- Long-term vascular access is difficult to obtain and maintain in chelonians.
- Central venous catheters provide flexibility and length to avoid catheter dislodgement.
- The Seldinger or guide wire technique for placement of central venous catheters is simple to learn and only requires sedation and pre-assembled kits.
- Central lines are an effective tool that allow serial blood measurements and can be used for anesthesia administration, intravenous drug delivery, blood product transfusions, and continuous fluid therapy or continuous rate infusions.
The unique anatomy of turtles and tortoises makes vascular access a unique challenge. The jugular vein provides the most rapid and secure route for vascular access in chelonians, however, catheters can be difficult to place, and are challenging to maintain when the neck is moved.
Although vascular catheterization is not required for blood collection or for administration of fluids and drugs, it is considered the standard of care when treating critically ill patients that require repeated or continuous drug administration or repeated blood sampling. Intravenous (IV) medications are delivered more quickly and more reliably. Continuous IV access can also reduce the variables, such as temperature, hydration, and perfusion, that influence pharmacokinetics and onset of action of medications administered through alternate routes in critically ill patients (Davis 2015).
Central venous catheters have been shown to provide flexibility and sampling access, while minimizing catheter displacement in chelonians (Fig 1). Although the jugular vein is most commonly catheterized, any vessel capable of supporting the diameter and length of these central lines can be a good candidate.
Central venous catheters are recommended for any critically ill chelonian that requires IV administration of drugs and fluids in a reliable fashion or that require serial blood sampling. These catheters may stay in place for a few months with proper care. Proper caretaker training is possible, and patients may be sent home with catheters in place when the appropriate precautions are taken.
Appropriate patient selection is important. Patient size is dependent on the capacity of the patient’s vein to support catheterization and the catheter used, since catheters are available in multiple lengths and sizes (see catheter types below), however central lines have primarily been placed in relatively large tortoise patient. The smallest chelonian in which I have placed a central venous catheter is a 7.7-kg leopard tortoise (Stigmochelys pardalis).
Most complications associated with central lines are related to placement or dislodgement (Table 1). Central venous catheters are contraindicated with coagulopathies, cervical tumors, and intracranial disease.
|Table 1. Potential complications associated with central venous catheterization|
Long, multi-lumen, polyurethane catheters are available in a variety of sizes (as small as 5 Fr.) and lengths and may range from single to multiple lumen. Catheters are available through Mila International, Arrow International, and Cook Medical. Catheter selection should be based on vessel diameter and the catheter length required for the individual patient.
- Single lumen catheters may be appropriate when there is only one purpose for the central venous catheter, such as serial blood draws or fluid therapy.
- Multi-lumen catheters may contain up to four lumens and are useful in critical care settings (Fig 2). These catheters allow incompatible drugs and fluids to be delivered simultaneously, while other lumens can be used for blood sampling and measurements, such as central venous oxygen saturation.
A number of supplies are needed to place a central venous catheter (Table 2). Kits are commercially available that contain some of the equipment required (Fig 3).
|Table 2. Supplies needed for catheter placement|
*May be available in some bedside central venous catheter kits (Fig 3)
Select an anesthetic and analgesic plan that allow good restraint and prevents excessive movement. Manual restraint alone should not be used for this technique. Determine catheter depth before beginning the procedure. The catheter should extend from the approximate point of insertion in the jugular vein to the cranial border of the pectoral scutes, which should allow the catheter to sit just before the heart. Use a tape measure or another catheter to gauge the desired endpoint of the catheter
Using anesthesia or heavy sedation, direct the head down at a 20-30-degree angle (Fig 4). Identify the jugular vein, which lies very superficially on both lateral sides of the neck. The vessel runs from the tympanic membrane at the jaw angle to the base of the neck. The right jugular vein may be larger than the left in some species (Martinez-Jimenez & Hernandez-Divers 2007).
Due to variations among species, a simple to way to identify the jugular vein is to place an otoscope into the mouth and shine it laterally through the esophagus. Take care not to collapse the vein while pushing through the esophagus (Bel & Selleri 2017). Ultrasound can also be used to identify vessels and facilitate catheter placement by visualizing in real-time as the catheter is placed into the lumen of the vessel. This technique requires a linear probe and experience, however there are several successful documented reports in chelonians (Dutra et al 2014).
Surgically prepare and drape the jugular site in a standard fashion. Carefully make a small scalpel incision in the skin overlying the vessel, about midway down the length of the neck. Then expose the vessel using blunt dissection. Occlude the vein with digital pressure and then place an over-the-needle catheter in a caudal direction as an introduction catheter (Fig 5).
Remove the stylet from the over-the-needle catheter and introduce a J-tipped guide wire through the catheter (Fig 6), taking care to advance the wire to the level of the proximal humeral plastron scutes, and not to the level of the heart. Ideally, electrocardiogram monitoring is recommended since atrial or ventricular arrhythmias can be induced if the wire is introduced too far (CADT 2012).
After introducing the wire, carefully remove the introducing catheter while keeping the wire in place (Fig 7).
Thread the vein dilator, part of the central venous catheter kit, over the wire to stretch the skin and facilitate catheter entry. It is generally not necessary to completely introduce the dilator into the vein. Introduce the dilator a short distance into the vein while using a firm, forward twisting motion (Fig 8). In an Aldabra tortoise (Aldabrachelys gigantea), approximately 2 cm of vein dilator was introduced into the vessel.
Then remove the dilator while applying digital pressure to prevent blood loss (Fig 9).
Thread the catheter over the guide wire until the end of the wire appears through the uncapped distal catheter port (Fig 10).
Take care to hold the guide wire securely as the catheter is introduced. As the catheter is threaded over the wire and into the patient caudally, slowly remove the wire in a craniad direction. Introduce the catheter to the pre-measured depth.
Confirm correct placement using survey radiographs (Fig 15). The tip of the catheter should lay anterior to the heart. If the catheter is placed too far into the heart or past the heart, it should be backed out an appropriate distance until it is located in the desired area. In large chelonians, in which survey radiographs are not sensitive enough to confirm catheter placement, consider magnetic resonance imaging or computed tomography.
Monitoring and catheter maintenance
Gently clean catheter sites daily, removing any obvious organic material and replacing the Tegaderm patch as needed. If a catheter port is not currently being used for continuous infusion, flush the port twice daily with sterile saline or heparinized saline.
Central venous catheters are usually in place for the duration of hospitalization, but with proper care can be in place for up to 1-4 months. Monitor the insertion site daily for evidence of potential complications (Table 1), such as subcutaneous infiltration of fluids, thrombosis, swelling, erythema, heat, evidence of pain, and/or discharge. Catheters should be removed if any of these signs are observed.
Central venous catheters that are no longer patent or reliable can be replaced through an exchange technique. Only rewire catheters when there is no evidence of infection or inflammation and the insertion site is clean. Utilizing sterile technique, the Seldinger or guide wire technique is again used by passing the wire through the existing catheter and then removing the catheter while keeping the guide wire in place. The replacement catheter is then threaded over the wire and into the vein as previously described.
The difficulty associated with obtaining and maintaining vascular access in critically ill turtles and tortoises has important implications for patient care and serial clinicopathologic evaluations. Fortunately, the use of central venous catheters offers a solution for these difficulties. This technique is simple and allows the patient to be comfortable while providing the clinician with the ability to provide the best standard of care and perform hematological diagnostics.