Stent-Grafts, Coils, and Plugs

Introduction

Hemorrhage is the leading cause of preventable death in trauma patients, with 96% of those patients dying from noncompressible torso or junctional hemorrhage. As endovascular techniques have become more ubiquitous for elective and emergent vascular cases, there has been a shift toward endovascular interventions for trauma patients. Angioembolization devices, such as particulate, plug, or coil embolization have been the standard of care for nonoperative management of hemodynamically normal trauma patients with solid organ injury and contrast extravasation on imaging. More recently, endovascular stent-grafts have become an adjunct for control of hemorrhage from axial vessels while maintaining antegrade flow to distal structures. The acceptance and use of endovascular adjuncts in trauma patients with arterial injury have been rapidly increasing. Only 3% of vascular injuries captured in the National Trauma Data Bank (NTDB) in 2004 were managed with endovascular therapy. Ten years later, 9% of vascular injuries were being managed with an endovascular approach. It is especially appealing to use endovascular interventions for injured junctional vessels including subclavian, innominate, axillary, and iliac arteries, where the morbidity from a high thoracotomy, median sternotomy, or laparotomy may be avoided. Endovascular interventions may decrease the physiologic penalty on these patients with polytrauma, avoid the need to enter a second body cavity, limit vessel exposure with possible damage to adjacent structures or nerves, and possibly spare the need for general anesthesia. This chapter reviews the current literature for management of solid organ, pelvic, junctional, and peripheral vascular injuries. Resuscitative endovascular balloon occlusion of the aorta (REBOA) and endovascular management of aortic injuries will be discussed elsewhere in this textbook.

Principles of Endovascular Hemorrhage Control

Appropriate patient selection is fundamental to optimizing outcomes in trauma patients undergoing endovascular interventions for hemorrhage. Patients who are hemodynamically unstable, have diffuse peritonitis, or evidence of hollow viscus injury should be taken for emergent open intervention. Patients who are hemodynamically normal or responders to fluid resuscitation may undergo multidetector computed tomography (MDCT) with IV contrast. Based on the results of imaging, these patients may require urgent operative intervention, endovascular hemorrhage control, or observation. The most common indication for endovascular hemorrhage control is evidence of bleeding, such as active extravasation from a liver, splenic, renal, or pelvic injury. Other indications include high-grade solid organ injuries or moderate hemoperitoneum. Additionally, patients who have an injury to a junctional vessel as evidenced by contrast extravasation, dissection flap, or pseudoaneurysm on imaging may be appropriate for stent-graft placement, which maintains distal perfusion while excluding the injured segment. For trauma patients managed in a hybrid operating room, there is the option for concurrent or sequential open and endovascular interventions. Several considerations that must be addressed when planning endovascular hemorrhage control include vascular site of access, size of the target vessels, urgency of treatment, blood supply, collaterals, distal perfusion, embolization agent, and potential for migration of occlusive agent. Age remains another factor of continued debate. There is minimal data looking at endovascular technology when deployed in growing vessels. Each of these considerations will be addressed in the following anatomic sections.

Embolization Agents

The ability to perform catheter-directed mechanical occlusion to a vascular territory or affected parenchyma within a specific organ has been an adjunct to open surgery for trauma since the 1970s. These catheter-directed techniques have evolved with the expansion of nonoperative management for solid organ injury. Over the past five decades, embolization has moved from improvised embolic agents, such as guidewires, suture material, or autologous clots to commercially available permanent and temporary embolic agents ( Table 10.1 ).

Table 10.1

Commonly Used Embolization Agents for Trauma

Embolization Agent	Size Vessel	Tips
Temporary
– Gelfoam	Large or small	Gelfoam slurry can be used for large vessels Gelfoam powder can be used for small vessels Recanalization is highly variable
– Fibrillated collagen	Small	Recanalization of vessels in 2–3 months
Permanent
– Coils	Large	Microcoils are also available Concern for distal embolization if not anchored or when used for arteriovenous fistula
– Amplatz Vascular Plug	Large	Multiple different shapes and lengths available Can be used to make a backstop for coils
– Particles	Small	Limited role in trauma Tends to cause more ischemia and necrosis than large vessel occlusion
– Liquid adhesive	Small	Risk of gluing catheter to vessel wall Delivery can be challenging with mixing of glue
– Thrombin	Small	May cause nontarget embolization Most commonly used for narrow neck pseudoaneurysms

Temporary Embolization Agents

Historically, biologic material such as autologous clots or soft tissue were used as temporary embolization agents. In current practice, Gelfoam (Pharmacia & Upjohn, Kalamazoo, MI) is the commercially available option most commonly used in trauma. Gelfoam is an insoluble porous product made from purified porcine skin, gelatin granules, and water. Although its use as an embolization agent is off-label, clinical experience using Gelfoam embolization extends back to the 1970s. During the embolization procedure, a slurry of 1 to 2 mm cubes of Gelfoam sponge and contrast medium is combined using two syringes with a three-way stopcock. The contents are alternated between the two syringes until a homogenous slurry is formed with the consistency of pudding. This may then be used for embolization of proximal vessels by administering puffs of the slurry under fluoroscopy. The contrast medium in the slurry allows for visualization of the Gelfoam cast in the target vessel. Once vessel occlusion is achieved, no additional agent is injected, as it may reflux into a more central vessel and cause unintended embolization elsewhere. Recanalization typically occurs within 3 weeks but may take up to 3 months. The rate of recanalization is very unpredictable with Gelfoam. A powdered form of Gelfoam is also available but has a small diameter of only 10 to 100 µm. This and other small diameter temporary occlusive such as starch microspheres and fibrillated collagen tend to travel more distally, increasing the likelihood of tissue ischemia, and have limited utility in controlling the injured larger parenchymal vessels in solid organ trauma.

Permanent Embolization Agents

Permanent embolization agents include coils, plugs, and particles. The decision of which agent to use is based on the size of the target vessel, the blood supply to the affected organ, and if ischemia is desired. In the setting of severe injury, tissue ischemia should be minimized, which makes the use of a large number of permanent small-particle embolic agents less desirable. Polyvinyl alcohol (PVA) particles, tris-acryl gelatin (TAGM), and other types of microspheres, and liquid adhesives or sclerosants are frequently used for elective vessel ablation and embolization of targeted tissue. Experience in trauma is currently limited for these agents, given the delivery systems can be difficult to control, resulting in unintended distal ischemia or reflux into central vessels delivering embolization agent to other unintended locations. They are not without advantages, however, as liquid adhesives function independent of the clotting cascade and can occlude a vessel of a coagulopathic patient. In the setting of trauma, large-vessel embolic agents are most commonly used. In this setting, large vessels are considered any vessel that can be seen on angiography.

Thrombin

Although not commonly used for catheter-directed therapy, thrombin is used routinely for treatment of pseudoaneurysms at arterial access sites. Thrombin directly acts on fibrinogen, converting it to fibrin monomers thereby allowing it to cross-link and polymerize. This reaction results in almost immediate clot production with administration of thrombin. It is approved as a topical agent, and intraarterial use is off-label, though there has been extensive experience using this agent. When treating a postcatheterization pseudoaneurysm or posttraumatic peripheral pseudoaneurysm, the target is accessed by direct puncture and a small syringe is used to administer small aliquots of thrombin until thrombosis of pseudoaneurysm is achieved. This generally takes less than 1000 units (1 mL of 1000 unit per mL preparation). Extreme care must be taken when injecting thrombin, as embolization of an unintended target can have severe consequences, including irreversible ischemia. Although there are reports of using thrombin to treat posttraumatic solid organ pseudoaneurysms, we do not advocate this practice.

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