Effect of mechanical brushing on survival and hemodynamic characteristics of tunneled hemodialysis catheters.

PURPOSE: Tunneled catheters used for hemodialysis treatment often become dysfunctional due to deposition of clotting material within the catheter lumen. In a retrospective study design we investigated the effect of mechanical brushing of dysfunctional tunneled catheters using a metal guide wire with simultaneous installation of urokinase. MATERIALS AND METHODS: During a period of 26 months all together 24 different catheters in 21 chronic hemodialysis patients were brushed due to insufficient blood flow or increased arterial or venous line pressures resulting in repeated alarms during dialysis treatments. RESULTS: Median functional survival after brushing was 45 days with 8 catheters being exchanged (n=5) or rebrushed (n=3) within 10 dialysis sessions (4 weeks). After 2 months all together 13 (54%) catheters were exchanged due to repeated dysfunction and by 3 months functional survival was only about 35%. The catheters needing exchange were characterized by low flow and high arterial line resistance already in the dialysis sessions immediately following the brushing procedure. Median survival of the exchanged catheters was considerably longer (>400 days) as compared to the brushed catheters. CONCLUSIONS: In conclusion mechanical brushing of dysfunctional tunneled hemodialysis catheters can prolong short term function but only affects long term catheter survival in a minority of the patients.

Computational fluid dynamics simulation of a-v fistulas: from MRI and ultrasound scans to numeric evaluation of hemodynamics.

PURPOSE: A-v anastomosis entails dramatic changes in hemodynamic conditions, which may lead to major alterations to the vessels involved; primarily dilatations and devastating stenoses. Wall shear stress is thought to play a key role in the remodeling of the vessels exposed to abnormal levels and oscillating wall shear stress. In this study we sought to develop a framework suitable for thorough in vivo analyses of wall shear stress and vessel morphology of a-v fistulas in patients. METHODS: Using ultrasound and magnetic resonance imaging (MRI) transverse image stacks from six patient a-v fistulas were obtained. From the image stacks three-dimensional geometries of the patient fistulas were created using dedicated segmentation software. Geometries of three a-v fistulas were imported into finite element software in order to perform fluid flow simulations of blood flows and frictional forces on the vessel walls in the a-v fistulas. Boundary conditions for the simulations were obtained using both a MRI phase contrast and an ultrasound Doppler technique. RESULTS: The segmentation of the six fistulas of very different age and morphology (two end-to-side and four side-to-side) showed the ability of the approach to create geometries of various fistula morphologies. Simulations of the three fistulas showed an instant picture of the present status of the exposure to different levels of wall shear stress and the morphological status in the vessel remodeling process. CONCLUSION: The study demonstrated the capability of the CFD framework to analyze patient a-v fistulas on a regular basis using both MRI and ultrasound-based approaches.

Measurements of cortical interstitium in biopsies from human kidney grafts: how representative and how reproducible?

BACKGROUND: The aim of the study was to evaluate how well a biopsy from one region of a human renal allograft represented biopsies from other regions regarding the renal interstitial tissue assessed by stereology. Furthermore, we wanted to evaluate the reproducibility of the measurements. METHODS: Punch biopsies (3 mm) from six regions in each kidney were obtained from seven explanted renal grafts with varying degrees of clinically diagnosed chronic and acute rejection. One kidney, removed for a minor pelvic tumour, served as reference material. Using point counting on PAS-stained sections, the volume fraction of the interstitial tissue per glomerular cortex V(V)(interstitium/cortex) was estimated. From each kidney, two of the six biopsies were re-evaluated by the same observer. RESULTS: V(V)(interstitium/cortex) varied from 0.25 to 0.78 between the explanted kidneys vs 0.26 in the reference kidney. Variations within the kidneys were low, expressed by standard deviations (SD) of between 0.04 and 0.06, and coefficients of variation (CV) between 0.06 and 0.22. The SD estimated from repeated measurements was 0.04 and CV was 0.07. CONCLUSIONS: Biopsies from one region of the kidney were found to be representative for estimates of interstitial tissue in explanted human kidney grafts, and the degree of reproducibility was high when using point counting, as in the present study.