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In-Situ Treatment of Aortic Graft Infection with Prosthetic Grafts and Allografts
Aortic graft infection is one of the most devastating complications in vascular surgery. Because of routine antibiotic prophylaxis before surgical procedures and adherence to aseptic surgical technique, the overall incidence of infection involving synthetic vascular grafts is relatively low. When infection does occur, however, the consequences can be potentially catastrophic.
The reported incidence of infection involving a vascular graft varies in the literature, occurring after 0.2% to 5% of operation. The etiology of these infections is multifactorial but is primarily influenced by the implant site, indication for the intervention, and host defense mechanism. It is widely recognized that the potential for graft infection extends well beyond the perioperative period. Hallett and colleagues estimated the incidence of graft infection to be 5% in a population-based study examining prosthetic grafting of the aorta over a 10-year period. They found that graft infection occurred much less commonly than wound infections, with the incidence of early (<30-day) graft infection being in the range of 1% of procedures. They concluded that the infection risk was higher in grafts placed during emergency procedures and when the graft was anastomosed to the femoral artery in the groin.
The management goals for prosthetic vascular graft infection include eradication of the septic process and maintenance of normal arterial perfusion. Traditional management includes excision of the infected graft, oversewing of the infrarenal aorta, and extra-anatomic bypass. Despite aggressive surgical treatment, however, O’Hara reported that the 30-day mortality rate was 28% and the 1-year mortality rate was 58%. Furthermore, 27% of the patients they treated went on to require major amputation. Quinones-Baldrich and colleagues reported similar findings. In treating 45 patients with aortic graft infection, their 30-day mortality rate was 24%. The 3-year axillofemoral bypass graft patency rate was 43% and the 5-year amputation rate was 34%. These results regarding the standard surgical treatment of aortic graft infection fueled interest in developing surgical alternatives for the treatment of aortic graft infections.
An in situ replacement for aortic graft infections may be favorably compared to extra-anatomic bypass because most late-appearing infections are caused by the low-grade biofilm producing Staphylococcus epidermidis, which can require prosthetic or autogenous vein replacement. Several authors have reported using antibiotic-bonded prosthetic grafts, cryopreserved arterial homografts, lower limb deep veins, and partial or complete graft preservation to treat these complications.
Antibiotic or Silver-Coated Prosthetic Grafts
In-situ replacement with antibiotic-bonded prosthetic grafts is an option in the treatment armamentarium for infected aortic grafts. Early attempts at this treatment strategy were hindered by the rapid attenuation of drug concentrations in and around the replacement graft site. However, coating of the graft with either collagen or gelatin allows a chemical bond to form between the graft and the antibiotic, thus allowing the grafts to retain antimicrobial activity for an extended period of time.
Rifampin has become popular for this application because of its broad-spectrum activity against staphyloccal species as well as other gram-positive and gram-negative organisms. Furthermore, rifampin does not redistribute rapidly into the systemic circulation owing to its relative hydrophobic nature. Because it is rarely used as an antimicrobial agent in vascular surgery, there is relatively low prevalence of resistance to the drug. In an experimental animal model, Bandyk and colleagues demonstrated the absorption of rifampin to graft surfaces at high drug concentrations within 15 minutes at 60 mg/mL concentrations. They also demonstrated that in-vivo bactericidal concentrations to staphyloccal species reside in the graft for at least 48 hours after implantation.
Hayes and colleagues from the Leicester Royal Infirmary reported on the outcome of 11 patients with aortic graft infection who underwent total graft excision and in-situ replacement with rifampin-bonded grafts. The early (≤30 days) and late mortality rates were 18% and 36%, respectively. Both of the early deaths and one late death were in patients initially treated for ruptured abdominal aortic aneurysm (AAA). However, seven patients experienced long-term survival and remained clinically free from infection. The results of the Leicester series are comparable with other series that used either extra-anatomic bypass procedures or in-situ replacement. These findings led the group to conclude that a poorer long-term outcome is associated with patients treated with in-situ rifampin-coated prosthetic grafts who originally underwent emergency procedures, patients with aortoenteric fistulas, and patients who come to the hospital with methicillin-resistant Staphylococcus aureus (MRSA) or more virulent infections. However, others have reported excellent results with this strategy to treat aortic graft-enteric fistulas.
Bandyk and colleagues reported a larger series of 22 patients with aortic graft infections. Of the 22 patients, 20 were treated with in-situ rifampin-bonded prosthetic grafts. In this group of 22 patients, there was one death in a kidney-transplant patient who developed an infected femorofemoral extended polytetrafluoroethylene (ePTFE) bypass graft that subsequently caused infection of the in-situ aortic graft. During a mean follow-up period of 17 months, there were no deaths or lower limb amputations as a result of graft infection in the surviving patients. Additionally, duplex ultrasound demonstrated a healed, incorporated graft absent of perigraft fluid or anastomotic aneurysm in all but one of the replaced segments.
More recent reports have contradicted the previous suggestion that aortoenteric fistulas do not respond well to in-situ treatment with rifampin-bonded grafts. Oderich and colleagues from the Mayo Clinic reported on the use of in-situ rifampin-soaked prosthetic grafts to treat 54 patients with aortoenteric fistula. Forty-two patients had infections isolated to a portion of the graft body or limb. Total graft excision was performed in 31 patients and partial excision in 23 patients. There were five postoperative deaths. The operative mortality for stable patients was 2.3%, and it rose to 40% in patients who come to the hospital in hemorrhagic shock. Five-year survival was 59%, primary graft patency was 92%, and limb-salvage rates were 100%. There were no late graft-related deaths; however, four patients did develop graft reinfection.
In conclusion, the use of in-situ rifampin-bonded gelatin-sealed vascular grafts should be considered a safe and durable option for the treatment of patients with low-grade biofilm (S. epidermidis) aortic graft infections. Excellent durability, relative freedom from thrombosis and reinfection, and a low rate of limb amputation renders this strategy an attractive treatment alternative.
Silver-coated Dacron grafts are alternatives to rifampin-bonded grafts that can be used successfully to treat aortic graft infections. Bisdas and colleagues recently reported their results of 56 patients who underwent in-situ arterial reconstruction for abdominal aortic infection. Eleven patients were treated with in-situ silver-coated Dacron grafts. Thirty-day mortality was 18% and the 2-year mortality rate was 27%. After 2 years, limb salvage and graft patency were 100%. Major complications reported with the silver-coated grafts were graft reinfection in two patients.
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