Your catheter measurements are accurate. All French sizes are the
outer diameter measured in mm X 3. So a 6 French catheter would have
an outer diameter of 2 mm. I would agree that you desire to reduce the
internal vein diameter and blood flow by no more than 1/3 or 1/2 is
reasonable. It is also realistic to use ultrasound to measure vein
diameter but what you are seeing is the outer vein diameter. We must
consider that the inner vein lumen is smaller. Please correct me if I
am wrong, but I don't think that an ultrasound will allow you to
determine vein wall thickness and what is the actual vein lumen
diameter. I do think your practice is a good place to start though.
Lynn
At 2:31 PM -0400 10/19/06, Cheryl Kelley wrote:
This area of discussion is not scientific mind you, because there has not been data collection on it yet, as far as I know. But I would be happy to share the measurements with you that I use in my institution.
A 6F PICC is 2mm in size, and likely a 3F is 1mm in size. (Our team has the I-Look by Sono-Site, which has the capability to provide these measurements. The Site Rite 5 has recently been updated to include a visual interpretation of the vessel size) I ball part the 4F at 1.3mm and the 5F at 1.7mm. These are the base line measurements that we go from. I then look at the hypercoagulability of the patient, based on Virchow's Triad of Stasis and have deducted the following. If a patient has no risk factors according to the triad, then my goal is to decrease the blood flow in the vein by no more than 50%, therefore a 6R (2mm) catheter would need a vessel size of at least 4mm. The vessel is scanned to assess for narrowing on up the vein and if it is 4mm to the axillary, then I would place it. As far as a 5F (1.7MM) the vessel would need to be at least 3.5mm in size. When a tapered catheter is introduced, then as you can see, the size of the taper can be as much as 8-9F, or up to 3mm. Is the vessel at least 3mm at the point of introduction of the catheter? Maybe not, that is why I think that we are seeing some thrombus, beginning at the insertion site of the PICC.
If a patient is hypercoagulable, then the criteria changes. For a 6F, I want to decrease the blood flow only by 1/3 or 33%, therefore a vessel would need to be 6mm. Realistically, not a lot of patients have a vessel that is 6mm in size unless you go high in the arm, where the basilic and the brachials often join.
As far as what meets the criteria for hypercoagulabiliy, I look at three things--the vein condition, blood flow thru the veins and the underlying medical condition that can naturally predispose the patient to thrombus formation.
Sorry to be so long winded, but I think that this is necessary information for clinicians to understand when placing large lumened catheters. I have a great interest in this subject. If you want to talk further, please email me off the list so as not to clog it up!
Before you say, show me the data.....I will remind you that I am basing this on what I think and what I have seen, not published data.
Cheryl Kelley RN
PICC Nurse and Infusion Consultant
and
PICC Nurse at West Virginia University Hospitals
304-823-3196 or 304-669-3061
--
Lynn Hadaway, M.Ed., RNC, CRNI
Lynn Hadaway Associates, Inc.
126 Main Street, PO Box 10
Milner, GA 30257
http://www.hadawayassociates.com
office 770-358-7861
Lynn Hadaway Associates, Inc.
126 Main Street, PO Box 10
Milner, GA 30257
http://www.hadawayassociates.com
office 770-358-7861
