion and extraction periods.

Can you do it a slightly different way? Use a Y-adapter near the balloon so you don't need to disconnect the first syringe to connect the second one? Are you using screw-on adapters for the syringes and tubing now, or just attaching the syringe to the tubing by forcing it into the tubing opening?

Like the Y-adapter near the end of this multi-port system (note the screw-on adapters):

http://cdnll.sharn.com/images/xxl/codan-anesthesia-iv-extension-sets.jpg

 

[blah2222]

That is an interesting idea. I might give this a try.

All connections are Luer-lock type.

 

[256bits]

To secure the implantation, the end of the catheter is flared with a lighter to make a small lip, then it is placed into the balloon via a small hole and sealed using a purse-string suture.

The flared end of the tube is patent and not obstructed. It is usually the first try or so of the extraction that doesn't work but after moving the catheter around inside the balloon and wiggling it, I can eventually start the extraction.

Are you collapsing the wall of the catheter by this technique?

 

[blah2222]

Nope. Catheter is in good shape. I think it may be air getting into the catheter before extracting.

 

[NTL2009]

Nope. Catheter is in good shape. I think it may be air getting into the catheter before extracting.

But air would not increase resistance (as stated in your OP), would it?. Since the balloon is compliant (I'm assuming, can't picture it any other way), it seems it would need to be a blockage of some sort. I thought the collapsing tubing was a good suggestion (it might collapse under vacuum, but allow flow under pressure), but you say that was eliminated as a cause. Any other component that might collapse like that?

Any chance the fluid becomes more viscous, or develops 'clumps' after filling that might block the tube? I like the idea of a 'Tee' so you don't need to change anything to go from filling to drawing.