Vascular Trauma: Epidemiology and Natural History

Evolution Through Military Conflict

The incidence, nature and management of vascular injury are often described within the framework of major periods of conflict or war. The sheer volume and severity of trauma associated with combat provides unique opportunity to study vascular injury patterns, create novel surgical techniques, and implement change aimed at mitigation of risk. However, the changing nature of warfare over time inherently influences the distribution of vascular injury patterns, requiring ongoing evolution of our techniques and practices.

A classic paper by DeBakey et al. characterizes the vascular injury burden during World War I and II, noting an incidence of vascular injury during both wars of approximately 1%. Of the 2471 arterial injuries documented during World War II, only 81 underwent attempted repair, with an amputation rate of 36%. In 40 patients, attempt was made to repair larger arterial disruptions using vein interposition grafts, unfortunately the amputation rate was 50%. There was a routine posture towards ligation of vessels in most patients. Although this practice was understood to be less than ideal, it was deemed necessary given resource constraints of this era.

The Korean War experience beginning in 1952 resulted in an increased incidence of vascular injuries at approximately 2% of all casualties relative to previous conflicts. This may reflect improved evacuation methods during this conflict, increasing the number of patients with vascular injuries surviving to definitive surgical therapy. There was a paradigm shift in the management of vascular injuries witnessed during this era, with 88% undergoing an attempt at primary repair/anastomosis (60%) or interposition graft (27%). ^, While early reconstruction strategies employed cadaveric femoral artery as an interposition graft conduit, this was largely abandoned after some time due to an increased failure and amputation rate (33%) compared with vein grafts (12%). Several more comprehensive reports on successful arterial repair performed during the Korean War followed, including classic papers from Colonel Carl Hughes, demonstrating an impressive reduction in the amputation rate among 269 repairs, from 40% in World War II to 13% during the Korean War. While improvements in casualty evacuation during the Korean War were achieved, significant time delays and resuscitation requirements remained hindrances to successful vascular injury management. Despite these improvements, the burden of vascular injury and its effect on mortality remained obscure.

The Vietnam War ushered in several significant advances in vascular injury management, particularly the creation of the Vietnam Vascular Registry. This provided the ability to characterize injury patterns and outcomes following intervention. Rich et al. published landmark reports of the first 500 and 1000 patients, describing increased repair rates (93%) with improved patency and lower amputation rates. In total, this registry captures nearly 10,000 vascular injuries in over 7500 injured warfighters. There was also an increased emphasis on routine repair of venous injury as a vital component of limb salvage strategies, albeit controversial. ^,

For decades to follow, the vascular injury experience of these previous wars was thought to be unapproachable with regard to the duration of conflict and the number of injuries. With more than 10,000 deaths (US military and civilian contractors) and over 60,000 combat-related injuries in more than a decade, the Global War on Terror (GWOT) has proved to be a formidable and sustained military campaign. During this conflict, modern advances have allowed a concerted effort to reduce deaths from potentially survivable vascular injuries and to improve the quality of functional extremity salvage (i.e., saving life and limb).

The development of the Joint Theater Trauma System has improved surgical care and reduced mortality by implementing clinical practice guidelines and performing outcomes research emerging from the Joint Theater Trauma Registry (JTTR). The GWOT Vascular Initiative is a comprehensive registry designed to study patterns of vessel injury and methods of vascular repair and to provide more complete long-term analysis of patient outcomes.

At the beginning of the GWOT, the Department of Defense implemented a testing, training, and fielding program for battlefield tourniquets. Although widespread tourniquet use began with trepidation, the forward deployment of surgical capabilities has provided for limited tourniquet duration, thus increasing the effectiveness of tourniquets and reducing the rate of associated complications. The effectiveness of early tourniquet application observed in Iraq and Afghanistan has led to doctrinal changes that have produced a surge of patients with vascular injuries who, in the past, would not have reached a field hospital alive (see Fig. 179.1 ). ^, The application of tourniquets for extremity vascular injury is now routine and has been formalized in the Tactical Combat Casualty Care (TCCC) guidelines. Of interest, the 12% incidence of vascular injuries based on data from the JTTR is the highest ever reported during wartime. Certainly the widespread application of tourniquets contributes to this statistic, however improved detailed data collection as well as a shift in injury mechanism from conventional weaponry to the improvised explosive devices (IEDs) likely impacts this as well. Additionally, the widespread use of body armor in conjunction with increased exposure to IEDs has led to an epidemiologic shift in injury patterns, with a proportionally higher rate of extremity vascular injury (53%) and decreased rate of major truncal vascular injury (15%). Not surprisingly, there has been an increased incidence of vascular ligation (35%), underscoring the devastating nature of many extremity wounds in modern warfare, negating attempts at limb salvage.

Other modern advances include application of surgical adjuncts, such as temporary vascular shunts to facilitate delayed definitive vascular repair and the routine performance of fasciotomies to minimize the incidence of undiagnosed compartment syndrome. Progress in the management of increasing complex vascular injury patterns and the associated management of complex soft tissue wounds through closed negative pressure wound therapy has been impressive. Last, the application of endovascular technologies for the diagnosis and treatment of certain types of vascular, pelvic, and solid organ war-related injuries has become more widespread and generally accepted as a mainstay of surgical care.

Despite these tremendous achievements, it is challenging to draw definitive comparisons between modern and historical conflicts with regard to killed in action, died of wounds and other outcomes measures given the heterogeneity of not only the technological advancements but also due to the changing tactical environment and subsequent injury patterns. Nonetheless, many warfighters continue to succumb to potentially survivable injuries on the battlefield. In several contemporary studies evaluating combat-related mortalities from Operation Enduring Freedom and Operation Iraqi Freedom, approximately 15%–25% of casualties were deemed to have potentially survivable injury patterns at the time of autopsy, of which 80%–87% are attributed to hemorrhage. ^{, , ,} This not only underscores the lethality of vascular injury and hemorrhage, but alludes to the fact that viable strategies for more timely intervention remain elusive.

Data Repositories and Registries

One of the most important factors in understanding the epidemiology and patterns of vascular injuries is the collection of thorough and reliable data, which was traditionally done by single centers performing chart review analyses or by analysis of wartime experience with limited follow-up data. Computerized databases, automated data collection, and establishment of trauma systems with dedicated registrars have facilitated the collection and analysis of large, multicenter trauma data. An early example and model for future development was the establishment of the Vietnam Vascular Registry, with subsequent landmark reports on the epidemiology and outcomes of a wide variety of vascular injuries. The recognized importance of the prospective collection of data from wartime experiences led to the establishment of the Joint Theater Trauma System and the Joint Theater Trauma Registry, which collects critical information from combat operations in Iraq and Afghanistan. Additional examples include the establishment of the National Trauma Data Bank (NTDB) by the American College of Surgeons, which is the largest trauma registry ever assembled. The NTDB data is subject to extensive auditing to ensure data quality and accuracy and enables uniform data collection across institutions. The NTDB does possess certain limitations that influence its ability to accurately characterize the epidemiology of traumatic injury, particularly certain vascular injury patterns. One limitation is that non-admitted patients are uniformly not captured in this database. This is important in that patients who die without transport to a treatment facility are not captured. Thus, major vascular injuries where exsanguination results in rapid demise are likely underrepresented, creating an inherent selection bias for more stable, less severely injured patients, confounding analyses aimed at characterizing certain injury patterns, particularly truncal injury patterns. The NTDB is also not a true population-based dataset, as the data reflects only participating institutions. Hence, the experience of non-participating facilities, likely smaller community and rural hospitals, will not be reflected in the NTDB data set. Also, the database does not fully characterize the outcomes following vascular injury and is limited to in-hospital outcomes and complications.

The PROspective Vascular Injury Treatment (PROOVIT) registry, supported by the American Association for the Surgery of Trauma, has been established to address key limitations of the NTDB. The initial publication of this data set included 542 patients from 14 centers from March 2013 to February 2014, in whom 484 sustained arterial injuries and 71 experienced isolated venous injuries. Additional strengths of this database include the capture of key elements of pre-hospital care such as the application of tourniquets, seen in 20% of patients within this series.

Vascular Injury Classification and Scoring

The ideal vascular injury classification and scoring system has yet to be developed. Standard injury scoring systems such as the Injury Severity Score (ISS), Revised Trauma Score (RTS) and Trauma and Injury Severity Score (TRISS) fail to accurately and reliably capture the impact of major vascular injury on morbidity and mortality. ^, Beyond this, the myriad factors that influence mortality independent of the injury itself cannot be effectively captured using ISS, specifically. In a study by Markov, mortality rates for patients with ISS >15 following civilian vs. military-related vascular trauma with similar injury patterns was 40% and 10%, respectively, further underscoring the limitations of ISS to characterize vascular injury outcomes.

The American Association for the Surgery of Trauma Organ Injury Scaling (AAST-OIS) system is the most widely used grading system for traumatic injuries and is well validated for predicting outcomes and need for intervention in solid organ injuries. This grading system is organized primarily around the exact identity of the vessel rather than the severity of the vascular injury or the degree of hemorrhage or ischemia and thus provides little additional information about treatment or outcomes. For major extremity fractures and soft tissue injury, several scoring systems have been developed to characterize the “mangled extremity,” including the Mangled Extremity Severity Score (MESS), the Mangled Extremity Syndrome Index, the Predictive Salvage Index, and the Limb Salvage Index. Although they contain different components, the presence of vascular injury and limb ischemia is a universal key variable. In addition to providing an objective classification system for epidemiologic purposes, these scores have been studied for their ability to predict the need for extremity amputation in both civilian and military settings. ^, Although they have been correlated with the need for amputation, prospective trials have found that they lack adequate predictive ability to be used for individual patients and did not correlate with limb salvage when arterial reconstruction was performed. This is likely due to improved techniques in the management, including endovascular therapies, tourniquets and shunting, resulting in improved limb salvage rates even in the face of severe injury scores.

Contemporary Civilian Vascular Injury

Impact of Age and Gender on Vascular Injury

One of the largest determinants of risk for traumatic injury is age, with the overwhelming burden impacting young adults. According the 2015 NTDB report, traumatic injury increases progressively beginning at age 14, peaking at approximately age 21, and progressively declining thereafter. The majority of overall traumatic injuries are due to motorized vehicle collisions between ages 14 and 49, with falls as the dominant injury mechanism in all other age groups. While penetrating injury due to firearms accounts for less than one third of injuries in the peak age demographic, the case fatality rate is nearly four times greater at approximately 15%. Greater than 70% of traumatic injuries in the peak age group occur in males, with up to 90% for penetrating extremity wounds.

The overall incidence of vascular injury in the pediatric population (age <16) is 0.6%, compared to 1.6% in adults based on a recent NTDB analysis. Injuries to vessels in the thorax were approximately seven times lower in children as compared to adults. Penetrating injury patterns were less common in children (41.8%) as compared to adults (51.2%). Unfortunately, firearm and stab wounds accounted for the majority of penetrating injuries in children, with a mortality rate of 20% for those injured by a gun. The upper extremity was the most common location of pediatric vascular injury (37.9%), with most injuries involving either the radial or ulnar arteries (22%). The upper extremity is also the most common site of penetrating vascular injury for both adults and children. With regard to blunt injury patterns, the upper extremity (33%) and chest (33%) are the most common sites of blunt vascular injury in children and adults, respectively. The amputation rates for both children and adults were similar.

The incidence of vascular injury in the geriatric population (mean age 70 years) is similar to that of the pediatric population, at 0.7%. There is still a gender bias towards injury in males at 60%, albeit less pronounced than in the younger adult population. Blunt mechanisms (MVC and falls) account for the overwhelming majority of injuries (84%), with blunt thoracic aortic injury being most frequent (39%). Mortality rates were higher in the geriatric population compared to younger adults (44% vs. 22%), with injury to the thorax carrying a high mortality rate of 66%. For penetrating injuries, the forearm vessels are most commonly injured (31.5%). Amputation rates following extremity vascular injury were similar in both populations.

Ethnicity and Socioeconomic Factors

Disparity in healthcare outcomes has been extensively documented for multiple disease processes, with traumatic injury being no exception. Beyond outcomes, there is also a disparate distribution in the burden of traumatic injury within society, based on race and socioeconomic status. The effect of race and insurance status has been explored in multiple studies, with most indicating pronounced effects. ^, However, there appears to be a lack of uniformity across various injury patterns.

In a large review of the NTDB from the years 2001–2005, Haider et al. demonstrated marked differences in the incidence of penetrating trauma as a function of both race and insurance status. The overall incidence of penetrating injury in this sample was 8.7%. For insured patients the incidence by race was as follows: white = 3.1%, black = 18.3%, and Hispanic = 11.7%. For the uninsured patients, a similar distribution was seen: white = 7.4%, black 31%, and Hispanic = 21.8%. Unadjusted mortality rates were statistically different for white, black and Hispanic patients at 5.7%, 8.2%, and 9.1%, respectively. When stratified by insurance status these findings persisted, with mortality rates for uninsured white, black, and Hispanic patients at 7.9%, 11.4%, and 11.3%, respectively. These findings continued to persist despite adjustment for injury severity and demographic variables.

Several authors point to heterogeneity within the trauma population as a potential confounding factor in explaining outcomes based on race and insurance status. To control for this, Crandall et al. analyzed the outcomes in a more homogeneous populations involving patients who sustained isolated lower extremity vascular injury. Mortality rates were higher for uninsured patients (31.7% vs. 21.5%), however when stratified by mechanism only penetrating injury remained significant. In a risk-adjusted model, race remained a predictor of increased mortality following penetrating lower extremity vascular injury in Black Americans (OR 1.45, P = 0.03). In another study evaluating outcomes of pedestrians struck by motor vehicles, Maybury demonstrated that Black Americans (OR 1.22) and Hispanics (OR 1.33) had a significantly higher mortality rate than Whites utilizing a multivariate risk-adjusted model, with uninsured status also an independent predictor of increased mortality. Explanation for these outcome disparities prove challenging and may include variables that are not appropriately captured within the NTDB. Nonetheless, these findings highlight the need for further research and outreach programs aimed at minimizing the impact of traumatic injury in at-risk populations.

Mechanisms of Injury, Ballistics, and Biomechanics

The clinical presentation, pattern of associated injuries, need for intervention, and outcomes after traumatic vascular injury will be highly dependent on the mechanism of injury and the specific characteristics of that mechanism. For blunt injury, this mainly involves the velocity or forces of impact, the use of restraints or protective devices, and the primary anatomic areas that sustain the brunt of the kinetic forces. In addition, patients sustaining blunt trauma may suffer penetrating-type vascular injury from impalements, glass or sharp debris, and puncture by bone fragments. The most common blunt mechanism associated with major vascular injury is motor vehicle collision, resulting in injury from stretching and shearing forces or from vascular avulsion (usually due to rapid deceleration). Several additional etiologic factors have been proposed, including the generation of a sudden spike in intravascular pressure as well as forward inertial deceleration of blood impacting the anterior vessel wall (“water-hammer” effect). ^,

For penetrating trauma, the wounds can be primarily classified as due to stab/puncture or from missiles/projectiles. Stab and puncture wounds result in direct vascular injury without significant transmission of kinetic energy or damage to surrounding tissues. Missiles may injure vascular structures by direct laceration or by transfer of energy due to proximity, with an impact kinetic energy (iKE) related to the mass (M) and velocity (V) of the projectile (iKE = ½ MV ). Terms such as “high velocity” are often used but are frequently poorly defined or misunderstood. There are multiple projectile characteristics, such as shape, deformity, fragmentation, pitch, and yaw, that are as important, if not more so, than velocity. Additional injury to surrounding tissue has been attributed to both the “sonic wave” and the stretching of tissue due to the pressure wave (“temporary cavity”). While histologic evidence of vessel injury can be seen in grossly normal-appearing vessels, this does not correlate with outcome following repair, thus excessive debridement of grossly normal vessel or surrounding tissues is not required. Finally, mention should be made of shotgun injuries, which are classified as low velocity, yet result in diffuse devascularization from multiple pellets that can be greater than high-velocity gunshots. ^, Although less common, they are associated with vascular injury in up to 25% of wounds, creating vessel micropunctures that are difficult to diagnose. ^,

Blast injury, such as that seen with improvised explosive devices in the wars in Iraq and Afghanistan, has unique wounding patterns and mechanisms. These injuries include a combination of blunt force, penetrating fragment injuries, and thermal injury. Blast injuries in modern combat series now outnumber standard gunshot wounds and account for 73% of vascular injuries among wounded soldiers. Blast effects are classified as primary (direct blast pressure), secondary (penetrating fragments), tertiary (collision with objects or vehicles), and quaternary (thermal injury). The relative distribution of each varies by type of explosive, enclosed versus outdoors, and presence of protective equipment. Most vascular and other injuries are due to secondary and tertiary blast effect (81%). Blast-induced extremity vascular injury with coexisting fracture is associated with a 50% amputation rate with attempts at limb salvage and a 77% amputation rate overall. Blast injuries may also occur with civilian incidents such as terrorist bombings, and vascular injuries have been identified in up to 10% of victims.