Blunt aortic injury (BAI) represents one of the most feared
and devastating injuries in trauma. Patients with BAIs often present to the
emergency department in hemorrhagic shock with multiple concomitant traumatic
injuries such as complex orthopedic fractures, intracranial hemorrhage and/or
solid organ lacerations. Historically, open repair of these injuries has been
the standard approach.1 However, open
repair has a number of downsides, including the need for systemic
anticoagulation, a high incidence of paraplegia, and the coordination in
management of other potentially devastating injuries requiring urgent or
emergent intervention. With the rise in the popularity and expertise in the endovascular
repair of aortic aneurysms, addressing BAI endovascularly has become a viable
option.2
Little has changed in the incidence of BAI over the past several
decades despite increased use of restraints and automobile safety. BAIs are the second leading cause of
traumatic death and account for 15-20% of fatalities. Typically they are a result of head on or
passenger side collisions and 80% of patients will die on the scene or in
transit to the hospital. Because these
injuries are typically the result of a significant traumatic event, 20-90% of
patients will have associated injuries. If BAIs are not recognized and
appropriately treated, up to 30% will die in 24 hours and 90% within 4 months.3
Three theories
exist regarding the mechanism of BAI. The first is the osseous pinch where the chest
wall collapses into the bony spine compressing the aorta. The second involves
the torsion, stretching and shearing effect of the fixed aortic isthmus after
significant blunt trauma. Last, the so-called “water hammer effect” may occur
where the simultaneous occlusion of the aorta at the diaphragmatic hiatus with
a sudden increase in blood pressure causes an injury to the aortic wall. BAI is
likely the result of a combination of these three forces.3 The most common
location of injury by far is the aortic isthmus where the aorta is fixed by the
ductus arteriosis. This is the site of injury in in approximately 90% of cases.
In general, rupture occurs in the intimal and medial layers
of the aortic wall. After a period of unpredictable duration, rupture of the
external adventitial aortic wall occurs and the patient will exsanguinate and
die.4
Given the
devastating nature of a missed BAI, timely diagnosis and intervention is life
saving. Classic chest x-ray findings concerning for a BAI includes any of the
following: pleural effusion, widened mediastinum, loss of the aorticopulmonary window,
tracheal deviation, and/or apical capping. However, the utility of CXR as a screening
tool for BAI is low as over 10% of patients with BAI may have a completely
normal CXR and up to 44% will have a normal mediastinum.3,5
Given the limitation
of CXR, currently the diagnostic study of choice is a CT angiogram. At Cook
County, a CT of the aortic arch is obtained in accelerating/decelerating
injuries >30mph, falls >30feet, or if sudden compression of the chest
(e.g., car falling off the jack) occurs and at least one of the following is
present: physical findings (e.g., abrasions or tenderness on chest),
abnormalities on CXR, or historical factors (e.g., fatalities on the scene). Importantly,
if a BAI is suspected or diagnosed, it is key to immediately administer
antihypertensive medications (e.g., esmolol) to a goal systolic blood pressure
target of 100 and certainly less than 120.
As stated above, there are a number of concerns with the
traditional open repair of BAIs. These include but are not limited to patient
positioning considerations (right lateral decubitus), high myocardial stress of
cross clamping the aorta, high paraplegia risk, long operative time and blood
loss, morbidity of the open thoracotomy and finally high mortality rates. These
concerns led many in the field seek alternative management strategies;
particularly apply endovascular techniques for aortic aneurysm repairs to BAIs.
This is the preferred approach at Cook County Trauma Center.
In one the largest studies comparing open vs. endovascular
repair, Demetriades and colleagues prospectively collected data from 18 trauma
centers across the country. This study included 193 patients, of which 68
underwent open, and 125 endovascular repair for BAI. Thirty percent of patients
had critical concomitant extrathoracic injuries. After adjustment for comorbitidies and injury
severity, the open approach was associated with a 13-fold increased likelihood
of death in patients without extrathoracic injuries and nearly 6-fold
likelihood of death among patients with extrathoracic injuries.6
Despite these findings, there are a number of limitations to the use of
endovascular repair of BAI including graft availability and size limitations,
technical expertise, costs, graft surveillance, and long-term results. These
issues are outside the scope of this report.
In conclusion, BAI remains a devastating injury requiring a
high index of suspicion. The optimal management of these patients continues to
evolve, and endovascular approaches appears to be a viable strategy in many
patients, particularly as the technology improves.
REFERENCES
By
Ryan P. Merkow, MD, MS
No comments:
Post a Comment