Q&A Report: Successful Modification of a Rodent Surgical Procedure and Device for Vascular Access in Minipigs (Vascular Access Button)
The answers to these questions have been provided by:
Adrian Zeltner, SRT
Owner
AZE Consulting
When you place two catheters in the jugular vein, do you use the same vessel incision for both catheters? Also, is one catheter longer than the other or the same length?
The two catheters are inserted into the vein through the same incision. Veins in Minipigs have a large diameter so there is plenty of room for two catheters. The length is different; depending on the size of the patient, it can be anything between 15 and 30mm difference. I make a note of the difference and which colour of the port corresponds to the longer catheter.
Does this system require a locking solution?
Yes, the use of a lock solution is advised. If the time between sampling is short, I only rinse with saline and lock the system at the end of the day.
Are there incidences of infection around VAB in the long run?
The few infections I have seen were mainly in the first period and only in cases when the felt/button did not grow it properly. The infections seemed to be secondary, in the sense that because the felt was not ingrown and sealing, the opening got infected (not the other way round). Please use strict aseptic technique while implanting. In the long run I have seen some slight necrosis around the neck of the button, but it was dry and because the felt was properly ingrown there were no infections.
How to we get the taller VAB? Which company did you get it from?
I managed to convince Instech to do a few prototypes and after testing them, we settled for a length that seemed appropriate. After that Instech produced a batch for me. I believe the stock is almost used up and it is time to have some more produced. As Instech has to change all machine settings, the long neck buttons have to be produced in batches of at least 100. At the moment I am collecting information of people that are interested in buying long necked buttons so I can get back to Instech and ask for the production of another batch. If you would like to join in, please write to me with the number of buttons you expect to use during 2024 at adrian@azecon.dk. Collectively we will have more bargaining power.
Do you utilize any imaging to confirm catheter placement near the heart?
No, I don’t. I work by landmark and experience. Catheter tip position is crucial when implanting in rodents, whereas pigs are more forgiving as the 3F catheter is in a large vessel with high blood flow even when it is in the cranial vena cava or even in the jugular vein. The catheters are not radiopaque but iohexol contrast with fluoroscopy could be used according to a webinar attendee’s comment. If you implant in a growing patient, the catheter tip will be pulled back from its original position as it grows.
For venous infusion, are there limitations for volume and rate?
There is no limit as such using this system. Of course, you need to observe the general recommendations for infusions based on the size, blood volume, and properties of the compound, like with any other infusion. The limit might be the viscosity of the compound you intend to use. The smallest diameter of the system is actually not in the port or catheter, it is in the PinPort injector that you have to use to access the system. I believe it is 27ga.
How much length of catheter is inserted in the vein? Do you insert all the way to the right atrium?
This depends a lot on the size of the patient. The insertion length of as 10kg Göttingen is around 7cm whereas in a 25kg it is 10cm. The tip of the long catheter should be just at the right atrium.
Have you gotten the buttons to last longer than 2 months? If yes, what is the longest period of time you've maintained patency?
Two months was typically my cut off time, but I had some up to 4 months. I have feedback from customers that they managed 6 months. Good and proper maintenance is the key for long patency.
Have the VABs been used on any other species other than rats and pigs?
To my knowledge the VAB have been used in mice, rats, ferrets, pigs, minipigs, and rabbits. See Webinar 2 of this series to hear of their use in rabbits.
Do you use rounded tipped catheters and what are they made out of (polyurethane, silicone, etc)?
The catheters are made by Instech, have rounded tips, and are made of polyurethane (PU). It is important that you buy them from Instech as they have to fit perfectly in diameter to the Vascular Access Button (VAB).
Do you leave a stress loop of catheter length to accommodate growth?
Stress relief loops do not work in pigs. Foreign material is encapsulated within days, so if you do a loop, it is a fixed as it can be, it will not move and adds only to the dead volume. The encapsulation is just like a vessel around the catheter and it can move lengthwise. So, I give a bit of slack (extra length) to the catheter so it has the possibility to stretch later on.
Is there an advantage of using port buttons over traditional catheters (aside from the ability to group house)?
Traditional percutaneous catheters have a higher risk of infection at the exit point and need a bandage or a harness. They are fine in some (probably more short term) cases, but in others the VAB is more beneficial. The VAB on the other hand is not always the best solution but it adds another tool that can be used for vascular access. It does not solve all the challenges either. Consider all the aspects of the study design and then make a decision.
Why do you use two catheters in the same vein?
It has two benefits. The idea is that if one catheter is not patent anymore, then there is a second as backup. They are offset at their tips to prevent any build-up of fibrin and clots to spill over from one to the other catheter. The second reason is to make infusion and sampling possible. The toxicologists do not like to use the same catheter for both because of cross contamination. The infusion should be through the long catheter (downstream) for the same reason.
Do you have any preference in lock solutions?
I have been talking to people about lock solution for more than 15 years and read a fair bit of literature (mainly from the human sector) about it. It seems to me that it is more religion than science as to what is best. Most important in my view is: Use a lock solution. Make sure it is sterile. It has to be consistent in quality. It should not interfere with the goals of the study and use it with positive pressure when finishing. I use a product which is made for humans, based in Taurolidine citrate (TCS), and also contains heparin. This is not because it is superior to other good quality products, it’s because it is sterile, easily available for me with short delivery time, and is consistent as it has strict quality control.