20g-18g – 30%

The numbers may seem confusing but I’ve always wondered something and when I found a few expired saline bags in the storage closet I decided to do a completely scientific and infallible test.

Now that Rogue Medic is sitting up in his chair I will confess this is in no way an “accurate” demonstration, but all elements were equal so I can only assume that the same thing would happen proportionately under different situations.

Like, say, actually starting lines on people.

In the past I have made the in field decision, like many of us do, to get the 18g when others may try for the 16g.  But if I know I can get the 20g, but maybe get the 18g, shouldn’t I err on the side of some access is better than no access?

Maybe, maybe not.

So I went out to the workbench, hooked up a 20g angiocath and opened the line wide open.

How long do you think it took to empty a 1000ml bag?  More on that later.

Taking into account the widespread myth that D50 can’t fit through a 20g needle (then where does it go?) what is the difference between a 20g and an 18g?

“Large bore.”

In my wonderfully arranged protocol manual there is an entry under abdominal pain and multi-systems trauma that mentions starting “2 large bore IVs…” but does that mean a 16g? 18g?  Certainly not a 20g, right?

But it seems like such a small difference to step from the 18g to the 20g and slamming fluid into these kinds of patients can be debated all year long, but I have to follow my protocols.  So what is the difference in fluid flow between those two catheters?

30%

The 20g drained in 18:08.

The 18g drained in 12:31.

That’s a considerable difference and far more than I would have expected.  Maybe a few minutes, but 6?  So now wondering how fast a 16g can go, alas, I am out of expired bags.  But if the trend continues I would expect to be able to drain that 1000ml bag in 6 minutes or so.

6 minutes to run in a liter of fluid or 18 minutes just from going 16g to 20g?  That’s huge.

We all know that in a bumpy rig with other concerns that line can get away from us sometimes and you look up at what you thought was a slow bolus and see an empty bag, so I used to err on the side of time instead of volume, just in case.

But that was back when I had 45 minute transport times.  Now that I’m just a few minutes out should I change my way of thinking of getting access?

We’ll see, but I just wanted to pass along my experiment.

Stay safe,

HM

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18 thoughts on “20g-18g – 30%”

  1. I’ts just like fire hose and friction loss, also the length of the cath will have a suprising effect also, we did a bench test just like you with a short 14g and a long (I think 2″) 12g and the 14g was faster but I dont remember the times.

  2. Interesting! You can push D50 through a 20 but I much prefer an 18 or larger. I have class tonite so I’ll have to bring that up. I know we have expired bags laying around, I’ll have to see if my instructor will be willing to let us experiment!

  3. I'ts just like fire hose and friction loss, also the length of the cath will have a suprising effect also, we did a bench test just like you with a short 14g and a long (I think 2″) 12g and the 14g was faster but I dont remember the times.

  4. Happy, You know they list the flow rate on the package of the IV cath? You can mathematically prove that larger IV cannula will run fluid better (just like friction loss from engineer’s class).

    Why always transport immediately? You can start you IV before you start transport then you have any IV choice you want. Patient care is not always speed related.

    1. True, and true. But reading it on the packaging and watching it go really made an impression on me. But also keep in mind my Amiodarone says NOT FOR IV INFUSION and my King tubes say NOT FOR EMERGENCY USE. Packaging is great, practicing had more of an impact for me.
      And my caths have no marking on the package, perhaps it is on the box they all came in?

  5. Interesting! You can push D50 through a 20 but I much prefer an 18 or larger. I have class tonite so I'll have to bring that up. I know we have expired bags laying around, I'll have to see if my instructor will be willing to let us experiment!

  6. Happy, You know they list the flow rate on the package of the IV cath? You can mathematically prove that larger IV cannula will run fluid better (just like friction loss from engineer's class).

    Why always transport immediately? You can start you IV before you start transport then you have any IV choice you want. Patient care is not always speed related.

  7. True, and true. But reading it on the packaging and watching it go really made an impression on me. But also keep in mind my Amiodarone says NOT FOR IV INFUSION and my King tubes say NOT FOR EMERGENCY USE. Packaging is great, practicing had more of an impact for me.
    And my caths have no marking on the package, perhaps it is on the box they all came in?

  8. True, and true. But reading it on the packaging and watching it go really made an impression on me. But also keep in mind my Amiodarone says NOT FOR IV INFUSION and my King tubes say NOT FOR EMERGENCY USE. Packaging is great, practicing had more of an impact for me.
    And my caths have no marking on the package, perhaps it is on the box they all came in?

  9. True, and true. But reading it on the packaging and watching it go really made an impression on me. But also keep in mind my Amiodarone says NOT FOR IV INFUSION and my King tubes say NOT FOR EMERGENCY USE. Packaging is great, practicing had more of an impact for me.
    And my caths have no marking on the package, perhaps it is on the box they all came in?

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