Hemodialysis arteriovenous fistula maturity: US evaluation

Obesity-related decrease in intraoperative blood flow is associated with maturation failure of radiocephalic arteriovenous fistula

OBJECTIVE

Successful arteriovenous fistula (AVF) maturation is often challenging in obese patients. Optimal initial intraoperative blood flow (IOBF) is essential for adequate AVF maturation. This study was conducted to elucidate the effect of obesity on IOBF and radiocephalic AVF maturation.

METHODS

Patients with a newly created radiocephalic AVF were included (N = 252). Obesity was defined as a baseline body mass index (BMI) ≥25 kg/m(2), and primary maturation failure was defined as failure to use the AVF successfully by 3 months after its creation. IOBF was measured immediately after construction of the AVF with a VeriQ system (MediStim, Oslo, Norway).

RESULTS

The mean BMI was 24.1 ± 3.9 kg/m(2), and the prevalence of obesity was 31.3%. Particularly, 8.3% (21 patients) had a BMI ≥30 kg/m(2). Primary maturation failure occurred in 100 patients (39.7%), and an IOBF <190 mL/min was closely associated with the risk of maturation failure (relative risk, 3.05; 95% confidence interval, 1.52-6.11). Compared with nonobese patients, obese subjects had a significantly higher prevalence of diabetes and elevated high-sensitivity C-reactive protein levels, whereas diameters of vessels were similar. When the patients were further divided into three groups as BMI <25, 25 to 29.9, and ≥30 kg/m(2), patients in the higher BMI group showed significantly lower IOBF and higher maturation failure rate. According to multivariate analysis, the statistically significant variables that determined maturation failure were obesity, previous vascular disease, increased high-sensitivity C-reactive protein levels, and IOBF <190 mL/min.

CONCLUSIONS

Obese patients had a significantly lower IOBF, and both obesity and low IOBF contributed to the primary maturation failure of AVF. Obesity-associated inflammation and atherosclerosis might play roles in this association.

Preoperative arterial microcalcification and clinical outcomes of arteriovenous fistulas for hemodialysis

BACKGROUND

Arteriovenous fistulas (AVFs) often fail to mature, but the mechanism of AVF nonmaturation is poorly understood. Arterial microcalcification is common in patients with chronic kidney disease (CKD) and may limit vascular dilatation, thereby contributing to early postoperative juxta-anastomotic AVF stenosis and impaired AVF maturation. This study evaluated whether preexisting arterial microcalcification adversely affects AVF outcomes.

STUDY DESIGN

Prospective study.

SETTING & PARTICIPANTS

127 patients with CKD undergoing AVF surgery at a large academic medical center.

PREDICTORS

Preexisting arterial microcalcification (≥1% of media area) assessed independently by von Kossa stains of arterial specimens obtained during AVF surgery and by preoperative ultrasound.

OUTCOMES

Juxta-anastomotic AVF stenosis (ascertained by ultrasound obtained 4-6 weeks postoperatively), AVF nonmaturation (inability to cannulate with 2 needles with dialysis blood flow ≥ 300mL/min for ≥6 sessions in 1 month within 6 months of AVF creation), and duration of primary unassisted AVF survival after successful use (time to first intervention).

RESULTS

Arterial microcalcification was present by histologic evaluation in 40% of patients undergoing AVF surgery. The frequency of a postoperative juxta-anastomotic AVF stenosis was similar in patients with or without preexisting arterial microcalcification (32% vs 42%; OR, 0.65; 95% CI, 0.28-1.52; P=0.3). AVF nonmaturation was observed in 29%, 33%, 33%, and 33% of patients with <1%, 1% to 4.9%, 5% to 9.9%, and ≥10% arterial microcalcification, respectively (P=0.9). Sonographic arterial microcalcification was found in 39% of patients and was associated with histologic calcification (P=0.001), but did not predict AVF nonmaturation. Finally, among AVFs that matured, unassisted AVF maturation (time to first intervention) was similar for patients with and without preexisting arterial microcalcification (HR, 0.64; 95% CI, 0.35-1.21; P=0.2).

LIMITATIONS

Single-center study.

CONCLUSIONS

Arterial microcalcification is common in patients with advanced CKD, but does not explain postoperative AVF stenosis, AVF nonmaturation, or AVF failure after successful cannulation.

Accuracy of doppler ultrasonography in the evaluation of hemodialysis arteriovenous fistula maturity

<sec><title>OBJECTIVE:</title><p> to determine the accuracy of Doppler ultrasonography (USD) for hemodialysis arteriovenous fistula (AVF) maturity.</p></sec><sec><title>METHODS:</title><p> we included patients with no prior AVF. Each patient underwent two USD examinations. After initiation of hemodialysis, we followed the patients during the first month of the access use and verified its adequacy to hemodialysis sessions. At statistical analysis we measured specificity, sensitivity, accuracy, ROC curve (Receiver operator characteristic) curve, TG-ROC (Two graph - receiver operator characteristic) and logistic regression.</p></sec><sec><title>RESULTS:</title><p> we included 76 patients, of which 51 completed the study. They formed two groups, those who have had good adequacy for hemodialysis (45) and those who had not (6). The average flow volume (FV) and the average draining vein diameter (DVD) of each group were, respectively: 940mL/min (95% CI: 829-1052) and 325mL/min (95% CI: 140-510); and 0.48cm (95% CI: 0.45-0.52) and 0.33cm (95% CI: 0.27-0.40). The area under the ROC curve of FV and DVD were 0.926 and 0.766, respectively.</p></sec><sec><title>CONCLUSION:</title><p> the accuracy of the measured volume flow measured at the draining vein to evaluate maturation of hemodialysis arteriovenous fistula was 85%.</p></sec>

Role of vascular function in predicting arteriovenous fistula outcomes: an observational pilot study

BACKGROUND

Many arteriovenous fistula (AVF) fail prior to use due to lack of maturation or thrombosis. Determining vascular function prior to surgery may be helpful to predict subsequent AVF success. This is a feasibility study to describe the vascular function in a cohort of chronic kidney disease (CKD) patients who are awaiting AVF creation.

METHODS

A prospective cohort of 28 CKD patients expected to progress to HD underwent arterial stiffness (pulse wave velocity, PWV) and endothelial function testing (flow mediated dilation FMD, and peripheral arterial tonometry, PAT) one week prior to AVF creation. AVF success was defined as maintaining patency and achieving maturation. Post operative fistula assessment at 8 weeks evaluated maturation (clinical assessment of adequate fistula flowand ultrasound diameter ≥ 0.5 cm).

RESULTS

The median age 72 years (62 - 78), 75% males, eGFR 15 ml/min/1.73 m(2) (12 - 18). 20 (71%) patients had successful AVF surgery with a mature AVF at 8 weeks. Patients with AVF success had higher mean PAT values 1.87 ± 0.52 than those with failed AVF 1.41 ± 0.24 p = 0.03.

CONCLUSIONS

Microvascular endothelial function as measured using PAT may be useful as a predictor of AVF maturation and function. This simple non invasive marker of vascular function may be a useful tool to predict AVF outcomes.

The effect of in-plane arterial curvature on blood flow and oxygen transport in arterio-venous fistulae

Arterio-Venous Fistulae (AVF) are the preferred method of vascular access for patients with end stage renal disease who need hemodialysis. In this study, simulations of blood flow and oxygen transport were undertaken in various idealized AVF configurations. The objective of the study was to understand how arterial curvature affects blood flow and oxygen transport patterns within AVF, with a focus on how curvature alters metrics known to correlate with vascular pathology such as Intimal Hyperplasia (IH). If one subscribes to the hypothesis that unsteady flow causes IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto the outer-curvature of a curved artery. However, if one subscribes to the hypothesis that low wall shear stress and/or low lumen-to-wall oxygen flux (leading to wall hypoxia) cause IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto a straight artery, or the inner-curvature of a curved artery. We note that the recommendations are incompatible-highlighting the importance of ascertaining the exact mechanisms underlying development of IH in AVF. Nonetheless, the results clearly illustrate the important role played by arterial curvature in determining AVF hemodynamics, which to our knowledge has been overlooked in all previous studies.

Primary Intraoperative Transluminal Angioplasty: A New Approach to Reduce the Early Failure of Distal Arteriovenous Fistulas

Purpose

About 8 years ago, we approached an intraoperative transluminal angioplasty (ITA) performed during the arteriovenous fistula (AVF) creation, to treat arterial or venous stenosis diagnosed by a preliminary ultrasound examination. Objective of this study is to validate the efficacy of ITA.

Methods

Early failure (EF) and failure to mature (FTM) were evaluated in 69 AVFs with ITA created in 58 patients in the last 3 years. In the same period, 160 patients received 188 AVFs without ITA and were considered control group. Of the two groups, age, comorbid factors, sex, primary and secondary patency rate (PR) were also analysed.

Results

The two groups were homogeneous for gender and age (70.4 + 11.1 years of ITA group vs. 66.3 + 14.4, p = 0.059). The incidence of diabetes, heart disease and peripheral artery disease was higher in the ITA group (43% vs. 17%, p<0.0001, 35% vs. 6%, p<0.0001 and 56% vs. 15%, p<0.0001, respectively). EF and FTM occurred in seven and eight cases in the ITA group and in 15 and 13 cases in the controls, respectively. Total failure occurred in 24% of ITA group and 14% of the controls (p = 0.2). The primary PR at 6, 12 and 24 months was 78%, 72% and 59% for ITA group and 85%, 78% and 78 % for control group (p<0.01). The secondary PR at 6, 12 and 24 months was 91%, 86% and 80% for ITA group and 95%, 95% and 92% for the controls (p<0.01).

Conclusions

Our ITA approach has allowed satisfactory results in patients at a high risk of AVF failure.

Assisted maturation of native fistula in two patients with a continuous flow left ventricular assist device

Patients who receive a left ventricular assist device (LVAD) are prone to develop end-stage renal disease. Primary arteriovenous fistula (AVF) maturation in these patients may be unsuccessful secondary to the nonpulsatile flow with an LVAD. Two patients with LVADs are described in whom assisted maturation aided long-term AVF patency.

The key role of color Doppler ultrasound in the work-up of hemodialysis vascular access

Vascular access (VA) is the lifeline for the hemodialysis patient and the native arterio-venous fistula (AVF) is the first-choice access. Among the different tests used in the VA domain, color Doppler ultrasound (CD-US) plays a key role in the clinical work-up. At the present time, three are the main fields of CD-US application: (i) evaluation of forearm arteries and veins in surgical planning; (ii) testing of AVF maturation; (iii) VA complications. Specifically, during the AVF maturation, CD-US allows to measure the diameter and flow volume in the brachial artery and calculate the peak systolic velocity (PSV) of the arterial axis, anastomosis and efferent vein, to detect critical stenosis. The borderline stenosis, revealed by the discrepancies between access flow rate and PSV, should be followed up with subsequent tests to detect progression of stenosis; the cases with significant changes in brachial flow should be referred to angiography. In conclusion, clinical monitoring remains the backbone of any VA program. CD-US is of utmost importance in a patient-centered VA evaluation, because it allows the appropriate management of all aspects of VA care. These are the main reasons why we strongly advocate the adoption of a VA surveillance program based on CD-US.

Predictors of sustained arteriovenous access use for haemodialysis

BACKGROUND

Guidelines encourage early arteriovenous (AV) fistula (AVF) planning for haemodialysis (HD). The aim of this study was to estimate the likelihood of sustained AV access use taking into account age, sex, comorbidity, anatomical site of first AVF and, for pre-dialysis patients, eGFR and proteinuria.

METHODS

1,092 patients attending our centre who had AVF as their first AV access procedure between January 1, 2000 and August 23, 2012 were identified from the electronic patient record. The primary end-point was time to first sustained AV access use, defined as use of any AV access for a minimum of 30 consecutive HD sessions.

RESULTS

52.9% (n = 578) of the patients ultimately achieved sustained AV access use. The main reasons for AV access non-use were AVF failure to mature and death. The 3-year Kaplan-Meier probability of sustained AV access use was 68.8% for those not on renal replacement therapy (RRT) (n = 688) and 74.2% for those already on RRT (n = 404) at the time of first AVF. By multivariate analysis in patients not on RRT, male sex (HR 2.22; p < 0.001), uPCR (HR 1.03; p = 0.03) and eGFR (hazard ratio, HR 0.85; p < 0.001) were independent predictors of AV access use. In patients already on RRT, age (HR 0.98; p < 0.001) and peripheral vascular disease (HR 0.48; p = 0.02) were independent predictors of AV access use.

CONCLUSION

Our data suggest that refinement of the current guideline for timing of AV access creation in planning RRT is justified to take into account individual factors that contribute to the likelihood of technical success and clinical need.

Postoperative Assessment of Vascular Access

Vascular access problems lead to increased patient morbidity and mortality. Autologous arteriovenous fistulas (AVFs) are preferred over grafts. An increase in utilization of AVFs results in an increased incidence of early AVF failure and nonmaturation. A thorough evaluation of a new AVF after 4-6 weeks after creation should be considered mandatory. Experienced persons can examine AVF and predict its utility as a dialysis access. Detailed physical examination of the access performed by educated and trained staff can provide, in most cases, adequate information about the main causes for AVF dysfunction in case of nonmaturation or in case of late access complications. Physical examination has been shown to be very accurate in assessing fistula and is not difficult to learn. Doppler ultrasound (DU) is an additional diagnostic method to predict the ultimate maturation of newly created AVFs and is also very useful in further defining problems that have been detected by physical examination. DU also provides additional information that is of the utmost importance for the surgical or interventional treatment. In this review, basic principles of physical examination and of DU examination of early and late AVF/graft complications are shown.

Pre-Operative Ultrasonography and Arteriovenous Fistulae Maturation

Background

Arteriovenous fistulae (AVF) are preferred for haemodialysis access, but maturation is unpredictable.

Results

Clinical examination alone is unreliable for AVF planning. Duplex ultrasonography may provide useful anatomical and physiological data to allow more accurate prediction of likely AVF success.

Conclusion

Selective use of duplex ultrasonography appears to enhance AVF success rates, but there are insufficient data to recommend routine duplex screening of AVF candidates. Agreed vessel criteria are needed.

Mechanical enhancement of AVF maturation

A native arteriovenous fistula (AVF) should be systematically evaluated at 4 to 6 weeks after creation. Any clinical indications of nonmaturation should be promptly followed up and confirmed by detailed duplex ultrasonography looking for a deep vein or inadequate access flow due to stenoses. Once vein depth has been ruled out, a significant stenosis is invariably identified and should therefore be operated on or dilated. Predilation angiography should be performed preferably through the brachial artery. Arterial lesions are frequent causes of nonmaturation of forearm AVFs and should therefore be dilated. The best results are obtained when the juxta-anastomotic vein and the feeding artery are dilated with 6 and 4 mm dilation balloons, respectively. Our opinion is that there is no or only the very rare indication for ligation or embolization of collaterals. Rupture of the weak venous or arterial wall is common (15% of cases), the majority of which can be managed with prolonged balloon tamponade. Nonmaturing AVFs are ideally needled only 7 to 14 days after successful dilation to allow hematomas caused by cannulation and local anesthesia to resorb. Including initial failures, 1-year primary and secondary patency rates reported by interventional radiologists range from 34% to 39% and 68% to 79%, respectively. Results after dilation of diseased radial arteries feeding normal veins are even better, with primary patency rates ranging for 65% to 83%, and secondary patency rates of over 90%. Using an aggressive and multidisciplinary treatment strategy, nonmaturing dialysis fistulas can be identified, evaluated and salvaged with angioplasty.

Hemodialysis Vascular access Construction in the Upper Extremity: A Review

Purpose

This article reviews the conventional vascular access types in the upper extremities for hemodialysis.

Methods

We performed a literature search for autogenous arteriovenous fistula in the upper extremities.

Results

The upper extremities have four potential sites: radio-cephalic or radio-basilic transposition in the forearm, and brachio-cephalic or brachio-basilic transposition in the upper arm. A pre-operative Duplex ultrasound provides valuable information regarding arterial inflow and venous outflow. The surgical approach to fistula formation and final product depends on vein diameter and length as well as proximal vein patency. The discussion focuses on access outcomes and management of common complications.

Conclusions

The upper extremity arteriovenous fistula is the preferred access for hemodialysis. A number of arteriovenous fistulas can be created in the upper extremities. The Duplex ultrasound identifies suitable arteries and veins for successful arteriovenous hemodialysis fistula creation. Arteriovenous hemodialysis fistula has the best long-term patency outcomes and the lowest associated morbidity and mortality. Early detection and intervention can save the fistula when complications occur.

Accuracy of Early Postoperative Clinical and Ultrasound Examination of Arteriovenous Fistulae to Predict Dialysis Use

Aim

The aim of this article is to assess the accuracy of early clinical and ultrasound (US) examination in terms of predicting arteriovenous fistula (AVF) dialysis use.

Methods

Physical and US examination of patent AVF was performed 4 weeks after fistula creation. AVF dialysis use was defined as subsequent use of an AVF for at least six consecutive dialysis sessions with two needles and a blood flow of more than 200 mL/min.

Results

Of 119 AVF patent at 4 weeks, 26 (22%) failed. Clinical examination was 96% sensitive for predicting successful dialysis, but only 21% specific for failure. Vein diameter above 5 mm and an arterial end-diastolic velocity above 110 cm/s were the best US predictors for dialysis use. Vein diameter was slightly better than arterial velocity in terms of predicting maturity (sensitivity: 83% vs 67%, specificity: 68% vs 65%). All assessments predicted AVF maturity (positive predictive value: clinical = 81%, US diameter = 90%, US velocity = 87%) much better than AVF failure (negative predictive value: clinical = 63%, US diameter = 53%, US velocity = 37%).

Conclusion

One month after surgery, a new AVF with a thrill or a vein diameter >5 mm is likely to be used for dialysis. An AVF not meeting these criteria has an increased risk of failure and further investigations may be required.

Fistula eligibility: a work in progress

Effective hemodialysis requires a reliable vascular access. Clinical practice guidelines strongly recommend the fistula as the preferred option followed by arteriovenous (AV) grafts, with central venous catheters being least preferred. Recently, there has been a growing awareness of the limitations of the fistula, its high rate of primary failure and that a fistula may not be appropriate for all patients initiating or on hemodialysis. However, determinates for fistula eligibility have not been clearly defined. The creation and use of a fistula requires the complex integration of patient, biological, and surgical factors, none of which can be easily predicted or planned. There have been several successful initiatives over the last decade addressing patient suitability for AV access, but none have validated defined criteria for fistula eligibility. We discuss these initiatives by addressing: 1) process of care, 2) radiological and nonradiological tests and procedures, and 3) alternative surgical approaches. Careful clinical judgment, appropriate vascular access assessment and placement, and an individualized approach to the risks and benefits will optimize patient health outcomes while minimizing prolonged catheter dependence among hemodialysis patients.

Vein graft adaptation and fistula maturation in the arterial environment

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases, veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared with the venous environment. Successful venous adaptation to the arterial environment is critical for long-term success of the vein graft or AVF and, in both cases, is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low-pressure arterial environment and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high-pressure arterial environment and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.

Arteriovenous Fistula Creation Using the Optiflow™ Vascular Anastomotic Connector: The Open (Optiflow PatEncy and MaturatioN) Study

Purpose

Arteriovenous fistulas (AVFs) are the preferred form of vascular access for hemodialysis. However, non-maturation and patency are major clinical problems. The Optiflow™ device is an implantable anastomotic connector used to standardize the creation of an AVF. Studies have suggested that the geometry of the anastomosis and experience of the surgeon impact patency and maturation rates. The Optiflow serves as a surgical template whereby the geometry and flow path of the anastomosis are predetermined. This prospective study was intended to evaluate maturation, patency and safety of the Optiflow.

Methods

Forty-one upper arm AVFs were created in 41 end-stage renal disease patients using the Optiflow device at two investigational sites. Patients were followed for 90 days with serial Doppler ultrasounds performed at approximately 14, 42 and 90 days to determine AVF maturation. The primary performance endpoint was unassisted maturation, defined as an outflow vein that was equal to or greater than 5 mm in diameter, and with flow equal to or greater than 500 mL/min without the need for any intervention intended to promote or maintain maturation. The primary safety endpoint was the rate of device-related serious adverse events.

Results

Unassisted maturation rates were 76%, 72% and 68% and unassisted patency rates were 93%, 88% and 78%, at 14, 42 and 90 days, respectively. There were no device-related serious adverse events.

Conclusions

The results suggest that the Optiflow is safe for its intended use and could play an important role in enhancing AVF maturation while standardizing the anastomotic technique.

Internal jugular and vertebral vein volume flow in patients with clinically isolated syndrome or mild multiple sclerosis and healthy controls: results from a prospective sonographer-blinded study

OBJECTIVES & METHODS

We evaluated internal jugular vein and vertebral vein volume flow using ultrasound, in patients with clinically isolated syndrome or mild multiple sclerosis and controls, to determine whether volume flow was different between the two groups.

RESULTS

In patients and controls, internal jugular vein volume flow increased from superior to inferior segments, consistent with recruitment from collateral veins. Internal jugular vein and vertebral vein volume flow were greater on the right in supine and sitting positions. Internal jugular vein volume flow was higher in the supine posture. Vertebral vein volume flow was higher in the sitting posture. Regression analyses of cube root transformed volume flow data, adjusted for supine/sitting, right/left and internal jugular vein/vertebral vein, revealed no significant difference in volume flow in patients compared to controls.

CONCLUSIONS

Our findings further refute the concept of venous obstruction as a causal factor in the pathogenesis of multiple sclerosis. Control volume flow data may provide useful normative reference values.

Vascular access for hemodialysis: postoperative evaluation and function monitoring

Vascular access (VA) survival is a crucial issue associated with morbidity and mortality of patients undergoing maintenance hemodialysis. The development of stenosis is the major factor that leads to VA failure. Strategies for early detection of lesions within a VA system before serious complications arise are therefore crucial. The implementation of a VA surveillance program could lead to timely detection of VA dysfunction and referral for correction, reduction in central venous catheter use and decrease in hospitalization and VA-related cost. Suggested methods for arteriovenous fistulae and grafts surveillance include blood flow measurement, static pressure evaluation and duplex ultrasonography. Physical examination is an accepted method in contrast to nonstandardized dynamic pressure measurement for grafts. Access recirculation (not urea based) and dynamic pressure measurements are accepted methods for fistulae. Decreasing URR or Kt/V (otherwise unexplained) and increased (negative) arterial pressure in the dialysis machine are methods of limited sensitivity and specificity for both fistulae and grafts. Measurement of access blood flow has been proposed as the gold standard for the screening of all types of VA. Access flow can be measured by various techniques which are direct or indirect. Several studies about VA surveillance programs have demonstrated conflicting results. Larger, randomized controlled trials need to be carried out in order to clarify whether surveillance programs are necessary and which is the best surveillance strategy for each type of VA.

Objectives and design of the hemodialysis fistula maturation study

BACKGROUND

A large proportion of newly created arteriovenous fistulas cannot be used for dialysis because they fail to mature adequately to support the hemodialysis blood circuit. The Hemodialysis Fistula Maturation (HFM) Study was designed to elucidate clinical and biological factors associated with fistula maturation outcomes.

STUDY DESIGN

Multicenter prospective cohort study.

SETTING & PARTICIPANTS

Approximately 600 patients undergoing creation of a new hemodialysis fistula will be enrolled at 7 centers in the United States and followed up for as long as 4 years.

PREDICTORS

Clinical, anatomical, biological, and process-of-care attributes identified pre-, intra-, or postoperatively.

OUTCOMES

The primary outcome is unassisted clinical maturation, defined as successful use of the fistula for dialysis for 4 weeks without maturation-enhancing procedures. Secondary outcomes include assisted clinical maturation, ultrasound-based anatomical maturation, fistula procedures, fistula abandonment, and central venous catheter use.

MEASUREMENTS

Preoperative ultrasound arterial and venous mapping, flow-mediated and nitroglycerin-mediated brachial artery dilation, arterial pulse wave velocity, and venous distensibility; intraoperative vein tissue collection for histopathologic and molecular analyses; postoperative ultrasounds at 1 day, 2 weeks, 6 weeks, and prior to fistula intervention and initial cannulation.

RESULTS

Assuming complete data, no covariate adjustment, and unassisted clinical maturation of 50%, there will be 80% power to detect ORs of 1.83 and 1.61 for dichotomous predictor variables with exposure prevalences of 20% and 50%, respectively.

LIMITATIONS

Exclusion of 2-stage transposition fistulas limits generalizability. The requirement for study visits may result in a cohort that is healthier than the overall population of patients undergoing fistula creation.

CONCLUSIONS

The HFM Study will be of sufficient size and scope to: (1) evaluate a broad range of mechanistic hypotheses, (2) identify clinical practices associated with maturation outcomes, (3) assess the predictive utility of early indicators of fistula outcome, and (4) establish targets for novel therapeutic interventions to improve fistula maturation.

Preoperative venous intimal hyperplasia, postoperative arteriovenous fistula stenosis, and clinical fistula outcomes

BACKGROUND AND OBJECTIVES

Arteriovenous fistulas often fail to mature, and nonmaturation has been attributed to postoperative stenosis caused by aggressive neointimal hyperplasia. Preexisting intimal hyperplasia in the native veins of uremic patients may predispose to postoperative arteriovenous fistula stenosis and arteriovenous fistula nonmaturation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This work explored the relationship between preexisting venous intimal hyperplasia, postoperative arteriovenous fistula stenosis, and clinical arteriovenous fistula outcomes in 145 patients. Venous specimens obtained during arteriovenous fistula creation were quantified for maximal intimal thickness (median thickness=22.3 μm). Postoperative ultrasounds at 4-6 weeks were evaluated for arteriovenous fistula stenosis. Arteriovenous fistula maturation within 6 months of creation was determined clinically.

RESULTS

Postoperative arteriovenous fistula stenosis was equally frequent in patients with preexisting venous intimal hyperplasia (thickness>22.3 μm) and patients without hyperplasia (46% versus 53%; P=0.49). Arteriovenous fistula nonmaturation occurred in 30% of patients with postoperative stenosis versus 7% of those patients without stenosis (hazard ratio, 4.33; 95% confidence interval, 1.55 to 12.06; P=0.001). The annual frequency of interventions to maintain arteriovenous fistula patency for dialysis after maturation was higher in patients with postoperative stenosis than patients without stenosis (0.83 [95% confidence interval, 0.58 to 1.14] versus 0.42 [95% confidence interval, 0.28 to 0.62]; P=0.008).

CONCLUSIONS

Preexisting venous intimal hyperplasia does not predispose to postoperative arteriovenous fistula stenosis. Postoperative arteriovenous fistula stenosis is associated with a higher arteriovenous fistula nonmaturation rate. Arteriovenous fistulas with hemodynamically significant stenosis frequently mature without an intervention. Postoperative arteriovenous fistula stenosis is associated with an increased frequency of interventions to maintain long-term arteriovenous fistula patency after maturation.

Practical aspects of arteriovenous fistula formation in the pediatric population

The principle of "Fistula First" for hemodialysis has been widely adopted among adults with end-stage renal failure (ESRF). UK national targets aim to have 85 % of prevalent patients using permanent access (arteriovenous fistula or graft). Currently, hemodialysis in children relies heavily on central venous catheters (CVC). However, there is significant evidence that arteriovenous fistulae (AVF) are preferable for long-term dialysis in the pediatric population. We describe the principles of fistula formation including pre-operative work-up, surgical techniques for AVF creation, and post-operative monitoring.

Morphologic and Functional Vessels Characteristics Assessed by Ultrasonography for Prediction of Radiocephalic Fistula Maturation

Purpose

Although native radiocephalic arteriovenous fistula (RCAVF) is the best vascular access for hemodialysis (HD), a major obstacle to increase its use is high frequency of fistulas that fail to mature. The aim of this study was to investigate and define cut-off values of morphologic and functional vessel parameters influencing successful RCAVF maturation using ultrasound.

Methods

A prospective, observational study was performed on 122 patients (66 men) who underwent primary RCAVF creation. Internal diameters of cephalic vein (CVd) and radial artery (ARd), venous distensibility (VD), resistance index (RI) and endothelial function by flow mediated dilatation (FMD) were determined by ultrasound examination before AVF placement. AVF maturation was observed by measuring blood flow (Qa) and CVd 0, 14 and 28 days after creation. Depending on the time when AVFs attained maturity (Qa ≥500 mL/min, CVd ≥5 mm), patients were divided into three groups: (i) successful maturation (after four weeks), (ii) prolonged maturation (within eight weeks) and (iii) failure to mature.

Results

Only 11% of patients failed to achieve a mature RCAVF. Successful AVF maturation occurred in 53% of patients and prolonged maturation in 36% of patients. ROC analysis defined the limits of variables relevant for RCAVF success (CVd >1.8 mm, ARd >1.6 mm, VD >0.4 mm). Female sex was associated with prolonged maturation (OR 0.35, 95% CI=0.17-0.72; P=0.005) having a significantly smaller ARd (1.83 vs. 2.01 mm, P=0.01) but better FMD (2981.5 vs. 2689.5, P=0.02) compared to men.

Conclusions

ARd ≤1.6 mm, CVd ≤1.8 mm and VD ≤0.4 mm are exact cut-off points, which best predict nonmaturation of RCAVF. Women need extended time for adequately matured AVF.

Flash pulmonary oedema after relief of haemodialysis graft stenosis

Heart failure (HF) and chronic kidney disease (CKD) are undoubtedly very much interrelated, especially in patients with end-stage renal disease (ESRD) who are dependent on renal replacement therapy. Haemodialysis (HD) is of particular interest in cardiovascular patients due to the creation of a haemodialysis vascular access and the haemodynamic changes associated with it. Adequate HD though is very dependent on a properly functioning vascular access. Unfortunately, these surgical vascular accesses are vulnerable to stenoses and occlusions. Percutaneous endovascular treatment of these stenoses is often performed and has been found to be safe and effective. Despite its frequent use, acute medical complications of this percutaneous procedure have not been well-documented. In this report, we describe a patient who developed flash pulmonary oedema after balloon angioplasty treatment of an arteriovenous graft (AVG) stenosis.

Vascular remodeling in autogenous arterio-venous fistulas by MRI and CFD

Hemodynamic parameters play an important role in regulating vascular remodeling in arterio-venous fistula (AVF) maturation. Investigating the changes in hemodynamic parameters during AVF maturation is expected to improve our understanding of fistula failure, but very little data on actual temporal changes in human AVFs is available. The present study aimed to assess the feasibility of using a noncontrast-enhanced MRI protocol combined with CFD modeling to relate hemodynamic changes to vascular remodeling following native AVF placement. MR angiography (MRA) and MR velocimetry (MRV) data was acquired peri-operatively, 1 month, and 3 months later in three patients. Vascular geometries were obtained by segmentation of the MRA images. Pulsatile flow simulations were performed in the patient specific vascular geometries with time-dependent boundary conditions prescribed from MRV measurements. A principal result of the study is the description of WSS changes over time in the same patients. The disturbed flow observed in the venous segments resulted in a variability of the WSS distribution and could be responsible for the non-uniform remodeling of the vessel. The artery did not show regions of disturbed flow upstream from the anastomosis, which would be consistent with the uniform remodeling. MRI use demonstrated the ability to provide a comprehensive evaluation of clinically relevant information for the investigation of upper extremity AVFs. 3D geometry from MRA in combination with MRV provides the opportunity to perform detailed CFD analysis of local hemodynamics in order to determine flow descriptors affecting fistula maturation.

A multi-center, dose-escalation study of human type I pancreatic elastase (PRT-201) administered after arteriovenous fistula creation

Purpose

To explore the safety and efficacy of PRT-201.

Methods

Randomized, double-blind, placebo-controlled, single-dose escalation study of PRT-201 (0.0033 to 9 mg) applied after arteriovenous fistula (AVF) creation. Participants were followed for one year. The primary outcome measure was safety. Efficacy measures were the proportion with intra-operative increases in AVF outflow vein diameter or blood flow ≥25% (primary), changes in outflow vein diameter and blood flow, AVF maturation and lumen stenosis by ultrasound criteria and AVF patency.

Results

The adverse events in the PRT-201 group (n=45) were similar to those in the placebo group (n=21). There were no differences in the proportion with ≥25% increase in vein diameter or blood flow, successful maturation or lumen stenosis. There was no statistically significant difference in primary patency between the dose groups (placebo n=21, Low Dose n=16, Medium Dose n=17 and High Dose n=12). In a subgroup analysis that excluded three participants with early surgical failures, the hazard ratio (HR) for primary patency loss of Low Dose compared with placebo was 0.38 (95% CI 0.10-1.41, P=0.15). In a Cox model, Low Dose (HR 0.27, 95% CI 0.04-0.79, P=0.09), white race (HR 0.17, 95% CI 0.03-0.79, P=0.02), and age <65 years (HR 0.25, CI 0.05-1.15, P=0.08) were associated (P<0.10) with a decreased risk of primary patency loss.

Conclusions

PRT-201 was not different from placebo for safety or efficacy measures. There was a suggestion for improved AVF primary patency with Low Dose PRT-201 that is now being studied in a larger clinical trial.

To BAM or not to BAM?: A closer look at balloon-assisted maturation

BACKGROUND

Balloon assisted maturation (BAM) is a recent, innovative, yet controversial method for developing autogenous arterio-venous fistulae (AVF), with little supportive data. Few retrospective studies have addressed the efficacy of BAM and cofactors affecting successful maturation. We conducted a retrospective analysis of our vascular access database to compare possible factors associated with a successful BAM, as determined by increase in volume flow of the fistulae.

METHODS

Between 2009 and 2010, data was prospectively collected on patients undergoing BAM of their AVF under ultrasound guidance at our institution. 30 of these patients, consisting of 143 BAMs, were retrospectively analyzed. Data collection included: past medical history, age, number of BAM procedures preformed, volume flow measurement (VFM) in mid-fistulae, size of balloon used, and presence of post procedural wall hematoma. VFM was determined with duplex within one month prior to and subsequent to each BAM performed.

RESULTS

Of the 30 patients, consisting of 143 BAMs, the average age was 69 years old + 15 (range 38-92) with 20 males and 10 females. The most common risk factors were hypertension (n = 27) and diabetes mellitus (n = 16). The average BAM per patient was 4.8 (range 1-7). Of the 143 BAM procedures, 4 were excluded due to absence of preoperative or postoperative duplex. In 139 BAMs, 74 developed a post procedural hematoma as observed on duplex, and 76 showed an increase in VFM. In all BAMs analyzed, there was no correlation observed between the presence of a hematoma and increase in VFM (P = 0.87). Hematomas occurred most frequently during the second BAM procedure, with 24.3% of all hematomas observed. In 139 BAMs, 8 different balloon sizes were used, 3 mm-10 mm, with the 7mm balloon being the most frequently used (n = 34). No significant difference was noted between increase in VFM in 3 mm to 7 mm balloons. A 8 mm balloon was used in 31 BAMs with 22 developing hematomas. Of the 8mm balloon group, a statistical difference was noted between percent increase in VFM with presence of a hematoma and percent increase in VFM without presence of a hematoma (P = 0.027).

CONCLUSIONS

These preliminary data, suggest that a more aggressive approach to BAM, with use of larger balloons to create hematoma formation and minimizing excessive dilatation procedures, may have a significant impact on performing a successful maturation in respects to increase in VFM.

Clinical significance of upper-arm cephalic vein patency in autogenous radial-cephalic wrist fistulas for hemodialysis

OBJECTIVES

To investigate the significance of upper-arm cephalic veins (UACVs) in radial-cephalic arteriovenous fistulas (RCAVFs), the medical records of 183 patients who had undergone RCAVF creation were reviewed retrospectively.

METHODS

The patients were divided into two groups according to the status of the UACV upon preoperative venography: group A of 153 cases (83.6%) with a patent UACV and group B of 30 cases (16.3%) with a stenosed or occluded UACV. The clinical outcomes were compared.

RESULT

RCAVFs in group B had a significantly higher maturation failure rate (26.7% vs. 9.8%, p = 0.009) and lower primary/secondary patency rates (log-rank test, p < 0.0001) than those in the group A. The patients in group B required more frequent endovascular intervention to maintain access function (p = 0.002). The most common stenosis site was a draining vein in group B, in comparison to juxta-anastomosis in group A. In the multivariate analyses, the status of the UACV was an independent predictor of the primary and secondary patency rates of RCAVFs (p < 0.005).

CONCLUSION

UACV patency has a significant impact on clinical outcome for RCAVFs. When planning an RCAVF placement, venous status including the UACV should be considered.

Ultrasound measurement of brachial artery elasticity prior to hemodialysis access placement: a pilot study

OBJECTIVES

Successful hemodialysis requires reliable vascular access that can deliver adequate blood flow. An arteriovenous fistula is preferred for access because of its longevity and low frequency of complications, but up to 60% of arteriovenous fistulas created surgically are never suitable for hemodialysis because of nonmaturation (insufficient vascular dilatation). Decreased arterial elasticity may impair dilatation, thereby affecting fistula maturation. This study evaluated the feasibility of brachial artery elasticity measurement in patients with chronic kidney disease obtained during routine pre-operative mapping ultrasound (US) imaging before hemodialysis access placement and compared the measurements to those obtained in healthy volunteers.

METHODS

Brachial artery functional US studies were collected from 75 patients undergoing routine preoperative mapping for hemodialysis access and 50 healthy volunteers. Vascular strain was calculated from the change in intima-media thickness between end systole and end diastole, and vascular stress was estimated from the pulse pressure. Assuming a linear elastic medium, the elastic modulus was estimated as the ratio of vascular stress to strain.

RESULTS

Elastic modulus measurements were significantly higher in patients than in volunteers (130 versus 100 kPa; P = .01). With combined volunteer and patient data, there was a significant correlation between elasticity and systolic blood pressure (R2 = 0.23; P < .001). Elasticity was correlated with age in volunteers but not in patients (R2 = 0.14; P = .017; R2 < .001; P = .829, respectively).

CONCLUSIONS

This analysis of clinical arterial vessel biomechanics shows that a noninvasive US measurement can detect elastic modulus differences between patients with chronic kidney disease and healthy individuals. Future studies will correlate the elastic modulus with histologic characteristics and eventual arteriovenous fistula maturation, which may provide supplemental information on arterial biomechanical properties as a useful addition to current predictors of fistula success.

Duplex ultrasound evaluation of hemodialysis access: a detailed protocol

A detailed protocol for the performance and interpretation of duplex ultrasound evaluation of hemodialysis access is described.

Diagnosis of arteriovenous fistula dysfunction

Arteriovenous fistula (AVF) dysfunction remains a major contributor to the morbidity and mortality of hemodialysis patients. The failure of a newly created AVF to mature and development of stenosis in an established AVF are two common clinical predicaments. The goal is to identify a dysfunctional AVF early enough to intervene in a timely manner to either assist with the maturation process or to prevent thrombosis. The currently available tools in our armamentarium include clinical evaluation, physical examination of the AVF, and surveillance tests. Physical examination has been recognized as a simple and cost-effective tool, but is often not implemented either because of lack of training or time constraints. Surveillance tests include measurement of access flow or pressure as a surrogate marker of AVF dysfunction. Surveillance tests often require expensive equipment, additional personnel, and are controversial. Currently, there are guidelines and recommendations to include all of these measures while evaluating an AVF. Implementing judicious use of these tools in clinical practice can facilitate early diagnosis for timely intervention in the appropriate population. Furthermore, this strategy may avoid unnecessary interventions and assist with healthcare cost containment.

The choice of vascular access for therapeutic apheresis

Therapeutic apheresis (TA) is performed using either centrifugation-based or filter-based systems. The blood flow rate (BFR) used for TA using centrifugation-based systems is less than 100 mL/min. Because of this low BFR requirement, even peripheral veins can be considered as an option for TA, especially for less-frequent treatments and those performed for short periods. Other options for vascular access (VA) include central venous catheters (temporary or tunneled), totally implantable ports, and arteriovenous fistulae (AVF) or grafts (AVG). Nontunneled catheters should be considered as the choice of VA for relatively short-term treatments mainly in the inpatient settings. For long-term treatments, ports and tunneled catheters should be considered because of lower rates of infections compared to nontunneled catheters. However, studies in hemodialysis (HD) patients have demonstrated significantly higher morbidity and mortality rates associated with the use of tunneled catheters as compared to AVF. Therefore, if TA is being considered for several years, AVG and AVF would be the preferred options of VA. Studies in HD population indicate far better outcomes with the use of AVF as compared to AVG. This article, as presented at the Therapeutic Apheresis Academy in September 2011, is an overview of the available VA options for TA based on indication and duration of treatment. Pros and cons of each option are mentioned briefly. Finally, for those considered for AVF placement for chronic TA, specific recommendations are made for the care of AVF based on our own experience at University of Virginia.

Experimental validation of a pulse wave propagation model for predicting hemodynamics after vascular access surgery

Hemodialysis patients require a vascular access that is, preferably, surgically created by connecting an artery and vein in the arm, i.e. an arteriovenous fistula (AVF). The site for AVF creation is chosen by the surgeon based on preoperative diagnostics, but AVFs are still compromised by flow-associated complications. Previously, it was shown that a computational 1D-model is able to describe pressure and flow after AVF surgery. However, predicted flows differed from measurements in 4/10 patients. Differences can be attributed to inaccuracies in Doppler measurements and input data, to neglecting physiological mechanisms or to an incomplete physical description of the pulse wave propagation after AVF surgery. The physical description can be checked by validating against an experimental setup consisting of silicone tubes mimicking the aorta and arm vasculature both before and after AVF surgery, which is the aim of the current study. In such an analysis, the output uncertainty resulting from measurement uncertainty in model input should be quantified. The computational model was fed by geometrical and mechanical properties collected from the setup. Pressure and flow waveforms were simulated and compared with experimental waveforms. The precision of the simulations was determined by performing a Monte Carlo study. It was concluded that the computational model was able to simulate mean pressures and flows accurately, whereas simulated waveforms were less attenuated than experimental ones, likely resulting from neglecting viscoelasticity. Furthermore, it was found that in the analysis output uncertainties, resulting from input uncertainties, cannot be neglected and should thus be considered.