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Approaches Vascular
ОглавлениеThe majority of veterinary IO vascular procedures are performed through major vessels including the carotid artery, femoral artery, femoral vein, and jugular vein. For all approaches, the hair over the surgical site is clipped, and the site is prepared with an aseptic technique and draped. The approach to the carotid artery and jugular vein is made with the animal in dorsal recumbency; the neck is outstretched (often with a towel under) and the head is maintained parallel to the tabletop. For a femoral artery or vein approach, the patient is also placed in dorsal recumbency and the femoral pulse is palpated. The hind limb will often need to be pulled gently away from the body to allow for appropriate exposure of the inguinal region.
In human medicine, ultrasound guidance is often used to gain vascular access (Ahmad et al. 2008; Arthurs et al. 2008); in veterinary patients, this is less common but should be explored further. A 1–2 cm skin incision is made directly over the vessel to be accessed; generally, the incision is parallel to the direction of the vessel. The subcutaneous tissue is bluntly and sharply dissected until the desired vessel is easily palpable or visible. The tissue surrounding the vessel is then gently dissected, and the vessel is manipulated to allow circumferential freeing of the vessel. A length of at least 1 cm of vessel should be freed from the surrounding tissue. When approaching the femoral or carotid artery, the vessels may be ligated (in dogs) at the conclusion of the procedure (Perkins and Edmark 1971; Moss 1974; Clendenin and Conrad 1979a, 1979b). A stab incision into the skin can be used when approaching the jugular vein or femoral vein, and dissection is generally not necessary. Given the lower pressures found in the venous system, ligation is not necessary, as gentle pressure applied at the conclusion of the procedure will often maintain hemostasis.
The original technique for gaining vascular access was described by Seldinger (1953), and this technique remains the primary means for obtaining vascular access for IO procedures (Higgs et al. 2005). An over‐the‐needle IV catheter (generally 18 or 22 gauge) is used to puncture the vessel, and the catheter is then advanced into the vessel. When puncturing the vessel, the needle should be advanced into the vessel at a 45° angle (Valji 2006; Stavropoulos et al. 2006). When a sufficient flash of blood has been noted (in humans, this is considered a 4‐ to 6‐inch spurt in a normotensive person), the needle is removed, and a guidewire is introduced into the IV catheter and subsequently into the vessel. The IV catheter is then removed by backing it out of the vessel over the guidewire. A vascular access sheath‐dilator combination is placed over the guidewire and gentle pressure is applied to manipulate the vascular access sheath‐dilator combination into the vessel. A slight twisting motion may be necessary to introduce the vascular access sheath‐dilator combination into the vessel. The dilator is removed from the vascular access sheath over the guidewire.
With the guidewire and vascular access sheath in place, specific vessels can be selected. A catheter is often placed over the guidewire and through the vascular access sheath to perform a myriad of diagnostic and treatment techniques. Agents such as contrast and embolic materials can be injected through the catheter when the area of interest has been identified. Additionally, other catheters and guidewires can be used through the specialized catheter using the coaxial technique.