Keywords

1 Introduction

Prosthetic graft or endograft infection is a rare but devastating complication of aortic surgery. The incidence of infected descending and thoracoabdominal prosthetic grafts is reported between 0.5 and 1.7%, including early and late infections with and without aortoesophageal fistulae [1, 2]. The prevalence of infected aortic endografts is 0.25–4% [3,4,5]. The management of infected descending thoracic or thoracoabdominal aortic grafts or endografts is complex, requiring multiple steps, including initial stabilization, systemic antibiotics, graft or endograft excision, debridement of devitalized tissues, repair of aortobronchial or aortoesophageal fistula when present, revascularization, and pedicled flap coverage [1]. There are reports of non-excisional management, but this should be reserved for exceptional cases [6, 7]. Stent graft deployment to stabilize patients with massive hemoptysis or hematemesis in cases of aortobronchial or aortoesophageal fistulae is considered a suitable emergent treatment. However, this should be considered a bridging procedure in preparation for definitive repair [8,9,10].

2 Diagnostic Testing

Constitutional symptoms of infection, such as fever, sweats, lethargy, and pain often prompt medical attention. However, many cases are nonspecific and subtle [11]. Once there is a suspicion of graft infection, laboratory testing is obtained, including complete blood count, metabolic panel, and blood cultures. Broad-spectrum intravenous antibiotics are begun after cultures are obtained. The test of choice for initial imaging study is computed tomography (CT) scan with aortic-phase intravenous contrast (Fig. 80.1). Signs of graft infection include gas pockets surrounding the graft, new pseudoaneurysm, or tissue stranding [12]. CT has a sensitivity and specificity of 94% and 85%, respectively, in detecting graft infection, but sensitivity decreases significantly to 55% in chronic infection [13, 14]. Magnetic resonance imaging (MRI) is an acceptable alternative and has similar sensitivity and specificity as CT. However, MRI does not differentiate between the signal void created by calcification and air [1, 2]. Labeled white cell scans demonstrate varying sensitivity in detecting graft infection ranging from 60 to 100% [11, 14]. This study is utilized more in subacute and late infections. The inability to define presence or absence of graft involvement in adjacent soft tissue infection is considered one of its limitations [15, 16].

Fig. 80.1
figure 1

(a) Axial view of thoracic CTA of an infected descending thoracic aortic graft demonstrating air pockets in the left hemothorax (arrow). (b) Sagittal reconstruction of the same CTA. (c) Axial view of thoracic CT of an infected thoracic aortic endograft (arrow)

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Fluorodeoxyglucose positron-emission tomography (FDG-PET) (Fig. 80.2) with co-registered CT (FDG-PET/CT) combines conventional scintigraphy and CT. FDG-PET and FDG-PET/CT have been shown to have a high sensitivity of 91% and 93% and a specificity of 64% and 88%, respectively [17,18,19]. However, FDG-PET/CT may lead to false-positive results, since tissue surrounding vascular grafts often displays high accumulation of 18 F-FDG without infection [17, 19,20,21].

Fig. 80.2
figure 2

Coronal reconstruction of FDG-PET/CT for and infected thoracic aortic graft

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3 Treatment

Infections of grafts and endografts of the descending/thoracoabdominal aorta are life threatening and require early diagnosis and appropriate treatment, including surgical intervention and antimicrobial therapy to improve survival. The operative mortality of open surgical repairs in such cases is reported between 25 and 75% [7, 22,23,24]. The aim of surgical treatment is debridement of devitalized tissue, removal of grossly infected material, and revascularization of the distal aorta and branches.

4 Anatomy

The previous graft/endograft position is important in planning the second surgery. In some cases, access to the aortic arch may be required for proximal clamp placement. Many thoracic endografts are positioned at or near the origin of the left subclavian artery. Some have bare metal struts extending proximally into the aortic arch. In such cases, consideration should be given to performing the procedure with cardiopulmonary bypass and deep hypothermic circulatory arrest. (Fig. 80.3).

Fig. 80.3
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Establishment of cardiopulmonary bypass in preparation for deep hypothermic circulatory arrest in descending aortic repair

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In other cases, a thoracoabdominal aortic exposure is required for distal aortic clamping, for example, when fenestrated or branched endografts were used or when a thoracic endograft with distal uncovered struts extends into the thoracoabdominal aorta, e.g., Cook TX2 distal extensions.

5 Graft Excision and Extra-anatomic Bypass

Graft excision without revascularization is not possible in the descending thoracic/thoracoabdominal aorta. Although revascularization with extra-anatomic bypass is often utilized in the abdominal aortic graft infections, this is frequently not possible in the descending thoracic/thoracoabdominal aorta without compromising renal and visceral arteries [25].

The most appropriate extra-anatomic bypass described for the descending thoracic aorta is a prosthetic graft bypass from the ascending aorta via median sternotomy or right thoracotomy to the abdominal aorta [26,27,28] (Fig. 80.4). The main advantage of this bypass is that it is routed through a non-infected tract and at a safe distance from the contaminated previous graft. There are some disadvantages and contraindications for such bypass, including the need to reattach intercostal arteries for spinal cord blood supply and visceral arteries or massive hemorrhage that requires immediate control of the aorta. In some centers, an endovascular stent graft repair is a reasonable option for emergency control of hemorrhage as a bridge to more definite treatment [8, 9].

Fig. 80.4
figure 4

A prosthetic graft bypass from the ascending aorta via median sternotomy to the abdominal aorta

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6 Graft Excision with In Situ Bypass

6.1 Cadaveric Allografts

The use of arterial allografts was described over a decade ago in animal experiments [29, 30]. In the years to follow, case reports using fresh allografts have been described [31, 32]. However, when fresh allografts were used in replacement of infected infrarenal aortic grafts, 9% of the patients required reoperation after 1 year due to pathological changes of the allografts, such as aneurysmal degeneration [33].

Using cryopreserved homografts requires special preparation and thawing prior to usage. When large vascular segments are involved in the infection (such as the thoracoabdominal aorta), several allografts are needed to achieve adequate reconstruction, and allografts may be more expensive than conventional prosthetic grafts. In a retrospective review, Vogt et al. compared conventional techniques using prosthetic grafts with allograft surgery for infrarenal aortic graft infections, and the results in the allograft group were superior to the conventional group. In the earlier series, they reported allograft-related technical complications in 20% of the cases, including friability of the grafts and graft-enteric fistulae developing between tied side branches and the bowel [34,35,36,37,38,39]. In our previous experience, we also had difficulty with fracture of the intercostal branches that were tied using polypropylene suture that led us to resecure all intercostal side branches with silk sutures. Other publications have described the use of allograft in descending and thoracoabdominal aortic graft infections, with particular benefit in the presence of aortoesophageal and aortobronchial fistula [35, 40, 41]. The major disadvantages of cadaveric allografts are availability and cost. Many patients with thoracic graft infection present as an emergency and cannot wait for appropriate allograft procurement [38]. One solution to this is on-site storage. At our institution, we keep a selection of grafts on hand, but this is expensive. The US cryopreserved aortic allograft registry reviewed 31 institutions’ experience with cryopreserved aortic allograft placement. The mean follow-up period was 5.3 months, and overall mortality rate was 25%. They failed to prove superiority and justify the preferential use of allografts over conventional prosthetic grafts for primary graft infection, mycotic aneurysm, or aortic graft-enteric fistula [42]. Nevertheless, homograft replacement of infected grafts remains a useful option.

6.2 Other Biological Alternatives to Allografts

The use of autologous femoral or iliac veins in reconstructing the aorta has been described in the infrarenal abdominal aorta [43,44,45,46]. It has a limited role in the treatment of descending thoracic aortic graft infections due to diameter discrepancy and the need for extended vein length. However, it has been described in several cases where the infection was limited to a short segment of the descending aorta [47, 48].

6.2.1 Tissue-Engineered Vascular Grafts

Tissue-engineered vascular graft (TEVG) was first reported in 1986 by Weinberg and Bell [49]. The goal of tissue engineering is to produce a biological tissue that can replace a damaged human tissue/organ and restore its function. The concept of tissue engineering requires three components: the extracellular matrix (ECM), the cells, and the signaling system for remodeling [50]. Over the last two decades, multiple publications have demonstrated the clinical application of tissue engineering, starting in animal models and continuing to human trials [50,51,52,53].

CorMatrix is a Food and Drug Administration-approved ECM for use in cardiovascular surgery. It is a decellularized ECM from porcine small intestinal submucosa, which has been reported as an alternative to synthetic grafts/patches in cardiovascular surgery [54,55,56,57,58,59]. TEVG have the potential to become a promising alternative in the future for allografts and prosthetic grafts in cardiovascular surgery. However, better understanding of the remodeling process and the neotissue formation is required prior to a broader use of TEVG.

6.3 Prosthetic Grafts

Excision and replacement of the infected graft/endograft are the most common and expedient conduit. In situ replacement with a new prosthetic graft, along with wide infected tissue debridement and graft coverage with rotated muscle or omental flap, is the most commonly used treatment method [25, 60, 61].

“Stump blowout” is our primary concern with extra-anatomic bypass for the descending thoracic aorta, such as the ascending aorta to the abdominal aorta bypass. Therefore, we prefer in situ revascularization after infected thoracic graft/endograft resection for replacing the thoracic and thoracoabdominal aorta. For the most part, we use the spinal protective adjuncts of distal aortic perfusion and moderate passive hypothermia. We use deep hypothermic circulatory arrest when a proximal aortic cross-clamp cannot be placed safely.

7 Management

7.1 Anesthesia and Monitoring Lines

After induction of general endotracheal anesthesia, a double-lumen endotracheal tube is placed. Arterial monitoring (usually right radial) and central venous lines with a pulmonary artery catheter are placed. The patient is placed in the right lateral decubitus position. In general, we avoid placement of a cerebrospinal fluid (CSF) drainage catheter in infected cases due to the potential concern of seeding the cerebrospinal space, leading to meningitis. We use motor- and somatosensory-evoked potential neuromonitoring (MEP and SSEP) to guide our repair (Fig. 80.5).

Fig. 80.5
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(a) Sensory-evoked potential monitoring procedure. (b) Motor-evoked potential monitoring procedure

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7.2 Surgical Technique

The left femoral artery is exposed and encircled through an oblique groin incision. A left thoracotomy incision is made over the sixth rib followed by deflation of the left lung by anesthesia. The chest is entered via the fifth intercostal space, and the costal margin is cut (a modified thoracoabdominal incision). This allows us to have complete exposure of the entire thoracic aorta. Adhesions from previous procedures or inflammation from the infection are often encountered. The lung is carefully dissected off of the parietal pleura and aortic graft. If by preoperative radiographic evaluation a pseudoaneurysm contained by the lung parenchyma is suspected, no further mobilization of the lung is performed. When distal transverse arch can be mobilized safely, we use distal aortic perfusion, avoiding the need for deep hypothermic circulatory arrest through femoral arterial and venous cannulation [62, 63].

7.3 Infected Graft Resection

Distal aortic perfusion is initiated, followed by a sharp and blunt dissection, exposing the junction between the infected graft and native aorta. The left vagus and recurrent laryngeal nerve are protected. We dissect native aorta circumferentially and clamp either proximal or distal to the left subclavian artery. The distal clamp is applied to the native aorta distal to the infected graft. When the proximal aortic clamp is placed proximal to the subclavian artery, a separate clamp is placed on the left subclavian artery. The infected graft is completely excised, and all suture materials are resected. The infected tissue in the aortic bed is debrided, until we get healthy margins proximally and distally.

7.4 Graft Reconstruction

We generally use gelatin- or collagen-impregnated woven Dacron grafts. Once the appropriate-sized graft is selected, it is soaked in rifampin saline solution (1 mg rifampin per mL saline) for at least 15 min [64,65,66]. End-to-end proximal anastomosis is performed using running 3-0 polypropylene suture. If the aorta is thinned, such as after stent graft removal, we prefer to use 4-0 polypropylene suture. We then use interrupted 4-0 pledgeted polypropylene sutures to buttress the anastomosis.

For the distal anastomosis, the graft is stretched and transected to the appropriate length. Occasionally, we bevel the graft to allow reincorporation of patent distal intercostal arteries, especially T8–T12. More frequently, we reattach them using a 14 mm woven Dacron looped graft (Fig. 80.6) or as a patch to the main graft. If there are no changes on intraoperative spinal cord monitoring with MEP and SSEP, some intercostal arteries can be ligated without reattachment. When the repair is complete, distal aortic perfusion is stopped, and the clamps are slowly released.

Fig. 80.6
figure 6

Dacron loop graft (arrow), for reimplantation of patent distal intercostal arteries

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During the procedure, we allow the patient’s body temperature to passively cool to 32 °C. Once the repair is complete, the patient is rewarmed to 36 °C nasopharyngeally and weaned from distal aortic perfusion. We then remove the arterial and venous cannulas. Heparin is reversed by slowly infusing intravenous protamine at 1 mg per 1 mg heparin. We avoid applying topical hemostatic agents on the anastomoses.

7.5 Omental Flap

The omentum is known for its vascularity and lymphatic supply and the ability to induce neovascularity. Multiple publications have demonstrated its use in treatment of aortic graft infections [60, 67,68,69,70,71,72]. An extension of the thoracotomy incision over the abdomen or a separate supraumbilical minilaparotomy is made. The omentum is divided off of the transverse colon while preserving the epigastric arteries to assure blood supply to the flap (Fig. 80.7). The colon is placed back in the abdomen, and the omental flap is tunneled through a diaphragmatic window (Fig. 80.8). The omental flap should reach the distal aortic arch if constructed properly. It is circumferentially wrapped around the graft and secured in position with interrupted sutures.

Fig. 80.7
figure 7

The omentum divided off of the transverse colon while preserving the epigastric arteries to assure blood supply to the flap

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Fig. 80.8
figure 8

Omental flap tunneled through into the thoracic cavity

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7.6 Latissimus Dorsi Muscle Flap

In some patients, especially after previous abdominal surgeries, it is easier to utilize the latissimus dorsi muscle (LDM) than the omentum. The LDM flap has been described in the past in cardiomyoplasty procedures where the left LDM pedicle is wrapped around the heart through the left pleural cavity [73]. The preparation of the LDM flap is performed at the beginning of the procedure. After making the skin incision for the thoracotomy, the LDM is identified under the subcutaneous tissue. The muscle is dissected, starting with its surface, afterward dissecting it free from all attachments (thoracic, lumbar, sacral vertebrae, supraspinal ligament, and iliac crest attachments) and preserving the superior neurovascular pedicle [74] (Fig. 80.9). After replacing the infected graft, we make an incision in a superior intercostal space (usually third) and pass the LDM flap through it into the pleural cavity and wrap it around the new graft in the left chest (Fig. 80.10).

Fig. 80.9
figure 9

Latissimus dorsi muscle (LDM) pedicle

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Fig. 80.10
figure 10

Latissimus dorsi muscle pedicle wrapped around a descending aortic graft

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7.7 Closure

The chest wall is closed in layers after placement of two #32 French chest tubes. When coagulopathy or hemodynamic instability is present at the end of the case, we perform temporary abbreviated closure with negative pressure dressing. Delayed primary closure can be performed in 1–2 days, once the patient is stabilized and coagulopathy is resolved.

8 Endovascular Treatment

In the last decade, various publications have described acceptable short- and mid-term results of endovascular treatment for infected aortic aneurysms. However, the long-term results are still poor, with the need for additional procedures, such as debridement, sac irrigations, late explantation, and open reconstructive surgery. The endovascular approach may be considered in very high-risk patients and, mostly, as a bridging procedure [8, 75,76,77,78].

9 In Situ Debridement with Graft Preservation Therapy

The high mortality and morbidity rates in surgeries for infected aortic grafts have forced surgeons, even in the earlier series, to treat some patients who were at high risk for surgery with only debridement, graft preservation, and lifelong antibiotic treatment. Recently, multiple studies have described conservative treatment in selected patients with infected thoracic and abdominal aortic grafts/endografts with low early mortality [79,80,81,82,83,84]. There are certain cases in which this conservative approach is preferable. They include patients with comorbidities and high risk for surgery, those with high-risk anatomy, in which graft excision will result in organ malperfusion, such as the aortic arch or thoracoabdominal aorta, infection with indolent Gram-positive organisms, and infection involving only the body of the graft [85].

10 Antibiotic Treatment

The strategy for the treatment of aortic graft infections consists of antibiotic treatment as a necessary adjunct. An empiric, broad-spectrum antibiotic should be started with diagnosis of graft infection. Later in the course of treatment, this should be altered based on culture growth. An intravenous antibiotic should be administrated for a minimum of 2 weeks and up to 6 weeks, followed by long-term oral antibiotic treatment. The duration of the oral antibiotic treatment varies in the literature, from 6 weeks to 6 months, and some report the need for lifelong treatment [8, 86, 87].

11 Antibiotic-Loaded Beads

The use of antibiotic polymethyl methacrylate (PMMA) cement beads has been previously described as an adjunct in the treatment of orthopedic prosthesis and ventricular assist devices [88, 89]. Recently, its use has been implemented in vascular infections as well, mostly extracavitary and abdominal aortic graft infections. During surgery, the infected tissue is debrided, and the antibiotic-loaded beads are made in the operating room. They are then wrapped around the graft with temporary wound closure, usually using a negative pressure dressing. The beads are removed before pedicled flap placement and final closure [90, 91].

12 Follow-Up and Surveillance

Once microbiologic data becomes available from preoperative blood cultures and intraoperative samples, the systemic antibiotics are tailored to the infecting organism. Prior to discharge, patients are switched to oral antibiotics. The length of treatment differs in the literature. Most publications describe at least 2 weeks of IV antibiotic followed by 6–8 weeks of oral treatment, and others advocate 6 months or lifelong treatment [87, 92, 93]. Close follow-up is recommended, but there is a lack of standardization regarding follow-up protocols. Our group suggests obtaining surveillance chest CT scans at 1, 6, and 12 months and then annually thereafter [87].

13 Outcomes

Despite the advancements in surgical techniques and adjuncts, the mid-term mortality rate remains high and ranges from 25 to 80% [1, 27, 60, 93]. Yamanaka et al. recently reported a series of 70 patients with aortic-related infections. The in-hospital mortality was 17.1%, mean follow-up of 26.7 ± 26 months, and an overall 3-year survival of 60.1 ± 6.7%. In this report, there was a trend of improved infection-related deaths since 2008. They attribute this improvement to better maximal debridement of surrounding tissue in the later years [86]. There are limited data in the literature regarding long-term outcomes and reinfection rates following treatment of infected thoracic aortic grafts. We recently published our data of 25% reinfection rate following resection and revascularization of infected abdominal aortic grafts [87].

14 Conclusions

Prosthetic graft/endograft infection after descending thoracic/thoracoabdominal aortic aneurysm repair remains a challenge. Improvements in surgical techniques, endovascular therapies as bridging procedures, and perioperative care have led to improved in-hospital survival. Replacement of the infected graft with pedicled flap coverage leads to reasonable long-term results. Additional studies are needed before widespread adoption of graft preservation techniques.