Key Words:
vascular conduit , autologous vein , artery , prosthetic , ePTFE , Dacron , infection
Introduction
In 1949, Jean Kunlin performed the first saphenous vein bypass in the lower extremity of a patient suffering from ischemia. The work was not the result of chance alone as his predecessors in vascular surgery had been working on perfecting the technique of arterial surgery. Individuals such as Alexis Carrel developed the technique of a meticulous anastomosis, as well as experimenting with venous interposition grafts and the use of allografts; and Jay McClean discovered heparin, which was utilized in Kunlin’s successful procedure. In the same manner, our current treatment of vascular trauma is based on lessons learned in civilian trauma as well as military experiences. For example, in World War II (WW II), the majority of vascular injuries were treated with ligation, leading to an amputation rate of 49%. During WW II, vein grafts were employed in a very small number of patients (40), resulting in an amputation rate of 58%. At that time, ligation of vascular injuries was felt to be necessary due to the long transport time required for wounded service personnel. With decreased transport times and knowledge of these past experiences, Rich and colleagues successfully implemented arterial repair in the majority of patients in the Vietnam War and subsequently reported an amputation rate of 13%. In that experience, nearly all interposition grafts were reversed great saphenous vein; and that form of reconstruction was used in 46% of the cases. In the civilian setting in the 1960s and 1970s, the abandonment of ligation as treatment for vascular trauma led to amputation rates that ranged from 2% to 10%. It is these advances, both in the civilian and the military settings, that have led to the current standard of repairing vascular injury—in those that will tolerate repair—with interposition or bypass grafting as needed.
Definition of Problem Identification of the Optimal Vascular Conduit
The search for the optimal vascular conduit, in both elective and emergency situations, has been a source of debate and the source of many research projects. The ideal vascular conduit should be durable , resistant to infection , and readily accessible or available . In numerous studies of elective peripheral vascular bypass, autologous vein has proven superior to prosthetic modalities in the lower extremities, whereas prosthetic grafts are generally better suited for the larger caliber central arteries. Unlike elective situations, trauma cases differ in the sense that patients are generally younger and have healthy vessels free of atherosclerotic occlusive disease that can complicate repair. The limiting factor in trauma is the fact that the majority of individuals may have concomitant orthopedic, soft-tissue, or abdominal injuries that need to be addressed in addition to the vascular injury. Furthermore, although vascular repair is usually feasible, it is the ability to place the repair conduit through a contaminated wound or soft-tissue deficit that often limits success. Specifically, the need to assure adequate soft-tissue coverage to protect the conduit from contamination and disruption often determines ultimate success or failure.
As documented throughout this text, the approach to vascular trauma is generally straightforward. Approaches to the injured vessel include primary repair or restoration of perfusion using an interposition or bypass graft. The technique of patch angioplasty is also a useful approach in select injuries that are less severe. Finally, ligation may be used as an approach in select cases. When considering whether to reconstruct or ligate an arterial injury, one should consider the patient’s physiologic condition and other coexisting injuries. Also, one must consider the degree of ischemia likely to result from vessel ligation. If the artery is minimally disrupted, it may be able to be débrided, mobilized, and repaired primarily.
In the situation where the artery cannot be repaired primarily or cannot be safely ligated, there is the need for an interposition or longer bypass graft. Temporary vascular shunts are useful as bridges to interposition or bypass grafting when ligation is not an option, but this adjunct is discussed later in this book. When considering interposition or bypass grafting, one must address the same technical factors that are important in elective vascular reconstruction as follows: (1) inflow vessel, (2) outflow vessel, and (3) conduit. Although the vascular injury itself may be straightforward, the patient is often not straightforward and may have suffered multiple injuries. The overall injury severity and any degree of hemodynamic instability will impact the choice of conduit and the outcome of the procedure ( Fig. 18-1 ). The ease of availability and necessary length of conduit needed are also factors to be considered when pursuing this type of reconstruction. It would be nice to imagine that one solution applies to both military and civilian scenario, but the settings (and the nature of the wounds) are most often different. This chapter will describe the options for selection of the vascular conduit to be used for repair of vascular injury.
Types of Conduit
The use of a vascular conduit in vascular trauma is, in principle, the same as its use for atherosclerotic occlusive or aneurysmal disease. Vascular conduits can be considered in the following categories: (1) autologous vein and artery (i.e., autografts), (2) prosthetics, and (3) biologics. Vascular trauma has a rate of wound contamination that is proportional to the mechanism of injury and to the degree of soft-tissue injury. The degree of contamination can be minor such as with a single stab wound or a laceration with a piece of glass, or it can be major such as with an open femur fracture with soft-tissue wound. More than a decade of war in Afghanistan and Iraq has laid bare the complexities associated with vascular trauma in highly contaminated wounds resulting from improvised explosive devices (IEDs). Traditional teaching has emphasized the use of autologous vein grafts for vascular repair in the setting of contamination. However, due to the complexities of different trauma scenarios such as bilateral lower extremity injury, this conduit may not be feasible or appropriate. If autologous vein is not available, vascular hemorrhage can be controlled by ligation, by the use of temporary vascular shunts, or by reconstruction using a commercially available prosthetic or biologic conduit.
Autologous Conduit
The gold-standard conduit is autologous tissue and most commonly a vein. In rare cases, one may choose to use an arterial conduit for vascular reconstruction. Because the venous system has multiple redundant outflow tracts, there are several choices for vein harvest. The lower extremity has the longest and most commonly used options, including the greater and lesser saphenous veins, the femoral vein, and even and dorsal foot vein. The cephalic and basilic veins of the upper extremity can be used independently or as a longer single segment graft. In the neck, the anterior, exterior, and internal jugular veins are options for vascular conduit. The veins of the neck are most commonly used as adjuncts for carotid artery repair because of their proximity.
Use of autologous vein requires adhering to the tenants of safe and effective dissection and procurement. In general, superficial veins may be harvested using a single continuous incision, skip incisions, or a newer minimally invasive technique. The single incision is the most expedient and most commonly described technique for greater saphenous vein harvest. However, this is associated with wound infection and dehiscence in 17% to 44% of patients. In an effort to decrease wound complications, attempts have been made to harvest this vein with multiple, shorter incisions and intervening “skin bridges.” Although this technique may take additional time and familiarity with the approach, it has been shown to decrease wound complications (9.6%) in at least one large series. The least invasive technique for saphenous vein harvesting is the endoscopic approach. With this technique the vein is harvested with electrocautery through several percutaneous incisions. Although risk of wound infection is decreased with the endoscopic technique, this does carry the added risk of thermal injury to the vein. Although it is desirable to reduce wound morbidity associated with saphenous vein harvest, it seems that as the method becomes less invasive and that the time needed for the procedure increases, as does the need for familiarity or expertise with the procedure. Because of this, the less-invasive approaches to saphenous vein harvest are not practical in most centers for cases of vascular trauma.
Although rarely used, arterial conduits may provide a better size match for the injured vessel and they do not require lysis of valves. Arterial conduits may also have improved handling characteristics, better compliance match and even superior patency. The use of autologous arterial conduit is feasible and efficacious but remains limited in the setting of trauma due to the paucity of harvest sites, their challenging anatomic locations, and the lack of redundancy or length. The internal mammary (internal thoracic) artery is the most commonly used arterial conduit. However, due to its confined location, access is only feasible through a median sternotomy. The gastroepiploic artery has also been used with favorable patency in coronary artery bypass surgery when the internal mammary artery and the saphenous vein are not available. The most commonly explanted autologous artery is the radial artery, which ranges from 2 mm to 4 mm. The internal iliac artery can be used, but this is infrequent except in select cases of pediatric injury. Klonaris et al described the benefits of using the internal iliac artery for repair of infected femoral artery pseudoaneurysm resulting from trauma from repeated access during illicit drug use. This report describes the use of internal iliac artery for reconstruction in 9 (5 patch, 4 interposition graft) of 12 patients. At a mean of 19 months after repair, Klonaris et al reported no complications or instances of limb loss. Finally, the external carotid artery can serve as an autologous conduit in repair of proximal internal carotid artery injuries. In these cases, the external carotid can be transposed onto the mid or distal internal carotid in situations where the proximal portion is injured. Other arteries such as the deep inferior epigastric may be used as a microvascular graft to replace a damaged arterial segment, but these smaller arteries are not typically a consideration in trauma.
Prosthetic Conduits
Since the first prosthetic graft made of woven nylon, a variety of grafts have been developed, including collagen-impregnated woven nylon (Hemashield Dacron, Maquet Germany), heparin-bonded Dacron, expanded polytetrafluoroethylene (ePTFE), heparin-bonded ePTFE (PROPATEN, Gore Medical, Flagstaff, AZ), hooded PTFE (Distaflo, Bard PV, Tempe, AZ), ring reinforced ePTFE, and even a hybrid consisting of woven nylon and ePTFE (Triplex, Vascutek Terumo, Scotland, UK). In large vessels such as the aorta and iliac arteries, prosthetic grafts have been used with great success. However, higher rates of thrombosis remain a disadvantage of prosthetic grafts in smaller vessels regardless of conduit composition. In the classic studies of Bergen and Veith, comparing vein to ePTFE for reconstruction of age-related disease, short-term (2-year) patency was comparable between the conduits. When longer-term patency rates of these studies were reported, saphenous vein was found to be superior. Prosthetic grafts are used today for elective bypass procedures but mainly in the femoral and above-knee location. Adjuncts such as heparin bonding of the luminal surface of the ePTFE have been used with modest or mixed results in attempts to improve patency. The use of prosthetic grafts in trauma has been espoused by some who purport that short segment or length prosthetics are durable and react more favorably than vein in contaminated fields. Some of these studies also point to preservation of the autologous vein for future revascularization as an advantage of using prosthetic conduits as the initial option.
Biologic Conduits: Allografts
The most modern construct of the vascular conduit is the biologic graft. These may be allografts or xenografts. Allografts consist of cryopreserved vein, cryopreserved artery, or preserved treated human umbilical vein (HUV). Dardik began work on HUV as a conduit starting in the 1970s. At 37 to 40 weeks of gestation, the HUV (2 mm to 3 mm diameter) is of similar caliber to that of small arteries and contains moderate amounts of collagen and elastin to provide elasticity. In a qualitative analysis of the microstructure of HUVs, Li et al showed that the collagen : elastin ratio in these vessels is similar to an artery of the same caliber. Studies by Li and colleagues also demonstrated that HUV had comparable morphologic and microstructural indices as similar-size arteries. These authors concluded that because of similarities HUV may be a substitute for small-caliber arteries such as coronary, brachial, radial, and tibial. In a review of 211 femoral–to-popliteal bypass operations (using the second-generation glutaraldehyde-stabilized HUV grafts), Neufang et al reported the primary, primary-assisted, secondary patency, and limb salvage after 5 years as 54%, 63%, 76%, and 92%, respectively, (with no difference between above-knee and below-knee grafts).
Cryopreserved saphenous vein allografts, also referred to as cadaveric saphenous vein, have been utilized as an alternative conduit. Early results with this conduit demonstrated poor patency. Walker et al studied 35 patients who underwent lower extremity bypass grafts for symptomatic ischemia. The primary patency was 67% at 1 month, 28% at 12 months, and 14% at 18 months. In an effort to improve patency of cryopreserved vein, Buckley et al prospectively enrolled patients for femoral to below-knee popliteal artery bypass using an anticoagulation protocol. Twenty-four patients with ischemic lower limbs underwent bypass with cryopreserved vein and were treated with aspirin, low-dose heparin, low-molecular-weight dextran 40, dipyridamole, and warfarin. The limb salvage rate in this study was 88% at 6 months and 80% at 24 months. Although this report demonstrated improved patency, it enrolled a small number, and patients required high levels of anticoagulation to obtain the results.
Cryopreserved arterial allografts have been developed as an alternative to cryopreserved vein. Cryopreserved artery is derived from the descending thoracic and infrarenal aorta, as well as the iliac and femoral arteries of human cadavers. Due to the variety of diameters, one can find an appropriately sized cryopreserved allograft for any vessel in the body. Cryopreserved allografts are commonly used for in-line arterial reconstruction in the treatment of prosthetic graft infections or contaminated wounds such as a mycotic aneurysm or aortoenteric fistula. Although cryopreserved arterial allografts have been anecdotally reported in the repair of vascular trauma with contaminated wounds, there are no large series. Reports on the use of this conduit in infected abdominal and extremity vascular beds suggest that it would be a safe consideration in the setting of resistant or recurrent infection and that it may have applicability in trauma.
Biologic Conduits: Xenografts
Animal-derived conduits (xenografts) include bovine carotid artery (Artegraft, North Brunswick, NJ), bovine pericardium, bovine jugular vein (Contegra, Contegra, Medtronic, Santa Rosa, CA) as well as a porcine pulmonic xenograft. The use of bovine carotid as a hemodialysis graft was initially reported by Chinitz. The patency of bovine carotid has been compared to ePTFE in hemodialysis grafts by Kennealey. Although there was no difference in secondary patency, primary and assisted primary patency were higher with bovine carotid than with ePTFE (60% versus 10% and 60% versus 21% at 1 year, respectively). Although bovine carotid has not been studied in vascular trauma, experience suggests that it may be a valid consideration in select cases. Similarly, bovine jugular vein plays a role in reconstruction of the right ventricular outflow tract in congenital heart surgery. Although its use in trauma remains to be defined, this conduit is available in diameters from 12 mm to 22 mm and would appear to be an appropriate size match for torso vascular structures.
Autologous Conduit
The gold-standard conduit is autologous tissue and most commonly a vein. In rare cases, one may choose to use an arterial conduit for vascular reconstruction. Because the venous system has multiple redundant outflow tracts, there are several choices for vein harvest. The lower extremity has the longest and most commonly used options, including the greater and lesser saphenous veins, the femoral vein, and even and dorsal foot vein. The cephalic and basilic veins of the upper extremity can be used independently or as a longer single segment graft. In the neck, the anterior, exterior, and internal jugular veins are options for vascular conduit. The veins of the neck are most commonly used as adjuncts for carotid artery repair because of their proximity.
Use of autologous vein requires adhering to the tenants of safe and effective dissection and procurement. In general, superficial veins may be harvested using a single continuous incision, skip incisions, or a newer minimally invasive technique. The single incision is the most expedient and most commonly described technique for greater saphenous vein harvest. However, this is associated with wound infection and dehiscence in 17% to 44% of patients. In an effort to decrease wound complications, attempts have been made to harvest this vein with multiple, shorter incisions and intervening “skin bridges.” Although this technique may take additional time and familiarity with the approach, it has been shown to decrease wound complications (9.6%) in at least one large series. The least invasive technique for saphenous vein harvesting is the endoscopic approach. With this technique the vein is harvested with electrocautery through several percutaneous incisions. Although risk of wound infection is decreased with the endoscopic technique, this does carry the added risk of thermal injury to the vein. Although it is desirable to reduce wound morbidity associated with saphenous vein harvest, it seems that as the method becomes less invasive and that the time needed for the procedure increases, as does the need for familiarity or expertise with the procedure. Because of this, the less-invasive approaches to saphenous vein harvest are not practical in most centers for cases of vascular trauma.
Although rarely used, arterial conduits may provide a better size match for the injured vessel and they do not require lysis of valves. Arterial conduits may also have improved handling characteristics, better compliance match and even superior patency. The use of autologous arterial conduit is feasible and efficacious but remains limited in the setting of trauma due to the paucity of harvest sites, their challenging anatomic locations, and the lack of redundancy or length. The internal mammary (internal thoracic) artery is the most commonly used arterial conduit. However, due to its confined location, access is only feasible through a median sternotomy. The gastroepiploic artery has also been used with favorable patency in coronary artery bypass surgery when the internal mammary artery and the saphenous vein are not available. The most commonly explanted autologous artery is the radial artery, which ranges from 2 mm to 4 mm. The internal iliac artery can be used, but this is infrequent except in select cases of pediatric injury. Klonaris et al described the benefits of using the internal iliac artery for repair of infected femoral artery pseudoaneurysm resulting from trauma from repeated access during illicit drug use. This report describes the use of internal iliac artery for reconstruction in 9 (5 patch, 4 interposition graft) of 12 patients. At a mean of 19 months after repair, Klonaris et al reported no complications or instances of limb loss. Finally, the external carotid artery can serve as an autologous conduit in repair of proximal internal carotid artery injuries. In these cases, the external carotid can be transposed onto the mid or distal internal carotid in situations where the proximal portion is injured. Other arteries such as the deep inferior epigastric may be used as a microvascular graft to replace a damaged arterial segment, but these smaller arteries are not typically a consideration in trauma.
Prosthetic Conduits
Since the first prosthetic graft made of woven nylon, a variety of grafts have been developed, including collagen-impregnated woven nylon (Hemashield Dacron, Maquet Germany), heparin-bonded Dacron, expanded polytetrafluoroethylene (ePTFE), heparin-bonded ePTFE (PROPATEN, Gore Medical, Flagstaff, AZ), hooded PTFE (Distaflo, Bard PV, Tempe, AZ), ring reinforced ePTFE, and even a hybrid consisting of woven nylon and ePTFE (Triplex, Vascutek Terumo, Scotland, UK). In large vessels such as the aorta and iliac arteries, prosthetic grafts have been used with great success. However, higher rates of thrombosis remain a disadvantage of prosthetic grafts in smaller vessels regardless of conduit composition. In the classic studies of Bergen and Veith, comparing vein to ePTFE for reconstruction of age-related disease, short-term (2-year) patency was comparable between the conduits. When longer-term patency rates of these studies were reported, saphenous vein was found to be superior. Prosthetic grafts are used today for elective bypass procedures but mainly in the femoral and above-knee location. Adjuncts such as heparin bonding of the luminal surface of the ePTFE have been used with modest or mixed results in attempts to improve patency. The use of prosthetic grafts in trauma has been espoused by some who purport that short segment or length prosthetics are durable and react more favorably than vein in contaminated fields. Some of these studies also point to preservation of the autologous vein for future revascularization as an advantage of using prosthetic conduits as the initial option.
Biologic Conduits: Allografts
The most modern construct of the vascular conduit is the biologic graft. These may be allografts or xenografts. Allografts consist of cryopreserved vein, cryopreserved artery, or preserved treated human umbilical vein (HUV). Dardik began work on HUV as a conduit starting in the 1970s. At 37 to 40 weeks of gestation, the HUV (2 mm to 3 mm diameter) is of similar caliber to that of small arteries and contains moderate amounts of collagen and elastin to provide elasticity. In a qualitative analysis of the microstructure of HUVs, Li et al showed that the collagen : elastin ratio in these vessels is similar to an artery of the same caliber. Studies by Li and colleagues also demonstrated that HUV had comparable morphologic and microstructural indices as similar-size arteries. These authors concluded that because of similarities HUV may be a substitute for small-caliber arteries such as coronary, brachial, radial, and tibial. In a review of 211 femoral–to-popliteal bypass operations (using the second-generation glutaraldehyde-stabilized HUV grafts), Neufang et al reported the primary, primary-assisted, secondary patency, and limb salvage after 5 years as 54%, 63%, 76%, and 92%, respectively, (with no difference between above-knee and below-knee grafts).
Cryopreserved saphenous vein allografts, also referred to as cadaveric saphenous vein, have been utilized as an alternative conduit. Early results with this conduit demonstrated poor patency. Walker et al studied 35 patients who underwent lower extremity bypass grafts for symptomatic ischemia. The primary patency was 67% at 1 month, 28% at 12 months, and 14% at 18 months. In an effort to improve patency of cryopreserved vein, Buckley et al prospectively enrolled patients for femoral to below-knee popliteal artery bypass using an anticoagulation protocol. Twenty-four patients with ischemic lower limbs underwent bypass with cryopreserved vein and were treated with aspirin, low-dose heparin, low-molecular-weight dextran 40, dipyridamole, and warfarin. The limb salvage rate in this study was 88% at 6 months and 80% at 24 months. Although this report demonstrated improved patency, it enrolled a small number, and patients required high levels of anticoagulation to obtain the results.
Cryopreserved arterial allografts have been developed as an alternative to cryopreserved vein. Cryopreserved artery is derived from the descending thoracic and infrarenal aorta, as well as the iliac and femoral arteries of human cadavers. Due to the variety of diameters, one can find an appropriately sized cryopreserved allograft for any vessel in the body. Cryopreserved allografts are commonly used for in-line arterial reconstruction in the treatment of prosthetic graft infections or contaminated wounds such as a mycotic aneurysm or aortoenteric fistula. Although cryopreserved arterial allografts have been anecdotally reported in the repair of vascular trauma with contaminated wounds, there are no large series. Reports on the use of this conduit in infected abdominal and extremity vascular beds suggest that it would be a safe consideration in the setting of resistant or recurrent infection and that it may have applicability in trauma.
Biologic Conduits: Xenografts
Animal-derived conduits (xenografts) include bovine carotid artery (Artegraft, North Brunswick, NJ), bovine pericardium, bovine jugular vein (Contegra, Contegra, Medtronic, Santa Rosa, CA) as well as a porcine pulmonic xenograft. The use of bovine carotid as a hemodialysis graft was initially reported by Chinitz. The patency of bovine carotid has been compared to ePTFE in hemodialysis grafts by Kennealey. Although there was no difference in secondary patency, primary and assisted primary patency were higher with bovine carotid than with ePTFE (60% versus 10% and 60% versus 21% at 1 year, respectively). Although bovine carotid has not been studied in vascular trauma, experience suggests that it may be a valid consideration in select cases. Similarly, bovine jugular vein plays a role in reconstruction of the right ventricular outflow tract in congenital heart surgery. Although its use in trauma remains to be defined, this conduit is available in diameters from 12 mm to 22 mm and would appear to be an appropriate size match for torso vascular structures.
Decision Making in the Choice of Conduit
Location and Nature of the Injury
The anatomic location of the vascular injury plays an important role in consideration of conduit. If the environment in which conduit will be used is relatively innocuous, such as a low-velocity penetrating wound, the injury may be amenable to anatomic or in situ interposition graft reconstruction. In contrast, if the injury is more extensive, is heavily contaminated, or is associated with soft-tissue injury, there may not be viable soft tissue to cover an in situ graft. These more severe cases may preclude anatomic or in situ reconstruction and instead require positioning or routing of the conduit in an alternative or extraanatomic location. Understanding the size of the injured vessel and the extent of contamination and soft-tissue injury allow one to make a judgment about the best type of conduit. Table 18-1 provides a summary of approximate sizes of vessels that may be affected in the setting of severe injury.
| Artery | Normal Diameter (mm) |
|---|---|
| Common carotid | 10 |
| Innominate | 12-14 |
| Subclavian | 10 |
| Axillary | 8-10 |
| Radial | 4-6 |
| Thoracic aorta | 20-25 |
| Abdominal aorta | 15-20 |
| Common iliac | 10-14 |
| External iliac | 8-10 |
| Internal iliac | 8-10 |
| Common femoral | 8-10 |
| Superficial femoral | 6-8 |
| Profunda femoral | 6-8 |
| Popliteal | 6-8 |
Thoracic and Abdominal Injuries
The thoracic aorta and its branches are protected by the bone and muscular structures of the thorax. Blunt injuries that carry enough force to disrupt these vessels often result in death. In the civilian setting blunt aortic injury (BAI) is often manifested as a transection of the proximal descending aorta at or immediately distal to the ligamentum arteriosum. In this scenario a patient will survive based on the integrity of the periadventitial tissue in the mediastinum. Although this situation is not stable in the long-term, a contained BAI may allow the patient to be transported to a trauma center and treated with an open interposition graft or an endovascular stent-graft. Penetrating injury to the thoracic aorta is often lethal due to the numerous vital structures in the vicinity. Even low velocity penetrating injuries (i.e., stab wounds) may be lethal in this location. Blunt injury to the abdominal aorta is infrequent and accounts for 5% of aortic injuries. The majority of abdominal aortic trauma involves the infrarenal segment but its branches may also be injured. Penetrating injuries to the abdominal aorta and its branches are often complicated by injuries to solid or hollow viscus organs leading to bleeding and or enteric contamination.
Extremity Vessels
Blunt arterial extremity injury classically leads to disruption of the intima and flow-limiting defects. The difficulty with blunt trauma is confirming the diagnosis and specific location of vascular injury. As discussed in other chapters of this text, this scenario is often delineated with imaging such as duplex, contrast computed tomography (CT), or conventional arteriography. Penetrating injuries may lead to vessel transection or intimal injury due direct or indirect contusion (i.e., concussive effect). Partial transection of the vessel may prevent retraction and vasoconstriction and may lead to more bleeding from the injury. In contrast, complete transection of the elastic arteries in the upper extremities often results in vessel retraction, vasoconstriction and a relative degree of hemostasis. In the upper extremity, the axillary and brachial arteries are frequently injured by penetrating mechanisms; and in the lower extremity, the superficial femoral and popliteal arteries are most affected. The smaller infrageniculate vessels can also be injured. However, if in isolation, these injuries are associated with lower rates of mortality and morbidity than the larger, more-proximal vessels. If multiple tibial vessels are injured in the same extremity, the degree of ischemia and even the propensity for limb loss are likely to be worse.
Ideal Conduit for Vascular Trauma
The ideal characteristics of conduit include durability (i.e., life of the patient), resistance to infection, ability to incorporate with surrounding tissues, and appropriate diameter for the vessel being reconstructed. There is a general consensus that, until artificial biologic conduits are developed, autologous vein is the favored conduit option. However, given the varied mechanisms of trauma and the different sizes of injured vessels, one will need to be familiar with more than just saphenous vein for vascular conduit. Table 18-2 lists several commonly used conduits, each with real or perceived advantages and disadvantages.
| Conduit Type | Accessibility | Durability | Resistance to Infection | Size Matched | Miscellaneous Issues |
|---|---|---|---|---|---|
| Autologous vein (e.g., GSV) | Easily accessible if there is not polytrauma (i.e., bilateral IED injury to the lower extremities) | Extremely good | Good if there is adequate tissue coverage | Excellent for the upper and lower extremities | Can lead to pseudoaneurysm or blowout if not properly covered |
| Prosthetic | “Off the shelf” | Not the same as GSV but adequate | Good; antibiotic impregnation available | Excellent size for all injuries | Can lead to pseudoaneurysm or thrombosis if placed in contaminated field |
| Cryopreserved allograft | Accessible if cold storage available | Very good | Numerous reports for intraabdominal replacement with good success | Very good for a variety of sizes | Requires freezer and time to thaw; not available in austere or military settings |
As noted, the choice of conduit depends on the anatomic region of injury. Since the Vietnam War—and especially during the wars in Afghanistan and Iraq—the percentage of cervical and extremity vascular injuries has increased. Although rare and associated with high mortality, torso injuries do occur in the wartime setting. Larger-diameter torso injuries often require reconstruction with ePTFE or Dacron. These conduits are favored in the torso because of their ready availability and their larger diameters. For smaller torso vessels or in cases of enteric contamination, one may consider autologous vein as conduit. In these cases, depending on the extent of injury, one may use the deep femoral or the saphenous vein.
The aorta is most commonly repaired primarily or with a prosthetic conduit for reasons already mentioned. The aorta may also be reconstructed with a bifurcated graft comprised of the deep femoral veins sewn side-to-side for 5 cm to create a large common channel that approximates aortic diameter. This neoaorta procedure is almost exclusively used in the elective or the semielective setting following removal of an infected prosthetic aortic graft and should rarely be used as the primary procedure for trauma. Reconstruction of the iliac artery may be accomplished with prosthetic or with saphenous or femoral vein depending on the setting. One strategy to construct a larger caliber conduit using saphenous vein is referred to as a “panel graft.” In this case, a long length of the great saphenous is opened longitudinally and divided into two approximately equal segments or “panels.” The panels are then sewn side–to-side and closed over a small or midsized chest tube. Variations of the panel graft exist, and the strategy can result in an autologous vein conduit with a caliber that is twice that of the original saphenous vein diameter.
Because of the constraints involved with autologous repair of torso vascular injuries, particularly with regard to the larger-caliber vessels, repair has traditionally been performed using prosthetic of collagen impregnated, woven nylon, or ePTFE. Woven nylon grafts have the disadvantage of stretching up to 40% over the lifetime of the graft. As such, the diameter of the woven nylon graft should be relatively undersized compared to the diameter of the native artery being repaired. ePTFE grafts are relatively porous and are prone to leaching serous fluid through the graft material. This phenomenon also referred to as “sweating” can lead to formation of seromas in the graft tract. In an effort to mitigate each of these disadvantages, a multilayered woven nylon and ePTFE graft is available. The new Triplex prosthetic conduit (Vascutek Terumo, Renfreswshire, Scotland) consists of three layers. The inner layer is a standard uncoated Dacron graft (DuPont, Wilmington, DE), and the outer is a standard ePTFE graft. These two layers are fused together by a central layer of self-sealing elastomeric membrane.
Adjunctive maneuvers such as presoaking a woven nylon graft with rifampin (60 mg/ml) can be performed as a measure to deliver antibiotic to the field of injury and to reduce the risk of graft infection. Similarly, ePTFE grafts can be treated to decrease infections when placed in a contaminated field. Fisher et al describes a method by which minocycline and rifampin are bound to ePTFE graft using a unique methylacrylate technology to promote controlled antibiotic elution and to reduce infection risk. In vitro, the antibiotic-bound ePTFE grafts sustained gradual local release of the antibiotics that provided resistance from infection by Staphylococcus aureus and Staphylococcus epidermis for up to 2 weeks.
The available and best suited conduit for the repair of upper and lower extremity arterial injury is the greater saphenous vein. It is generally recommended that this autologous conduit should be harvested from the leg contralateral to any injury to decrease the risk of any venous congestion resulting from trauma. This is especially important if the injured lower extremity has concomitant arterial and venous injuries. In McCready’s series of patients with extremity trauma, it was found that 43 of 49 patients with femoral and popliteal artery injuries reconstructed with saphenous vein experienced an excellent outcome 33 months after the event. Similar outcomes have been reported in other series although lack of follow-up with this subset of the population means longer-term results are not known. Late thrombosis of saphenous vein grafts does not necessarily mean catastrophe. In Rich’s Vietnam experience, 24 of 34 who experienced vein graft thrombosis required no operative intervention because of adequate collateral circulation to maintain limb viability. It is likely that other associated extremities injuries (e.g., bone, nerve) limited use of the limb and the degree to which mild to moderate ischemia resulting from graft thrombosis would result in symptoms such as claudication.
If saphenous vein is not available as conduit, the upper extremity veins such as the cephalic and basilic can be used. The basilic vein has been described for use in bypass and exclusion of a popliteal artery aneurysm. The basilic vein can be easily harvested from the arm while simultaneous exposure of the lower extremity artery is performed by another surgical team. Tal et al described basilic vein grafts used to bypass and exclude popliteal artery aneurysm in 5 patients with good results up to 3 years after the repair. In another small series from Parmar et al, basilic vein was employed for the replacement of infected prosthetic grafts in the iliac and femoral arterial regions. The basilic vein provided appropriate size match and was used for in situ replacement. Although arm vein performs favorably with respect to patency and limb salvage when compared to synthetic conduit, it does require more-frequent secondary interventions to maintain patency. In a series of 37 arm vein bypasses, Varcoe et al reported a 30-day primary and secondary patency of 89% and 95%, respectively, with 95% limb salvage.
If one is to reconstruct arterial injuries in the distal extremities (e.g., forearm, leg), the conduit must be small caliber. Autologous artery or vein is still preferred in these challenging situations. To obtain an appropriate size match, the distal greater saphenous vein at the ankle or the lesser saphenous vein provides relatively familiar options. Rockwell et al, described use of epigastric artery and dorsal hand vein transposition for thumb reimplantation following traumatic amputation. The dorsal hand or foot veins are of good caliber, but harvesting will leave a significant scar, and there is potential for injury to the extensor tendons of the hand or fibrotic scar formation resulting in decreased function. In the case of hypothenar hammer syndrome, trauma to the hypothenar eminence of the palm causes injury to the ulnar artery often with formation of a symptomatic aneurysm. Traditional vein graft repair of a thrombosed ulnar artery using reversed saphenous vein has been reported. However, Temming et al proposed that an arterial autograft would be superior conduit (i.e., better size, durability) compared to vein graft in this scenarios. This group subsequently reported 3 successful cases of ulnar artery reconstruction using the descending branch of the lateral circumflex artery. In this novel report, patency of the reconstruction was confirmed by duplex ultrasound at periods as long as 28 months after repair.
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