It is about 11 PM on a warm Saturday night in early spring and you have been on duty in the ED for four relatively quiet hours when the local EMS radio crackles to life.

EMS Radio Report

"County emergency! This is EMS Unit 201 en route with a single patient from a two car, head-on road crash. The patient is a 21-year-old male unrestrained passenger who was briefly trapped in the vehicle. The steering wheel was deformed and the windshield starred. Bystanders report that the patient was unconscious for a few minutes prior to our arrival. However, he has been awake and combative since we arrived on the scene."

"Vital signs are as follows: BP 110/Palpable, P 102, RR 22, Glasgow Coma Scale 14. The patient has facial lacerations and blood in both nares. Breath sounds are clear and equal bilaterally and the abdomen is soft and non-tender. The patient has no obvious extremity deformities and there is no sensory or motor deficit in any of the extremities. The patient has been placed in full cervical immobilization, with c-collar and long spin board, placed on O₂by non-rebreathing (NRB) mask, and has two 14-guage IV lines of saline 0.9%."

"We will be in the department in two minutes."

Initial ED Evaluation

On arrival in the ED, the patient is loudly complaining of neck, back, chest and knee pain. He is noted to be uncooperative with the ED staff. Vital signs in the ED are: BP 129/P, P 138, RR 22, pulse oximetery is 100% on NRB mask O₂. The physical exam reveals two facial lacerations of one and three cms above the right eyebrow and dried blood in both nares. Pupils are equal and reactive; extra ocular motion is intact. There is no midline neck or back tenderness and neurological exam is non-focal. Breath sounds reveal some crackles in the left posterior lung fields. There are no murmurs or gallops. The abdomen is soft and minimally tender with no rebound or guarding. Extremities show no deformity and all distal pulses are strong and equal. You order cervical-spine, chest and pelvis films. The chest film is shown below.

Q. What findings are seen on this film?

A. The chest film shows widening of the mediastinum and blurring of the aortic knob.

Q. What is the significance of these findings?

A. These findings indicate the possibility of an aortic disruption.

Traumatic Aortic Disruption

Aortic injury in trauma patients carries a high mortality and morbidity rate. About 80-90% of aortic injuries do not reach the ED alive. Among those who do, the natural history is that of a continually, rapidly fatal injury with 20-30% mortality in the first six hours, 40-50% mortality in the first 24 hours, and 60-80% mortality in the first week post injury.

Mechanism of Injury

The mechanism of injury to the aorta is believed to be shearing forces from rapid deceleration that can be seen in high speed front and side impact motor vehicle accidents (MVA) and in a fall from a significant height. In MVA associated aortic injury, the most common location for aortic disruption, about 90%, is at the isthmus, between the origin of the left subclavian artery and the ligamentum arteriosum. At the isthmus, the aorta is the most relatively fixed (by the great vessels and ligamentum arteriosum). The distal thoracic aorta is more mobile and will apply traction to the arch during deceleration, causing a shearing injury at the arch. Another, much less common, site of traumatic aortic disruption is the aortic root. This is usually seen in patients who have fallen from a significant height.

The aorta is made up of three layers of tissue: the inner elastic intima, the media or muscular middle layer, and the tough external adventitia. Disruption of the aorta usually begins at the intima and extends outward with increasing injury force. In survivors, there is usually a tear of the intima alone or the intima and media with bleeding tamponaded by the adventitia and other mediastinal structures resulting in the formation of an aortic pseudoaneurysm. If there is complete disruption, exsanguination and death are rapid and the patient rarely reaches medical care alive.

Diagnosis

In those patients who do live to reach medical care, aortic injury can be very difficult to detect but the examining physician should have a high index of suspicion based on mechanism of injury or even chest injury. Additionally, many patients at risk for aortic injury will have other potentially life threatening injuries that can distract the unwary physician. A few patients may present with chest or upper back pain that increases as blood pressure increases, possibly heralding an impending complete rupture. Even fewer will have complaints of dysphagia, dysphonia, hoarseness or dyspnea from the mediastinal hematoma of an aortic tear. Many are asymptomatic from their aortic injury.

The physical exam may also be deceptively normal. As mentioned above, up to one-third or more patients with aortic injury may have no external signs of chest trauma. Some signs that can occasionally be seen on physical exam include:

• upper extremity hypertension, with or without associated lower extremity hypotension
• a harsh systolic murmur heard over the anterior precordium or the interscapular area posteriorly, which is thought to be due to blood flow across the area of partial transection
• and, in the case of near complete obstruction of blood flow to the distal aorta, anuria or lower extremity paralysis.

The diagnosis is often first suspected on chest x-ray. The American College of Surgeons recommends that all trauma patients receive at least cervical spine, chest and pelvis x-rays. The most common findings of aortic injury on chest x-ray are mediastinal widening of >8.0 cm and/or blurring of the aortic knob. The most sensitive finding is deviation of the esophagus to the right > 1-2 cm at the level of T-4. This is most readily seen when nasogastric tube deviation is noted.(2) Other clues to aortic injury that may be seen on chest film are listed below.

Findings on Chest Film Suspicious for Aortic Disruption

• mediastinal widening >8.0cm
• blurring of the aortic knob
• mediastinal to chest ratio of >0.25
• deviation of the esophagus >1-2 cm to the right at the level of T-4
• deviation of the trachea
• depression of the left mainstem bronchus > 40 degrees below the horizontal
• obliteration of the clear space between the aortic knob and the left pulmonary artery
• apical cap
• widening of the right paratracheal stripe >0.5cm
• small left hemothorax
• fracture of the left 1st or 2nd rib

Although a negative chest film does not completely rule out aortic injury, an upright PA chest film taken at six feet has a specificity of 25% and a sensitivity of 98%. False positive on chest film may be caused by supine, AP films or films taken at <3 feet 4 inches tube to film distance, which describes the conditions of most, if not all, initial portable chest films obtained on trauma patients. For those patients who are able to stand once their initial evaluation is completed, a repeat film, done upright and PA, may eliminate the need for further imaging. Many acutely injured patients are unable to stand for an optimal chest film. Poor inspiration can also lead to a misleading chest film.

Q. What would be the next step in evaluation of a suspected aortic injury?

A. This is a more controversial area. For many years, aortography was considered the definitive test for thoracic vascular injuries. Aortography, however, does have some drawbacks. It requires moving the patient to the radiology suite, which can be difficult and hazardous in a critically injured patient. Iodinated contrast must also be used. While today's contrast agents do not have the same frequency of reactions as the old agents, there is still the possibility of either a local or systemic reaction or of kidney damage, especially in a volume depleted patient or one with underlying renal disease, from the contrast media. Because of these issues, researchers have begun looking at alternative methods of diagnosing aortic injuries.

New Diagnostic Techniques

Transesophageal echocardiography (TEE) has recently been investigated in several centers as a diagnostic tool in great vessel injuries, especially those involving the aorta. TEE can be performed at the bedside and does not require the use of any contrast agent. Several recent publications have indicated that TEE is up to 91% sensitive and 100% specific in detecting aortic injuries.(9) TEE is limited in patients with suspected aortic injury and an intact gag reflex, as the resultant increased pressure may lead to complete rupture of the injured vessel and exsanguination in the ED. TEE may also be difficult to impossible to perform in patients with severe maxilofacial injuries.(10)

Contrast-enhanced CT has also been proposed as a diagnostic modality in aortic injury. CT has received mixed reports as to its usefulness in evaluation of the thoracic aorta. While CT has been shown to be positive in most patients with aortic injury, the most common finding is a mediastinal hematoma, which is non-specific.(8) Additionally, CT does not give the surgeon a good anatomical picture of the injury, necessitating aortography following a positive scan. In our institution, we do use contrast chest CT as a secondary screening tool in cases where there is a lower index of suspicion for aortic injury but there is mediastinal widening on a subotimal chest film and an upright chest film is contraindicated.

Q. How would you manage this patient in the ED?

p>A. Definitive treatment of aortic disruption is surgical repair.

Surgical Repair

Two commonly used techniques of operative repair are the clamp and sew technique and the use of cardiopulmonary bypass. The clamp and sew technique involves cross-clamping the aorta, proximal to the injury, and rapidly closing the defect. Timing is critical with this procedure as cross clamp times of >35minutes are associated with an increased rate of complications, including lower extremity paralysis and renal failure from inadequate perfusion of the distal spinal cord and kidneys. Use of cardiopulmonary bypass reduces the risk of these complications by eliminating the need for cross-clamping the aorta.(3) However, bypass procedures typically require heparinization, which may increase the risk of bleeding complications from associated injuries.

The timing of operative repair of traumatic aortic disruption varies with the patient's condition and other associated injuries and medical conditions. In a patient who is unstable due to his /her aortic injury, surgical repair should be done on an emergency basis.

Some recent studies have shown that in patients with contained aortic injuries, operative repair can be delayed without an increase in mortality.(11) Since the forces involved in aortic injury are usually great, there are often associated injuries, especially intra-abdominal, that may be more immediately life threatening. In these cases, it may be necessary to delay the repair of the aorta until the other injuries have been explored and the patient stabilized.(4)

Prior to definitive treatment, hypertension should be studiously avoided. A systolic pressure of no greater than 120mmHg is recommended. Elevated blood pressure is thought to increase the risk of completing the injury, resulting in rapid exsanguination. Some authors have suggested that mild hypotension, defined as a systolic pressure of 90mmHg, may be protective in patients with great vessel injuries. Fluid resuscitation should be cautious and pressor use avoided. Procedures, such as nasogastric tube (NGT) placement that induce gagging and vomiting, should be avoided and the patient given adequate pain relief to prevent physiologic increases in arterial pressure.

Emergency physicians working in centers without trauma or vascular surgery capabilities should be prepared to rapidly transfer patients with suspected aortic injury to the nearest trauma center.(3),(4),(8),(11)