Introduction

Epidemiology (from the Greek: the study of that which befalls the people ) is defined as the study of the distribution and determinants of health-related states or events in human populations, and the application of this study to the prevention and control of health problems. The global burden and impact of trauma as an agent of death and disability is increasingly well characterized ( Table 2-1 ). However, while the prevalence and incidence of individual vascular injury patterns have been well depicted in local situations, the epidemiological study of vascular trauma is a relatively underexploited field. Possible reasons for this include the many causes of vascular injury, the heterogeneity of the circumstances in which vascular injury may be sustained, the protean direct and indirect consequences of vascular injury to bodily systems, and the unsuitability of modern trauma scoring methodologies to capture the specific effects of vascular injury on patient outcome. Nonetheless, understanding the historic and contemporary epidemiology of vascular trauma is important. Box 2-1 lists the generic components of epidemiological endeavor. With respect to trauma, recognizing the prevalent populations underpins the alignment and targeting of hospital resource and provider education, in essence informing the design of trauma and vascular-care systems. More widely, better description of mechanisms, case mix and demography empowers comparison of properly stratified outcomes from injury, whether used to assess performance within or between institutions, or to track outcomes with respect to time. Case mix and other epidemiological data are used to inform quality-improvement initiatives, to construct fair reimbursement schedules for treating hospitals, to understand the impact of external socioeconomic realities, to influence the design and assessment of preventative public health interventions, and to inform wider health and social policy. In essence, if vascular and trauma clinicians are to anticipate injury patterns, to track changes, and to put into place effective programs to prevent or to mitigate the effects of vascular trauma, then the study of injury epidemiology is an essential function of practice.

The aim of this chapter is to outline the general circumstances, incidence, and population effects of vascular trauma, as viewed from the epidemiological perspective, in order to provide the context to more-detailed illustrations and epidemiological profiles of specific anatomical injuries given elsewhere in the text.

Context and Categorization of Vascular Trauma

As explained, attempting to directly compare and contrast vascular injury epidemiology is hampered by the protean nature of trauma and the multiple and interrelated factors that determine functional outcome (such as co-injury to critical soft tissue, as well as bony and neurological structures). This difficulty is made more acute by the lack of uniformity among authors as to appropriate injury descriptors, outcome metrics and follow-up periods. Most studies in both the military and civilian domains offer descriptions of cohorts comprising specific vascular regions (extremities) or anatomical areas (e.g., crural vessels); this provides detail at the expense of proper epidemiological perspective. Rates of vascular trauma are conflicted by use of different definitions of population-at-risk, invoking different denominators and inflating or deflating prevalence accordingly. Outcomes are defined differently and with varying degrees of accuracy. For instance, mortality rates may variously be built on definitions such as death while an inpatient, ignoring those who expire before reaching the hospital. Epidemiology is dependent on data; countries with mature trauma systems where accurate data collection is mandated offer a more fruitful if narrow perspective on injury rates and causes. Similarly, while wartime populations often have higher vascular injury rates than peacetime cohorts, the presence of detailed injury data (with accurate description of the denominator populations) is directly related to whether a trauma systems approach to injury data collection is deployed by the medical services of the combatant parties. It is fair to say that countries without a trauma systems approach to injury management, whether in their military or civilian populations, are usually unable to describe the effect of vascular trauma in populations-at-risk. Because most developing countries fall into such categories, it is correct to assume that the global burden of vascular trauma is unknown.

Vascular trauma may be broadly categorized according to mechanism of injury (iatrogenic, blunt, penetrating, blast, combination injuries), anatomical site of injury (further subdivided into compressible and noncompressible hemorrhage), and by wider contextual circumstances (military, civilian). Each of these domains may be further stratified, with military injury being subdivided by patient status (combatant, noncombatant) and category of conflict (civil war, counterinsurgency warfare, maneuver warfare). Civilian injuries may be similarly contextualized by local circumstances (e.g., urban trauma, rural trauma). For the purposes of this chapter, the context will be considered under two broad conditions concerning the injurious mechanism: vascular injury caused during military conflict (whether between interstate, intrastate, or nonstate actors) and vascular injury that occurs in the context of peacetime circumstances.

Vascular Trauma and Military Conflict

Vascular injuries that occurred in World War I (WWI), World War II (WWII), Korea, and Vietnam can be conceived as products of industrial war waged between nation states. Warfare over the past 2 decades has lost many of the characteristics that defined previous engagements; the phrase “war among the people” has gained credibility as the ability of nations to employ force with utility has declined. This refers to the modern scenario where “the reality in which the people in the streets and houses and fields—all the people, anywhere—are the battlefield. Military engagements can take place anywhere, with civilians around, against civilians, in defense of civilians. Civilians are the targets, objectives to be won, as much as an opposing force”. As such, vascular trauma inflicted by high-energy military ballistic projectiles and purpose-built or improvised blast weaponry can affect two populations-at-risk: combatants and noncombatant (civilians).

Vascular Trauma in Combat Troops

Contemporary and recent data confirm that exsanguination is the major cause of death in fatally wounded soldiers. Chapter 1 reviews the changing nature of wartime and civilian vascular trauma over the ages; but the prevalence also seems to have changed markedly over the past century of conflict. Estimates from allied surgeons in WWI suggested overall vascular trauma rates of 0.4% to 1.3%. DeBakey characterized the vascular injury burden in WWII as affecting 0.96% of all patients; but, for the Korean and Vietnam wars, the rate of vascular injury was judged to be higher at 2% to 3%.

Coalition militaries engaged in combat operations in Afghanistan (2001-) and Iraq (2003-2011) have invested substantially in detailed trauma registries in order to capture injury data. Such databases have been used to characterize miscellaneous injury patterns so that force protection (body armor, vehicle design) and treatment protocols can be continually updated and aligned to contemporary trauma archetypes. Interestingly, present rates of wartime vascular trauma confirm a much higher prevalence than in previous campaigns.

In a comprehensive study summarizing recent U.S. military experience, White and colleagues analyzed vascular cases entered in to the United States Joint Theater Trauma Registry (JTTR) from 2002-2009. Defining the denominator as battle-related injuries sufficiently severe to prevent return to duty into the combat theater, the specific incidence of vascular injury (defined as the “total incidence injury ” ) was found to be 12% (1570 of 13,076 cases). The incidence of injuries requiring surgery (defined as the “operative incidence”) was found to be 9% (1212 of 13,076 cases). The analysis looked for differences in vascular injury incidence between troops deployed to Iraq and Afghanistan and found significantly different rates of 12.5% and 9%, respectively. Peak rates of injury in either theater differed with combat tempo, accounting for 15% of all injuries in 2004 (Iraq) and 11% in 2009 (Afghanistan). Other differences included causative mechanism, with blast accounting for 74% and 67% of injuries in Iraq and Afghanistan (with an overall contribution of 73%). There was no difference in the anatomical distribution of the injuries, nor the died of wounds (DOW) rate (6.4%), between theaters. Wounds were principally sustained to the extremities (79%), torso (12%), and cervical regions (8%). In the torso, the most commonly injured vessels were the iliacs (3.8%), followed by the aorta (2.9%) and subclavian arteries (2.3%), and then followed by injuries to the inferior vena cava (1.4%). In the neck, 109 carotid injuries accounted for 7% of injuries. It was noted that the vascular injury burden borne by the extremities was remarkably similar to that noted by DeBakey in WW2, although the higher contemporary rate of cervical and aortic injury was attributed to increased survivability and far-shortened medivac times.

Overall, the authors concluded that the rate of vascular injury in these wars was 5 times that previously reported from Vietnam and Korea. Interestingly, this estimation of incidence also ran substantially higher than that reported from early analyses—of around 4.4% to 4.8%—published from U.S. military hospitals in Iraq. However, it is important to note that these reports did not include nonoperated cases and were generally confined to descriptions of vascular cases identified as “in theaters.” When the analysis includes such cases, the overall rate of vascular incidence rises. For instance, by determining rates among patients repatriated back to the continental United States and screened for additional, unrecognized vascular injury on reception, Fox and colleagues described a prevalence of 7%.

The marked increase in rates of vascular injury recorded by these contemporary authors, as opposed to that documented by previous generations, is striking. The reasons for this finding are unconfirmed. As well as increased wound survivability, other reasons may include: a) the very high rate of blast-related injury etiology in these campaigns, b) overestimation of the population-at-risk in earlier reports (thus deflating the denominator), and c) more accurate capture of “minor” nonoperated vascular wounds (adding to the numerator).

In a similar but smaller British study, Stannard and colleagues scrutinized the records of 1203 UK servicemen injured through enemy action between 2003 and 2008. Unlike the U.S. JTTR, the British JTTR dataset also included patients who were killed in action (KIA)—that is, who died before reaching a medical treatment facility, an aspect of injury burden not scrutinized in U.S. accounts. Characterization of injury was made from clinical data and from postmortem examinations conducted by the UK Coroner system. It was determined that 110 (9.1%) of this cohort sustained injuries to named vessels, two-thirds of which had extremity vascular injuries. Blast wounds accounted for 54% and 76% of patients sustaining torso-cervical and extremity wounds, respectively. Some 66 of the 110 died before any surgical intervention could be undertaken, indicating the highly lethal nature of vascular wounding patterns. In particular, no patient with a combination of vascular injuries affecting more than one body region (torso, extremity, cervical) survived to surgery. A further defining difference in wound patterns observed between patients surviving to surgery (versus those who did not) was presence or absence of a torso vascular injury—with none of those sustaining an injury to a named vessel in the abdomen or thorax undergoing operative intervention. Cervical vascular injuries also proved highly lethal, with 13 of 17 patients succumbing. On the other hand, of 76 patients with extremity vascular injuries, 37 survived to surgery with one postoperative death. Interventions on 38 limbs included 19 damage-control procedures (15 primary amputations, 4 vessel ligations in a group characterized by a median mangled extremity score of 9) and 19 definitive limb-revascularization procedures (11 interposition vein grafts, 8 direct repairs), with a limb salvage (primary assisted patency) rate of 84%. This UK group concluded that while favorable limb-salvage rates are achievable in casualties able to withstand revascularization, torso vascular injury is not usually amenable to successful surgical intervention.