Treatment of aortic graft infection by in situ reconstruction with Omniflow II biosynthetic prosthesis

Abstract

Currently available conduits for in situ reconstruction after excision of infected aortic grafts have significant limitations. The Omniflow II vascular prosthesis is a biosynthetic graft associated with a low incidence of infection that has succesfully been used in the treatment of infected infrainguinal bypass. We report on the first use of the Omniflow II prosthesis for in situ reconstruction after aortic graft infection.

A bifurcated biosynthetic bypass was created by spatulating and anastomosing two 8-mm tubular Omniflow II grafts. This bypass was used for in situ reconstruction after excision of infected aortic grafts in three cases. After a mean follow-up of 2.2 years, no occlusion, degeneration, or rupture of the Omniflow II grafts was observed. Although one patient suffered from graft reinfection, the bypass retained structural integrity and no anastomotic dehiscence was observed.

Treatment of aortic graft infection by in situ reconstruction with the Omniflow II vascular prosthesis is feasible. Its resistance to infection and off-the-shelf availability make this graft a promising conduit for aortoiliac reconstruction.

Keywords

Graft infection aortic surgery vascular prosthesis

Introduction

Aortic graft infection is a challenging condition complicating 5% of open abdominal aortic surgeries.¹ Long-term administration of antibiotics with graft retention results in relapse of infection in the majority of cases.² In contrast, surgical revision of infected aortic grafts can provide long-term cure, but is associated with early mortality rates of 7–18%.³ Although long considered the surgical treatment of choice, excision of the aortic graft with extra-anatomic axillobifemoral bypass is associated with inferior outcomes as compared to in situ reconstruction.³

The material to be used for in situ aortic repair remains an area of debate. Reconstruction with autologous vein—either femoral vein or spiral vein constructed from great saphenous veins—increases procedure time and morbidity to the patient.^4,5 Cryopreserved arterial allografts can be used without increasing surgical complexity, but are not readily available to most surgeons.⁶ Finally, prosthetic grafts impregnated with antibiotics or silver can be used off-the-shelf but are associated with higher risk of reinfection.^3,7 Taken together, no ideal conduit for reconstruction after excision of infected aortic grafts has been reported to date.

The Omniflow II vascular prosthesis is a commercially available biosynthetic graft that is composed of a synthetic layer of polyester embedded within an ovine collagen matrix cross-linked by glutaraldehyde. This composite of a durable synthetic mesh covered with biological material was designed to resist long-term degeneration while allowing ingrowth of host tissue, reducing the risk of graft infection. Preclinical studies in dogs show that the collagen tube will eventually be covered with host endothelium, neointima, and adventitia.⁸ The Omniflow II prosthesis has successfully been used for infra-inguinal bypass and arteriovenous shunt surgery with very low infection rates.^9,10 We present the first three cases of aortic graft infection treated by in situ reconstruction with the biosynthetic Omniflow II prosthesis.

Materials and methods

Patients

In this case series, we report all patients with aortic graft infection treated by excision of the infected graft and in situ reconstruction with Omniflow II prostheses at our center until 1st January 2015. Graft infection was defined according to the criteria of the Centers for Disease Control and Prevention and diagnosed by clinical findings, laboratory studies and PET-CT imaging.¹¹ The extent of graft infection was defined according to the modified Bunt classification.¹² In all patients, the great saphenous veins could not be used for reconstruction. No patient had graft-enteric or graft-ureteric fistulae. All patients gave informed consent prior to surgery.

Surgical technique

All patients were electively operated under general anesthesia after administration of antibiotics. A median laparotomy was performed to excise all prosthetic graft material and infected tissue after suprarenal aortic clamping. Two commercially available Omniflow II straight 8-mm vascular prostheses (BioNova, North Melbourne, Australia) were prepared according to the instructions for use. A bifurcated bypass was created by spatulating the tubular grafts for 30 mm and anastomosing the two grafts with a Prolene 4/0 running suture (Figure 1(a) and (b)). After irrigation of the debrided tissue and tunnel tracts with povidone–iodine, the bifurcated Omniflow II graft was anastomosed end-to-end to the infrarenal aorta and end-to-side to the common femoral or external iliac arteries with Prolene 4/0 running sutures (Figure 1(c)). In one patient, a combined cryopreserved aortoiliac bifurcation allograft (Bislife, Leiden, the Netherlands) with Omniflow II graft extensions (end-to-end anastomosis to the allograft iliac arteries with Prolene 4/0 running suture) was used for reconstruction. The femoral anastomoses were not covered with muscle flaps and the skin was closed primarily without the use of vacuum assisted closure devices.

Figure 1.

(a) Construction of a bifurcated biosynthetic graft by anastomosing two spatulated 8-mm Omniflow II vascular prostheses with Prolene 4/0 running suture; (b) bifurcated Omniflow II graft before implantation; and (c) in situ aortobiiliac reconstruction with a bifurcated Omniflow II graft (Case 3).

Follow-up

All patients received oral antibiotic treatment with amoxicilline and clavulanic acid for 6–12 weeks after surgery. Patients were seen in the outpatient clinic with white blood cell counts, erythrocyte sedimentation rate, and C-reactive protein measurements every three months in the first year and every six months thereafter. Grafts were imaged with duplex or CT angiography every six months; a PET-CT scan was made once during follow-up. Fluorodeoxyglucose (FDG) uptake was quantified using the ratio of the maximal standardized uptake values of the aortic graft to the mediastinum.¹³

Results

Case 1

Patient and operative characteristics are summarized in Tables 1 and 2. The first patient was treated with an aortobiiliac bypass for aortoiliac occlusive disease. The surgery was complicated by abdominal sepsis and early infection of the aortic graft. Cultures grew multiresistant enterococcus faecalis, bacteroides fragilis, and candida tropicalis. Four months later, the graft was excised (although prosthetic stumps were left on both iliac anastomoses that retained FDG uptake on PET-CT [Figure 2(a)]) and an axillobifemoral bypass was constructed. Serous fluid collections around the bypass that persisted despite percutaneous drainage led us to excise the axillobifemoral graft and perform an in situ aortobifemoral reconstruction with an Omniflow II vascular prosthesis three years after the index procedure. All cultures including the excised graft were negative. Recovery from surgery was complicated by readmission to the intensive care unit for respiratory insufficiency due to pneumonia. Five months after surgery, a fluid collection around the left femoral limb was drained percutaneously with negative cultures. Since PET-CT showed reinfection of the Omniflow II graft (Figure 2(b)), treatment with amoxicillin and clavulanic acid was started, which controlled infection until the patient died of pulmonary hemorrhage as a consequence of lung carcinoma 11 months later.

Table 1.

Patient characteristics.

	Patient 1	Patient 2	Patient 3
Age (years)	64	67	66
Sex	Female	Male	Male
BMI (kg/m²)	23	24	26
ASA	3	2	2
Hypertension	Yes	Yes	Yes
Hypercholesterolemia	Yes	Yes	No
Diabetes mellitus	No	No	Yes
Coronary artery disease	No	No	No
Myocardial infarction	No	No	No
Peripheral vascular disease	Yes	Yes	No
COPD	Yes	No	No
eGFR (ml/min)	58	90	69
Smoking	Yes	Yes	Yes
Body temperature	Normal	Normal	Normal
Leukocytes (10⁹/L)	2	9	12
C-reactive protein (mg/L)	2	11	103
Erythrocyte sedimentation rate (mm/h)	5	59	99

Note: ASA: American Society of Anesthesiologists; BMI: body mass index; COPD: Chronic obstructive pulmonary disease; eGFR: Estimated glomerular filtration rate.

Table 2.

Operative characteristics.

	Patient 1	Patient 2	Patient 3
Extent of disease	P1	P2	P0
Preoperative antibiotics	Amoxicilline/clavulanic acid/gentamycin	Amoxicillin/clavulanic acid	Cefazolin
Pus	Yes	Yes	No
Bypass	Axillobifemoral	Aortobifemoral	Aortobiiliac
Omentoplasty	No	No	Yes
Duration of surgery (min)	330	240	300
Blood loss (ml)	1800	5800	6000
Length of hospital stay (days)	19	7	14
Length of follow-up (months)	16 (died)	48	16
Preoperative FDG uptake^a	2.6	1.9	3.9
Postoperative FDG uptake^a	5.5	1.1	1.7

Ža

FDG uptake was quantified using the ratio of the maximal standardized uptake values of the aortic graft to the mediastinum.¹³

Figure 2.

PET-CT imaging before and after in situ reconstruction with the Omniflow II vascular prosthesis for aortic graft infection. (a) Focal FDG uptake at the right common iliac artery at the retained stump of the infected aortobiiliac prosthesis; (b) diffuse inhomogeneous FDG uptake at the fluid collection along the left femoral limb of the Omniflow II graft and at the hydronephrosis of the left kidney; (c) focal FDG uptake along both limbs of the infected aortobifemoral prosthesis; (d) reduced diffuse homogeneous FDG uptake along after in situ reconstruction with a cryopreserved aortoiliac bifurcation allograft with Omniflow II extensions; (e) focal FDG uptake at a pseudoaneurysm at the proximal anastomosis of the infected aortobiiliac prosthesis; and (f) Reduced diffuse homogeneous FDG uptake along the Omniflow II graft after in situ reconstruction.

Case 2

The second patient was treated for a symptomatic aneurysm of the infrarenal aorta with an aortouniiliac stent graft and femorofemoral crossover bypass. A second aortouniiliac stent was placed to correct for stent migration and occluded one year later. An axillobifemoral bypass was constructed, but suffered from infection at the axillary anastomosis. The infected bypass was excised along with the aortic stent grafts and circulation to the legs was restored with a rifampicin impregnated silver graft from the aorta to the right external iliac artery and left common femoral artery. Three years later, the left limb of the bypass was revised to treat a pseudoaneurysm at the femoral anastomosis. Since PET-CT showed persisting infection of the aortic graft with a pseudoaneurysm of the aortic anastomosis (Figure 2(c)), the infected aortic graft was excised and replaced with a cryopreserved aortoiliac bifurcation allograft with Omniflow II extensions to both common femoral arteries six years after the index procedure. All cultures including the excised grafts were negative. Two years after surgery, a significant stenosis at the origin of the left external iliac artery of the cryopreserved arterial allograft was treated with percutaneous transluminal angioplasty and stenting. Follow-up PET-CT showed reduced FDG uptake along the aortobifemoral graft without signs of infection (Figure 2(d)).

Case 3

The third patient was treated with an aortobiiliac bypass for an asymptomatic aneurysm of the infrarenal aorta and right common iliac artery. Six years after the index procedure, an asymptomatic pseudoaneurysm of the aortic anastomosis with increased FDG uptake on PET-CT was found (Figure 2(e)). The infected aortic graft was excised and reconstructed with a bifurcated Omniflow II vascular prosthesis to both external iliac arteries. The graft was covered with an omentoplasty. All cultures including the excised graft were negative. Follow-up PET-CT showed reduced FDG uptake along the aortobifemoral graft without signs of infection (Figure 2(f)).

Discussion

This case series reports the first use of the Omniflow II vascular prosthesis for in situ reconstruction after excision of infected aortic grafts. We did not observe late occlusion, degeneration, or rupture of the Omniflow II grafts, and no major limb amputations were performed during follow-up. One patient suffered from reinfection of the Omniflow II prosthesis, which may have been caused by the retained stumps of the infected prosthesis at the iliac anastomoses that continued to show FDG uptake on PET-CT. In spite of reinfection, the Omniflow II graft retained structural integrity and no anastomotic dehiscence was observed during follow-up.

Aortic graft infection is a challenging condition for which various treatment strategies have been proposed. Conservative treatment with antibiotics is generally reserved for patients with high surgical risk and fails to resolve infection in the majority of cases.² In the present case series, conservative treatment had already failed or was not considered appropriate because of anastomotic dehiscence. Surgical treatment consists of excision of the infected graft and restoring blood flow to the legs. To prevent reinfection, either an extra-anatomical axillobifemoral bypass or an in situ reconstruction with autologous vein, arterial allografts, or prosthetic grafts coated with antibiotics or silver can be used. The evidence supporting each type of reconstruction is limited to case series and small cohort studies with heterogeneous patient populations. Furthermore, publication bias is likely as small studies with negative results are underreported.³ In spite of these difficulties, a systematic review and meta-analysis of reconstructions after excision of infected aortic grafts showed that extra-anatomical axillobifemoral bypass is associated with increased rates of early mortality, graft failure, lower limb amputation, and reinfection as compared to in situ reconstructions.³ Furthermore, antibiotic-impregnated prosthetic grafts seem to be associated with greater reinfection rates than biological conduits.^3,7 Recent cohort studies confirm the low long-term complication rates with cryopreserved arterial allograft and autologous femoral vein reconstructions (graft occlusion in 4% and 7%, graft degeneration in 7% and 0%, graft infection in 4% and 0% of cases, respectively).^4,6 Unfortunately, arterial allografts are not readily available to most surgeons, whereas recovery of femoral veins results in prolonged operative times and additional morbidity to the patient.

The biosynthetic Omniflow II prosthesis was introduced for clinical use in infrainguinal bypass and arteriovenous shunt surgery in the 1980s. Its use is associated with good long-term patency and remarkably low infection rates.^9,10 In contrast, a recent animal study showed that the Omniflow II prosthesis was more susceptible to methicillin-resistant Staphylococcus aureus infection than polytetrafluoroethylene (PTFE) prosthesis immediately after subcutaneous implantation.¹⁴ Nevertheless, the Omniflow II prosthesis has successfully been used to replace infected infrainguinal prosthetic grafts.¹⁵ Cryopreserved allografts have a low risk of reinfection, but have been associated with degenerative complications such as early graft rupture in 4–11% of cases.^6,16 These issues are not observed with the Omniflow II vascular prosthesis, with the largest series reporting long-term aneurysmal degeneration in 0–1% of cases.^9,10 This suggests that the polyester layer may confer resistance to graft degeneration of the Omniflow II biosynthetic prosthesis, whereas its resistance to infection may be a result of the cross-linked ovine collagen matrix that allows ingrowth of host vascular tissue.

The diagnosis of aortic graft infection is complex and mainly relies on imaging studies.¹⁷ In all our cases, PET-CT showed enhanced focal FDG uptake of the aortic grafts before surgery and reduced FDG uptake after revision with Omniflow II vascular prostheses. In contrast to the findings of these imaging studies, cultures taken during surgery turned out negative. There is ongoing debate about the optimal imaging modality to diagnose graft infection and about the accuracy of PET-CT in particular. Indeed, uninfected Dacron grafts are associated with diffuse low-grade FDG uptake.¹³ Moreover, the sensitivity and specificity of PET-CT for detection of vascular graft infection vary widely between studies (75–93% and 63–95%, respectively).^18–22 Therefore, further work with larger patient groups is necessary to establish the diagnostic accuracy of PET-CT for aortic graft infection.

In conclusion, we report the first cases of in situ reconstruction for aortic graft infection with the biosynthetic Omniflow II vascular prosthesis. The use of this biosynthetic graft is feasible and resulted in long-term infection control without graft-related complications in our patients. Now that we have demonstrated proof of principle, larger series with longer follow-up are needed to establish its role in vascular reconstruction for aortic graft infection, graft-enteric fistulae, and mycotic aortic aneurysms. Its intrinsic resistance to infection and off-the-shelf availability may well make the biosynthetic Omniflow II prosthesis a promising conduit for aortoiliac reconstruction.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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