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Objective: Clinical guidelines provide recommendations on the minimal blood vessel diameters required for arteriovenous fistula creation but the evidence for these recommendations is limited. We compared vascular access outcomes of fistulas created in agreement with the ESVS Clinical Practice Guidelines (i.e. arteries and veins >2 mm for forearm fistulas and >3 mm for upper arm fistulas) with fistulas created outside these recommendations., Methods: The multicenter Shunt Simulation Study cohort contains 211 hemodialysis patients who received a first radiocephalic, brachiocephalic, or brachiobasilic fistula before publication of the ESVS Clinical Practice Guidelines. All patients had preoperative duplex ultrasound measurements according to a standardized protocol. Outcomes included duplex ultrasound findings at 6 weeks after surgery, vascular access function, and intervention rates until 1 year after surgery., Results: In 55% of patients, fistulas were created in agreement with the ESVS Clinical Practice Guidelines recommendations on minimal blood vessel diameters. Concordance with the guideline recommendations was more frequent for forearm fistulas than for upper arm fistulas (65% vs 46%, p  = 0.01). In the entire cohort, agreement with the guideline recommendations was not associated with an increased proportion of functional vascular accesses (70% vs 66% for fistulas created within and outside guideline recommendations, respectively; p  = 0.61) or with decreased access-related intervention rates (1.45 vs 1.68 per patient-year, p  = 0.20). In forearm fistulas, however, only 52% of arteriovenous fistulas created outside these recommendations developed into a timely functional vascular access., Conclusions: Whereas upper arm arteriovenous fistulas with preoperative blood vessel diameters <3 mm had similar vascular access function as fistulas created with larger blood vessels, forearm arteriovenous fistulas with preoperative blood vessel diameters <2 mm had poor clinical outcomes. These results support that clinical decision-making should be guided by an individual approach., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Objective: Although clinical guidelines on arteriovenous fistula (AVF) creation advocate minimum luminal arterial and venous diameters, assessed by duplex ultrasonography (DUS), the clinical value of routine DUS examination is under debate. DUS might be an insufficiently repeatable and/or reproducible imaging modality because of its operator dependency. The present study aimed to assess intra- and inter-observer agreement of DUS examination in support of AVF surgery planning., Methods: Ten end stage renal disease patients were included, to assess intra- and inter-observer agreement of pre-operative DUS measurements. All measurements were performed by two trained and experienced vascular technicians, blinded to measurement readings. From the routine DUS protocol, representative measurements (venous diameters, and arterial diameters and volume flow in the upper arm and forearm) were selected. For intra-observer agreement the measurements were performed in triplicate, with the probe released from the skin between each. Intraclass correlation coefficients were calculated for intra- and inter-observer agreement, and Bland-Altman plots used to graphically display mean measurement differences and limits of agreement., Results: Ten patients (6 male, 59.4±19.7 years) consented to participate, and all predefined measurements were obtained. Intraclass correlation coefficients for intra-observer agreement of diameter measurements were at least 0.90 (95% CI 0.74-0.97; radial artery). Inter-observer agreement was at least 0.83 (0.46-0.96; lateral diameter upper arm cephalic vein). The Bland-Altman plots showed acceptable mean measurement differences and limits of agreement., Conclusion: In experienced hands, excellent intra- and inter-observer agreement can be reached for the discrete pre-operative DUS measurements advocated in clinical guidelines. DUS is therefore a reliable imaging modality to support AVF surgery planning. The content of DUS protocols, however, needs further standardisation., (Copyright © 2017 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.)

Introduction: The arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis patients. Unfortunately, 20-40% of all constructed AVFs fail to mature (FTM), and are therefore not usable for hemodialysis. AVF maturation importantly depends on postoperative blood volume flow. Predicting patient-specific immediate postoperative flow could therefore support surgical planning. A computational model predicting blood volume flow is available, but the effect of blood flow predictions on the clinical endpoint of maturation (at least 500 mL/min blood volume flow, diameter of the venous cannulation segment ≥4 mm) remains undetermined., Methods: A multicenter randomized clinical trial will be conducted in which 372 patients will be randomized (1:1 allocation ratio) between conventional healthcare and computational model-aided decision making. All patients are extensively examined using duplex ultrasonography (DUS) during preoperative assessment (12 venous and 11 arterial diameter measurements; 3 arterial volume flow measurements). The computational model will predict patient-specific immediate postoperative blood volume flows based on this DUS examination. Using these predictions, the preferred AVF configuration is recommended for the individual patient (radiocephalic, brachiocephalic, or brachiobasilic). The primary endpoint is FTM rate at six weeks in both groups, secondary endpoints include AVF functionality and patency rates at 6 and 12 months postoperatively., Trial Registration: ClinicalTrials.gov (NCT02453412), and ToetsingOnline.nl (NL51610.068.14).

Purpose: Flow reduction is advised in hemodialysis (HD) patients with a high-flow (>2 L/min) arteriovenous fistula (AVF). The revision using distal inflow (RUDI) technique is based on the premise that access flow is attenuated once inflow is provided by a smaller caliber forearm artery. Aim of the study was to evaluate the efficacy of RUDI during a 1-year follow-up., Methods: All HD patients undergoing a RUDI operation using a greater saphenous vein (GSV) or a basilic vein (BaV) interposition for a high-flow access (HFA, >2 L/min) during a 3.5-year time period were included. Serial access flow, percentage of freedom from recurrent high flow and complications were determined., Results: A total of 19 HFA patients were studied (11 males, age 55 ± 3 years). All AVFs were brachial artery based (brachiocephalic, n = 14; brachiobasilic, n = 5). RUDI immediately reduced access flow by almost 2 L/min (3,080 ± 200 to 1,170 ± 160 mL/min (p = 0.001)). Access flows at 1, 6 and 12 months were 1,150 ± 160, 1,460 ± 200 and 1,580 ± 260 mL/min, respectively. Postoperative complications included insufficient flow reduction (n = 1, BaV) and occlusion requiring revision (n = 1, GSV). Recurrent HFA occurred three times (n = 2 BaV, n = 1 GSV). Access flows were significantly (p<0.05) higher in the BaV group compared to the GSV group., Conclusions: RUDI effectively reduces access flow in a brachial artery-based high-flow HD vascular access. A flow-reducing effect is sustained at 1-year follow-up in most patients. GSV is preferred as an interposition graft compared to a BaV.

Purpose: Absolute treatment criteria for reducing the access volume of a high-flow access (HFA, access flow>2 L/min) are absent. Previous studies suggested that a HFA may influence the systemic circulation including blood pressure (BP) and heart rate (HR). The aim of this study was to determine these parameters after access clamping in hemodialysis patients undergoing flow-reducing access surgery., Methods: Systolic BP (SBP), diastolic BP (DBP) and HR in HFA patients undergoing flow-reducing surgery were measured intraoperatively before and after access clamping. Data were compared to values obtained in patients receiving surgery for severe hand ischemia due to an access (HAIDI, hemodialysis access-induced distal ischemia)., Results: In 8 years, 34 patients underwent surgery for HFA (n=23) or HAIDI (n=11). Preoperative access flows in HFA were larger compared to HAIDI (3,026±147 vs 1,078±139 mL/min, respectively, p<0.001). Temporary clamping (15 sec) caused a 12±2 mm Hg increase in SBP (111±6 to 123±6 mm Hg, p<0.05) and a 6±1 mm Hg rise in DBP (57±4 to 63±5 mm Hg, p<0.05) in HFA patients. In contrast, SBP and DBP increases were not significant in HAIDI patients (+6±3 and +2±2 mm Hg, respectively, p=0.37). HR was modestly reduced in both groups following access clamping (-3±1 beats/min). The relationship between access flow volume and alterations in SBP best fitted a quadratic regression model, suggesting cardiovascular exhaustion with progressively higher access flows>2-2.5 L/min., Conclusions: HFA may influence systemic hemodynamics in some hemodialysis patients. The findings of this study may contribute to a tailored management of a high-flow fistula in this population.

Purpose: The aim of this work was to establish the relationship between traditional blood vessel mapping for vascular access (VA) creation by B-mode ultrasound (US) and novel non contrast-enhanced magnetic resonance angiography 
(NCE-MRA), and to study the potential influence of the diameter assessment technique on the choice of hemodialysis vascular access., Methods: A total of 27 end-stage renal-disease patients were included. They received routine US and a NCE-MRA examination of the upper extremity. Diameters were measured manually on US and semi-automatically on NCE-MRA. These measurements were statistically compared for the arteries and veins and for each measurement location. Furthermore, sensitivity and specificity of both modalities to predict VA location was investigated by comparison with an experienced surgeon. This analysis gave insight into the potential influence of vessel mapping modality on decision-making., Results: Comparison of NCE-MRA with US for the arteries and veins, demonstrated a bias of 9% (limits -33%-78%) and 38% (limits -36%-198%), respectively. Statistically significant differences between the modalities on the individual locations were mainly found for the venous locations. The sensitivity and specificity for US to predict VA location was 1.0 and 0.74, respectively, while for NCE-MRA this was 0.88 and 0.39, respectively., Conclusions: The results obtained indicate that extreme caution should be exercised when replacing one diameter measurement modality with the other. A further need exists to improve both vessel mapping protocols to obtain a geometric description of the upper extremity vasculature regardless of acquisition modality.

Introduction: Vascular access (VA) surgery, a prerequisite for hemodialysis treatment of end-stage renal-disease (ESRD) patients, is hampered by complication rates, which are frequently related to flow enhancement. To assist in VA surgery planning, a patient-specific computer model for postoperative flow enhancement was developed. The purpose of this study is to assess the benefit of non contrast-enhanced magnetic resonance angiography (NCE-MRA) data as patient-specific geometrical input for the model-based prediction of surgery outcome., Methods: 25 ESRD patients were included in this study. All patients received a NCE-MRA examination of the upper extremity blood vessels in addition to routine ultrasound (US). Local arterial radii were assessed from NCE-MRA and converted to model input using a linear fit per artery. Venous radii were determined with US. The effect of radius measurement uncertainty on model predictions was accounted for by performing Monte-Carlo simulations. The resulting flow prediction interval of the computer model was compared with the postoperative flow obtained from US. Patients with no overlap between model-based prediction and postoperative measurement were further analyzed to determine whether an increase in geometrical detail improved computer model prediction., Results: Overlap between postoperative flows and model-based predictions was obtained for 71% of patients. Detailed inspection of non-overlapping cases revealed that the geometrical details that could be assessed from NCE-MRA explained most of the differences, and moreover, upon addition of these details in the computer model the flow predictions improved., Conclusions: The results demonstrate clearly that NCE-MRA does provide valuable geometrical information for VA surgery planning. Therefore, it is recommended to use this modality, at least for patients at risk for local or global narrowing of the blood vessels as well as for patients for whom an US-based model prediction would not overlap with surgical choice, as the geometrical details are crucial for obtaining accurate flow predictions.

Purpose: Arteries continuously respond to changing tissue demands and to hemodynamic conditions by altering their diameter and wall structure. The relatively slow dilatation of the feeding artery of vascular accesses continues at least two years after access creation with a continuous decrease in wall shear rate (WSR), which however, remains highly supra-physiological. The aim of this study was to test the hypothesis that after a longer time period the WSR returns to its baseline value., Methods: In a cross-sectional study patients with arteriovenous fistulae were classified into four groups according to the access vintage (from new access to accesses older than six years). The WSR, cross-sectional area, and mean circumferential wall stress were measured and compared between groups., Results: WSR decreased from group 1 (fistula < ninety days old) to group 4 (fistulae > six years old) with a concomitant increase in internal diameter. Patients with the oldest access had normal WSR values (compared to the contralateral brachial artery) and the largest internal diameter of the feeding artery. In diabetic patients the absolute values of WSR were higher and internal diameter was lower compared to nondiabetic patients., Conclusions: Brachial artery WSR is normal in accesses older than six years with an increased internal diameter and wall cross-sectional area as compared to "younger" accesses. This suggests a process of vascular remodeling with an increase in vascular wall mass and normalization of WSR to physiologic values at the price of increased mean cross-sectional wall stress.

Introduction: Inadequate flow enhancement on the one hand, and excessive flow enhancement on the other hand, remain frequent complications of arteriovenous fistula (AVF) creation, and hamper hemodialysis therapy in patients with end-stage renal disease. In an effort to reduce these, a patient-specific computational model, capable of predicting postoperative flow, has been developed. The purpose of this study was to determine the accuracy of the patient-specific model and to investigate its feasibility to support decision-making in AVF surgery., Methods: Patient-specific pulse wave propagation models were created for 25 patients awaiting AVF creation. Model input parameters were obtained from clinical measurements and literature. For every patient, a radiocephalic AVF, a brachiocephalic AVF, and a brachiobasilic AVF configuration were simulated and analyzed for their postoperative flow. The most distal configuration with a predicted flow between 400 and 1500 ml/min was considered the preferred location for AVF surgery. The suggestion of the model was compared to the choice of an experienced vascular surgeon. Furthermore, predicted flows were compared to measured postoperative flows., Results: Taken into account the confidence interval (25(th) and 75(th) percentile interval), overlap between predicted and measured postoperative flows was observed in 70% of the patients. Differentiation between upper and lower arm configuration was similar in 76% of the patients, whereas discrimination between two upper arm AVF configurations was more difficult. In 3 patients the surgeon created an upper arm AVF, while model based predictions allowed for lower arm AVF creation, thereby preserving proximal vessels. In one patient early thrombosis in a radiocephalic AVF was observed which might have been indicated by the low predicted postoperative flow., Conclusions: Postoperative flow can be predicted relatively accurately for multiple AVF configurations by using computational modeling. This model may therefore be considered a valuable additional tool in the preoperative work-up of patients awaiting AVF creation.

Background: Vascular access is the lifeline for end-stage renal disease patients needing hemodialysis treatment. For dialysis treatment two needles are placed into the vascular access. Few studies on needle hemodynamics have been published., Methods: We investigated needle hemodynamics by means of Doppler ultrasonography, both in B-mode and in pulsed Doppler mode., Results: Direct visualization of the needles, turbulence around the arterial needle and blood flow jet from the venous needle are presented., Conclusions: Ultrasound investigation of the hemodynamics of the dialysis needles is feasible. The extreme blood flow jet through the arterial needle was directed in all patients to the anterior vessel wall.

Access flow (Qa) has an important effect on systemic hemodynamics in dialysis patients. A Qa : cardiac output (CO) ratio higher than 0.3 is considered a risk factor for high-output cardiac failure. However, the effect of different types of vascular access in hemodialysis patients has not yet been studied. The aim of the present study was to assess the relationship between Qa and systemic hemodynamics and to compare systemic hemodynamics between patients with elbow/upperarm access with forearm access types. Qa, CO, cardiac index (CI), central blood volume (CBV), and peripheral vascular resistance (PVR) were studied by the saline dilution technique in 58 hemodialysis patients (18 with elbow/upperarm access; 40 with forearm access types). This article found that Qa was significantly and positively related to CO and CI, and inversely related to PVR. CBV, Qa, and presence of cardiac failure were independent determinants of CI. Qa and the Qa : CO ratio were significantly higher, and PVR significantly lower, in patients with elbow/upperarm access compared to patients with forearm access types. When patients with cardiac failure were excluded, CO and CI were also significantly higher in patients with elbow/upperarm access types. Eleven percent of patients with elbow/upperarm fistula had a Qa : CO ratio above 0.3. In conclusion, Qa is strongly related to systemic hemodynamics in dialysis patients. In patients without cardiac failure, CO and CI are significantly higher in patients with elbow/upperarm access compared to patients with forearm access types. However, only a small percentage of patients with elbow/upperarm fistulae appeared to be in the risk zone for development of high-output cardiac failure.