Associated injuries, management, and outcomes of blunt abdominal aortic injury

From the Society for Vascular Surgery Associated injuries, management, and outcomes of blunt abdominal aortic injury Charles de Mestral, MD, a Andrew D. Dueck, MD, MS, FRCSC, b David Gomez, MD, a Barbara Haas, MD, a and Avery B. Nathens, MD, PhD, FRCSC, MPH, a Toronto, Ontario, Canada Objective: Blunt abdominal aortic injury (BAAI) is very rare, and current literature is limited to case series of single-center experience. Through an analysis of the National Trauma Data Bank, the largest aggregation of United States trauma registry data, our aim was to characterize the associated injury pattern, contemporary management, and in-hospital outcomes of patients with BAAI. Methods: We used a nested case-control design. The overall cohort consisted of adult patients (age >16 years) severely injured (Injury Severity Score >16) after blunt trauma who were treated at a level 1 or 2 trauma center in years 2007 to 2009. Cases were patients with BAAI and were frequency-matched by age group and mechanism to randomly selected controls at a one-to-five ratio. Multivariable matched analysis (conditional logistic regression) was used to derive adjusted measures of association between BAAI and adjacent arterial, intra-abdominal, and bony injuries. Results: We identified 436 patients with BAAI from 180 centers. The mean Injury Severity Score was 35 14, and most patients were injured in motor vehicle crashes (84%). Multivariable analysis showed injury to the thoracic aorta, renal and iliac artery, small bowel, colon, liver, pancreas, and kidney, as well as lumbar spine fractures were independently associated with BAAI. A total of 394 patients (90%) were managed nonoperatively, and 42 (10%) underwent repair. Of these 42 patients, 29 (69%) underwent endovascular repair, with 11 patients undergoing open aortic repair and two extraanatomic bypasses. Median time from admission to repair was 1 day (interquartile range, 1-2 days). Overall mortality was 29%. A total of 271 (69%) patients managed nonoperatively survived to hospital discharge. Conclusions: The index of suspicion for BAAI should be raised in severely injured patients by the presence of injuries to the lumbar spine, bowel, retroperitoneal organs, and adjacent major arteries. Although endovascular repair is the most common intervention, most patients are managed nonoperatively and survive to hospital discharge. (J Vasc Surg 2012; 56:656-60.) Blunt abdominal aortic injury (BAAI) is extremely rare and accounts for approximately 5% of all traumatic aortic injuries. 1-3 Although the presentation and management of thoracic aortic injury has been characterized to a far greater extent, current literature focusing on injury to the abdominal aorta is limited to case reports and case series of single-center experiences. The most extensive review to date was published in 1997 when diagnostic sensitivity may have been limited by early-generation computed tomography imaging and well before the widespread use of endovascular repair. 4 Given the advances in diagnosis and management since then, our objective was to characterize the associated injury pattern, contemporary management strategies, and in-hospital outcomes of patients with BAAI, across the United States. From the Li Ka Shing Knowledge Institute of St. Michael s Hospital, a and the Department of Surgery, Division of Cardiac and Vascular Surgery, Sunnybrook Health Science Center. b Author conflict of interest: none. Presented at the 2011 Vascular Annual Meeting of the Society for Vascular Surgery, Chicago, Ill, June 16-18, 2011. Reprint requests: Avery B. Nathens, MD, PhD, MPH, FRCSC, FACS, Professor, Department of Surgery, Director of Trauma and Division Head of General Surgery, St. Michael s Hospital, 30 Bond, Queen 3-076, Toronto, ON M5B 1W8, Canada (e-mail: abnathens@gmail.com). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 0741-5214/$36.00 Copyright 2012 by the Society for Vascular Surgery. doi:10.1016/j.jvs.2012.02.027 656 METHODS Research ethics approval for this study was obtained from the St Michael s Hospital Research Ethics Board. Study design. We used a nested case-control design with data derived from the National Trauma Data Bank (NTDB) version 10 (American College of Surgeons, Chicago, Ill) for years 2007 to 2009. NTDB is the largest aggregation of United States trauma registry data. NTDB includes data on patient demographics, diagnoses, procedures, and in-hospital outcomes submitted from 600 registered trauma centers in the United States. NTDB data are collected and maintained by the American College of Surgeons Committee on Trauma. The cohort included adults (aged 16 years) severely injured (Injury Severity Score [ISS] 16) after blunt trauma and cared for at a level 1 or 2 trauma center. ISS 16 is a widely used cutoff for identifying patients with severe traumatic injury 5-7 and also corresponds to the minimum ISS possible for any patient with BAAI. We excluded patients dead on arrival and those who died in the emergency department because of potentially limited evaluation of associated injuries as well as minimal opportunity for salvage interventions. From this cohort of severely injured patients we identified cases with traumatic abdominal aortic injury based on the International Classification of Diseases, 9th Revision (ICD-9), diagnosis code 902.0 (injury to abdominal aorta). Controls without blunt abdominal aortic injury were ran-

JOURNAL OF VASCULAR SURGERY Volume 56, Number 3 de Mestral et al 657 Table I. Classification of International Classification of Disease, 9th Revision (ICD-9) procedure codes for repair in patients with blunt abdominal aortic injury (BAAI) Code Description Open repair 38.04 Incision of vessel, aorta 38.14 Endarterectomy, aorta 38.34 Resection of vessel with anastomosis, aorta 38.44 Resection of vessel with replacement, aorta 38.64 Excision of vessel, aorta Endovascular repair 39.71 Endovascular implantation of graft in abdominal aorta Extra-anatomic bypass 39.29 Peripheral vascular bypass, axillofemoral bypass domly selected from the overall cohort based on frequency matching by age group (10-year intervals) and mechanism (motor vehicle crash, fall, other blunt trauma) at a five-toone ratio with cases. Associated injuries and outcomes. Associated injuries and procedures were identified based on ICD-9 diagnosis and procedure codes. We focused on selected injuries potentially associated with BAAI based on a literature review and an a priori clinical hypothesis. These included injuries to adjacent major arteries (thoracic aorta, renal arteries, iliac arteries), intra-abdominal organs (liver, spleen, small bowel, colon), retroperitoneal organs (pancreas, kidneys), and fractures (lumbar spine, pelvis). Repair procedure codes were categorized as open repair, endovascular repair, or extra-anatomic bypass (Table I). Common in-hospital complications were derived from ICD-9 diagnosis codes and the NTDB complications field. Statistical analysis. To evaluate whether specific injuries were over-represented in patients with BAAI, we evaluated the relative frequency of the selected injuries described above in the cases compared with controls. Despite matching of cases and controls, residual confounding of the relationship between BAAI and other injuries remained; therefore, we performed a multivariable matched analysis using conditional logistic regression (CLR). Similarly to standard (unconditional) logistic regression, CLR is based on maximum likelihood estimation to derive regression coefficients in the setting of a binary dependent variable. 8 While accounting for matched strata, CLR allows for controlling of confounders on which cases and controls have not been matched. 8,9 Using all cases and controls in our regression model, we derived measures of association between each individual injury and our binary outcome: presence or absence of BAAI. Discrepancy in overall extraabdominal injury severity between cases and controls, and binary variables for the presence or absence of severe injury (Abbreviated Injury Severity Score 3) to the head, chest, and extremities were included in the reduced model as confounders. As a result, in using CLR, we adjusted for differences in injury severity using more granular components (Abbreviated Injury Severity Score and individual injuries) that contribute to overall ISS. P.05 was used as the indicator of statistical significance. All statistical analysis was performed with SAS 9.1 software (SAS Institute, Cary, NC). RESULTS The cohort included 262,785 patients from 414 centers who were severely injured after blunt trauma. Within this cohort, 436 patients across 180 centers sustained BAAI. An additional 10 patients with a BAAI diagnosis code were identified but excluded from the analysis because they were dead on arrival or died in the emergency department and thus were unlikely to be salvaged. Each center managed a median of two cases (interquartile range [IQR], one to three cases) during the 3-year study period. Most patients with BAAI were men (67%) with a mean age of 46 25 years. Motor vehicle crash was the dominant mechanism of injury (84%) and mean ISS was 35 14. Table II presents the baseline characteristics of patients with BAAI alongside those of the 2180 controls matched for age and mechanism without BAAI. As reported in Table II, matching cases and controls for age and mechanism resulted in balanced baseline characteristics; however, the overall injury severity was greater, and severe head injury was more common in cases. Conditional logistic regression was used to account for this residual confounding. Associated injuries. Associated injury frequency in cases and controls is presented in Table III. Although 119 patients (27%) sustained BAAI without any of the injuries listed in Table III, the most common associated injuries were lumbar spine fractures (26%), pelvic fractures (25%), and splenic injuries (22%). Injuries to adjacent arteries (thoracic aorta, renal artery, and iliac artery) were uncommon but most strongly associated with aortic injury on unadjusted and adjusted analyses. Also independently associated with BAAI were injuries to the small bowel, colon, liver, pancreas, and kidney, as well as lumbar spine fractures. Management. Of 436 patients with BAAI, 42 (10%) underwent repair, of whom 29 (69%) underwent endovascular repair, including open aortic repair in 11 and extraanatomic bypass in two. In all patients undergoing repair, the median time from admission to repair was 1 day (IQR, 1-2 days). When comparing patients managed nonoperatively with those having aortic repair, there was no significant difference in overall injury severity (mean ISS, 36 14 vs 35 12; P.77) or frequency of severe head injury (22% vs 19%; P.70). Operative repair was as frequent in patients with associated injuries from Table III as in those without any of these injuries. Patients who underwent open repair compared with those managed with endovascular repair also did not differ in overall injury severity (mean ISS, 34 12 vs 38 12; P.26). None of the 42 patients managed operatively required subsequent operative or endovascular reintervention during their hospital stay.

658 de Mestral et al JOURNAL OF VASCULAR SURGERY September 2012 Table II. Baseline characteristics and global injury pattern of cases with blunt abdominal aortic injury (BAAI) and controls Variable a Cases (n 436) Controls (n 2180) P Age, years 46 25 47 23.76 Age group (matched),.99 years 16-25 74 (17) 370 (17) 26-35 66 (15) 330 (15) 36-45 73 (17) 365 (17) 46-55 72 (17) 360 (17) 56-65 50 (11) 250 (11) 66-75 40 (9) 200 (9) 76-85 47 (11) 235 (11) 85 14 (3) 70 (3) Sex.34 Male 294 (67) 1519 (70) Female 142 (33) 661 (30) Race.33 White 315 (72) 1590 (73) African American 50 (12) 203 (9) Other 71 (16) 387 (18) Comorbidity count.18 0 288 (66) 1344 (62) 1 92 (21) 512 (23) 2 56 (13) 324 (15) Atherosclerosis 12 (3) 87 (4).21 Diabetes 30 (7) 199 (9).12 Mechanism (matched).99 Motor vehicle crash 366 (84) 1830 (84) Fall 52 (12) 260 (12) Other blunt 18 (4) 90 (4) Injury Severity Score 35 14 25 9.001 Severe injury Head 93 (21) 790 (36).001 Chest 168 (39) 829 (38).84 Extremity 99 (22) 463 (21).49 a Continuous data are expressed as mean standard deviation and categoric data as number (%). Outcomes. In patients with BAAI, overall in-hospital mortality was 29% and the five most commonly coded complications were acute respiratory distress syndrome (11%), pneumonia (9%), cardiac arrest (7%), acute renal failure (5%), and deep vein thrombosis (3%). Compared with age-matched and mechanism-matched controls, patients with BAAI more frequently had cardiac arrest (7% vs 2%; P.001) and acute renal failure (5% vs 2%; P.001). Of the 394 patients managed nonoperatively, 271 (69%) survived to hospital discharge. Patients managed nonoperatively, compared with those who underwent repair, had the same frequency of common complications but a higher in-hospital mortality rate of 31% vs 12% (P.01) and a shorter median length of stay of 6 days (IQR, 2-17 days) vs 13 days (IQR, 7-22 days; P.001). Patients who underwent open repair and those managed with endovascular repair had a similar frequency of common complications, with a mortality rate of 6.9% in open patients compared with 7.1% after endovascular repair (P.30). DISCUSSION Given the scarcity of recent data on BAAI, we sought to characterize the associated injury pattern, contemporary management strategies, and in-hospital outcomes in patients with this injury. By using the NTDB we captured a large number of patients from a wide range of levels 1 and 2 trauma centers in the United States. After adjusting for potential confounders, BAAI was found most strongly associated with injury to the thoracic aorta, renal and iliac arteries, and being independently associated with injuries to the small bowel, colon, liver, pancreas, and kidney, as well as lumbar spine fractures. Furthermore, although endovascular repair was the most common intervention (69% of repairs), 90% of patients were managed nonoperatively. Of those managed nonoperatively, 69% survived to hospital discharge. That BAAI resulted from motor vehicle crashes in 80% of cases is consistent with prior reports that have also suggested that BAAI occurs frequently in association with seat-belt use, both two- and three-point restraint types. 4,10-15 In the context of existing literature, patients injured in motor vehicle collisions may sustain BAAI as part of a seat-belt injury complex. A deceleration mechanism leading to shear injury, which is well documented in traumatic thoracic aortic injury, 16 may be less important in BAAI compared with the predominant mechanism of direct blunt force to the abdomen or back. 4,10 Also of interest is that although atherosclerosis has been suggested as a risk factor for BAAI by contributing to reduced tensile strength of the aortic wall, 4,15 after accounting for age through matching, we found the prevalence of symptomatic atherosclerosis (comorbidity code of prior stroke, coronary artery disease, or peripheral arterial disease) was no greater in patients with BAAI compared with controls. With respect to injury patterns, many authors have reported a high prevalence of lumbar spine fractures in patients with BAAI; however, small sample sizes limited the potential for a robust characterization of associated injuries. 4,17 We looked at adjacent arterial, abdominal, and bony injuries and found that thoracic aorta, renal, and iliac artery injuries were most strongly associated with BAAI, although the absolute frequency of these injuries was 10%. Of the three most common injuries lumbar spine, pelvic, and splenic injuries only lumbar spine fractures remained significantly associated with BAAI on multivariable analysis. The independent association of BAAI with bowel injuries, injuries to retroperitoneal organs, and lumbar spine fractures on multivariable analysis suggests that particular attention should be paid to the abdominal aorta on initial computed tomography imaging in all patients with these injuries. Furthermore, in hemodynamically unstable patients who go directly to the operating room for other injuries, these results can also provide some guidance for which patients should be scanned postoperatively to look for aortic injuries that may not be evident intraoperatively.

JOURNAL OF VASCULAR SURGERY Volume 56, Number 3 de Mestral et al 659 Table III. Injury frequency in cases and controls and odds ratio of associated blunt abdominal aortic injury (BAAI) by type of injury Injury Cases a (n 436) Controls a (n 2180) Unadjusted OR (95% CI) Adjusted b Renal artery 23 (5) 6 (0.3) 20.3 (8.2-50.1) 10.7 (4.0-28.5) Thoracic aorta 36 (8) 24 (1) 8.1 (4.8-13.7) 7.7 (4.3-13.7) Iliac artery 24 (6) 10 (0.5) 12.6 (6.0-26.5) 7.7 (3.3-17.6) Colon and rectum 43 (10) 38 (2) 6.3 (4.0-9.9) 4.1 (2.4-6.9) Pancreas 21 (5) 16 (1) 6.9 (3.6-13.3) 3.6 (1.7-7.7) Kidney 72 (17) 102 (5) 4.1 (3.0-5.7) 2.5 (1.7-3.6) Small bowel 40 (9) 40 (2) 5.4 (3.5-8.5) 2.0 (1.1-3.4) Liver 87 (20) 207 (10) 2.5 (1.9-3.3) 1.7 (1.2-2.4) Spleen 97 (22) 277 (13) 2.0 (1.6-2.6) 1.3 (0.9-1.7) Lumbar spine fracture 113 (26) 352 (16) 1.8 (1.4-2.3) 1.5 (1.1-1.9) Pelvic fracture 107 (25) 407 (19) 1.4 (1.1-1.8) 1.0 (0.8-1.4) CI, Confidence interval; OR, odds ratio. a Data are shown as number (%). b Adjusted for severe injury to head, chest, and extremities, as well as other listed individual injuries. Most patients in this study were managed nonoperatively, and in the event of repair, the predominant approach was endovascular. The therapeutic options for BAAI include open repair (flap suture, endarterectomy, or aortic interposition graft), endovascular stent placement, nonoperative management, and in rare cases, open ligation and extra-anatomic bypass. 10-15,17,18 Choice of management strategy depends on many factors, including aortic injury severity, location of aortic injury, aortic anatomy, time of diagnosis, overall patient injury profile, presence of other specific injuries (eg, bowel injury with peritoneal contamination), and presence of distal ischemia from complete aortic occlusion or emboli. Although a clear understanding of the indications for intervention and the reasons for a higher mortality in patients managed nonoperatively is limited with NTDB data alone, our results are clearly hypothesis-generating. It is plausible that early death precluded intervention in some of the patients managed nonoperatively, but 69% of patients managed nonoperatively did survive to hospital discharge. As such, a considerable proportion of all patients may have had only minimal aortic injury without ischemia or hemorrhage mandating emergency intervention. Experience with nonoperative management of minimal thoracic aortic injury is likely informing similar practices with regard to minimal abdominal aortic injury. Furthermore, in an NTDB cohort of patients with blunt thoracic aortic injury, Arthurs et al 19 reported that the 68% who did not undergo had a 65% mortality, whereas we found a 31% mortality in BAAI patients managed nonoperatively. This difference supports a hypothesis that death precluding repair is less common in blunt thoracic than in blunt abdominal aortic injury. We also noted that among patients who underwent repair, repair occurred early in hospitalization. This observation raises two potential explanations: First, if BAAI was recognized early, delayed injury progression led to death before possible aortic intervention or occurred rarely during hospital admission. Second, in the setting of a delayed BAAI diagnosis, ischemia or hemorrhage mandating emergency intervention is unlikely. Nonetheless, that the no-repair group had more than twice the mortality rate but a similar overall ISS as the repair group, coupled with a high frequency of cardiac arrest (7%), raises the possibility of an underutilization of operative intervention and subsequent aortic rupture. Finally, although patients with associated injuries had a higher mortality rate, we did not find any difference in distribution of severe head injury or associated injuries to further elucidate indications for operative intervention. Our study has some limitations. After matching, regression techniques allowed us to account for differences remaining between cases and controls in evaluating the relationship of BAAI with associated injuries. Given the study design, we cannot exclude additional residual confounding by unmeasured patient and injury characteristics. Furthermore, differences in detection of associated injuries in cases and controls also cannot be completely ruled out; however, by nesting cases and controls within a cohort of severely injured patients (ISS 16), we have minimized measurement bias because all patients would have had an extensive workup owing to the severity of their injuries. Finally, our data allow only a limited understanding of the indications for repair, which may have been related to different aortic injury severity not accurately captured by ICD-9 coding, to vascular complications, or to physician bias. Nevertheless, we have presented a generalizable characterization of the management of BAAI in a large study sample and have used the available data to generate hypotheses regarding the indications for repair. CONCLUSIONS With this analysis of a large cohort of patients with BAAI, from trauma centers throughout the United States, we have presented the most rigorous characterization to date of injuries associated with BAAI. Furthermore, we

660 de Mestral et al JOURNAL OF VASCULAR SURGERY September 2012 have shown that nonoperative repair during the initial admission is frequent in adults, with most patients surviving to hospital discharge. Future research on BAAI should follow what has been undertaken for thoracic aortic injury: a prospective, multicenter study. 20 Open repair will remain the standard approach for hemodynamically unstable patients who are undergoing a trauma laparotomy; however, a comparative evaluation, with standardized radiologic aortic injury grading, of the roles of endovascular repair and nonoperative management in hemodynamically stable patients should be the next focus of research on blunt abdominal aortic injury. AUTHOR CONTRIBUTIONS Conception and design: CM, AD, AN Analysis and interpretation: CM, AD, DG, BH, AN Data collection: CM, DG, BH, AN Writing the article: CM, AD, DG, BH, AN Critical revision of the article: CM, AD, DG, BH, AN Final approval of the article: CM, AD, DG, BH, AN Statistical analysis: CM, AN Obtained funding: Not applicable Overall responsibility: CM REFERENCES 1. Kirsh MM, Behrendt DM, Orringer MB, Gago O, Gray LA Jr, Mills LJ, et al. The treatment of acute traumatic rupture of the aorta: a 10-year experience. Ann Surg 1976;184:308-16. 2. Feczko JD, Lynch L, Pless JE, Clark MA, McClain J, Hawley DA. An autopsy case review of 142 nonpenetrating (blunt) injuries of the aorta. J Trauma 1992;33:846-9. 3. Parmley LF, Mattingly TW, Manion WC, Jahnke EJ Jr. Nonpenetrating traumatic injury of the aorta. Circulation 1958;17:1086-101. 4. Roth SM, Wheeler JR, Gregory RT, Gayle RG, Parent FN 3rd, Demasi R, et al. Blunt injury of the abdominal aorta: a review. J Trauma 1997;42:748-55. 5. Baker SP, O Neill B, Haddon W Jr, Long WB. The injury severity score: a method for describing patients with multiple injuries and evaluating emergency care. J Trauma 1974;14:187-96. 6. Copes WS, Champion HR, Sacco WJ, Lawnick MM, Keast SL, Bain LW. The injury severity score revisited. J Trauma 1988;28:69-77. 7. Linn S. The injury severity score importance and uses. Ann Epidemiol 1995;5:440-6. 8. Kleinbaum DG, Klein M. Logistic regression. 3rd ed. New York: Springer; 2010. p. 390-429. 9. Daly LE, Bourke GJ. Interpretation and uses of medical statistics. 5th ed. Oxford: Blackwell Science; 2000. p. 161-72. 10. Naude GP, Back M, Perry MO, Bongard FS. Blunt disruption of the abdominal aorta: report of a case and review of the literature. J Vasc Surg 1997;25:931-5. 11. Choit RL, Tredwell SJ, Leblanc JG, Reilly CW, Mulpuri K. Abdominal aortic injuries associated with chance fractures in pediatric patients. J Pediatr Surg 2006;41:1184-90. 12. Lalancette M, Scalabrini B, Martinet O. Seat-belt aorta: a rare injury associated with blunt abdominal trauma. Ann Vasc Surg 2006;20: 681-3. 13. Dajee H, Richardson IW, Iype MO. Seat belt aorta: acute dissection and thrombosis of the abdominal aorta. Surgery 1979;85:263-7. 14. Clyne CA, Ashbrooke EA. Seat-belt aorta: isolated abdominal aortic injury following blunt trauma. Br J Surg 1985;72:239. 15. Lassonde J, Laurendeau F. Blunt injury of the abdominal aorta. Ann Surg 1981;194:745-8. 16. Neschis DG, Scalea TM, Flinn WR, Griffith BP. Blunt aortic injury. N Engl J Med 2008;359:1708-16. 17. Inaba K, Kirkpatrick AW, Finkelstein J, Murphy J, Brenneman FD, Boulanger BR, et al. Blunt abdominal aortic trauma in association with thoracolumbar spine fractures. Injury 2001;32:201-7. 18. Huang JT, Heckman JT, Gunduz Y, Ohki T. Endovascular management of stenosis of the infrarenal aorta secondary to blunt abdominal aortic trauma in a multiply injured patient. J Trauma 2009;66:E81-5. 19. Arthurs ZM, Starnes BW, Sohn VY, Singh N, Martin MJ, Andersen CA. Functional and survival outcomes in traumatic blunt thoracic aortic injuries: an analysis of the national trauma databank. J Vasc Surg 2009;49:988-94. 20. Demetriades D, Velmahos GC, Scalea TM, Jurkovich GJ, Karmy-Jones R, Teixeira PG, et al. Operative repair or endovascular stent graft in blunt traumatic thoracic aortic injuries: results of an American Association for the Surgery of Trauma multicenter study. J Trauma 2008;64: 561-70. Submitted Nov 28, 2011; accepted Feb 9, 2012.