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Evaluation of three techniques for documenting Staphylococcus epidermidis vascular prosthetic graft infections
A O Peter1, S Spangler, L F Martin
1Department of Surgery, M.S. Hershey Medical Center, Hershey, PA 17033.
Abstract:
Staphylococcus epidermidis (S. epidermidis) vascular prosthetic graft infections are notoriously hard to detect. Three different techniques of determining whether vascular prosthetic grafts were infected using a dog model were evaluated. Aortic angiograms were compared with nuclear magnetic resonance (NMR) imaging and systemic norepinephrine (NE) kinetics to determine if either newer technique would be more reliable than standard angiograms. Twelve dogs were randomized to control (n = 6) or infected groups (n = 6). All dogs had a 5 cm section of their infrarenal aorta replaced with knitted Dacron vascular prosthetic graft. The grafts in the infected group were contaminated by soaking them in a broth containing S. epidermidis. NE production and clearance rates were calculated for all animals after an infusion of 3H-NE using the steady-state radionuclide tracer methodology. One week following graft insertion, dogs were reanesthetized, and the 3H-NE infusion and measurements were repeated. Standard angiograms and NMR imaging were also performed. Once all tests were performed, the prosthetic grafts were removed for cultures. Comparisons between the initial and final norepinephrine measurements for each group were made using the nonparametric Wilcoxon two-sample test, while comparisons between the groups were made by chi square or the Student's t test. Angiogram results were similar for control and infected animals. Angiograms missed disruption of the proximal anastomosis found in three of the six infected dogs at graft removal. None of the six control animals, while five of the six infected animals, had localized areas of high signal intensity on NMR imaging (P less than 0.01) suggesting abscess formation.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Nuclear magnetic resonance (NMR) imaging is more reliable than standard angiograms for detecting Staphylococcus epidermidis infections in vascular prosthetic grafts. NMR imaging identified abscesses in infected dogs, while angiograms missed graft disruptions.
Area of Science:
- Vascular surgery
- Infectious disease imaging
- Diagnostic techniques
Background:
- Staphylococcus epidermidis infections of vascular prosthetic grafts are difficult to diagnose.
- Early detection is crucial for effective treatment and patient outcomes.
Purpose of the Study:
- To compare the efficacy of aortic angiograms, nuclear magnetic resonance (NMR) imaging, and norepinephrine (NE) kinetics in detecting S. epidermidis vascular prosthetic graft infections in a canine model.
- To determine if newer imaging techniques offer improved reliability over standard angiograms.
Main Methods:
- A canine model was used with 12 dogs randomized into control and S. epidermidis-infected groups, each receiving a Dacron aortic graft.
- Infected grafts were contaminated with S. epidermidis broth.
- Aortic angiograms, NMR imaging, and systemic norepinephrine (NE) kinetics (using 3H-NE tracer) were performed one week post-implantation.
- Prosthetic grafts were cultured post-mortem to confirm infection.
Main Results:
- Angiograms showed similar results in both control and infected groups, failing to detect proximal anastomosis disruptions in three infected dogs.
- NMR imaging revealed localized high signal intensity, indicative of abscess formation, in five of six infected dogs (P < 0.01), while no control dogs showed this finding.
- Norepinephrine kinetics data was also analyzed for diagnostic potential.
Conclusions:
- NMR imaging is a more sensitive and reliable technique than standard angiograms for diagnosing Staphylococcus epidermidis vascular prosthetic graft infections.
- NMR imaging's ability to detect abscess formation offers a significant advantage in identifying these challenging infections.