Vascular Catheterization Frequently Asked Questions

General FAQs

What are the factors influencing patency duration?

There are five factors influencing patency duration. The first and most important factor is the catheter tip position. The other four factors are: the use of a closed system such as the Vascular Access Button™ (VAB™), catheter material and tip profile, the utilization of sterile supplies including flush and lock solutions and the application of the positive pressure technique when locking the catheter. Learn more

How long will my catheter stay patent?

Catheter patency duration is affected by multiple factors. If all factors are followed, patency for all vessels in both mice and rats, can last many months. Read the Five Keys to Patency

Why should I follow aseptic technique and use sterile flush and lock solutions?

Adhering to a strict aseptic technique including using sterile flush and lock solutions is non-negotiable when it comes to survival surgery and catheter maintenance. A breach in aseptic technique and using non-sterile supplies and lock and flush solutions may lead to infections and the formation of biofilm at the catheter tip decreasing patency duration. Learn more

What does Fr (French) mean?

The term ‘French’ (Fr, Fg, FR, F, CH or Ch) is a unit of measure invented by Joseph-Frédéric-Benoît Charrière, a Swiss-born French manufacturer of surgical instruments. His name Charrière was difficult to pronounce for people who did not speak French, leading to naming the unit of measure French instead of Charrière. 

How does the French scale work?

The French scale refers to the catheter's outside diameter. 1Fr is equal to 0.33 mm, 2Fr is equal to .666 mm, 3Fr is equal to 1 mm and so forth.

How much blood can I withdraw as a single sample?

As a general rule, the maximum of blood that should be withdrawn for one sample should not exceed 10% of the circulating blood volume. If more samples are needed, a recovery period of 3-4 weeks should be allowed in between samples.

How do I calculate this for a rat?

The total circulating blood volume of a rat is, on average, 64 ml/kg. The blood volume for a 250 g rat is ~16ml, therefore the volume for one sample should not exceed 1.6ml.

How do I calculate this for a mouse?

The total circulating blood volume of a mouse is, on average, 58 ml/kg. The total blood volume for a 25 g mouse is ~1.45 ml, therefore the volume for one sample should not exceed 0.15 ml or 150 µl. 

How much blood can I withdraw for multiple samples?

As a general rule, for multiple samples on mice and rats, no more than 1% of the circulating volume per day can be withdrawn.


Catheter and Catheter Maintenance FAQs

Why should I use a polyurethane catheter?

PU is the material of choice because of its biocompatibility. PU is a happy medium between silicone and polyethylene. It is less porous than silicone and less rigid than polyethylene. It is also the best material for subcutaneous connections, such as when the catheter is attached to the VAB™’s connector. Learn more

Why should I use a round tip catheter?

A round tip catheter, compared to square or bevel tips, is less traumatic to the endothelial cells of the blood vessels, therefore reducing blood clot formation and increasing patency duration. Learn more

What is the collar or bead used for on the catheter?

The main purpose of the collar (also called bead) on the catheter is to define the catheter insertion length. It also serves as an anchor by placing sutures cranially and caudally to it during surgery. Our catheters come with either a fixed or movable collar. Make sure you order the one that will best fit your needs. See all Catheters

Why should I apply Positive Pressure Technique?

If positive pressure is not applied when disconnecting the syringe from the VAB™’s port, blood will enter into the catheter at its tip and may clot, leading to catheter blockage and loss of patency. See this blog and video for more information 

How frequently should I maintain my catheter?

When using a closed system such as with the VAB™, the recommended maintenance schedule is seven days. If the catheter is exteriorized, or if using an open system, the catheter should be maintained every three to four days. 

What solution should I use to flush my catheter?

Sterile isotonic saline solution or sterile heparinized isotonic saline solution (usually at a low heparin concentration of 10 or 20USP/ml) are used as flushed solutions during surgery, catheter maintenance or after compound infusion.

What solution should I use to lock my catheter?

The 500 USP/mL Heparin/Dextrose or Heparin/Glycerol lock solutions have been widely used and have been evaluated, as seen in the CRL/Dr. Luo study from 2000, for example. In that study, catheters were implanted in the venous system, more specifically in the femoral vein, and were exteriorized and sealed with plugs resulting in an open system. The high viscosity of the Heparin/Glycerol lock solution prevents evaporation of fluids in the exteriorized catheter while the Heparin/Dextrose solution minimizes bacterial growth. These two solutions are desirable with an open system, but they are not necessarily needed nor an advantage when using a closed system as provided by the Vascular Access Button™. When using a VAB™, the catheter completely lies subcutaneously, negating the need to prevent fluid evaporation. Additionally, the septum of the VAB™’s port provides a closed system which offers a clean way to connect to the vascular system, consequently minimizing the risks of infections. 

When using a high heparin concentration solution there is a risk of introducing hazardous amounts of heparin into the bloodstream. Therefore, the best approach might be to use a lower and safer concentration heparin solution such as the 10 or 20 USP/mL heparinized saline (called flush solutions) with the VAB™ in the venous system to lock the catheter. This formulation is available in the form of pharmaceutical-grade, easy to use prefilled sterile syringes

The high viscosity of the Heparin/Glycerol solution may be beneficial in the arterial system as the high blood pressure present in the arteries may cause blood to infiltrate into the catheter and form a thrombus. Instech has formulated a lock solution which consists of glycerol with a lower concentration of heparin at 50 USP/mL in order to prevent hazardous amounts of heparin into the bloodstream. This formulation is available in the form of vials with or without Instech’s needle-free PinPort™ technology built into the cap

In summary, when using a VAB™, the 10 or 20 USP/mL heparinized saline flush solution is getting more and more popular as a lock solution, especially within the venous system. The heparin/glycerol may be beneficial in the arterial system and the low heparin formulation minimizes the risk of introducing hazardous amounts of heparin into the bloodstream. The bottom line is, choose and use the lock solution that works best for you and your animals. There are no set rules when it comes to which solutions will perform best in different species or vessels but remember to be cautious if you opt out for a high heparin concentration lock solution. 

What is the dead volume of a 1Fr catheter per centimeter?

The dead volume is 0.3µl per centimeter.

What is the dead volume of a 2Fr catheter per centimeter?

The dead volume is 1.5µl per centimeter.

What is the dead volume of a 3Fr catheter per centimeter?

The dead volume is 3µl per centimeter.

Does laminar flow affect the catheter’s dead volume?

Yes, the flow of fluids in rodent catheters is almost always governed by laminar flow. In laminar flow, fluid at the center of the tube moves faster than fluid at the edge which is held up by contact with the tube wall. This means that you may have to increase the volume of the lock solution to ensure the catheter’s dead volume is completely filled. The more viscous the solution is, the more laminar flow effect there will be. See this blog for more information. 


Vascular Access Button™ (VAB™) FAQs

Are there recommended Instructions for Use available?

Yes! Instructions for use are available for both mouse and rat VABs™ and can be accessed through the following links: 
Mouse VAB™ Instructions for Use | Rat VAB™ Instructions for Use

Why should I use a Vascular Access Button™ (VAB™)?

There are many reasons why you should use a VAB™: Low-stress sampling and infusion, extended catheter patency duration and the possibility of group housing your animals with the addition of the metal cap on the VAB™’s port are just a few. Learn more

What is the dead volume of the VAB™?

Rat VAB™ Dead Volumes (VABR)

Part Number
VABR1B/27
VABR1B/25
VABR1B/22
VABR2B/22
VABR3B/22
VABR4B/22
White Port
2µl 3µl 4µl 4µl 4µl 4µl
Red Port
      4µl 5µl 4µl
Blue Port
        4µl 4µl
Green Port
          4µl

 

Mouse VAB™ Dead Volumes (VABM)

Part Number
VABM1B/25
VABM1B/22
VABM1BSM/25
VABM2JB/25R25
VABM2JBSM/25R25
White Port
3µl 4µl 3µl 2µl 2µl
Red Port
      2µl 2µl

 

Should I soak the felt disk of my VAB™prior to implanting it subcutaneously?

Yes, we recommend soaking the felt disk aseptically in sterile saline prior to its subcutaneous implantation. Placing it in sterile saline when starting the procedure will ensure an appropriate saturated disk. A dry felt disk may cause some irritation to the adjacent tissues, especially in mice.
Download the Rat VAB™ Instructions for Use
Download the Mouse VAB™ Instructions for Use

Can I reuse the metal caps I utilized to group house my animals?

Yes, the metal caps can be cleaned, autoclaved and reused multiple times.

The metal cap covering the VAB™ is stuck, how can I remove it?

Metal caps can occasionally adhere to the VAB™ base due to dried fluid buildup from the surgical site. It can also occur if a dextrose lock solution is used. To loosen the cap, apply warm sterile saline to the site with a syringe or with some sterile swabs saturated with sterile saline. If needed, sterile forceps can be used to help in breaking the dried buildup of fluids or lock solution.

Can I reuse the VAB™?

It is not practical to reuse the VAB™ on multiple animals as the felt disk will be covered with blood and fluids making it impossible to be cleaned and reused. There is also no guarantee the internal port and its septum are completely clean to avoid cross-contamination. If you are practicing and not recovering animals, it is fine to reuse the VAB™ throughout the day.

Is there a maximum of times the VAB™’s port can be punctured?

Our Vascular Access Button™'s ports have been tested and can be punctured over 200x over its lifetime. 

Can I use the VAB™ with any types of vessels?

Yes, the VAB™ can be used with veins or arteries. It can also be utilized for organs such as the stomach and intestines, ducts such as the bile duct, or simply to access the subcutaneous space.


Surgical FAQs

What is the ideal catheter tip placement for the jugular vein?

The ideal tip placement for a jugular vein catheterization is the entrance of the right atrium. See this blog for more information

What is the ideal catheter tip placement for the carotid artery? 

The ideal tip placement for a carotid artery catheterization is the entrance of the aortic arch. See this blog for more information

What is the ideal catheter tip placement for the femoral vein?

The ideal tip placement for a femoral vein catheterization is in the inferior vena cava caudal to the renal veins.

What is the ideal catheter tip placement for the femoral artery?

The ideal tip placement for a femoral artery catheterization is the abdominal aorta caudal to the renal arteries.

How can I predict the tip location during surgery?

The catheter tip location can be predicted by measurements carried out on cadavers prior to performing the survival surgery. Such measurements should be taken from anatomical landmarks where the vessel ligature will be placed to the ideal catheter tip placement. These measurements will become the catheter insertion length and the catheter collar should be placed accordingly.

How do I secure the catheter in place once in the vessel?

The catheter is secured in place by tying both the proximal and distal sutures around it. The proximal suture is tied over the catheter and vessel. The distal suture, which was used to ligate the vessel, is then tied over the catheter itself.

What type of suture material should I use to ligate the vessel and to secure the catheter once in the vessel?

Non absorbable suture must be used and silk is the best option as it provides the optimal knot security for a non absorbable suture. 6.0 silk works very well for these applications in both mice and rats. 

Should I use the right or left jugular vein for catheterization?

The jugular on the animal’s right side should be used for catheterization. The right jugular vein has a more direct, shorter route compared to the left jugular vein when the catheter is directed toward the right atrium.

Should I use the right or left carotid artery for catheterization?

The carotid on the animal’s left side should be used for catheterization as it originates directly from the aortic arch.  The right carotid does not originate from the aortic arch but from the brachiocephalic artery (also called the Innominate artery). 

Should I use the right or left femoral vein or the left or right artery for catheterization?

It does not matter as much with the femoral vein or artery as there are no anatomical differences between the right and left sides. 

What is the best position for the VAB™?

The VAB™’s felt disk should be placed subcutaneously in the animal’s interscapular area.

In which direction should the VAB™’s connector be oriented?

A common practice is to orient the connector caudally (toward the tail of the animal). But we have also seen some connectors oriented cranially (toward the head) or laterally  (toward the side). There is no right or wrong but ensure the connector does not get in the way of animal movement as if placed too cranially, for example. Ensure there is some slack to the catheter allowing for animal growth and movement.

What causes seromas?

Seromas are caused by forming an overlarge subcutaneous pocket for the VAB™’s disk. This generates dead space which will later be filled with an abnormal accumulation of serous fluids. Seromas are seen most commonly in rats as compared to mice. 

How can I prevent seromas?

Making the subcutaneous pocket the right size for the VAB™’s disk is the best way to prevent seroma formation. Closing the subcutaneous layer of tissues is also helpful in minimizing dead space. Ensure the pocket is not too small as this can put some pressure on the skin causing irritation or worse, pressure necrosis of the skin.

How long should it take me to perform a vascular catheterization?

An experienced surgeon takes about 20 minutes to complete the entire procedure. As a general guideline, anyone planning on performing survival surgery should practice without recovering animals until reaching approximately 30 minutes per procedure. 

Does Instech offer surgical training?

Yes, Instech has launched an education program and now provides online surgical training. Learn more 

Should I use a microscope to do catheterizations?

A microscope is the best tool to support an atraumatic surgery. It allows the viewing of fine details that could not otherwise be detected with the naked eye. It also encourages an ergonomic posture when performing the procedure. A microscope with a tilting binocular head is ideal as it further helps with ergonomics. An illumination source, such as a microscope ring light or a dual gooseneck fiber optic light, is a must to enhance viewing.

What instruments should I use to perform catheterizations?

Micro instruments such as those sold by Fine Science Tools (FST) are ideal to perform catheterizations on rodents. For ease and convenience, Instech and FST collaborated and put together these Vascular Catheterization Surgical Packs