intravascular

Intravascular Access Options in Reptiles : What’s Reasonable?

C.A. E. Mosley

College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA.

Intravascular injection sites have been described for all of the major reptile Classes and can be used to obtain blood samples for diagnostic testing or the administration of drugs. Intravascular injection decreases the time to onset and the variability of uptake that can be associated with intramuscular injections in reptiles. In addition, some drugs are irritating when given intramuscularly and intravenous injection can avoid some of the discomfort and tissue damage associated with these drugs. In addition to using these sites for injections and blood sampling many can be used to place intravascular catheters. Intravenous catheterization techniques have been described for many of these sites. Some techniques are "blind" while others are accomplished by direct visualization. Some vessels in some species can be seen percutaneously while others require a small skin incision for visualization and catheterization. The section below describes the more common sites for intravascular access; not all sites are good options for intravenous catheterization (ie, venous sinuses). Over-the-needle catheters are most often used although catheter placement using the Seldinger technique (using a wire guide) can also be performed and may facilitate difficult catheterization in some species. The placement of all intraosseous catheters and most cut-down procedures should be performed using a local or general anesthetic technique to desensitize the tissues and facilitate successful catheter placement.

SQUAMATES (SNAKES)

The coccygeal vein is located on the ventral midline of the tail. The needle should be inserted sufficiently caudal to the vent in order to avoid the hemipenes and anal sacs. The vessel is entered via a ventral midline approach; the needle is advanced with gentle suction until the vein is contacted.

The jugular vein can be used but requires a skin incision to visualize. An incision is made 4 to 7 scutes cranial to the heart at the junction of the ventral scutes and lateral body scales. The vein is then identified using blunt dissection just medial to the tips of the ribs. The right jugular tends to be larger.

The palatine vein is easily visualized in larger snakes and is located medial to the palatine teeth in the roof of the mouth. The technique is greatly facilitated by short- term anesthesia but it is possible to collect blood from these vessels in awake animals using a mouth speculum.

Use of the heart for venipuncture is not recommended except for emergency situations.

There are, to this author’s knowledge, no intraosseous sites described for drug administration in snakes.

SQUAMATES (LIZARDS)

The coccygeal vein is located on the ventral midline of the tail. The needle should be inserted sufficiently caudal to the vent in order to avoid the hemipenes. The vessel can be entered from either a ventral midline approach or laterally. The ventral approach is simple to perform. The needle is advanced with gentle suction until the vein is contacted. The lateral technique involves inserting the needle just ventral to the transverse process of the vertebral body and walked ventrally off the vertebral body until the vein is contacted.

The ventral abdominal vein is located on the ventral midline of the abdomen and can be entered percutaneously or via a small skin incision for direct visualization of the vessel.

The cephalic vein is located on the dorsal surface of the distal foreleg. A skin incision is generally required for visualization.

The jugular vein is located on the lateral surface of the neck at about the level of the tympanum and may be palpated in some species but is generally difficult to visualize. A small skin incision is often required for direct visualization. The jugular veins tend to be located more dorsal than those in mammals.

Intraosseous techniques have been described for the distal femur, proximal tibia, and proximal humerus. The techniques are similar to those described for other small animal patients.

CHELONIAN (TURTLES AND TORTOISES)

The dorsal coccygeal vein is located midline dorsal to the coccygeal vertebrae. It is a technique requiring minimal restraint. The needle is introduced in a craniad direction at a 45- to 90-degree angle from the skin

The dorsal cervical sinus (supravertebral) is located on the dorsolateral aspect of the neck in sea turtles. It is located one third the distance from the carapace to the head, cranial to the craniad edge of the carapace. The head is directed forward and down and the needle is introduced lateral to midline on either side.

The occipital venous sinus has been described in freshwater turtles and is located midline below the occipitus. It requires that the head be restrained firmly and in an extended ventroflexed (45- to 90-degree angle from the carapace) position. The needle is then introduced midline just caudal to the occipitus and nearly perpendicular to the spine.

The subcarpacial sinus or supravertebral sinus is located under the carapace just caudal to the last cervical vertebrae and craniad to the first thoracic vertebrae. This sinus can be approached by pressing the head into the shell and palpating for the first thoracic vertebrae (incorporated into the carapace). The needle should be directed through the skin just caudal to the juncture of the last cervical vertebrae up towards the carapace and first thoracic vertebrae.

Jugular veins are located on the lateral sides of the neck at about the level of the tympanum. In some species venipuncture of the jugular vein is relatively straightforward and can be visualized or a small skin incision can be made to facilitate direct visualization. Unfortunately this technique requires the neck to be fully extended and in uncooperative animals a short-acting anesthetic or tranquilizer may be required.

Intraosseous techniques have been described using the plastron/plastron bridge but this author has found most catheters end up in an intracoelomic rather than intraosseous position. The technique as described passes a needle at an angle through the bony bridge between the plastron and carapace.