Patients with infected aortic grafts may present anywhere along the spectrum from nonspecific complaints to overwhelming sepsis. The diagnosis is simplified in the presence of a draining sinus tract and/or an exposed graft, although this presentation is fairly unusual. Indeed, only 5% of the patients have positive blood cultures at the time of presentation. The majority of patients present with nonspecific symptoms, including a low-grade temperature, mildly elevated leukocyte count, an elevated sedimentation rate, malaise, and a generalized “failure to thrive.” Predictably, the diagnosis can be difficult. This is not particularly surprising given the low virulence of Staphylococcus epidermidis that accounts for a significant percentage of the infections. It is imperative that once the suspicion of an infected graft is raised, the appropriate evaluation should be initiated to confirm or refute the diagnosis. The initial operative report and immediate postoperative course should be reviewed for any complicating factors. All patients with gastrointestinal bleeding and a prosthetic aortic graft should be presumed to have an AEF until proven otherwise. Notably, both femoral pseudoaneurysms and limb thromboses after aortobifemoral bypass may result from graft infections, with the latter occurring in up to 25% of the cases.

A contrast CT scan is the diagnostic study of choice with sensitivities and specificities >90% (Fig. 49-1). The specific findings suggestive of an aortic graft infection include perigraft fluid collection and/or soft tissue swelling, ectopic gas, pseudoaneurysm (aortic or femoral anastomoses), retroperitoneal abscess, bowel wall thickening, or hydroureter. Indeed, the finding of a hydroureter in the absence of other findings should suggest an infected graft and is almost pathognomonic. Notably, it is difficult to diagnose an infected graft in the early postoperative period, because many of the normal postoperative changes are similar to those seen with an infected graft; gas around the graft resolves within 2 weeks postoperatively, while fluid around the graft can persist for up to 3 months.

A variety of other imaging studies have been used to confirm the diagnosis of an infected graft. MRI may be superior to CT because of its ability to resolve differences in the soft tissues, although the overall experience is somewhat limited and most surgeons are more familiar with CT images. Ultrasound may be helpful to identify perigraft fluid, particularly in the groin, and to confirm the presence of a pseudoaneurysm. Contrast can be injected in any tract (i.e., sinogram) that courses near the graft in an attempt to determine whether there is a communication with the graft itself. Several radionuclide functional studies have been used in this setting, with indium-labeled leukocytes being the most common. Although the associated sensitivity and specificities are reasonable, all the radionuclide studies suffer from the fact that areas of inflammation can lead to false positive findings, while antibiotic therapy can lead to false negatives. Regardless, they can be helpful in equivocal cases. Arteriography has no role in the diagnosis of an infected graft, although it is routinely used for operative planning. Surgical exploration is definitive and occasionally necessary; the finding of a graft that is not incorporated in the surrounding soft tissue is confirmatory.

AEF represent a small subset of infected grafts. Unlike the more common, bland infected aortic grafts, patients with AEF present with some evidence of gastrointestinal bleeding. Although this can be massive, the more common scenario is a more moderate, self-limited or “sentinel” bleed. As noted above, all gastrointestinal bleeding in patients with a prosthetic aortic graft should be presumed to be secondary to an AEF until proven otherwise, and the appropriate evaluation should be initiated urgently. Notably, approximately 40% of patients with an AEF will have a second episode of bleeding within the first 24 hours after the sentinel event. The source of the bleeding or the communication with the infected graft can occur anywhere along the gastrointestinal tract, although the portion of the duodenum (i.e., junction of 3rd and 4th parts) where it crosses over the aorta/aortic graft is the most common and accounts for approximately 75% of the cases. An esophagogastroduodenoscopy (EGD) should be performed to confirm the diagnosis and/or identify other sources of bleeding. It is important to communicate the concerns
about an AEF to the endoscopist, and ideally, the surgeon should be present during the procedure. The examination should include a complete interrogation of the 3rd and 4th portions of the duodenum and may require the use of a pediatric colonoscope. Importantly, identification of a bleeding site in the stomach or proximal duodenum (e.g., gastritis, gastric ulcer) should not lead to the premature termination of the procedure. Patients with evidence of massive bleeding should likely be endoscoped in the operating room, and adherent clots should be left undisturbed to prevent recurrent bleeding. Unfortunately, a normal upper endoscopy does not exclude the diagnosis of an AEF. A contrast CT scan should be performed in conjunction with the EGD to help confirm the diagnosis. Exploratory laparotomy is occasionally necessary as a diagnostic study in this setting and requires complete mobilization of the duodenum off the aorta/aortic graft after achieving proximal and distal aortic control. Evaluation of the colon with colonoscopy is useful to complete the evaluation for gastrointestinal bleeding.

Prosthetic aortic graft infections occur in approximately 1% to 2% of all infrarenal aortic reconstructions. The incidence is approximately 0.5% to 1% in grafts isolated to the abdomen (i.e., aortoaortic, aortobiliac) and approximately 1.5% to 3% for grafts involving the groin (i.e., aortobifemoral).

The etiology of the graft infections include contamination of the surgical wound/ graft in the peri-operative period, seeding of the graft from an episode of bacteremia, erosion of the graft into the bowel or genitourinary tract, and involvement of the graft from a contiguous infectious process. Contamination of the graft in the peri-operative period is likely the most common etiology and is associated with breaks in sterile technique, concomitant foot infections, groin wound breakdowns, and emergency procedures. Notably, bacteria can be isolated from the thrombus within abdominal aortic aneurysms and aortic atherosclerotic plaques in a significant percentage of patients (15% to 40%), although the contribution of these isolates to graft infections remains unknown. AEF can result from a direct communication with the suture line, a communication with an anastomotic pseudoaneurysm, or erosion of the prosthetic graft into the bowel itself. In most cases, the graft infection precedes the AEF.

The majority (approximately 60%) of prosthetic aortic graft infections are due to Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, with the balance comprised of gram negative, bacteroides, and nonhemolytic streptococcus organisms. The responsible organisms vary with the time course of the infection, with Staphylococcus aureus predominating in the early postoperative period and Staphylococcus epidermidis later. Notably, organisms may not be isolated in up to 25% of the cases despite an obvious graft infection. The majority of these cases are likely due to Staphylococcus epidermidis; specific culture techniques are required to disrupt the surface biofilm and isolate this organism.

Discussion of the etiology of prosthetic graft infections merits comment about the various preventive strategies. These are comprised of standard surgical techniques and include strict sterile technique, peri-operative skin site preparation, prophylactic antibiotics with redosing during the procedure as necessary, protecting the prosthetic grafts from contact with the skin, and juxtaposition of retroperitoneal tissue between the graft and the overlying bowel.

Operative treatment is required for all patients with an infected aortic graft. Although appealing, long-term antibiotics have no role as the sole treatment modality. Furthermore, the mortality rate associated with untreated AEF is virtually 100%.

Patients with infected aortic grafts usually have significant medical comorbidities. These comorbidities should be optimized to the greatest extent possible. Ankle-brachial indices should be obtained for all patients with additional noninvasive imaging dictated by the planned procedure. These potentially include segmental upper-extremity pressures and velocity waveforms to confirm the adequacy of the axillary artery as an arterial inflow and vein surveys of the saphenous and superficial femoral-popliteal veins. A standard aortogram and bilateral lower-extremity arteriograms should be obtained to plan the reconstructive procedure. It is rarely feasible to simply remove the graft without revascularizing the lower extremities. Indeed, remedial revascularization is complicated by the fact that the infected graft usually lies within the optimal anatomic position. Dedicated shots of the profunda femoris arteries should be obtained in the ipsilateral oblique projection. Additionally, an arch aortogram should be performed if an axillofemoral bypass is planned. Patients should be started on preoperative antibiotics, initially empiric, with adjusment based upon the results of culture data.