central line flushing

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hi everyone!

i am a first year nursing student and i have a question regarding flushing a central line. why a 10cc syringe? we were told that it creates less pressure going in, but wouldn't using a syringe that has a large diameter actually cause more pressure? since it's going from a larger area to a smaller area wouldn't greater pressure be exerted? or am i totally off in this thinking? i was also thinking in the way that if a smaller syringe was used it would take more exerted pressure to be able get the fluid going thereby causing increased pressure?

is there a study on this? data or anything to show that a 10cc syringe really is the best method for central line flushing?

thanks for your time!!

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Specializes in cardiac/critical care/ informatics.

larger syringe less pressure. for PICCs and Central Lines we are to use at least 10cc syringe. It isn't the pressure that is excerted it is the pressure that is created in the lumen.

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Specializes in CVICU, CCRN, now SRNA.

There doesn't need to be a study... it's just simple physics.

Think about a stilletto heel and how much pressure that exerts vs. a large flat shoe. It is much easier to create high pressure with a small syringe than with a large one. jmgrn is correct, that it's primarily the lumen pressures we're concerned about when they're sitting in a vessel so close to the heart.

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the shoe comparison doesnt quite make it.....the syringe tip/exit is the same size in ea of these syringes, why is that not the controlling factor?

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Specializes in Anesthesia.

Interesting...I wonder if there has ever been a study done? We have to use pre-filled 3cc syringes for NS flushes because that is all we have unless we spike a NS bag. The 3 cc NS syringes we have are the same diameter as the 10cc syringes just shorter.

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Specializes in ICU.

Those prefilled 3cc salines have the same diameter as a 10cc, so they have the same pressure as a 10cc. It is the diameter if the syringe that makes the difference, not the length or volume.

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Specializes in 2nd Year RN Student.

i had it shown to me and it made sense... grab a 3-way on-off connector and hook up a 10cc to one spot, then a 3cc at the 90 degree so that both can be open at the same time... then push one while resisting the other... you would think it would be the other way around but as omermero mentioned... when the diameter of the syringe is increased, but the opening (tip) remains the same... then you're going to have to exert more pressure to push that fluid through the opening... which translates to a larger-diameter syringe producing less pressure.

go grab a t from the icu and try this... it'll impress your instructors and the others in your class as well :) none of my instructors could explain why, so like you, i was left to figure it out on my own. once you set up this little demonstration you'll be amazed at the difference.

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