Vascular graft infection

Background

• May be extracavitary (in the groin or lower extremities) or intracavitary (in the abdomen or thorax)

Microbiology

• Staphylococcus aureus (30-60%)
• Coagulase-negative staphylococci (10-30%)
• Gram-negative bacilli (10-30%), including Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae
• Viridans group streptococci and enterococci (5%)
• Others: Candida species, polymicrobial infections
• Culture-negative (5-30%)

Etiologies

• Intraoperative contamination (most common)
• Contiguous spread from superficial infection or intraabdominal infection
• Direct inoculation during subsequent procedure
• Hematogenous spread, less common after the early postoperative period (first 2 months) due to endothelialization

Clinical Manfestations

• Varies by site of graft and infection
• Can be early-onset (first 2 months) or late-onset (after 2 months)
• Late-onset infections tend to be indolent without sepsis

Samson Classification

• Classification of peripheral arterial prosthetic graft infections 1
• Minor infections
  • Group I: infection no deeper than the dermis
  • Group II: infection of subcutaneous tissue without visible involvement of graft
• Group III: infections involving graft but not anastomosis
• Group IV: infections involving exposed anastomosis without bacteremia or anastomotic bleeding
• Group V: infections involving graft-to-artery anastomosis with bacteremia or anastomotic bleeding

Diagnosis

• Diagnosis is made clinically
• Ultrasound is usually the initial imaging procedure, followed by CTA or MRI if US is equivocal
• CT- or US-guided aspiration can be helpful for a microbiologic diagnosis

Imaging

• Imaging is a mainstay of diagnosis, and is reviewed in 2
• Ultrasound is typically the first-line choice, and can evaluate perigraft collections as well as guide aspiration
• CT-CTA is the first-line choice for intracavitary infections
  • CTA has sensitivity 67% and specificity 63%, but is more sensitive and specific for more complex infections
  • Can be hard to distinguish from post-operative changes
• MRI is less well studied, but may be better able to distinguish perigraft fluid from inflammation and fibrosis than CT
• Radiolabelled WBC scan can be very helpful in distinguishing sterile inflammation from infection and likely has very high sensitivity and specificity

MAGIC Case Definition

• Definitions for aortic graft infection, based on consensus3

	Major Criteria	Minor Criteria
Clinical	Pus (confirmed by microscopy) around graft or in aneurysm sac at surgery Open wound with exposed graft or communicating sinus Fistula development e.g. aorto-enteric or aorto-bronchial Graft insertion in an infected site, e.g. fistula, mycotic aneurysm, or infected pseudoaneurysm	Localized clinical features of AGI, e.g. erythema, warmth, swelling, purulent discharge, or pain Fever ≥38ºC with AGI as most likely cause
Radiologic	Peri-graft fluid on CT scan ≥3 months after insertion Peri-graft gas on CT scan ≥7 weeks after insertion Increase in peri-graft gas volume, demonstrated on serial imaging	Other radiographic finding, e.g. suspicious peri-graft gas, fluid, or soft tissue inflammation, aneurysm expansion, pseudoaneurysm formation, focal bowel wall thickening, discitis/osteomyelitis, suspicious metabolic activity on FDG PET/CT, radiolabeled leukocyte uptake
Laboratory	Organisms recovered from an explanted graft Organisms recovered from an intra-operative specimen Organisms recovered from a percutaneous, radiologically-guided aspirate or peri-graft fluid	Blood cultures positive and no apparent source except AGI Abnormally elevated inflammatory markers with AGI as most likely cause, e.g. ESR, CRP, white cell count

• Interpretation:
  • Diagnosed AGI: one major plus a major or minor criterion from another category
  • Suspected AGI: one major, or two minor criteria from different categories

Management

• Local infection without graft involvement: antibiotics with or without incision and drainage (groups I & II)
  • Duration 2 to 4 weeks
• Infection involving graft but without bacteremia or anastomotic bleeding (groups III & IV)
  • Incision and drainage
  • Preservation of graft, or reconstruction with allograft, autograft, or prosthetic material
  • 4 to 6 weeks of IV followed by 3 to 6 months of oral
• Infection with bacteremia or anastomotic bleeding (group V)
  • Extra-anatomic revascularization followed by graft excision
  • 4 to 6 weeks IV followed by 6 months oral

Further Reading

• Vascular Graft Infections, Mycotic Aneurysms, and Endovascular Infections: A Scientific Statement From the American Heart Association. Circulation. 2016;134:e412-e460. doi: 10.1161/CIR.0000000000000457