Prevalence and Outcome of Abdominal Vascular Injury in Severe Trauma Patients – An International Registry Analysis

Background Abdominal vascular injuries and the resulting hemorrhagic shock are still one of the main causes of death in trauma patients. This study details the etiology, frequency and effect of major vessel lesions of the abdomen in patients after polytrauma. Patients and methods All patients of TraumaRegister DGU® who met the following criteria were included: online documentation of European trauma centers, age 16-85 years, presence of abdominal vascular injury, and AIS ≥ 3. Patients were divided in three groups based on the type of vessel injuries: arterial injury only, venous injury only, mixed arterial and venous injuries. Results A of the inclusion A blunt of was more On the with were the same in patients with arterial alone (n= 606, 33%) and venous injury alone (n=95, 32%). Patients with venous injury alone or together with arterial had higher early (within rst 24h) mortality rates (isolated arterial injury OR: 1.31; 95%, CI 1.14-1.50, p<0.001; isolated venous injury OR: 1.48; 95%, CI 1.10-1.98, p=0.010) and also in-hospital mortality.


Introduction
Trauma-related abdominal vascular injuries are associated with a relevant mortality rate (1). Even in the setting of a Primary Trauma Center and after prompt diagnosis, abdominal trauma involving major vessel injury remains challenging to treat (2). Affected patients are very likely to require early and aggressive resuscitation measures in order to avoid or treat blood loss-associated acidosis, coagulopathy and hypothermia (3,4). The relevance of aortic or iliac artery injury for patients' outcome after blunt and penetrating abdominal trauma has been well described (5). However, literature dealing with the impact of major venous vessel injury on patients' outcome after polytrauma is scarce. If available, the impact of abdominal major venous vessel injury is displayed in combination with aortic or iliac artery lesion (1).
Outcome after isolated venous injury of all causes is directly related to a high mortality rate (6). Using the Europe-wide data assessment of the TraumaRegister DGU® we aimed to evaluate the impact of major abdominal vessel injury in severely injured polytrauma patients treated in primary trauma centers.
Furthermore, the relevance of major venous vessel trauma and its impact on patients' survival could be analyzed for the rst time in a multicentre registry setting.

Materials And Methods
In the present study, data is retrospectively analysed from the TraumaRegister DGU® (TR-DGU).

Database
The TraumaRegister DGU® of the German Trauma Society was founded in 1993. The aim of this multicentre database is a pseudonymised and standardized documentation of severely injured patients. Data are collected prospectively in four consecutive time phases from the site of the accident until discharge from hospital: A) Pre-hospital phase, B) Emergency room and initial surgery, C) Intensive care unit and D) Discharge. The documentation includes detailed information on demographics, injury pattern, comorbidities, pre-and in-hospital management, course on intensive care unit, relevant laboratory ndings including data on transfusion and outcome of each individual. The inclusion criterion is admission to hospital via emergency room with subsequent ICU/ICM care or reach the hospital with vital signs and die before admission to ICU.
The infrastructure for documentation, data management, and data analysis is provided by AUC -Academy for Trauma Surgery (AUC -Akademie der Unfallchirurgie GmbH), a company a liated to the German Trauma Society. The scienti c leadership is provided by the Committee on Emergency Medicine, Intensive Care and Trauma Management (Sektion NIS) of the German Trauma Society (DGU). The participating hospitals submit their data pseudonymised into a central database via a web-based application. Scienti c data analysis is approved according to a peer review procedure laid down in the publication guideline of TraumaRegister DGU®. The participating hospitals are primarily located in Germany (90%), but a rising number of hospitals of other countries contribute data as well (at the moment from Austria, Belgium, China, Finland, Luxembourg, Slovenia, Switzerland, The Netherlands, and the United Arab Emirates). Currently, almost 30,000 cases from more than 650 hospitals are entered into the database per year. Participation in TraumaRegister DGU® is voluntary. For hospitals associated with TraumaNetzwerk DGU®, however, the entry of at least a basic data set is obligatory for reasons of quality assurance.
The present study is in line with the publication guidelines of the TraumaRegister DGU® and registered as TR-DGU project ID 2018-027.
Data for the current research is obtained from TraumaRegister DGU® (TR-DGU) as a sizeable cohort in the period between 2002 and 2017.

Patient Groups and De nitions
Patient selection was carried out according to the following criteria: (1) online documentation of European trauma centers since 2002, (2) age 16-85 years, (3) patients with serious injury (maximum Abbreviated Injury Scale ≥ 3). Early transfer out patients (within 48 hours after admission) were excluded in order to avoid double counting from both hospitals. Patients with vascular injuries in the abdomen were divided in three groups based on type of abdominal vessel injuries: arterial injury only (AI), venous injury only (VI), and mixed arterial and venous injuries (AVI). Patients without a vascular trauma in the abdomen served as control group. The Abbreviated Injury Scale (AIS) and Injury Severity Score (ISS) has been applied for injury grading (7). The updated Revised Injury Severity Classi cation score (RISC II) (8) was used to adjust the observed mortality rates.
All participating hospitals are classi ed as supra-regional (level 1), regional (level 2) or local (level 3) trauma centers based on the availability of human and technical resources (9). Organ failure was de ned according to the Sequential Organ Failure Assessment (SOFA) where 3 or 4 points per organ was considered as organ failure. Multiple organ failure was de ned as parallel failure of two or more organs for at least two days. Sepsis was de ned according the ACCP/SCCM Consensus Conference (1992) as Systemic In ammatory Response Syndrome (SIRS) plus a documented infection (10).

Statistical Analysis
Descriptive analysis was presented as number of cases with percentage for categorical variables and mean with standard deviation (SD) for continuous measurements. No imputation was performed for missing data; all results refer to valid entries only. The effect of vascular injury on outcome (hospital mortality) was evaluated with a logistic regression analysis. Other independent predictors in this analysis were the RISC II score (a combination of 15 predictive factors available on admission), massive transfusion, and hospital level of care. Results are presented as odds ratio (OR) with 95% con dence interval (95%CI). All analyses were performed using SPSS statistical software (version 24, IBM Inc., Armonk, NY, USA). Table 1 summarizes the study group's basic characteristics; abdominal vascular injury was present in 2949 patients (1.6% of all patients considered). Isolated arterial injury seen among 83.4% of these patients (n = 2459). There were 383 patients (13%) admitted with isolated venous injury and 107 patients (3.6%) had both arterial and venous injuries. Number of patients with ISS above 16 was 341 (89%) in patients with VI, 2236 (92%) in patients with AI, and 98 (92%) in patients with AVI. Blunt trauma was the most common mechanism responsible for abdominal vascular injuries in all three groups. Tra c injuries were common (n = 1720, 69.9%). Within the group of 230 assaulted patients, 179 (77.8%) sustained stabbing injuries and 51 (22.2%) patients had gunshot wounds. Out of the 2949 patients, 948 (32.1%) were hemodynamically unstable at the time of admission. The distribution of arterial and venous injuries in patients with relevant injuries (AIS ≥ 3) of head, thoracic, abdomen and extremities are shown in Table 2. All types of vessel injuries were more prevalent in patients with relevant abdominal trauma followed by relevant thoracic trauma as the second most common cause. Patients with higher abdominal AIS were more unstable and required blood transfusion more frequently.

Results
In this subgroup of patients, rate of cessation of the trauma resuscitation algorithm and going under emergency surgery was higher with increasing abdominal AIS (Table 3). Total numbers and percentages of each group are given with the total number of available datasets for each characteristic in parenthesis.

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Total patient numbers may vary for each procedure and characteristic because of incomplete data transmission or transmission of basic datasets. Basic datasets do not include information on emergency/early surgery. Patients with VI or AVI had higher mortality rates within the rst 24h as well as increased in-hospital mortality rates (Table 4). Moreover, the rate of multiple organ failure, sepsis and kidney failure was higher in patients with VI or AVI. The mean hospital length of stay in patients suffering from AI, VI and AVI were 24, 21 and 27 days, respectively (Table 5). The analysis is based on 164,370 patients; Nagelkerke's R²=0.585 * reference group: supra regional trauma center (level 1) ** reference group: no such injury documented Blood (BT) and fresh-frozen plasma (FFP) transfusion rate as well as rate of massive transfusion (MT) were higher in patients with VI compared to AI (BT: 201 (53%) vs. 1120 (46%), FFP: 144 (38%) vs. 766 (32%) and MT: 86 (23%) vs. 396 (16%)) ( Table 4).
A multivariable logistic regression model was calculated to evaluate the potential impact of abdominal vascular injury on mortality. Further independent predictors were the RISC II score, massive transfusion, and hospital level of care. In this analysis, isolated VI and isolated AI were signi cantly related with hospital mortality. Venous trauma showed higher odds ratio for in-hospital mortality (isolate AI: OR: 1.31; 95%CI 1.14-1.50, p < 0.001; isolated VI: OR: 1.48; 95% CI 1.10-1.98, p = 0.010) ( Table 5).

Discussion
The mortality rate of severely injured persons is negatively in uenced by the presence of a hemorrhagic shock that is mainly due to severe abdominal and pelvic trauma.
According to our data, road accidents account for most of the abdominal vascular injuries, followed by fall from heights as the second most important cause. Results from preceding studies indicated blunt trauma especially following road tra c accident is the main mechanism of abdominal vascular injuries in trauma patients (11,12). AIs are more common in this setting, yet VIs are also likely to occur (Table 2) and should not be underestimated (13). Inferior vena cava (IVC) injuries lead to high rates of morbidity and mortality. Studies reported that more than one-third of patients with an IVC injury has a mortality rate of more than 60 % after admission to hospital (14,15). Accordingly, hemodynamic status and prompt identi cation of bleeding source are in focus when treating patients suffering from abdominal vascular injuries (16). In the vast majority of cases, intraabdominal hemorrhage may lead to metabolic acidosis followed by coagulopathy and hypothermia, the so-called lethal triad of trauma (17,18).
In terms of the diagnosis of abdominal vascular injuries, preoperative assessment of hemodynamically unstable patients may include Focused assessment with sonography for trauma (FAST) or diagnostic peritoneal lavage to con rm the hemoperitoneum (19,20). However, retroperitoneal injuries have no or just a small volume of free blood. Signi cant retroperitoneal VIs, such as those affecting the retrohepatic IVC, can be subtle, with patients presenting with no symptoms at all, or even with intermittent hypotension that reacts to resuscitation at the beginning. Asensio et al. reported 275 retroperitoneal hematoma in 302 patients with abdominal vessel injuries for an incidence of 91% (1). Concerning the rapid diagnosis of retroperitoneal injuries it is advocated that in stable patients suspected of abdominal vascular injuries, a triple-contrast abdominal CT scanning may be bene cial to localize the retroperitoneal vascular injuries and evaluate the extension of vessel involvement (21,22).
Although in current study the rate of hemodynamic instability at the time of admission was the same in patients with VI (36%) comparing to patients with AI (35%), the rate of adverse outcome was signi cantly higher in patient with VI. Based on the present data, an increase in mass transfusion and multiple organ failure correlated signi cantly with involvement of VIs in patient suffering from abdominal vascular injuries. Consecutively, an increase in mortality rates within the rst 24 hours and during the hospital stay can be assessed after VI or AVI (Tables 1 and 4).
The shortcomings of the study are by far similar to other studies using large registry databases. TR-DGU's initial aim was to register severely injured patients or those with multiple injuries and solely require ICU admission. It only includes in-hospital trauma fatalities, excluding victims that died at scene or during transport. Lack of follow-up outcomes for the included patient variables may have impacted both the univariate and modelling results.