In Situ Reconstruction Treats Aortic Graft Infections

CHICAGO -- In situ prosthetic reconstruction is an alternative in the treatment of select patients with infected aortic grafts.

Aortic graft infection is rare, less than 5% long term. Infection of grafts of the thoracic, thoracoabdominal, or suprarenal aorta is particularly difficult to treat and may necessitate in situ replacement because extra-anatomic alternatives are limited. The time-honored treatment of infrarenal aortic graft infection has been extra-anatomic (extracavitary) bypass followed by graft resection, said Dr. Thomas C. Bower at a vascular surgery symposium sponsored by Northwestern University.

In situ reconstruction with autogenous or prosthetic materials is becoming increasingly popular, with Dr. Bower and colleagues preferring to use a polyester graft soaked in a solution of rifampin at a concentration of 2.5 mg/mL for a minimum of 30 minutes prior to implantation. Silver-impregnated grafts may be promising, but are currently unavailable for routine use in the United States.

The key advantage of in situ prosthetic reconstruction is that it is often quicker than other techniques, and its procedure-related death rate is at least as good as that reported for other methods, with excellent limb salvage and patency rates, said Dr. Bower, professor of surgery and director of the vascular surgery fellowship, at Mayo Clinic, in Rochester, Minn.

In a Mayo Clinic study of 52 patients with aortic graft infection treated with rifampin-soaked grafts, the procedure-related death rate was 8% (J. Vasc. Surg. 2006;43:1166-74). At 5 years, primary patency was 89% and limb salvage 100%. However, along with the excellent outcomes was a higher risk of graft reinfection (11.5%), particularly for patients with frank perigraft purulence, Dr. Bower said. Five of the six patients with graft infection had perigraft purulence.

He suggests such patients may be better treated with femoropopliteal vein reconstruction or axillofemoral reconstructions with reported reinfection rates ranging from 3% to 15% and from 2% to 9%, respectively. Dr. Bower also cautioned against the use of prosthetic in situ reconstruction in patients with Pseudomonas infections, methicillin-resistant Staphylococcus aureus (MRSA), or large abscesses.

In the Mayo series of 52 patients, monomicrobial infections due to coagulase-negative staphylococcus species occurred in 33% of patients, Streptococcus viridans in 20%, enterococcus in 15%, and MRSA in 9%. Gram-positive species were more common in patients with localized and polymicrobial infections. Gram-negative species were more frequent with aortic graft enteric erosion (AGEE) or fistula (AGEF), and were particularly virulent.

Dr. Bower administers broad-spectrum IV antibiotics to all patients for 6-8 weeks postoperatively, and stressed the need to maintain these patients on organism-specific oral antibiotics for life, having had several patients return with graft reinfection after discontinuing their antibiotics.

The ideal candidates for in situ prosthetic replacement are patients with localized biofilms, either isolated or covering the entire graft, but the technique could also be applied to patients with AGEE or AGEF, or those with aneurysmal dilatation above the old graft in whom closure of the aortic stump would be challenging or difficult, he said.

"In our hands, successful treatment of these infections is centered on three areas: rapid assessment of patient comorbidities preoperatively, if time allows; definition, location, and extent of infection; and careful planning of the operation," Dr. Bower said.

Preoperative assessment of cardiac, pulmonary, and renal function includes a resting echocardiogram, bedside spirometry or pulmonary function studies, and resting arterial blood gas. A renal ultrasound is also performed in patients with underlying renal insufficiency.

Patients with a preoperative forced expiratory volume less than 1 L, resting hypoxemia or hypercarbia, or those on home oxygen, face a higher risk of postoperative pulmonary complications, Dr. Bower said. Patients with a baseline creatine greater than 2 mg/dL, small renal size (less than 8 cm), thin parenchyma, elevated renal resistive indices, or in whom placement of a supraceliac clamp is anticipated, are at increased risk of postoperative renal failure.

Either CT or MRI can be used to determine the extent of infection, although Dr. Bower said he finds CT scans easier to read. Signs of infection on imaging include periaortic and perigraft soft tissue stranding, edema, fluid, enhancing soft tissue rind, or air--the sine qua non of infection.

Preoperative indium-111-labeled white blood cell scans have a positive predictive value of 80% to 90%, but are only of value when they're positive, said Dr. Bower, who noted that he has operated on several patients with negative indium scans, especially those with AGEEs or AGEFs. Upper endoscopy and bronchoscopy are reserved for patients in whom there is concern regarding the the airway or GI tract.

The Mayo approach for prosthetic in situ replacement includes removing all infected portions of the prosthesis, if possible, and preservation of the incorporated graft; draining adjacent abscesses preoperatively to reduce bacterial burden, but only if there is no pseudoaneurysm or hemorrhage on the imaging study; lifelong antibiosis; and coverage of the new graft with omentum or other autogenous material.

When asked to comment, Dr. Ali F. AbuRahma, chief, vascular and endovascular surgery, Robert C. Byrd Health Sciences Center, West Virginia University, Charleston, stated, "Aortic graft infection carries high mortality and morbidity and makes selection of the proper therapy extremely critical. Allograft in situ replacement is generally recommended for invasive graft infections without sepsis and with no suitable autogenous conduit. Meanwhile, rifampin-bonded grafts are utilized for localized biofilm graft infection, particularly for staph epidermis infection. Graft preservation is recommended for early infection that is not associated with sepsis, except for patients with Pseudomonas infections. Patients with graft thrombosis with adequate collaterals and positive cultures are generally treated with graft excision alone.