Infection of vascular prostheses

Update on graft infections in thoracoabdominal aortic aneurysm surgery

The incidence of an aortic graft infection following the repair of thoracoabdominal aortic aneurysm, is a rare yet insidious complication which requires prompt recognition and management. The decision-making framework for management encompasses the choice or antimicrobial therapy alone versus pursuing surgical intervention, which can then also lead to considering the potential for allografts. The current literature on the matter is heavily burdened by limitations of the reported retrospective experiences consisting of small patient cohorts. Studies have reported the favored approach of surgical intervention, although statistical significance is not reached. There is a clear recognized impact that the event surrounding the initial repair has on the occurrence of graft infection itself; with emergency repairs, and incidence of nosocomial infection being associated with higher rates of graft infection. We must consider the influencers of this ominous complications, which go back to the perioperative events itself, whether the initial intervention was elective or an emergency, the impact of nosocomial infections, the choice of open versus endovascular for initial repair. Only with the appropriate management strategy that encompasses all these factors, will allow the best treatment to be provided for patients. A sound understanding and appreciation for the aforementioned can allow the stratification of the risk associated with the occurrence of an aortic graft infection, leading to surveillance opportunities to provide the crucial ability to rapidly recognize this complication.

Infections in vascular surgery

Infections in vascular surgery are usually of multifactorial nature resulting from a complex interplay of patient, surgical and environmental factors. Preventative measures initiated from the stage of pre-operative screening, maintenance of patient homeostasis and the use of organism-directed antibiotics can contribute to reduce infection rates. Graft preservation techniques are becoming increasingly popular as a method to treat established graft infections. In this article we report on the current trends and techniques on the management of infections in vascular surgery. Ongoing studies are required to continue to accumulate data on the effectiveness of these techniques.

Does the timing of reoperation influence the risk of graft infection?

OBJECTIVE

This study compared the incidence and characteristics of graft infection in patients who underwent early vs late revisional surgery of lower extremity arterial bypass grafts.

METHODS

Between 1992 and July 2005, 500 revisional procedures were performed on 198 lower extremity bypass grafts. Patients whose revisions were performed <30 days after the primary bypass were in the early revision (ER) group (n = 99), and those done >30 days after bypass were in the late revision (LR) group (n = 99). Infection was defined as cellulitis with graft exposure or purulence in continuity with a graft that required antibiotics and operation for infection control. Mean follow-up was 60 months (range, 2 to 60 months). Groups were compared using Student's t test.

RESULTS

The ER group included 66 autogenous and 33 prosthetic grafts. The LR group consisted of 53 autogenous and 46 prosthetic grafts. Of the 500 revisional procedures performed, 17 graft infections occurred (3.4%). Twelve (70.6%) were prosthetic grafts and five (29.4%) were autogenous grafts (P = .004). Defining the infection rate per graft rather than per revisional procedure, the ER group had a significantly higher graft infection rate at 11% (11/99) compared with 6.1% in the LR group (6/99; P = .012). The risk of infection for prosthetic grafts was significantly higher within the ER group at 27.3% (9/33) compared with autogenous grafts at 3.1% (2/66; P = .0001). Infection developed in three vein grafts and three prosthetic grafts in the LR group (P = NS). For prosthetic graft revisions only, infection risk was 27.3% (9/33) in the ER group and 6.5% (3/46) in the LR group (P = .005). The most common cultured pathogen was methicillin resistant Staphylococcus aureus (ER, 6/11 vs LR, 3/6; P = NS). Within the ER group, the prevalence of Pseudomonas aeruginosa was significantly higher at 27.3% (3/11) compared with 0% (0/6) in the LR group (P = .04).

CONCLUSIONS

Early revision of lower extremity arterial bypass grafts has a significantly higher risk of graft infection compared with revision >1 month after surgery. Infection will develop in approximately 25% (9/33) of prosthetic grafts that are reoperated on early. If feasible, reoperation should be delayed >1 month for prosthetic grafts needing revision. Endovascular or extra-anatomic interventions should be considered if early revision is mandated in this group.

Cyanoacrylate for Wound Closure in Prosthetic Vascular Graft Surgery to Prevent Infections Through Contamination

PURPOSE

Prosthetic vascular graft infection (PVGI) still occurs at an unacceptably high rate, despite the many measures that have proven effective against infection. The major cause of PVGI is perioperative contamination, which usually occurs before a histological barrier is completed and may threaten graft viability. We assessed the efficacy of cyanoacrylate as a tissue adhesive and barrier against early contamination through the skin.

METHOD

A 1 x 0.5-cm Dacron graft was placed subcutaneously under sterile conditions in 16 Sprague-Dawley rats. The skin was closed with polypropylene sutures in eight rats (group A) and with N-butyl 2-cyanoacrylate in eight rats (group B). The closed incisions were then contaminated with 75 x 10(6) cfu/ml methicillin-sensitive Staphylococcus aureus. Microbiological and histopathological assessments were done 7 days later, after the rats were killed.

RESULTS

All of the graft cultures from group A (8/8) were positive for S. aureus whereas all of those from group B (0/8) were negative. This difference was significant (p < 0.001). Histological examination revealed denser inflammatory cell infiltration in group A than in group B.

CONCLUSIONS

Maintaining skin integrity after closure is of the utmost importance because contamination during the first hours of the procedure may cause PVGI. Cyanoacrylate seems to be a promising molecule not only because of its bacteriostatic effects, but also because it seals the barrier effectively and immediately.

Systemic and local antibiotic prophylaxis in the prevention of prosthetic vascular graft infection: an experimental study

AIM

to determine if local, in addition to systemic antibiotic prophylaxis (compared to that provided by systemic prophylaxis alone) provides additional benefit in terms of reducing graft infection.

METHODS

gelatin-sealed Dacron grafts were interposed in the infrarenal aorta of 36 mongrels and inoculated with 1 ml of a S. aureus suspension. Group 1 (control group) received no prophylaxis and were inoculated with 1 ml containing 10(9)cfu/ml. Group 2 (n=6) received systemic prophylaxis (1 g cephamandole) and were inoculated with 10(5) cfu/ml (n=3) or 10(7) cfu/ml (n=3). Group 3 received systemic prophylaxis (1 g cephamandole) and were inoculated with 109 cfu/ml. Group 4 received systemic prophylaxis (2 g cephamandole) and were inoculated with 10(9)cfu/ml. In group 5 and 6 grafts were soaked in a rifampicin solution before use and inoculated with 10(9) cfu/ml. Group 5 received no systemic prophylaxis and group 6 received systemic prophylaxis (1 g cephamandole). Grafts were harvested at 2 weeks, and peritonitis, perigraft abscess, anastomotic disruption and graft occlusion recorded. Swabs were taken of the graft, the perigraft tissues and the peritoneal fluid. Graft segments were incubated in broth medium.

RESULTS

inoculation with 10(9) cfu/ml ensured graft infection. Systemic or local prophylaxis alone failed to prevent graft infection. Only systemic and local antibiotic prophylaxis provided significant better results than no prophylaxis at all (p<0.01) and local prophylaxis alone (p<0.05). However, total "graft sterility" was not achieved as bacteriologic analysis of the graft segments showed low bacterial counts (<10 bacteria/graft) in 5 of 6 grafts.

CONCLUSION

local and systemic prophylaxis provided more protection as demonstrated by the significant decrease in the incidence of "overt" graft infection. Total "graft sterility" cannot be expected in the case of an overwhelming bacterial challenge.

Distribution and serum concentration of sisomicin released from fibrin glue-sealed dacron graft in the rat and human

We investigated whether or not fibrin glue (FG) used as a sealant in vascular prostheses to prevent leakage might be useful as a carrier of antibiotics for the prevention of local graft infection. Sisomicin (SISO) was incorporated into fibrin glue (SISO-FG) and evaluated as to its safety and pharmacokinetics. SISO (1.75 mg) -FG Dacron grafts were implanted subcutaneously in the anterior abdominal region of Sprague-Dawley rats, and then the changes in SISO concentrations in the serum and in the tissue around the implantation sites were compared with those same sites in rats that had had intravenous injection of SISO (1.75 mg). The serum SISO concentrations were significantly lower in the SISO-FG Dacron graft group than they were in the intravenous injection group. However, until 4 h after implantation the SISO concentrations in the tissues around the implantation sites were significantly higher in the SISO-FG Dacron group than they were in the iv injection group, and the peak concentrations during that time were 5.8 times higher for the SISO-FG Dacron group than they were for the intravenous injection group. The ratio of the area under the tissue concentration time curve of SISO (AUC tissue) after implantation of the SISO-FG Dacron graft to that after intravenous injection of SISO was 13.08. Therefore, FG was considered to control the release of SISO into the serum and to maintain a high SISO concentration in the tissue around the implantation site. Clinically, SISO (45 mg) -FG was applied directly to the Dacron grafts implanted in 10 patients who underwent prosthetic vascular reconstruction. No graft infection was observed in any of the patients who received SISO-FG Dacron grafts. The mean serum concentration of SISO was 0.65+/-0.17 microg/mL after 1 h and 0.33+/- 0.21 microg/mL after 3 h. The results of these clinical applications are in close correlation with those of the animal experiment and suggest that FG is useful as a carrier of SISO, allowing its controlled release for the prevention of local infection.

Improved management of infrainguinal bypass graft infection with methicillin-resistant Staphylococcus aureus

BACKGROUND

There is considerable debate over the management of infected infrainguinal grafts. This report describes recent experience in this field and documents the change in clinical practice needed to deal with methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

All infected infrainguinal grafts between January 1991 and July 1997 were reviewed. In the light of the findings, clinical practice was modified considerably. A further 1 year was audited prospectively up to August 1998.

RESULTS

Twenty-six patients were treated for 27 infrainguinal graft infections (25 prosthetic, two vein). Twenty were treated by complete graft excision as the initial therapy; graft preservation was attempted in six patients. Before 1995, the infecting organisms were predominantly Pseudomonas aeruginosa or methicillin-sensitive staphylococci. Subsequently all 14 patients treated up to 1997 had infection with MRSA. The overall amputation rate was 17 of 26; ten amputations were in patients with MRSA. Four patients died, all with MRSA sepsis. As a result of this experience a policy of complete isolation was adopted for all patients infected with MRSA. In the 12 months since this policy was introduced, 77 infrainguinal grafts (61 vein, 16 prosthetic) have been inserted. Two grafts (3 per cent) have become infected, necessitating graft excision and amputation.

CONCLUSION

MRSA infection of an infrainguinal graft is a serious complication with high associated amputation and mortality rates. Isolation and barrier nursing appeared to contain the problem.

Conservative management of a methicillin-resistant Staphylococcus aureus (MRSA)-infected aortobifemoral graft: report of a case

A 63-year-old man was referred to our department for treatment of intermittent claudication in the right lower limb. The preoperative angiogram showed severe stenosis extending from the terminal aorta to the bilateral common femoral arteries, with occlusion of the right superficial femoral artery and the left popliteal artery. He underwent aortobifemoral bypass with thromboendarterectomy of the left common femoral artery, and right graft-popliteal artery bypass. The patient had an uneventful postoperative course; however, 14 days after the operation, a pulsatile mass suddenly appeared in the left groin. Emergency surgery revealed disruption of the left distal anastomosis of the aortobifemoral bypass and therefore, revision, in the form of graft-profunda femoris artery interposition with graft-superficial femoral artery bypass, was performed. Microscopic examination showed colonies of bacteria in the host artery adventitia adjacent to the anastomosis. Culture of the discharge from the right groin operative scar revealed methicillin-resistant Staphylococcus aureus (MRSA). The discharge resolved following the intravenous administration of vancomycin and the local application of vancomycin ointment. There were no operative complications other than the MRSA infection, and the patient was discharged 20 days after revision surgery. In the 14 months since the revision, all grafts have remained patent and there have been no further symptoms of graft infection.

Duration of antimicrobial prophylaxis in vascular surgery

BACKGROUND

This randomized clinical trial compares the incidence of wound infection after vascular surgery in patients who received prophylaxis using the same antibiotic as either a single-dose or a multiple-dose regimen (until the lines/drain tubes were removed, but not for more than 5 days).

METHODS

Each of the 302 patients who entered the study received ticarcillin 3.0 g/clavulanate 0.1 g (Timentin) intravenously immediately after the induction of anesthesia. Patients randomized to the multiple-dose group received an average of 14.3 doses (range 9 to 20).

RESULTS

The incidence of wound infections was 18% (28 of 153) for patients in the single-dose group and 10% (15 of 149) for patients in the multiple-dose group (P = 0.04; relative risk estimate = 2.00, 95% confidence interval = -1.02 to 3.92).

CONCLUSIONS

A multiple-dose antibiotic regimen, rather than single-dose therapy, provides optimal prophylaxis against wound infection for patients undergoing vascular surgery.

Rabbit model for the study of aortic graft infection

Despite improvements in surgical technique and antimicrobial therapy, prosthetic aortic graft infections remain a challenging clinical problem. Diagnosis is difficult, and treatment results are less than optimal. An animal model is needed that will allow critical investigation of novel approaches in the therapy of aortic graft infections. Three-millimeter internal diameter polytetrafluoroethylene vascular prostheses were anastomosed as aortic interposition grafts in 25 rabbits. Increasing concentrations of Staphylococcus aureus (no bacteria to 1 x 10(8)) were applied topically to inserted grafts to initiate infection. There were 15 long-term survivors. Surviving rabbits were sacrificed at 2 weeks postoperatively to evaluate the development of aortic graft infection. Of the 15 survivors, 6 developed graft infection. All infected prosthetic aortas were innoculated with 1 x 10(4) or higher concentrations of S. aureus. A cost-effective, reliable model has been developed suitable for the study of prosthetic aortic infection.

Development of a Staphylococcus epidermidis vascular graft infection model in sheep

Staphylococcus epidermidis is an increasingly recognized causative organism of vascular graft infections. To increase our understanding of this problem we have tried to establish Staph. epidermidis vascular graft infection in sheep by direct inoculation. A 2 cm long, 5 mm diameter polytetrafluoroethylene (PTFE) or a gelatin sealed Dacron vascular graft was inserted into the left carotid artery. At the completion of the operation 1 mL of normal saline containing either 10(4), 10(6), or 10(8) colony forming units (cfu) of a slime producing Staph. epidermidis was inoculated directly onto the graft. After 3 weeks the grafts were harvested in a sterile fashion. Swabs were taken of the perigraft tissues and the external and internal aspects of the grafts; a 3-5 mm segment of the graft was incubated in broth medium and a second segment was ground for 5 min and then incubated in broth medium. Note was made of the presence of abscess formation, anastomotic failure or thrombosis. Thirteen sheep received a PTFE graft and 14 received a gelatin sealed Dacron graft. Three sheep died immediately postoperatively. The rate of infection was 40% at 10(4), 67% at 10(6) and 80% at 10(8) cfu Staph. epidermidis. In only four cases were all five cultures positive. In nine cases two or less cultures were positive, the majority of these being the broth cultures. Nine other organisms were isolated from nine mixed infections. Nine out of 13 PTFE and seven out of 11 Dacron grafts were infected.(ABSTRACT TRUNCATED AT 250 WORDS)

Rifampicin impregnated Dacron grafts: no development of rifampicin resistance in an animal model

AIM

Rifampicin impregnated Dacron grafts have been shown to be effective at preventing vascular graft infection in different animal models. The development of resistance to rifampicin would be a major drawback to the widespread use of such a graft. We aimed to determine how readily this would occur by using a sheep animal model.

METHODS

Under general anaesthetic a 2cm long, 5mm diameter Dacron interposition graft inpregnated with 1.2 mg/ml rifampicin was placed in the left carotid artery. An extreme challenge of methicillin resistant Staphylococcus aureus (MRSA) using an inoculum of 10(9) colony forming units was placed directly onto the graft. The grafts were harvested at 3 weeks and cultures of the graft and tissues were taken. The presence or absence of any abscess formation, anastomotic disruption and graft thrombosis was noted. Any positive growths were identified and if found to be the same as the inoculum, the bacteria were used as the inoculum for another sheep. This was repeated once more. Thus we started with three sheep initially and used a total of nine sheep.

RESULTS

There were no deaths. All grafts were infected with the same MRSA strain, confirmed on phage typing. There were three abscess and one anastomotic disruption. Seven of the grafts were occluded. The minimal inhibitory concentration (MIC) of the infecting inoculum and the bacteria retrieved were determined using the agar dilutional method. The MIC for the three initial inocula was < 0.007 mg/l. All subsequent strains isolated had an MIC of < 0.015 mg/l. This was a difference of one dilution and not significant.

CONCLUSION

There was no development of rifampicin resistance using this animal model.