Prosthetic Graft Infections PGI

Aortic and lower extremity prosthetic grafts are widely used in vascular surgery. PGI is an uncommon complication, ranging from 1% for aortic, to 1.5-2% for aor-tofemoral and 6% for infra-inguinal prosthetic grafts. It is accompanied by increased mortality (up to 75% in infections of aortic grafts) and significant morbidity (up to 70% amputation rate reported in infections of lower extremity grafts) [18, 70, 87]. Identified risk factors are groin incision, wound complications (especially incisional haematoma), diabetes mellitus, urgent procedure, prolonged operative time, multiple interventions at the same site and obesity [18, 55, 70].

The clinical symptoms and signs and the microbiology of the PGIs are related to the time of presentation after surgical implantation. Early PGI develops within 6 months (according to some surgeons within 3 or 4 months) postoperatively, more usually affecting lower extremity grafts, presents with fever, leukocytosis and is often accompanied by surgical wound infection. The clinical presentation may also include abscess or pseudoan-eurysm formation, graft exposure, sepsis syndrome with bacteraemia or fungaemia, distal septic embolization and peripheral ischaemia. The most commonly encountered pathogen is S. aureus, followed by Gram-negative bacilli, such as Escherichia coli, Proteus spp., Pseudomonas aeruginosa, Klebsiella spp. and Enterobacter spp. [3, 6, 7].

Late PGI presents more insidiously, due to the lower virulence of the implicated microorganisms and the bio-film-based pathogenesis of the infection. Clinical presentation may include pseudoaneurysm formation, lack of graft incorporation, groin draining sinuses, abdominal pain, distal ischaemia and septic emboli, gastrointestinal haemorrhage due to graft-enteric fistula or erosion of the duodenal mucosa. In several cases of late PGI, the clinical presentation is subtle and nonspecific, leaving the diagnosis in doubt, until surgical exploration. Coagulase-negative staphylococci predominate, with S. epidermi-dis being the most commonly recovered pathogen. Skin flora inhabitants, such as Propionibacterium acnes and Corynebacterium spp., are less frequently recovered. Late abdominal aortic graft infections are very often polymi-crobial, comprising Gram-negative bacilli of the colon flora, enterocci and anaerobes such as Bacteroides fragilis strains. Fungi are rarely encountered, but Candida spp. is an increasingly implicated pathogen in infected devices, with mechanism of virulence expressed as biofilm production [46, 51]. Mycobacteria can be the cause in a minority of infections, in selected immunocompromised hosts. Biofilm formation in late PGIs often compromises the isolation of the responsible microorganism [3, 6, 7].

The diagnosis is established with clinical criteria in the case of graft exposure, or intraoperatively by the presence of pus collection or lack of graft incorporation. Imaging modalities CT and MRI are supportive of the diagnosis of infection. CT offers the advantage of guided aspiration of fluid collections, which aids microbiological diagnosis and has a reported sensitivity of 94% and specificity of 85%, while, for MRI, sensitivity and specificity are reported to be 85% and 100% respectively. Indium-labelled white blood cells and gallium scintigraphy are a second-line imaging technique. Endoscopy is an emergency diagnostic procedure in the case of gastrointestinal bleeding, which is a life-threatening complication of PGI. The third and fourth part of the duodenum are most usually affected [3, 6, 7].

The most effective way to manage PGI is eradication of infection through total graft excision with meticulous local debridement, followed by extra-anatomical revasculariza-tion and appropriate antibiotic treatment. Graft excision is urgent when the clinical presentation includes systemic sepsis or anastomotic bleeding. Graft excision without revascularization can be attempted in the rare case of a totally thrombosed vessel with a viable limb. Early PGIs have abetter outcome, but infections due to Pseudomonas spp. carry worse prognosis. Amputation rates range from 4% to 9%. Duration of antimicrobial treatment is not well defined in controlled trials. A minimum of 6 weeks of intravenous antibiotics is recommended by some, with or without 6 weeks of additional oral treatment. Other authors recommend 3 months of therapy as minimum duration. According to each vascular centre's expertise, a staged or sequenced procedure may be chosen. The staged approach, in which revascularization precedes and excision of the infected device follows after 2-3 days, avoids extended operative times and lowers the patient's physiological stress. In the sequenced approach, where the two operations are performed consecutively, prompt debridement of the infectious focus provides a minimal risk of re-infection of the new implant [3, 6,10].

Revascularization can be achieved via extra-anatomic by-pass or in situ replacement. Staged graft excision with extra-anatomic revascularization is considered the standard of care and is reported to have a 2-4.5% re-infection rate, 12-25% mortality, 0-1.4% amputation and 1.5-3% aortic stump rupture rates. These rates are significantly ameliorated when compared to the reported rates of older studies. Autologous vein grafts, with low proclivity to reinfection, are the preferred type of grafting and omental positioning should be achieved if possible [70, 87, 88].

In situ revascularization has the advantage of being a single-step procedure; in addition, it avoids local complications after saphenous vein harvesting, permits a shorter hospital stay and preserves aortic vascularization of the pelvis and limbs. It is recommended in infected grafts of the abdominal aorta that comprise the mesenteric, coeliac and renal arteries, and in local, mild infections, due to less virulent pathogens. Autogenous vein grafts are reported to have low mortality and amputation rates (8-10% and 2-3% respectively) and are probably the most indicated choice for in situ procedures [25, 97]. Good results have been recently reported with the use of prosthetic grafts for in situ replacement of 25 infected aortic grafts, followed by chronic suppressive antibiotic treatment. An 8% reduction of mortality rate and 100% improved limb salvage as compared to the extra-anatomic by-pass procedure are reported [100]. Rifampin-soaked grafts have not proven to offer protection against re-infection, whereas envelopment of the graft by autogenous tissue coverage such as omentum or muscular flaps provides significant protection [86, 97]. Rifampin-bonded grafts seem to be a safe and durable option for in situ replacement of grafts infected with S. epidermidis, but are less effective for more virulent pathogens [11,12, 29]. Silver-coated grafts do no seem to afford protection, while triclosan-coated grafts

Fig. 14.1.1 Axial spiral CT slice in a patient with infected bifurcated aortofemoral graft during the arterial phase post iv contrast administration. There is gas adjacent to the graft at the bifurcation (black arrow), haziness of the surrounding fat with indistinct borders and there is partial thrombosis of the left graft leg (white arrow). Calcifications of the occluded native arteries (black arrowhead) are also shown and a surgical drainage at the inflamed area (white stroked arrowhead)

Fig. 14.1.1 Axial spiral CT slice in a patient with infected bifurcated aortofemoral graft during the arterial phase post iv contrast administration. There is gas adjacent to the graft at the bifurcation (black arrow), haziness of the surrounding fat with indistinct borders and there is partial thrombosis of the left graft leg (white arrow). Calcifications of the occluded native arteries (black arrowhead) are also shown and a surgical drainage at the inflamed area (white stroked arrowhead)

display a lower prophylactic efficacy when compared to rifampin-bonded ones [44]. In situ replacement with cryopreserved or fresh allografts, although encouraging in some studies, has provided disappointing results in others and merits further evaluation [23, 36, 49, 69].

Graft preservation is advocated only in cases of aortic graft infections in patients who are not candidates for surgery, due to serious comorbidities. In these patients, long-term (sometimes lifelong) oral antimicrobial suppressive therapy is administered [19, 91]. In recent literature, a 70% rate of limb preservation is reported in PGI of the lower extremities, in the absence of haemorrhage, systemic sepsis or Pseudomonas infection, with antimicrobial regimens of 12 weeks to lifelong duration. In another study, a 7% relapse rate was reported. Partial excision is reported in recent series, with long-term antibiotic suppression [20, 21]. Topical negative pressure therapy by use of a vacuum sponge system or vacuum assisted closure (VAC) seems to promote healing and granulation tissue formation in groin infections adjacent to prosthetic material. Its utility as an adjunct to graft preservation measures remains to be further evaluated [30, 75].

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