Forum topic

11 posts / 0 new
Last post
Heather Nichols
Vein size for PICC placement

   I know this particular subject has been beaten like a dead horse, but I need some info on vein size related to PICC placement.  I know there are tons of info but I am wanting something quick and easy to understand.  Any suggestions?  Studies? Articles?  Thanks for any and all responses ahead of time!


mari fahrbach
Does anyone have problems

Does anyone have problems with getting anesthesia  to place Cl tips in the SVC? Our IR dept is totally on board , but anesthesia's standards seem to be blood return. As a result we see tip placemen in different sites outside the SVC.Nursing should not be using, but Anesthesia refuses to change.  Has anybody else delt with these issues and how did you resolve?  Thanks, Mari

Heather Nichols
     OK.  Does anybody
     OK.  Does anybody know how Bard came up with their vein size to catheter size ratios on their ultrasounds? (Site Rite 5 and 6)
Pam Jaspers
Heather, I cannot speak for


I cannot speak for exactly how Bard came up with the catheter sizes in relation to the vessel size on the Site Rite, but I did find a table on this website that does a fantastic job of showing what percentage of the vessel is filled with certain catheter sizes.

I was absolutely amazed to see that a 6 Fr catheter will only fill 16% of a .5cm vessel!

I have never seen any standard on how much vessel can safely be filled, but have heard that one should not fill any more than about 1/3-1/2 of the vessel.  I feel sure we will never get an absolute rule on this because there are so many factors that can contribute to the development of thrombosis, not just how much of the catheter is filled by the catheter (i.e., bedrest, coagulation status, hydration, underlying medical condition, medications etc.)   

I am trying to attach the table, but if it does not attach, I will try again on a new posting. 

Thanks to Mari K. Cordes for this document!

Have a great weekend!


Heather Nichols
      Thanks Pam.  I

      Thanks Pam.  I already found that one, but I could not find any supportive evidence for the size ratios.  I know that the diagnosis and any underlying conditions can contribute, especially one's like cancer, certain strokes, and quads, but my problem is that our vascular department will throw a PICC in anyone, and when they heard that we had been measuring the veins (for a long time now) and letting the docs know when and if a PICC was inappropriate, they wanted to know where we got our info from.  And you know the doc's..... Gimme the evidence baby!  Regular ole common sense won't get it.  I was looking for something concrete, and it looks like there isn't anything out there that is positive proof. The most I found was things like "biggest vein/smallest catheter" from INS standards, and the same goes for the PICC companies, but no one gives exact sizes, so that won't hold water.  Any ideas?  Anybody?



A 3FR catheter is 1mm, a 4FR

A 3FR catheter is 1mm, a 4FR Catheter is 1.34 mm, a 5FR catheter is 1.67 mm, a 6 FR catheter is 2mm.  And for those using reverse taper...7FR is 2.34mm, 8FR is 2.67, 9FR is 3mm.

Keep the size of the catheter at the point of insertion in mind.  That is what  you are comparing to the size of the vessel you are looking at under ultrasound.  

There should be an actual and accruate measurement of the actual vessel you are accessing to make this comparison, not an "ish" comparison based on pictures on the side of a machine.  If you measure your vessel in cm, mulitply by 10 to get mm.  So, if I look a vein in my arm, and it measures .34 cm across,  that would be 3.4mm.  If I place a 4FR catheter, I would be taking up 1.34mm, or 39%.  A quick way to do this multiply your FR size x2--that is the minimum size vessel you would put that in, as that would take up 50%.

Then compare your vessel in mm to the size of the catheter.  The rule of thumb based on the literature is the catheter should take up no more than 30-50% of the vein.  The more pieces of Virchow's triad you have, the higher the risk for thrombosis.  The more complications the patient has, err on the smaller side as not to add more to the risk. 

Dr. Markowicz at AVA 2007 presented an excellent program where he recommended 30-50%, and  Dr. nifong at his AVA 2007 presentation mentioned no more than 30%, I believe.

If your MDs are looking for evidence, discuss Virchow's triad with them, they should remember it from med school, that is what all discussions and literature surrounding thrombosis is based on.



While this is pretty much
While this is pretty much true, please keep in mind that you should take your measurements before applying the tourniquet. You will release your tourniquet after you place the line, so why take the measurement with it on, right? This will give you better results in the long run.
Pam Jaspers
I agree with measuring the

I agree with measuring the vessel with the tourniquet off, but we need to clear up the equation used to measure how much of the vessel will be filled with a given catheter.

Measuring the amount of space that a catheter will occupy needs to be based on a 2 dimensional measurement.  When one takes the diameter of the catheter and compares that to the diameter of the vessel, you are only measuring on a 1 dimensional scale (simply measuring a line).  In order to get 2 dimensional measurement (measuring a circle), you have to use the formula that will give you the area of the catheter compared to the area of the vessel.

Using the example given on 4/5/08, the area of the vessel that will be occupied would be 15%.  I am attaching the formula and the steps I used to reach this number.

I know this all is getting very technical, but the table from Mari K. Cordes does the work for us. 

I would also like to add that vessels are dynamic, not static entities and they can change size from minute to minute, as we all know when a vessel constricts and becomes pinpoint-size. 

As stated earlier, speak to your docs in terms of Virchow's triad. 

Heather, perhaps you can find something documented by either Dr Marcowicz or Dr. Nifong (as referenced above) regarding the 30-50% rule.  Once you have that, discuss the formula regarding the area of the vessel and the % of vessel filled by the area of the catheter and maybe that will be the evidence they are looking for.

I believe you have my number...feel free to call me anytime.

Halle Utter
Duh!  This makes so much

Duh!  This makes so much sense, and I have NEVER heard anyone discuss this before!  Am I dense or what!  I always thought when I looked with the Ultrasound at a vein with a catheter in it that it sure didn't look like it took up 30% of the space, but according to "the formula" that I was blindly following that's what it calculated out to be.  Now I see that this is not the case and I feel quite humbled.  (Always a good thing!)  Now my question is:  Does the rule of 30-50% refer to the AREA FOR SURE, and are there studies based on this that document it?  If so, smaller veins would accommodate larger catheters than we thought without causing a problem.  I would love to see some more discussion on this.  Just so this isn't missed by the experts out there I am going to post a new Topic so this important information isn't accidentally missed because it's only in a response.  


Halle Utter, RN, BSN

Intravenous Care, INC 

Hallene E Utter, RN, BSN Intravenous Care, INC

I would recommend using the

I would recommend using the vein to catheter size guide as only one tool in assessing patients for the right line.  When you do your U/S assessment, be sure to check the relative diameter (and compressibility) of as much of the length of the vein as you can.  Most veins will have some variability, even as they increase in size proximally.

We don't really know for sure that smaller veins would accomodate larger catheters - we need more research.

And - there are other risk factors (inflammatory disorders, CA, vein choice, insertion technique.....etc.).

Check out other threads on this website if you haven't already; there are some good discussions.






Mari Cordes, BS RN 

Nurse Educator IV Therapy
Fletcher Allen Health Care

Mari Cordes, BS RNIII VA-BC
Vascular Access Department
University of Vermont Medical Center

Thanks for your additions,

Thanks for your additions, Pam.  

Since I posted the mm squared (areas of vein and catheter cross sections) table, I've had 2 more engineers review the information and logic.  There is one small change - one engineer said that a 4Fr catheter is actually 1.33 in diameter, not 1.35.  It doesn't change the percentage calculation, however, and the rest of the reasoning and calculations are correct.

I'll be amending the table to reflect that shortly. 

Thanks to all once again for a very helpful discussion.



Mari Cordes, BS RN 

Nurse Educator IV Therapy
Fletcher Allen Health Care, Burlington VT

Mari Cordes, BS RNIII VA-BC
Vascular Access Department
University of Vermont Medical Center

Log in or register to post comments