Infusion

If you’ve read previous “Infusion Tips,” you should have a good idea of what characteristics your catheter should possess to meet your research goals. Your next logical question likely will be, “How do I implant it?” For continuous or multiple infusions over extended periods, such as multiple weeks or longer, surgical implantation with subcutaneous catheter anchoring is often a wise choice. In many instances however, the time investment, and expense associated with surgery can be avoided altogether. Here we will introduce you to a selection of non-surgically implanted catheters that can offer alternative approaches to surgery.

Over-the-needle IV Catheters
The simplest technique for vascular access, other than a needle, is the standard over-the-needle IV catheter routinely referred as an Angiocath™. This type of catheter is optimal for short-term or periodic (such as weekly) IV infusions in the dog or primate. Surgically implanting a long-term catheter in this situation is not necessary when an over-the-needle catheter can be inserted with relative ease. Using the over-the-needle IV catheter method, the researcher can gain access to the vein without sedating the animal, and infusion or sampling can begin immediately. This type of IV catheter is very common in both pre-clinical and clinical applications and they provide quick and easy short term access to vessels that can be visualized through the skin. They are available in sizes from 16G-28G, covering a wide range of pre-clinical species. While these catheters are convenient for acute access, they should not be left in the animal for extended periods due to their inherent stiffness and ease of premature removal if left unattended.

Tail Vein Catheters
The lateral tail vein in the mouse and rat may be the best choice for acute vascular access due to its superficial position and ease of access (one can place the animal in a restraint-device yet still have complete exposure of the tail). The most common method used to perform an IV infusion in rodents is a 26 or 28G needle inserted thru the skin and into the vessel. This technique is similar to the over the- needle procedure described above for large animals, in both method and application. It is a simple, easy and reliable technique used by many researchers, though a steady hand is required.

When repeated doses are required, such as daily doses for two weeks, the tail vein can experience stenotic damage, which in some instances leads to tail loss. To avoid or minimize tail vein damage associated with needle access, consider the use of a tail vein catheter designed specifically for the mouse and rat. This type of catheter can be placed in the tail vein via a simple percutaneous approach, and can be used immediately for bolus injections or short term infusions. In most instances, the tail vein catheters are removed following the infusion but can remain in the vessel for up to three days in rats.¹ The catheters are soft and flexible, so once implanted and secured, they flex with the tail as the animal’s position changes, thereby reducing vessel damage and the potential loss of tail vein integrity. The catheter can also be inserted further into the vessel, minimizing the potential for extravasation (back flow outside of the vessel) of the dosing solution.