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Tom Trimble RN CEN
Flolan - Question re Peripheral Infusion Cannula Size


Flolan outpatients come to our ED with central line problems, and we may need to bridge them by changing over to a peripheral infusion. We have P&P and competency training to support this.

However, I am questioning, in my mind, the following statement:

"Patients must have an alternate IV catheter available (e.g. peripheral saline lock) in the event the Flolan infusion catheter fails. If peripheral access is being used, a larger bore (i.e. 18 gauge) is preferable."

I have the impression that the drug would be irritating to peripheral vasculature, although there is no mention of it in standard references, other than an incidence of local pain or infection. Cardiovascular adverse effects listed focus on the systemic responses and clotting. Lexi-Comp, however, lists a pH of 10.2 - 10.8, which would support my belief.

On this forum, an old posting suggests central infusion due to short half-life, and that patients can feel the difference. Half life is listed as ~6 minutes, which is certainly greater than circulation time.

To me, (my hypothesis), if the drug is so alkaline (e.g. Dilantin is 10.0 - 12.3), then it would be prudent to use a very small cannula in a large vein to maximize mixing with available distal-to-proximal blood flow, rather than obstructing that flow with a large cannula nearly the size of the vein. I believe that the infusate would be more damaging to the intima, and less quickly distributed through the body. This strategy has been consistently successful with KCl and Phenytoin infusions. Since Flolan is infused only at very small volumes and rates as a dedicated line without other drugs or fluids, there is no reason to use a large cannula. This does not gainsay that other larger peripheral access may be needed in case of emergency treatment.

Alternatively, the P&P is silent, and therefore unclear as to the size of the Flolan catheter (specifically); but, the language contributes to an impression that a larger cannula should be used.

I believe that greater injury to a limited supply of peripheral infusion sites is unacceptable when no emergent conditions exist. 

Please help me understand if there is an evidenced reason that a large cannula should be used or that my hypothesis is wrong. I will approach the authors of our P&P, but I should like to know how infusion authorities feel, what evidence I may be missing, or what data shows.


Tom Trimble, RN CEN



Your thinking is clear,

Your thinking is clear, correct and on target. There is no reason for a large catheter. I have also seen these same recommendations in articles about IV Dilantin. I think there is the misconception that a larger catheters is more stable than a smaller catheter - no evidence to support this concept and much evidence to support the vein damage that it can do.

Also what you entered did not include any language about the type of pump being used. Gahart's Intravenous Medications puts a great emphasis on the mechanism of the infusion pump, etc. That is needed but also a smaller catheter is better.  


Lynn Hadaway, M.Ed., RN, BC, CRNI

Lynn Hadaway, M.Ed., NPD-BC, CRNI

Lynn Hadaway Associates, Inc.

PO Box 10

Milner, GA 30257


Office Phone 770-358-7861

Tom Trimble RN CEN
Thanks, a great deal! I am

Thanks, a great deal! I am grateful for the help.

We have standardized on the same CADD pump that our outpatients use (but supplied by the hospital while an inpatient) with, of course, back-ups of pumps, drug, vascular access to avoid any interruption. Those were not issues . . . just the seemingly mandatory 18 gauge in a person who will have much need for the use and availability of peripheral veins on a long term basis.


Tom Trimble, RN CEN

mary ann ferrannini
 I have found this to be a
 I have found this to be a common misconception as well. I am often asked to place a large gauge cannula for very irritating drugs,such as Dilantin and Calcium. I am always having to explain No that is incorrect and is just the opposite of what you are thinking.  But you got it understand the concept!!!
Tom Trimble RN CEN
Hi, Thank you for support. I


Thank you for support. I agree that one often needs to explain the difference between the need for a large-bore vein vs. a large-bore cannula; and, that a cannula not only infuses but also obstructs antegrade flow and wears upon the intima if it is too close a fit.


Tom Trimble, RN CEN

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