Bacterial Colonization of Thrombosed Dialysis Arteriovenous Grafts

Changes in umbilical catheters' microstructure in vivo: A prospective study

BACKGROUND

Umbilical vessels present after birth allow a unique central access for both venous and arterial catheterization, yet the catheterization complications can be misdiagnosed as the complications of prematurity per se.

METHODS

A prospective observational study of 41 used polyurethane umbilical catheters, both venous and arterial was conducted in a tertiary neonatal intensive care unit. The study consisted of bedside ultrasound imaging and post-removal microbiological and microstructural analysis to assess the in vivo catheters' changes and their clinical significance.

RESULTS

The study has shown that catheters' surface thrombosis and bacterial colonization happen more often within umbilical venous than within arterial catheters (31% vs 8% in both cases) and are inversely proportional to the patient's gestational age (thrombosis: Me: 28 weeks vs no thrombosis: 32 weeks; p = 0.05, bacterial colonization: 27 weeks vs no colonization: 30 weeks; p = 0.013), respectively. The clots formed near the catheter's tip are correlated with catheter's bacterial colonization. Chemical analysis with energy dispersive spectroscopy showed a higher calcium composition in used catheters (19.89% vs 0%, p = 0.016) and structure analysis in the scanning electron microscopy proved that within hours catheters become covered with an external coating of a constant thickness, not affected by the catheterization time.

CONCLUSION

The following observations give a better insight to the complex in vivo interactions and call for a more intense bedside-monitoring of the indwelling devices.

Transient bacteremia promotes catheter-related central venous thrombosis through neutrophil extracellular traps

Formation of intravenous catheter-related thrombosis leads to central venous stenosis in patients requiring renal replacement therapy or chemotherapy infusion, yet the triggering or mechanisms remain unclear, especially in patients without symptoms of infection. In this study, we found that neutrophil extracellular traps (NETs) could be detected in the fibrin sheaths from dialysis patients without clinical manifestations of infection. Confocal microscopy revealed bacteria imbedded in NETs in the fibrin sheaths. Thirty-nine of 50 (78%) fibrin sheath specimens contained bacteria detectable by 16S ribosomal RNA genome typing with a predominance of Staphylococcus aureus (69%). In rat models, transient bacteremia of S. aureus induced NETs in enlarged fibrin sheaths, and treatment with DNase I alone significantly reduced both NET and fibrin sheath formation surrounding the catheter. Therefore, transient bacteremia could be a silent trigger that induces NET-related immunothrombosis enhancing catheter-related central venous stenosis.

Current Concepts in Hemodialysis Vascular Access Infections

Infection-related causes are second only to cardiovascular events for mortality among end-stage renal disease patients. This review will provide an overview of hemodialysis catheter-, graft-, and fistula-related infections with emphasis on diagnosis and management in specific settings. Use of catheters at the initiation of dialysis has remained unchanged at 80%. Of all access-related bloodstream infections (BSIs), 70% occur in patients with catheters. The risk factors for BSIs in tunneled, cuffed catheters include the duration of the catheter, past catheter-related bacteremia, left-sided internal jugular vein catheters, hypoalbuminemia, and immunosuppression. Surprisingly, human immunodeficiency virus infection has not been associated with a higher risk of catheter-related bacteremia. Catheter-related bloodstream infection is a clinical definition that requires specific laboratory testing to identify the catheter as the source of the BSI. A central line-associated bloodstream infection is a primary BSI in a patient who had a catheter within the 48-h period before the development of the BSI with no other identifiable source. Guidewire exchange of catheter is a viable alternative in select patients to aid in preserving venous access sites. Catheter lock therapy can decrease infectious complications and mortality. Arteriovenous graft infections are prevalent with significant morbidity. Studies evaluating the impact of stent use in infection risks of the arteriovenous graft are sorely needed.

When the source of inflammation is hiding in plain sight: Failed kidney transplants, clotted arteriovenous grafts, and central venous catheters

Cardiovascular mortality accounts for most deaths among hemodialysis patients and far exceeds the cardiovascular mortality rate of the general population. One important aspect of cardiovascular risk among dialysis patients is chronic inflammation. Iatrogenic sources of chronic inflammation in the form of failed renal allografts, old clotted arteriovenous grafts, and hemodialysis catheters play important, sometimes, unrecognized roles in this inflammatory state. There is ample observational evidence that these sources of inflammation are associated with hypoalbuminemia, erythropoetin-resistant anemia, and increased markers of chronic inflammation. In dialysis patients with chronic inflammation from potentially modifiable sources, causes should be sought and correction undertaken if possible. Allograft nephrectomy should be offered to patients with a chronic inflammatory state and a failed renal transplant. Unused, clotted AV grafts should be considered a likely source of chronic inflammation as well as infection and should be removed when evidence of infection is present on indium scanning. Catheter rates ought to be kept to a minimum for the many well-recognized reasons for their undesirability as well as for their potential to produce chronic inflammation with all of its ill effects.

New therapeutic options provided by off-label deployment of stent graft for tailored arteriovenous access salvage: Two cases

A tailored therapy to patient requirements by combining endovascular and surgical steps can be necessary to prolong the life of a vascular access. Stent grafts play a growing role for the therapy of dialytic access complications. Randomized multi-center trials, however, support the on-label use of stent grafts in the treatment of graft venous outflow and in-stent restenosis. The main contraindication to their use is an ongoing infection. We report two cases of new off-label application of Viabahn (Gore, flagstaff, USA) stent graft. In the first case, the failure of a radiocephalic early cannulation graft was treated by stent graft placement on the arterial inflow anastomosis, when emergent angiographic examination revealed the previously unknown high takeoff of the radial artery from the axillary artery. At 13-month follow-up, the target lesion remained untreated. In the second case, elbow stent graft occlusion with extended thrombosis occurred in a right radiocephalic fistula after 3 years of unassisted patency. Being the last option for vascular access, successful endovascular recanalization was carried out. After 3 months, however, the clinical setting relapsed. A two-stage hybrid strategy with vascular surgeon was arranged due to ongoing signs of local infection. Flow was restored by emergent thromboaspiration associated with a new stent graft placement as a endovascular bridge to subsequent surgical treatment. After 2 days, the overlapped stent grafts were excised as planned. Surgical rerouting was completed by polytetrafluoroethylene prosthetic bridge implantation across the elbow. At 4 months, the follow-up remained uneventful. In selected instances, the off-label use of stent grafts may expand the therapeutic options of the vascular access team.