Continuing Education Activity

Innominate artery injuries can present either by penetrating or blunt force. A provider must make a quick decision on treatment to avoid the feared morbidity and mortality associated with this injury. This activity reviews the associated mechanisms of injury and the various ways to approach (open vs. endovascular) and repair (primary vs. stent-graft) innominate artery injuries. This activity also reviews the evaluation and management of innominate artery injury and highlights the role of the interprofessional team in evaluating and improving care for such patients.

Objectives:

• Innominate artery injuries may occur as a consequence of blunt or penetrating trauma to the chest, such as high-speed motor vehicle collisions, shootings, and stabbings, or by iatrogenic injury such as central line placement.
• The most common imaging findings of innominate artery injury include a widened mediastinum greater than 8 cm or a tracheal shift to the right on a chest x-ray but can also present with an intimal flap, thrombus, dissection or active arterial extravasation on a chest CT.
• Management of innominate artery injury in unstable patients is a primary open repair. In contrast, treatment for stable patients is endovascular repair with a completion angiogram to examine for any further extravasation or filling defects at the injured segment.
• Innominate artery injury management requires excellent interprofessional teamwork between the EMS, ER, and OR staff as well as rapid recognition and diagnosis for the appropriate treatment of the injury to avoid morbidity and mortality of the patient.

Introduction

Innominate artery injury is a rare but lethal injury. Most injuries are due to blunt trauma rather than penetrating injury. Injury to the innominate artery occurs in multiple different manners, including blunt, penetrating, or iatrogenic trauma. The innominate artery is also known as the brachiocephalic artery. Injury to the innominate artery requires fast diagnosis and a skilled surgeon to repair the injury, whether by open or endovascular repair.

Thoracic, vascular injuries, especially innominate artery injuries, require the surgeon to make swift decisions for repair as the wrong approach or incision can quickly lead to mortality. The surgeon must gain control over immediate hemorrhage to help prevent malperfusion to distal organs, the formation of pseudoaneurysms, or the rupture of the artery. Over the years, increasing technology has allowed improved imaging and approaches for diagnosis and management of innominate artery injuries. With the increase in diagnostic modalities, patients can now undergo open, endovascular, or non-operative management for traumatic injuries to the innominate artery.

The innominate artery branches off the proximal portion of the aortic arch and divides into the right common carotid and subclavian arteries, whereas the left common carotid artery and subclavian artery branch directly off the distal portion of the aortic arch. This is the normal aortic arch configuration and presents in 70 to 74% of the population.

Abnormal configurations of the aortic arch must also be considered, the most common being a bovine aortic arch when the left common carotid artery either shares a common origin (subtype 2) with the innominate artery or branches directly off it less than 1 cm above the arch (subtype 1). Subtype 1 and subtype 2 bovine aortic arches are present in 9% and 13 to 20% of the population, respectively. Other less common aortic arch anomalies include aberrant left vertebral artery, aberrant right subclavian artery, aberrant left subclavian artery, and right aortic arch.[1]

Etiology

Innominate artery injury is often a consequence of blunt or penetrating trauma. While the traumatic injury is often the most common cause of injury, iatrogenic injury can also cause injury to the innominate artery.[2][3][4] The most common mechanism of injury is MVC. Head-on collisions constitute the majority at speeds of more than 60 mph or change in speeds of greater than or equal to 20 mph.

Key clinical indicators of injury include the seat belt sign and steering wheel imprint. Blunt injury to the innominate artery is most commonly found at its origin from the aortic arch. A review of postmortem exams found that pedestrians struck by motor vehicles had the highest incidence of significant vessel injury. Patients who present to the hospital with this injury rarely show signs of life due to the severity of this type of injury. Penetrating injury to the innominate artery is often due to a gunshot or stabbing to the chest. Iatrogenic injury to the innominate artery can also occur due to central venous catheter placement or the creation of a tracheostomy. Another iatrogenic cause of innominate artery injury comes after the creation of a tracheostomy, which in rare cases, can lead to tracheoinnominate artery fistula.[5][6]

Epidemiology

The incidence of blunt and penetrating injuries is hard to account for due to the uncommon presentation as well as the survivability of innominate artery injury. The incidence of blunt thoracic trauma is estimated at 7,500 to 8,000 cases per year, with an associated mortality of greater than 80%. The current data implies 4% of patients die during transport to the hospital, while 19% die during the initial trauma evaluation when suffering from a blunt thoracic aortic injury. The innominate artery ranks second among the thoracic vessel injuries during blunt trauma to the chest. Aortic disruption at the base of the innominate artery is the second most common location for trauma to the thoracic aorta.

One of the most common findings is the disruption of the intima and media with the formation of a pseudoaneurysm. A review of meta-analysis from 2011 showed that in-hospital mortality of patients who underwent non-operative management was as high as 46%; however, when comparing endovascular treatment and open repair of the innominate artery, mortality measured 9% and 19%, respectively. Patients presenting with penetrating injury were often more unstable than those patients experiencing blunt injury of the innominate artery, as they usually require a much higher volume of fluid resuscitation and blood product administration.

Tracheoinnominate fistula creation occurs in less than 0.7% of post tracheostomies and usually occurs within two to three weeks after the placement of the tracheostomy in 72 percent of patients. Arterial injury after central line placement, specifically innominate artery injury, is infrequent with less than 1 percent occurrence. Overall, regardless of the mechanism of injury, whether it be blunt or penetrating trauma, patients presenting with other various injuries often had higher mortalities.[7][8][9][4][10][11]

History and Physical

Patients presenting to the hospital with acute trauma to their chest should undergo immediate advanced trauma life support. The entire primary, secondary, imaging, and stabilization of the patient must happen before focusing on one injury. A focused history should be obtained, and a physical exam performed for aortic injury based on their mechanism of injury. Patients can have symptoms such as chest pain, shortness of breath, trouble swallowing, hoarseness, or stridor.

Physical examination of the patient may include active bleeding from the injury site on the chest or hard signs of vascular injury, including actively enlarging hematoma, loss of pulses in the affected extremity, signs of distal ischemia, or palpable thrill over the area. Patients with blunt trauma may present with no signs of injury at the initial presentation or may have signs of ecchymosis over the chest, hoarseness, cardiac murmur, shortness of breath, paraplegia, or unequal blood pressures in the upper extremities. Patients may have vital signs showing hemodynamic instability with signs of hemorrhagic shock, but others may have normal vital signs. The most common injuries are rib fractures 46%and pneumothorax 36%.[12]

Evaluation

If the patient is hemodynamically unstable, they must undergo emergent surgical intervention regardless of the mechanism of blunt vs. penetrating injury.

Stable vital signs allow for a supine chest x-ray. An abnormal chest x-ray with findings of a widened mediastinum greater than 8 cm, tracheal shift to the right, blurred aortic contour, irregular or loss of aortic knob, depression of the left main bronchus, opacification of the aortopulmonary window, deviation of the nasogastric tube to the right, wide paraspinal lines, thoracic spine fracture, fracture to the first rib, clavicular fracture, pulmonary contusion, or left apical cap. If an abnormality is found, the patient will need to undergo CT imaging of their chest with contrast. You must always rule out other injuries to the brain, abdomen, and other areas of the chest, especially when dealing with penetrating trauma to the chest. Findings on CT imaging of the chest have nearly a 100% sensitivity and negative predictive value and can include intimal flap, thrombus, or dissection.[13]

Transesophageal echocardiography is a new emerging imaging technique that the trauma team and colleagues can add to their imaging armamentarium for better visualization of the aorta, including the branches of the arch. The anesthesia team often uses this technique during a laparotomy to view the chest for evaluation of the aorta and its vessels. This imaging technique does have limitations as it is operator dependent, and there is often a hematoma in the chest or surrounding tissues that limits visibility.

The gold standard for visualization of the aorta and its branches are aortography with a digital subtraction angiogram. Unstable patients with blunt or penetrating chest trauma or other life/limb-threatening injuries should not be taken to the endovascular suite. The patients that do meet the criteria for imaging with an angiogram should be taken immediately, as the sensitivity and specificity are nearly 100% when placed in an experienced endovascular surgeon’s hands. When in the endovascular suite for imaging and findings are compatible with endovascular repair, the surgeon can often place a stent graft over the damaged area.[14]

Treatment / Management

Indications for open repair include an unstable patient, a large rapidly expanding mediastinal or zone 1 of the neck hematoma, a penetrating injury to the chest, or failure of endovascular repair.

These patients should undergo median sternotomy with an extension of the incision toward the right side of the neck if needed for distal control. Innominate artery injuries are often found at the proximal aspect of the vessel. For better exposure of the brachiocephalic artery, the brachiocephalic vein can be ligated. As with any vascular injury, the first goal is to obtain proximal and distal control of the artery. Each injury and its repair should be individualized to each case. Depending on the location of the injury to the innominate artery, the cerebral perfusion pressures may dictate if cardiopulmonary bypass may be needed.[15]

The primary repair of the innominate artery requires full exposure of the entire length of the artery. After adequate exposure, you must expose the proximal aspect of the artery and open the pericardium to fully gain control of the aortic arch where the innominate arises. Once you have control, systemic heparinization is given, and the artery can be clamped via a partial occluding vascular clamp. Once the clamp is applied, you can perform debridement and establish the need for an interposition graft. An end-to-end or end-to-side anastomosis of the proximal aspect of the graft can take place. Once the innominate artery injury is identified, the final graft length and the appropriate type of graft, such as straight graft versus a y graft, can be chosen. At times a y graft is needed to obtain distal flow to the right carotid and right subclavian arteries separately. The anastomotic areas may need to be oversewn using pledgeted sutures for better strength and seal of the anastomosis.

Depending on the extent of the injury and the age of the patient, the collateral flow to the brain must be understood, and the risk of ischemia taken very seriously. If the distal brachiocephalic is clamped, perfusion can be maintained through the right carotid via retrograde flow through the right subclavian artery. There are multiple techniques for cerebral monitoring with cerebral protection. The recommended carotid stump pressure for shunting is 45-50 mmHg. Cardiopulmonary bypass, circulatory arrest with hypothermia, and carotid shunting are all options for cerebral protection for the patient. If concomitant vein injury is noted, you should place a pericardial patch between the newly placed graft and the vein repair to help avoid fistula formation or erosion into the graft.[16]

Patients presenting with bleeding from their tracheostomy site after placement of a tracheostomy must have careful consideration that it may be a ‘sentinel bleed.’ Tracheoinnominate fistula must be high on the differential as this is often a fatal complication of a tracheostomy placement. If rupture of the innominate does occur due to trach placement, the patient should undergo emergent treatment with endovascular graft placement in a hybrid operating room in case open repair is needed.

Indications for endovascular repair include a hemodynamically stable patient with pseudoaneurysm or dissection of the innominate artery.

Endovascular repair of an injured innominate artery is becoming more popular as endovascular imaging, and graft techniques are gaining use throughout the world. Using an endovascular approach requires knowledge of the landing zones for the adequate seal of the stent-grafts. The approach for placement of the stent-graft can be made via access to the femoral artery in the groin or the brachial artery. The primary limitation is a distal landing zone for placement of the graft before the innominate artery branches. If necessary, the right subclavian artery can be excluded, and a carotid subclavian artery bypass can be performed if ischemia is present.

The usual technique for stent-graft placement with endovascular approach usually involves an angiogram for measurement of the injured area with measurement of the landing zones. After the proper measurement, an embolic-protective device is placed into the right common carotid artery, and the covered stent graft can then be placed. Post-stent deployment balloon angioplasty can then be performed with a balloon to match the vessel diameter. A completion angiogram can be done to exam for any further extravasation or filling defects at the injured segment.

Differential Diagnosis

Blunt or penetrating trauma to the chest presents with a multitude of possible differential diagnoses.

• Proximal carotid artery injury
• Subclavian artery/vein injury
• Ascending aorta injury
• Descending aorta injury
• Aortic dissection
• Cardiac injury
• Lung contusions/lacerations
• Pneumothorax
• Hemothorax
• Tracheal injury
• Esophageal injury
• Sternal, first, second rib fractures

Prognosis

Blunt or penetrating chest injury often has a lethal effect on the patient in the pre-hospital setting. If the patient arrives at the hospital, they still have a high rate of mortality and morbidity, especially if they have other associated injuries. The exact morbidity and mortality range depends on the associate repairs and injuries that the patient has obtained. A review of the literature shows mortality of more than 30% even with hospital arrival.[2]

Complications

Endovascular approach complications include

• Stroke
• Groin hematoma
• Systemic contrast reaction
• Contrast nephropathy
• Femoral artery pseudoaneurysms
• Accidental coverage of the patent artery
• Rupture of the artery

Open technique complications include

• Damage to a recurrent laryngeal nerve or vagus nerve
• Stroke
• Wound complications

Deterrence and Patient Education

• Practice safe driving techniques and wear seat belts.
• Always inform patients of the potential complications of procedures and the treatment options.

Enhancing Healthcare Team Outcomes

Prehospital resuscitation can aid survival in trauma centers. Continued advancement in imaging and operative techniques will allow better overall morbidity and mortality with innominate artery injury. Upon arrival at the hospital, the patient should have prompt diagnosis with consultation by multiple interprofessional teams as this injury is best managed with trauma, thoracic, and vascular teams. With improved imaging and hybrid operating rooms with multidisciplinary teams, the future looks to have improved outcomes on treating innominate artery injuries and other injuries involving the aorta.