Restrain the mouse with physical or chemical restraint. Rotate the tail slightly to visualize vein. Disinfect injection site and insert needle (27-30 gauge) into the vein at a slight angle. You will not be able to aspirate, instead inject slowly and watch for clearing of the lumen. Incorrect positioning will result in a slight bulge in the tail. If this occurs, remove needle and repeat process proximal to previous site. Upon completion remove needle and apply pressure to injection site.
Tail Vein Injection further details
Before making an injection in a tail vein, it is helpful to induce peripheral vasodilation and make the vein more prominent for cannulation. You can raise the mouse’s body temperature with an incandescent lamp, soak the tail in warm water, or administer vasodilating agents such as xylazine or acepromazine. You can also use a light source to transilluminate the tail which will make the vein easy to see and access.
A safe water temperature is 110° Fahrenheit or 43° Celsius, which will gently warm the mouse. Although warming an anesthetized mouse is beneficial, be careful not to cause burns or overheat the animal.
The tail veins are located on each side of the tail, superficially just under the skin. When the needle is correctly placed in the vein, you may or may not see a flash of blood in the needle hub. You will get a sense that the needle has entered the vein because there will be less resistance to the advance of the needle inside the vein’s lumen than through the subcutaneous tissues. Likewise, upon injection, the fluid will flow easily into the vein, and the vein will become clear (changing from dark to light) as the fluid temporarily replaces the blood (as in the image below).
Tail or Saphenous Vein
Tail injection procedure same as in the mouse. For the saphenous vein, restrain the rat with the use of anesthesia. Extend the hind leg and shave hair to expose lateral saphenous vein. Disinfect the injection site and apply tourniquet-like pressure to the upper portion of the leg. Insert needle into the vein and aspirate. Release tourniquet pressure and inject. Upon completion remove needle and ensure proper hemostasis. The recommended needle size for IV injections in the rat is 22-25 gauge.
***Be sure there are no air pockets or bubbles in the solution to be injected, as this can kill small animals.