An Ultrasound-Guided Vascular Access Procedure in an Anesthetized Pig

Abstract

Source:
Rui Cerqueira^1,2, Liliana Costa¹, André Leite-Moreira¹, Adelino Leite-Moreira^1,2, André Lourenço¹, Pedro Mendes-Ferreira<sup>1

1</sup>Department of Surgery and Physiology, Faculty of Medicine of the University of Porto.

²Department of Cardiothoracic Surgery, Hospital Universitário de São João.

The video demonstrates a procedure for obtaining vascular access in an anesthetized pig using ultrasound guidance. After disinfecting the site and administering local anesthesia, an ultrasound probe is used to visualize the blood vessels. Under ultrasound guidance, a needle is inserted into the arterial lumen, a guidewire establishes a track, and a sheath is inserted and flushed with anticoagulant. Finally, a pressure line is connected, and the sheath is secured with sutures to ensure stable vascular access.

Protocol

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. Animal anesthesia and preparation

1. Anesthetize the animal following the in-house standard operating procedures. An example of a usual protocol includes pre-medication through an intramuscular injection of ketamine (15 mg/kg), midazolam (0.5 mg/kg), and azaperone (4 mg/kg), followed by anesthesia induction with a bolus of propofol (4 mg/kg) and fentanyl (10 µg/kg) to allow endotracheal intubation. Maintain anesthesia with propofol (10-20 mg/kg/h).
2. Monitor the animal by placing a pulse oximeter in the ear or tongue (peripheral oxygen saturation) and surface electrodes in extremities of the animal to measure the electrocardiogram (ECG).
3. Perform vascular access in animals under general anesthesia. Place the animal in a supine position, with the hind paws stretched downwards and secured. For cervical vascular access, extend the front paws and secure them in the caudal direction.
4. If the animal is to be recovered, thoroughly clean all access sites, disinfect with a 2% chlorhexidine alcoholic solution and drape the access area with sterile cloths or fenestrated drapes.

2. Arterial cannulation

1. Select the appropriate introducer sheath for the selected vessel/procedure.
   1. If only monitoring invasive blood pressure, use a standard arterial catheter (20-18 G) introduced in a peripheral artery (either a branch of the superficial femoral artery or the brachial artery).
   2. If the brachial artery is used, ensure that the correct positioning of the paw is maintained, as changes in the degree of paw extension can affect arterial tortuosity and compromise pressure signal transduction.
      NOTE: If performing catheterization procedures, plan in advance what are the different catheters needed in order to avoid exchanging the introducer sheath midway through the protocol. Whenever possible, use hemostasis systems that allow multiple catheters/guidewires to be introduced to avoid cannulating other arteries (such as luer lock hub introducer sheaths with dual port hemostasis valves).
2. Prepare the introducer sheath kit by flushing all the components with heparinized saline (50 IU/mL), including the Seldinger needle, the dilator and introducer sheath.
3. Infiltrate the area with subcutaneous 2% lidocaine (for longer protocols, consider infiltrating with lidocaine at the end of the procedure to account for lidocaine’s short duration of action).
4. Cover the linear ultrasound probe with a sterile probe cover. Make sure to add a sufficient amount of gel and manually remove any air bubbles. This step is only required if the animal is to be recovered afterwards.
5. Identify the artery to be cannulated (in this example, the common femoral artery) using the vascular settings and confirm the position of the ultrasound marker and correct depth.
   NOTE: Femoral artery puncture can be performed in short or long axis (or a combination of both (Figure 1), using a bi-plane modality in certain systems), depending on the user. In our laboratory the short axis approach is more frequently used. Needle visualization technology can help monitor the needle tract.
6. Make sure the 3-way stopcock in the introducer side port is in the off position towards the animal, to avoid blood loss when removing the dilator.
7. While holding the ultrasound probe, center the desired vessel in the center of the screen.
8. Using the midpoint of the ultrasound probe as a reference, puncture the skin and advance the needle at a 45 °C angle, with the needle tip bevel pointing upwards.
   NOTE: Puncturing the skin at 45ºC and at the same distance from the probe, as the depth of the vessel will ensure that the tip of the needle will come in contact with the vessel on the selected ultrasound image. Looking at the ultrasound image can help determine and correct the needle position relative to the intended vessel. Take into account that depending on the pig breed, the skin can be difficult to penetrate.
9. Ensure that the needle is easily identifiable in the ultrasound screen. Move the probe during the artery length to keep track of the needle tip position until the arterial lumen is reached.
10. The anterior wall of the artery will indent once the needle is immediately adjacent to it (Figure 2). Enter the arterial lumen with a secure and firm movement, avoiding transfixing the artery. Once the artery is punctured, pulsating arterial blood exiting through the hub of the needle should be seen.
11. Hold the needle in position and advance a guidewire into the artery. For smaller vessels use a soft tip guidewire, while for larger vessels, such as the femoral artery, a J-tip guidewire will be adequate. Either carefully place down the ultrasound probe and advance the guidewire, or have an assistant advance the guidewire while ensuring it is advancing through the artery lumen.
12. When advancing the guidewire, ensure no resistance is felt. If resistance is felt after the wire has exited the needle tip, it is likely that the needle tip is close to the posterior wall and the guidewire is being pushed against it. Try to readjust the needle by lowering the angle of entry without advancing further or removing it from the artery.
13. If resistance is still felt, stop the procedure, and remove the guidewire and needle in block, ensure hemostasis and restart the procedure. If the guidewire is pulled through the needle, its tip can be broken and embolize the artery.
    NOTE: Using fluoroscopy to visualize the guidewire can help determine the potential sources of resistance. For example, if the guidewire is exiting the needle at a steep angle, or if the guidewire has been pushed into a branch of the femoral artery instead of moving up the descending aorta. To avoid hematoma formation due to a failed arterial needle entry, use a micro access kit. This is advisable for less experienced researchers. These kits use small lumen needles and low-profile guidewires that can be exchanged stepwise into the intended introducer sheath.
14. Once the guidewire is confirmed inside the artery, remove the arterial needle, and keep pressure on the entry point to avoid bleeding.
15. Make a small nick in the skin using a scalpel blade, making sure that the cutting edge is pointed away from the guidewire to avoid damaging it.
    NOTE: If the introducer sheath is ≥7 Fr, predilate with a smaller dilator (5 Fr) followed by the introducer sheath dilator alone. If ≥10 Fr sheaths are used, predilate with 5 Fr, 8 Fr and the introducer sheath dilator alone. This will minimize complications related to unproper tissue dissection.
16. Advance the pre-flushed introducer sheath and dilator assembly over the guidewire. Remove the guidewire and dilator after ensuring that the 3-way stopcock of the introducer sheath's sidearm is in the off position towards the animal.
17. Connect a 10-20 cc syringe with heparinized saline to the 3-way stopcock, open it towards the animal and aspirate. Arterial blood should flow easily. Inject heparinize saline to flush the blood, ensuring that there are no air bubbles in the circuit.
18. Connect a pressure line to the 3-way stopcock to monitor invasive blood pressure. Flush the pressure line before opening it to the animal. Ensure that the fluid filled transducers are zeroed and at the level of the animal's right atrium.
19. Secure the introducer sheath by suturing it to the underlying skin using 2-0 silk suture. Alternatively, use adhesive to secure it in place, assuming that the animal will not move significantly. If the introducer sheath is used for catheterization, suture it to ensure that it does not dislodge, as significant bleeding or hematoma can occur if the introducer is moved accidentally.
    NOTE: Even if an arterial monitoring line is already in place in another location, connecting a pressure line to the femoral artery introducer sheath will help avoid blood clot formation, as it keeps a constant flow of saline (3 mL/h).

3. Venous cannulation

1. Follow steps 2.1-2.4.
2. Identify the vein of interest (in this example, the external jugular vein). The jugular vein It will be the most superficial large vessel in the lateral part of the neck, and it should collapse if pressure is applied with the ultrasound probe. Alternatively, the femoral vein can be cannulated. For recovery procedures, we prefer the jugular approach, as it offers a larger and easier access site, as the femoral vein runs in close proximity to the femoral artery.
3. Due to the shape of the neck and upper chest area of the pig, a groove on each side of the neck compromised visualization of the jugular vein in the short axis view (Figure 3), therefore the longitudinal view for jugular vein access is preferred.
4. Connect a 3-5 mL syringe to the needle hub for aspiration.
5. Using the ultrasound lateral notch as reference, puncture the skin and advance the needle at a 45° angle, with the needle tip bevel pointing upwards. Sometimes having a shallower angle will facilitate entering the vessel without transecting it.
6. Slightly adjust the needle as needed to ensure that the needle is in the plane of the jugular vein. Ensure that the walls of the jugular vein are clearly visible. Ensure that the diameter of the jugular vein is the maximum that can be obtained while slightly moving the probe side to side. This means that the needle is in the ideal position (middle of the vein) and that the puncture site will be as anterior as possible.
7. Advance the needle while visualizing its tip the whole time. Once the needle reaches the jugular vein, see the denting of the wall. Further advance the needle until its tip is seen inside the venous lumen.
8. Aspirate blood through the needle. Venous blood should easily flow. If not, slightly readjust the needle position, as it might be too little or too far advanced into the vessel.
9. Remove the syringe from the needle hub, while keeping the needle in place and follow steps 2.11 - 2.18.
   NOTE: Pay special attention to the ECG. When advancing the guidewire through the jugular vein, it can easily reach the right atrium and induce arrythmias, which can either resolve spontaneously when the guidewire is removed or lead to ventricular tachycardia that is not easily resolved. Therefore, controlling guidewire insertion depth is essential to avoid unwanted consequences.
10. Connect a pressure line for central venous pressure measurement if necessary. Since the venous introducer sheath is in the direction of flow, flushing it by hand is sufficient to avoid blood clot formation, eliminating the need for a continuous flush (as is the case for arterial accesses).
11. If venous/right heart catheterization is not going to be performed, use a central venous catheter instead of an introducer sheath. The procedure is the same for both catheters.
12. Secure the introducer sheath with a suture to the underlying skin to avoid accidental removal of the sheath.
13. For recovery purposes, once the procedure is finished, remove the sheaths and create hemostasis by manual compression. Achieve this by compressing the femoral puncture site for 10-15 min, when using up to 6 Fr sheaths. Alternatively, use vascular closure devices, which are effective but expensive.