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March 2011

Critical Care

Journal Club -- Surgical Critical Care

Reviewer Name:  David J. Dries, MSE, MD; Assistant Medical Director for Surgical Care, HealthPartners Medical Group and Professor of Surgery & Anesthesiology, John F. Perry, Jr. Chair of Trauma Surgery, University of Minnesota.

BACKGROUND AND OVERVIEW
Article Title/Citation:  Teixeria PGR, Inaba K, Barmparas G, et al.  Blunt Thoracic Aortic Injuries: An Autopsy Study.  J Trauma 2011; 70:197-202.

Study Objective/Purpose: Using autopsy data, this study identifies the incidence and patterns of thoracic aortic injury in a consecutive series of blunt traumatic deaths.  Pattern of associated injury is also examined. 

Brief Background:  There have been multiple changes in diagnostic and treatment strategies for aortic injury during the past several years.  Many of these patients are treated with stent grafts and CT imaging has revolutionized emergency department evaluation.  Using autopsy data, these authors present a contemporary picture of the development and presentation of blunt thoracic aortic injury. 

Funding Source:  No funding source was identified.

METHODS
Study Design and Methodology:  A review of all autopsies performed for blunt trauma in Los Angeles County during 2005 was performed.  Patients with a blunt mechanism and full autopsy data were included.  Autopsy data from a full year for Los Angeles County was gathered.

Patient Selection and Enrollment:  During 2005, there were 881 victims of fatal blunt trauma in Los Angeles County.  Three hundred-four of these victims (35%) underwent full autopsy and were included in the analysis.  No patients receiving full autopsy during the study interval were excluded. 

Interventions:  Full autopsy data was evaluated on patients dying with blunt trauma in Los Angeles County during calendar year 2005.    

Outcome Measures/Endpoints:  The incidence of thoracic injury was recorded as well as associated injuries in this selected population. 

Statistical Analysis:  After provision of simple statistics regarding the incidence of blunt thoracic aortic injury as a component of mortality following blunt trauma, associated injuries were also identified and patients with and without blunt thoracic aortic injury were compared.    

RESULTS
Enrollment & Baseline Characteristics:  In 2005, there were 881 fatal victims of blunt trauma in Los Angeles County.  Thirty-five percent of these victims or 304 subjects had full autopsy data and were included in the analysis.  Average age was 43 years and 71% of subjects were male.  Thirty-nine percent of these patients had a positive blood alcohol screen.  Motor vehicle collision was the mechanism of injury in 50% of subjects followed by pedestrians struck by automobiles (37%).  Traumatic thoracic aortic injury was identified in 102 or 34% of victims receiving full autopsy data. 

Summary of Primary & Secondary Outcomes:  The authors were careful to describe aortic injury.  Injuries identified were consistent with previous reports in that most of the injury occurred at the isthmus or proximal descending aorta.  Two-thirds of aortic injuries were at this site.  The aortic arch was injured in 11% of patients studied and aortic injury at multiple sites was noted in 18% of autopsies.  Death at the scene was significantly more frequent in patients with thoracic aortic injury compared to patients without that injury (80% versus 63%, p=0.002). 

Patients with thoracic injury were significantly more likely to have associated cardiac injury, hemothorax and rib fractures when compared to patients without aortic injury.  Notably, the presence of sternal fracture was not different between the two groups.  Intraabdominal injuries were identified in 74% of patients with thoracic aortic injury.  This rate was significantly higher than the patients who did not have thoracic aortic injury.  A second interesting finding was that head injuries were significantly less frequent in patients with thoracic aortic injury (52% versus 66%, p=0.019). 

AUTHOR’S DISCUSSION AND CONCLUSIONS
Summary of Author’s Main Discussion Points:  Despite changes in hospital management and improvements in vehicle construction and design, blunt thoracic aortic injury continues to be a lethal injury with a high fatality rate and mortality occurring prior to arrival at hospital.  These patients generally had multiple associated injuries focused on the torso.  In this contemporary autopsy series, mortality from blunt aortic injury due to motor vehicle accidents continues to be high.  These authors also point out a significant risk of aortic injury in pedestrians struck, a group which has received far less attention from the trauma community in earlier studies of blunt aortic injury.

Author’s Conclusions:  Thoracic aortic injuries occurred in one-third of blunt traumatic fatalities, with the majority of deaths occurring at the scene.  The risk for associated thoracic and intraabdominal injuries is significantly increased in patients with thoracic aortic injuries. 

REVIEWER’S DISCUSSION AND CONCULUSIONS
Study Strengths:  A large population of patients with complete autopsy data is reviewed.  A consistent autopsy technique is employed as only one coroner’s office is utilized.  The county involved (Los Angeles County) is large enough to generate a significant data set.  The authors have carefully examined this set of data. 

Study Limits:  The authors provide a large amount of epidemiologic data but fail to indicate whether aortic injury is the actual source of mortality in these patients.  Obviously, there will be cases where a true cause of death cannot be identified.  However, additional opportunity for various preventive strategies is lost if a proximal cause of death is not identified.

Applicability and Impact on Healthcare Providers:  In this carefully conducted review, clinicians evaluating patients for aortic injury should be aware that additional injuries focused on the torso are likely to be present.  On review of this data, it appears unlikely that significant thoracic aortic injury occurs in the absence of other torso trauma. 

Conclusions and Recommendations:  Aortic injury continues to be a common source of morbidity (and likely mortality) in blunt trauma.  This data confirms that blunt aortic injury is not found in isolation.  In addition to motor vehicle crash data, this large data set suggests a significant incidence of blunt thoracic injury in pedestrians struck.  While demonstrating the majority of injuries in the classic location at the aortic isthmus and proximal descending aorta, these authors also point out that multiple points in the aorta or the aortic arch may also be affected by blunt chest trauma.  Thus, imaging in patients surviving to hospital must provide global assessment of the thoracic aorta.