Intravenous (IV) tail vein injections remain one of the most technically demanding yet essential procedures in small animal research. Whether administering contrast agents for ultrasound imaging or delivering systemic therapeutics, the precision of this method directly impacts experimental consistency and animal welfare.
Preparation and Anesthesia
Proper vein dilation is the foundation of a successful injection. Pre-warm animals for 5–10 minutes using a heating pad or warming box to safely promote vasodilation. Most modern ECG platforms contain built-in heating systems to maintain animal body temperature during anesthesia. Another key factor affecting vein dilation is the anesthesia dose. Isoflurane generally causes a decrease in blood pressure in mice and this effect is dose-dependent. High concentrations (e.g. 3%) lead to significantly lower blood pressure — the lateral vein may not be visible. Such levels are achieved during induction, so stabilize the animal at maintenance levels of isoflurane (1.5–2%) before attempting catheter insertion.
Catheter Insertion Technique
Place the tail on the INJ tail-guide groove and the focused illumination will confirm the lateral vein's position even in dark animals — this step is particularly critical when animals are immobilized on an ECG plate. Use a 27–30 gauge needle and up to 1 mL syringe for mice. The needle should enter the vein bevel up, parallel to the tail, and be advanced toward the head. After insertion, place the catheter on the dedicated holder to stabilize the catheter line. The first injection should be slow; if resistance is felt or a pale area forms under the skin, withdraw and reposition. Always replace the needle after three attempts to maintain sharpness and minimize trauma.
Post-Injection Procedure
After catheter removal, apply gentle pressure to the site with gauze until bleeding stops. Monitor the post-anesthesia recovery closely before returning the animal to its cage.
Institutional Compliance
All procedures must strictly comply with your institution's IACUC (Institutional Animal Care and Use Committee) or equivalent animal welfare guidelines. Devices such as the INJ are designed to support precision and animal welfare but do not replace ethical and procedural oversight mandated by your institution.