Guidelines for the Diagnosis and Management of Blunt Aortic Injury: An EAST Practice Management Guidelines Work Group

STATEMENT OF THE PROBLEM Blunt injury to the aorta (BAI) is responsible for approximately 8,000 deaths each year in the United States. This injury most commonly results from motor vehicle collisions but may also result from pedestrian mishaps, falls from height, and crushing thoracic injuries. The majority of patients who sustain BAI die at the scene. The patients who reach the hospital alive have a reasonably good expectation of survival, providing their BAI is diagnosed and treated in a timely manner. These patients often have multiple injuries, a condition that complicates their diagnosis and treatment. In addition, operative management may result in complications such as paraplegia and acute renal failure. No single center has a large amount of experience with this injury; therefore, it is important to consider all of the available data when coming to conclusions regarding the best method of diagnosis and treatment of BAI. PROCESS Identification of References A MEDLINE search was performed for the years 1966 to 1997. All English language citations with the subject words thoracic aorta and wounds, nonpenetrating were retrieved. Letters to the editor, isolated case reports, animal studies, meta-analyses, and review articles were deleted from further review. However, the bibliography sections of review articles and meta-analyses were used to identify additional references not retrieved with the MEDLINE search. This process resulted in 137 articles that were reviewed by a group consisting of trauma surgeons, thoracic surgeons, and a trauma radiologist. This group collaborated to produce the above recommendations and the following evidentiary table (Table 1).Table 1: Blunt aortic injury: evidentiary tableaTable 1A: ContinuedTable 1B: ContinuedTable 1C: ContinuedTable 1D: ContinuedTable 1E: ContinuedTable 1F: ContinuedTable: Table 1G. ContinuedTable: Table 1H. ContinuedTable 1I: ContinuedTable: Table 1J. ContinuedQuality of the References The quality assessment instrument applied to the references was that developed by the Brain Trauma Foundation and subsequently adopted by the EAST Practice Management Guidelines Committee. Articles were classified as class I, II, or III according to the following definitions: Class I: A prospective randomized clinical trial. There were no Class I articles reviewed. Class II: A prospective noncomparative clinical study or a retrospective analysis based on reliable data. Class III: A retrospective case series or database review. RECOMMENDATIONS The level of the following recommendations corresponds roughly to the class of references that support it. Level I There is insufficient evidence to support a standard of care on this topic. Level II The possibility of a BAI should be considered in all patients who are involved in a motor vehicle collision, regardless of the direction of impact. The chest x-ray is a good screening tool for determining the need for further investigation. The most significant chest x-ray findings include (but are not limited to) widened mediastinum, obscured aortic knob, deviation of the left mainstem bronchus or nasogastric tube, and opacification of the aortopulmonary window. Angiography is a very sensitive, specific, and accurate test for the presence of BAI. It is the standard by which most other diagnostic tests are compared. Computed tomography of the chest is a useful diagnostic tool for both screening and diagnosis of BAI. Spiral or helical computed tomographic scanners have an extremely high negative predictive value and may be used alone to rule out BAI. When these scanners are used, angiography may be reserved for patients with indeterminate scans. Prompt repair of the BAI is preferred. If the patient has more immediately life-threatening injuries that require intervention such as emergent laparotomy or craniotomy, or if the patient is a poor operative candidate because of age or comorbidities, the aortic repair may be delayed. Medical control of blood pressure is advised until surgical repair can be accomplished. Level III The presence of physical findings such as pseudocoarctation or intrascapular murmur should be investigated further. Transesophageal echocardiography is also a sensitive and specific test. There are several limitations to this test. It does require training and expertise that may not be as readily available as angiography. Repair of the aortic injury is best accomplished with some method of distal perfusion, either bypass or shunt. Neurologic complications seem to correlate with ischemia time; therefore, this time should be kept to a minimum. SCIENTIFIC FOUNDATION BAI is the second most common cause of death in blunt trauma patients. 2 The majority of patients die at the scene, with only 13 to 15% arriving at the hospital with signs of life. 2,141 The remainder of patients will die within the first few days of hospitalization if the BAI is not promptly diagnosed and treated. 2 The most common mechanism of BAI seems to be from a motor vehicle collision with frontal and lateral impacts occurring with approximately equal frequency. 5,15 Other common mechanisms include pedestrian/vehicular incidents and falls. Most patients who sustain BAI die at the scene or during transport. Of the patients who arrive alive to the hospital, there are many varied signs and symptoms they may present with. The most commonly noted signs in these patients are pseudocoarctation and intrascapular murmur. 17,24,28,36 Absence of any of these signs does not entirely rule out BAI, as it has been reported with a normal physical examination. 22,23 The chest radiograph (CXR) has been studied extensively as a screening test. There is some evidence that an erect posteroanterior view is better than a supine anteroposterior view. 25 A widened mediastinum has been the most frequently cited CXR finding that triggers additional work-up for BAI. 1,2,14,20,22,24,26 The widened mediastinum may be defined as a measured width greater than 8 cm, 11,21,24,35 a mediastinal/chest width ratio of >0.38, 11 or simply the physician’s impression that the mediastinum is widened. 3,20 Mediastinal abnormalities on the CXR that are considered strongly suggestive of BAI include an obscure or indistinct aortic knob, 1,3,13,14,25,27,30,34,35 depression of the left mainstem bronchus, 6 deviation of the nasogastric tube, 6,19 and opacification of the aortopulmonary window, 1,4,25,30,35 Other commonly seen CXR findings include widened paratracheal and paraspinous stripes 4,12,25,30 and apical capping. 1 Findings such as pneumothorax and hemothorax are very nonspecific, 20 and there seems to be a negative association with fractures of the thoracic skeleton. 19,20,36 It is possible for BAI to occur in the presence of a normal CXR; therefore, patients injured by significant deceleration or acceleration mechanisms should undergo a screening test anyway. 7,10 Angiography has been used as the gold standard diagnostic test for BAI. 41–43 It is the test to which all others are compared. There is a small incidence of false-positive angiograms resulting from anatomic abnormalities such as ductus diverticulum 42 that the physician should be aware of. Various techniques have been studied in an attempt to reduce the required dye load. These include intravenous and intra-arterial digital subtraction angiography, 39,40,43,138 and there is some evidence that intra-arterial digital subtraction angiography is as accurate as conventional angiography. Computed tomography of the chest (CTC) seems to be a very useful diagnostic tool. 44,48 Its use ranges from the screening of all patients with blunt chest trauma 37,61,62 to studying only those patients with a normal or low suspicion CXR. 47,50–52 If the CTC is performed with a conventional scanner, most authors recommend following an abnormal CTC with angiography. 47,50,54 A potential problem with the CTC is that it may delay the time to angiography and, thus, to a definitive diagnosis. 57 This problem is resolved with newer generation scanners such as helical or spiral CT scanners. They are more sensitive 45,139 and seem to have 100% negative predictive value. 50,143,144 When helical or spiral CTC is used, angiography may be reserved for those patients with equivocal or indeterminate scans, because there is more anatomic detail present on the angiogram. 143,144 Transesophageal echocardiography (TEE) has gotten much attention in the past 6 years. It is also a very sensitive screening test 10,63,65,67,70,71 but many authors also follow an abnormal TEE with angiography. 64,68,72 Unfortunately, TEE requires specific training and expertise 140 and may not be as readily available as CTC or angiography. Its usefulness may lie in the ability to follow small intimal injuries that are not seen on angiography 63 or for diagnosis in the patient too unstable to move to the angiography suite. 66 TEE does not visualize the ascending aorta or the aortic branches well and may miss injuries to these vessels. 73,74 Once the diagnosis of BAI is made, most authors agree that prompt surgical repair is the best approach. 2,28,80,83 Immediate repair may not be possible for all patients, however, i.e., for patients unstable from intra-abdominal injuries who require laparotomy or patients with severe closed head injuries who require craniotomies. 76,84,86 Another subset of patients are those who are elderly or have comorbidities that prohibit emergency thoracic surgery. 77,81 These patients may be safely managed medically until these other factors have been resolved. 143 Pharmacologic control of blood pressure with beta-blockers or nitroprusside is extremely important when delayed or nonoperative management is contemplated. 78,79,82,88,91,143 The use of specialized monitoring devices such as a pulmonary artery catheter may be useful, especially in the patient who has sustained a significant blunt cardiac injury as well. 85 Several different techniques of repairing the BAI have been reported. These techniques include both direct suture repair 115,122 and placement of a prosthetic graft. 128 The most feared complications of BAI repair are paraplegia and renal failure, both of which result from ischemia during the repair. Ischemic complications correlate with the time the aorta is clamped. 2,102,106,114 In addition, there are more metabolic derangements resulting from reperfusion when the clamp and sew method is used. 124 Various methods of distal perfusion ranging from heparin-bonded (Gott) shunts 78,79,90,96,109,127 to partial or full cardiac bypass with and without systemic heparinization 55,98,99,103,105,114,116,118,128,130,133 have been shown to be helpful in minimizing distal ischemia. Although there is a theoretical risk of increased bleeding from head or abdominal injuries with systemic heparinization, Pate 116 found no increase in hemorrhage in his series. These methods should be used in all patients or at least in those patients in whom a prolonged clamp time is anticipated. 2,97,107 Other protective measures such as hypothermia may also be helpful. 94,98 A dedicated thoracic surgeon may be best qualified to repair BAI, 92 although Kim et al. 108 believes that full-time trauma surgeons have equally good results. Close communication between the surgical and anesthesia teams is essential. 104,124 SUMMARY In summary, BAI is a lethal result of severe blunt trauma. It should be considered in all patients who sustained injury by a deceleration or acceleration mechanism, especially in the face of physical or radiographic findings suggestive of mediastinal injury. Angiography remains the “gold standard” for diagnosis, although CT scanning is taking more of a role, especially for screening. Diagnosis should be followed by prompt surgical repair using some method of distal perfusion to minimize renal and spinal cord ischemia. If prompt repair is not feasible because of other injuries or comorbidities, medical control of blood pressure is warranted in the interim. FUTURE INVESTIGATION Less invasive diagnostic testing should be investigated as it becomes available in a prospective manner. In addition, the optimal method of distal perfusion during surgical repair should also be investigated in a prospective manner. As the number of patients who actually survive to surgery is relatively small, this may best be accomplished through a multicenter trial.