Fistula Dysfunction Research Articles

A Single-Center Retrospective Analysis of the Efficacy of a New Balloon Catheter in Autogenous Arteriovenous Fistula Dysfunction Resistant to Conventional Balloon Angioplasty

The purpose of the study was to present a new alternative balloon catheter option for autogenous arteriovenous fistula (AVF) dysfunction with a stiff constriction resistant to conventional balloon angioplasty. Our first series of 51 patients with autogenous AVF dysfunction who were simultaneously treated with VascuTrak™ balloon catheter, following failed conventional balloon therapy (failure was defined as residual stenosis of >30%), were retrospectively observed and analyzed. The indices that were used to evaluate the clinical efficacy of VascuTrak balloon catheter included the immediate technical success rate, residual stenosis, successful dilation times, degree of pain assessed using the Visual Analog Scale, complications, and follow-up patency rate. The stenotic or occlusive lesions of all 51 cases resistant to conventional balloon angioplasty were promptly eliminated or alleviated (residual stenosis rate≤30%), with a 100% immediate technical success rate. VascuTrak balloon catheters were successful in achieving full dilation under working pressure, of which 44 cases required a 1-time dilation (86.3%) and 7 cases required 2 dilations, which differed significantly from the average of 2.4 dilations required by the preceding conventional balloon therapy (P<0.0001). A statistically significant improvement in the degree of pain experienced by patients who received VascuTrak balloon dilation was observed compared to that of the preceding conventional balloon dilation (P<0.0001). One case of a brachial artery pseudoaneurysm complication occurred in the perioperative period. The primary patency rate was 88.2% at 6months and 74.5% at 12months. The use of VascuTrak balloon catheter to treat autogenous AVF dysfunction resistant to conventional balloon angioplasty appears to be safe and effective, although further, large randomized controlled trials are necessary.

Vigilance on use of drugs, herbal products, and food supplements during pregnancy: focus on fosfomycin

Purpose: Urinary tract infection (UTI) is defined as a common bacterial infection that can lead to significant morbidity such as stricture, fistula, abscess formation, bacteremia, sepsis, pyelonephritis, and kidney dysfunction with a mortality rates reported of 1% in men and 3% in women because of development of pyelonephritis. UTIs are more common in women and the 33% of them require antimicrobials treatment for at least one episode by the age of 24 years. UTIs are the most common infections observed during pregnancy and up to 30% of mothers with not treated asymptomatic bacteriuria may develop acute pyelonephritis which consequently can be associated to adverse maternal and fetal outcomes. All bacteriuria in pregnancy should be treated with antimicrobial treatments being safe for both the mother and the fetus. Approximately one every four women receives prescription of antibiotic treatment during pregnancy, nearly 80% of all the prescription medications during gestation. The use of fosfomycin to treat cystitis in pregnancy generally considered safe and effective. Even though use on antibiotics for urinary tract infections is considered generally safe for the fetus and mothers, this opinion is not based on specific studies monitoring the relationship of among urinary infections, consumption of antibiotics, and pregnancy outcomes. Materials and methods: On this basis we decided to analyze data from the database of our multicenter study PHYTOVIGGEST, reporting data from 5362 pregnancies, focusing on use of fosfomycin. Principal outcomes of pregnancy in women treated with fosfomycin were taken into consideration. Results: Women who have been treated with urinary antibiotics during the pregnancy were 183. With respect to the total number of pregnancies of our sample, these women represented the percentage of 3.49% (187/5362). Analysis of different outcomes of pregnancy such as gestational age, neonatal weight, and neonatal Apgar index did not show any significant difference. At the same time, analysis of data of pregnancy complicancies (such as urgent cesarean delivery, use of general anesthesia, need to induce labor) did not show any difference in women taking fosfomycin during pregnancy and those not taking it. Conclusions: Our data, based on a large number of pregnancies, confirm the safety use of fosfomycin use in pregnancy.

Challenges in Developing New Therapies for Vascular Access Dysfunction.

Vascular access dysfunction impedes the provision of effective hemodialysis. Dysfunction of arteriovenous fistulas (AVFs) largely reflects maturational failure, whereas dysfunction of arteriovenous grafts (AVGs) is mainly driven by recurrent stenosis and thrombosis at the venous anastomosis. There

Matrix-Metalloproteinase-2 Predicts Arteriovenous Fistula Failure in Hemodialysis Patients.

In hemodialysis patients the principal cause of arteriovenous fistula dysfunction is stenosis. Matrix-metalloproteinase-2 is implicated in the pathophysiological mechanism of stenosis development. Our study tried to assess the clinical impact of this protease on arteriovenous fistula survival. Seventy-nine prevalent dialysis patients with functional arteriovenous fistulas were included in the study. The presence of stenosis and the serum levels of matrix-metalloproteinase-2 were determined at the beginning of the study. The patency of the arteriovenous fistulas was followed- up for two years. In multivariate regression; matrix-metalloproteinase-2 was a significant predictor of vascular access loss (HR = 1.104, 95%CI 1.033-1.179, P = 0.003). Patients with a level of matrix-metalloproteinase-2 lower than 50 ng/mL had a better survival of the arteriovenous fistulas. Matrix-metalloproteinase-2 was an even stronger predictor of fistula failure in the stenosis group (HR = 1.076, 95%CI 1.027-1.127, P = 0.002). In our study matrix-metalloproteinase-2 has a predictive value for arteriovenous fistula failure.

Outcomes of intervention for cephalic arch stenosis in brachiocephalic arteriovenous fistulas

BackgroundDevelopment of recalcitrant stenotic lesions of the cephalic arch is a significant cause of dysfunction of brachiocephalic access arteriovenous fistulas (AVFs). Endovascular and surgical therapy can be used to treat cephalic arch stenosis. The aim of this study was to evaluate the outcomes of endovascular and surgical interventions for cephalic arch stenosis. MethodsA retrospective review of all patients during a 16-year period with a compromised but not occluded brachiocephalic AVF due to cephalic arch stenosis was undertaken. Patency, reintervention, infection, and functional dialysis rates were examined. ResultsFrom January 2000 to December 2015, 219 patients (67% female; mean age, 58 ± 20 years) with a failing brachiocephalic AVF underwent intervention at the cephalic arch. These interventions included angioplasty, primary stent placement, transposition, and bypass. The average time to intervention for cephalic arch stenosis was 1.7 years after primary access placement. The average number of percutaneous interventions before the decision to intervene surgically on the cephalic arch was three (range, two to six). Technical success was superior in the surgical groups (70% and 80% compared with 96% and 100% for balloon angioplasty, stenting, transposition, and bypass, respectively; P = .02). Major adverse cardiovascular events were overall low but significantly higher in the surgical groups (1%, 1%, 0.3%, and 0.3% for transposition, bypass, balloon angioplasty, and stenting, respectively; P = .02). Both surgical options carried significantly superior patency rates at 2 years for transposition, bypass, balloon angioplasty, and stenting, respectively (63%, 59%, 90%, and 92%; P = .04). There was a lower rate of interventions per person-year of follow-up in the surgical groups compared with the endovascular groups (1.9, 1.4, 3.5, and 3.1 for transposition, bypass, balloon angioplasty, and stenting, respectively; P = .04). Functional dialysis durations were significantly superior in the surgical groups compared with the endovascular group (P = .03). ConclusionsCephalic arch stenosis is a significant cause of brachiocephalic AVF malfunction. Surgical options offer superior long-term patency and functional results and should be considered earlier in the treatment of this disease.

Effect of angiotensin-converting enzyme blockade, alone or combined with blockade of soluble epoxide hydrolase, on the course of congestive heart failure and occurrence of renal dysfunction in Ren-2 transgenic hypertensive rats with aorto-caval fistula.

We showed recently that increasing kidney epoxyeicosatrienoic acids (EETs) by blocking soluble epoxide hydrolase (sEH), an enzyme responsible for EETs degradation, retarded the development of renal dysfunction and progression of aorto-caval fistula(ACF)-induced congestive heart failure (CHF) in Ren-2 transgenic hypertensive rats (TGR). In that study the final survival rate of untreated ACF TGR was only 14 % but increased to 41 % after sEH blockade. Here we examined if sEH inhibition added to renin-angiotensin system (RAS) blockade would further enhance protection against ACF-induced CHF in TGR. The treatment regimens were started one week after ACF creation and the follow-up period was 50 weeks. RAS was blocked using angiotensin-converting enzyme inhibitor (ACEi, trandolapril, 6 mg/l) and sEH with an sEH inhibitor (sEHi, c-AUCB, 3 mg/l). Renal hemodynamics and excretory function were determined two weeks post-ACF, just before the onset of decompensated phase of CHF. 29 weeks post-ACF no untreated animal survived. ACEi treatment greatly improved the survival rate, to 84 % at the end of study. Surprisingly, combined treatment with ACEi and sEHi worsened the rate (53 %). Untreated ACF TGR exhibited marked impairment of renal function and the treatment with ACEi alone or combined with sEH inhibition did not prevent it. In conclusion, addition of sEHi to ACEi treatment does not provide better protection against CHF progression and does not increase the survival rate in ACF TGR: indeed, the rate decreases significantly. Thus, combined treatment with sEHi and ACEi is not a promising approach to further attenuate renal dysfunction and retard progression of CHF.

Hyperbaric oxygen inhibits venous neointimal hyperplasia following arteriovenous fistulization

Hypoxia following arteriovenous fistulization results in venous neointimal hyperplasia(VNH), potentially causing early arteriovenous fistula(AVF) dysfunction. In this study, we used hyperbaric oxygen(HBO) in a rabbit model of AVF to determine whether it could ameliorate early AVF failure. Chronic renal failure was induced by adenine in 96adult rabbits randomly divided into 3groups(n=32in each group). The sham+HBO group underwent sham operation and received HBO. The AVF alone group underwent fistulization, but did not receive HBO. The AVF+HBO group underwent fistulization and received HBO. Each group was further divided into 4subgroups of 8rabbits each that were euthanized at 1,7, 14or 28days post-operatively. At each time point, blood flow changes in the AVF venous segment were detected using a high-frequency duplex ultrasonography system. Immunohistochemical staining for proliferating cell nuclear antigen(PCNA), and hematoxylin and eosin staining were performed to evaluate VNH. Western blot analysis was performed to confirm the expression of hypoxia-inducible factor(HIF)-1α. At 14and 28days following HBO treatment, blood flow in the AVF+HBO group was greater than that at day0. The AVF+HBO group had a smaller ratio of intima to media area, a lower HIF-1α protein expression, and a smaller percentage of PCNA-positive cells in the proximal vein than did the AVF alone group. Our results thus suggest that continuous HBO treatment following AVF significantly inhibits VNH and promotes blood flow. Therefore, early AVF failure may be prevented by the use of HBO therapy.

Endovascular treatment of dysfunctional arteriovenous fistula in hemodialyzed patients — the results of one year follow-up

Introduction. The arteriovenous fistula (AVF) dysfunction is a common reason for vascular access problem in chronically hemodialyzed patients. It is caused by stenosis or occlusion located either in inflow artery, anastomosis or outflow vein. Revascularization of these pathologies can be achieved in surgical or endovascular (PTA) manner. The aim of this study was to evaluate both immediate and late endovascular treatment results of dysfunctional fistulas in chronically hemodialyzed patients. Material and methods. We included in our observation 106 patients with end stage renal disease, who un-derwent PTA within arteriovenous fistulas. We used conventional and unified techniques of endovascular therapy. Procedural results were evaluated after 1, 3, 6 and 12 months based on fistula sufficiency during hemodialysis. Results. In 96 (90.6%) cases the initial result of PTA was good. We achieved improvement in blood flow through AVF and successful hemodialysis. In 10 cases (9.4%) results were not satisfactory. None of our patients developed neither worsening in the blood flow through AVF nor compromised blood circulation distally to AVF. No serious complications (MI, stroke, death) occurred during procedure or hospital stay. After 12 months, in 52 patients AVF were functioning properly. In 20 cases, because of fistula dysfunction, reintervention was necessary (primary patency 66%). Considering all patients, also these with successful reintervention, 69 AVF were functioning properly after 12 months (secondary patency 86%). Conclusions. To conclude, the immediate and long-term PTA outcomes of arteriovenous fistulas with currently available techniques and equipment are satisfying. PTA is a safe manner of prolonging patency rate of AVF in patients requiring permanent hemodialysis.

Complications of arteriovenous fistula in dialysis patients at Assiut University Hospital

Background Repeated access to the circulation is essential to perform adequate maintenance hemodialysis. Dysfunction of fistulas is the most common reason for secondary intervention and recurrent hospitalization. Aim The aim of this study was to report our experience regarding incidence, diagnosis, and different modalities of treatment of complications of arteriovenous fistula. Patients and methods This study was conducted prospectively on 239 end-stage renal disease patients who presented to the Department of Vascular Surgery of Assiut University Hospital with complicated arteriovenous (AV) accesses from January 2014 to January 2015. All patients underwent detailed history taking, and data were collected on age, sex, cardiovascular risk factors, history of previous accesses, and any complications that developed since the use of the access. Patients were further evaluated using clinical examination, duplex ultrasound, and fistulography if needed. Results There were 137 (42.7%) males and 102 (42.7%) females with a mean age of 57 ± 4 years. Hypertension was the risk factor in 103 (43.1%) patients, whereas diabetes mellitus was present in 45 patients. Of the 239 patients, 57 (23.8%) presented with infected AV access, 42 (17.6%) with thrombosed AV accesses, 33 (13.8%) with bleeding, and 31 (12.9%) with pseudoaneurysms. Venous hypertension was the presenting complication in 26 (10.9%) patients, whereas aneurysmal dilatation, hematoma, and ischemic steal were the presenting complications in 25 (10.5%), 20 (8.4%), and 5 (2.1%) patients, respectively. Conclusion Complications of hemodialysis access create significant problems for nephrologists and the healthcare system. Access interventions are often costly, challenging, and may require specialized surgical expertise. Management of complications associated with AV access is an integral part of planning individual hemoaccess procedures.

Application of pretreatment system for the risk factors of dysfunction in hemodialysis patients with arteriovenous fistula

Objective To analyze the application effect of pretreatment system for the risk factors of dysfunction in hemodialysis patients with arteriovenous fistula. Methods The pretreatment system for the risk factors of dysfunction was used in the maintenance practice of hemodialysis patients with arteriovenous fistula in our hospital since June 2014. Totally 50 patients undergoing maintenance hemodialysis from June 2013 to May 2014 in our hospital were selected as the control group, and 46 patients with similar practice from June 2014 to May 2015 were selected as the experimental group. The differences in related indexes between two groups after intervention were compared. Results The incidence of complications related to arteriovenous fistula, and the dysfunction rate of internal fistula in the experimental group were significantly lower than the control group. However, the score of quality of life in the experimental group was higher than that in the control group (P<0.05). Conclusions The application of pretreatment system for the risk factors of dysfunction in hemodialysis patients with arteriovenous fistula can significantly reduce the incidence of complications and the risk of fistula dysfunction, and improve patients′ quality of life. Key words: Renal dialysis; Nursing care; Internal fistula; Dysfunction; Risk; Prevention

Duplex ultrasound for the prediction of vascular events associated with arteriovenous fistulas in hemodialysis patients.

To determine if duplex ultrasound (US) for arteriovenous fistulas (AVFs) can predict vascular events (VEs; thrombosis and stenosis). Duplex US was performed for vascular access evaluation in 2557 maintenance hemodialysis (HD) patients between October 1, 2013 and March 31, 2016. Of these patients, 2184 patients were finally included in this study. AVF dysfunction was assessed using the brachial artery blood flow volume (Qa; mL/min), arterial blood flow resistance index (RI), and residual diameter of the fistula vein (RD; mm). Proximal, midpoint, and distal aspects of the fistulas were measured. The baseline measurements were the US assessments, and the endpoint was VEs requiring vascular access intervention therapy or vascular surgery. Associations of US findings and VEs were assessed with receiver operating characteristic curve analysis, log-rank analysis, and multivariate Cox hazard models. The mean Qa was 772.8 ± 441.4 mL/min; RI, 0.56 ± 0.1; and RD, 2.37 ± 1.0 mm. The optimal Qa cut-off point was calculated as 581.5 mL/min, RI cut-off as 0.56, and RD cut-off as 1.85 mm. VEs were more frequent in patients with a Qa <581.5 mL/min than in those with a Qa >581.5 mL/min (p<0.001). In multivariate analysis, Qa, ferritin, transferrin saturation, and warfarin use were significantly associated with VEs. US evaluation of AVFs in HD patients is a simple method to predict the risks of thrombosis and fistula dysfunction. Qa, ferritin, transferrin saturation, and warfarin use might be associated with VEs.

A novel factor for primary arteriovenous fistula failure: hyperinsulinism

Introduction: Dysfunction of vascular access is an important reason of morbidity for dialysis patients and it is a major factor affecting the economical burden of hemodialysis. The preferred type of vascular access is creation of an arteriovenous fistula (AVF). However, the problem of fistula maturation rate is still a challenge. Herein, we tried to search the role of hyperinsulinism and insulin resistance as a new predictor of primary AVF failure (pAVFF) that may be a cause of intimal damage.Methods: We included 119 patients (73 male and 46 female) with a diagnosis of end-stage renal disease (ESRD) who had undergone an AVF operation by a vascular surgeon. The AVF was examined for presence of thrill on the first postoperative day. A successful cannulation with two fistula needles with a blood flow of 250 mL/min for at least one complete dialysis session, after 4 weeks of AVF surgery was defined as functioning access. Insulin resistance in our patients was determined by the standard homeostasis model assessment (homa-IR). A logistic-regression analysis was performed to investigate the independent factors related with pAVFF.Findings: Detection of pAVFF occurred in 27 (22.7%) patients. The presence of thrill, amount of daily proteinuria, insulin levels, homa-IR, and serum albumin levels were found to be significantly different between patients with fistula failure and those without pAVFF. The logistic-regression analysis of preoperative factors revealed the following OR (odds ratio) and 95% CI values: homa-IR 1.205 (1.063–1.366) (p = 0.004), serum albumin 0.398 (0.178–0.892) (p = 0.025), and the amount of daily proteinuria 1.307 (1.012–1.688) (p = 0.041). Even after addition of the presence of postoperative thrill on AVF, which was a postoperative strong clinical factor to the analysis, mean homa-IR and mean serum albumin continued to be independent predictors of pAVFF.Discussion: Insulin resistance or hyperinsulinism may be a significant cause of pAVFF, which emphasizes the role of endothelium in fistula dysfunction.

Recurrent tracheoesophageal puncture fistula closure using a previous flap as donor: a case report

Tracheoesophageal puncture (TEP)-site fistula dysfunction is a serious complication of TEP prosthesis. We successfully addressed a recurrent TEP-site fistula dysfunction by utilizing the previously done deltopectoral flap. This avoided a fresh donor site. Utilization of sound plastic surgery principles helps in tackling these problems effectively.

Influence of blood pressure variability on the life of arteriovenous fistulae in maintenance hemodialysis patients.

Although numerous risk factors for arteriovenous fistulae (AVF) dysfunction have been identified, these risk factors do not explain all cases of AVF dysfunction. Because of the importance of blood pressure variability (BPV) in vascular injury, the predictive value of BPV for AVF dysfunction, was evaluated in this prospective cohort study. Twenty-four-hour BP monitoring at the intervals of dialysis was recorded every 3 months in 137 patients. The expression of smooth muscle actin (SMA) and the infiltration of mononuclear cells and T lymphocytes were determined by immunohistochemistry on the specimens of fistula vessels. Eighteen patients developed AVF dysfunction. Cox proportional hazards multivariate analysis revealed a significant relationship between fistula dysfunction and daytime systolic-BPV (d-SBPV), nighttime systolic-BPV (n-SBPV), diabetes mellitus, and initial venous diameter. Patients with AVF dysfunction were observed to have increased SMA expression and more infiltration of inflammatory cells in venous walls compared with the controls. A significant correlation between SBPV and the infiltration of CD68-positive cells was observed. Our study showed that the degrees of SBPV were significantly associated with the risk of AVF dysfunction. Potentially, the increase of SBPV will aggravate venous wall inflammation and may play a role in AVF dysfunction.

Complications associated with closure of defunctioning loop ileostomy in low anterior resection of rectal cancer

To analyze the complications of ileostomy closure and related risk factors. Patients undergoing ileostomy closure in the Department of Colorectal Surgery, Peking University Cancer Hospital from September 2006 to March 2013 were included in this study. Clinical features of these patients were reviewed, the complications rate was calculated, and univariate and multivariate analyses with regard to the risk factors of surgical site infection(SSI) were also conducted. A total of 245 consecutive patients were enrolled in the study. Thirty-nine complications were observed in thirty-three patients, the overall complication rate was 13.5%. Complication after primary closure of defunctioning ileostomy included surgical site infection (n=21, 8.6%), ileus (n=8, 3.3%), preoperatively undiagnosed anastomotic leakage or rectovaginal fistula (n=5, 2.0%), pulmonary infection (n=2, 0.8%), and anal sphincter dysfunction (n=2, 0.8%). No patient died in the perioperative period, and 5 patients (2.0%) underwent reoperation for ileus (n=3), anastomotic leakage (n=1) and rectovaginal fistula (n=1). Multivariate analysis showed that postoperative complications [OR=10.576, 95%CI:2.898-38.597, P=0.000] and total operation time>90 min[OR=4.862, 95% CI:1.758-13.451, P=0.002] were independent risk factors of SSI, and the presence of subcutaneous vacuum drainage [OR=0.063, 95%CI:0.007-0.540, P=0.012] was protective factor of SSI. Surgical site infection is the most common complication after primary closure of defunctioning ileostomy. Subcutaneous vacuum drainage is effective for reducing SSI in patients undergoing primary closure of ileostomy, and it is especially recommended for patients with operation time>90 min.

Non-contrast-enhanced MR angiography for detecting arteriovenous fistula dysfunction in haemodialysis patients

To assess the diagnostic value of non-contrast-enhanced magnetic resonance angiography (NCE-MRA), using time-of-flight and black-blood MRA, in the evaluation of arteriovenous fistulas in haemodialysis patients in comparison to multidetector computed tomography angiography (MDCTA). NCE-MRA and MDCTA were performed on the same day in 21 patients on maintenance haemodialysis with dysfunctional arteriovenous fistulas. The fistulas included three segments: arterial inflow, anastomosis, and venous outflow. Two experienced observers, who were blinded to the results of the NCE-MRA, recorded in consensus the significant stenoses (≥50%) seen on CTA. Two other experienced observers, unaware of the results of CTA, independently recorded significant stenoses (≥50%) in the NCE-MRA. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of NCE-MRA were calculated, with MDCTA as the standard reference. Sixty-three vascular segments in the 21 patients were clearly displayed. For the two observers of NCE-MRA, the accuracy was 98% and 95.4%; sensitivity 96.4% and 96.4%; specificity 97.1% and 94.3%; positive predictive value 96.4% and 93.1%; and, negative predictive value 97.1% and 97.1%. Inter-/intra-observer agreement for detecting stenosis was excellent for NCE-MRA, with a weighted kappa of 0.968 (95% confidence interval [CI], 0.874-1) and 0.936 (95% CI, 0.848-1). Non-contrast-enhanced MRA, using time-of-flight and black-blood MRA, is a reproducible and reliable imaging technique for detecting ≥50% stenosis in dysfunctional haemodialysis arteriovenous fistulas.

Bilateral photoplethysmography analysis for arteriovenous fistula dysfunction screening with fractional-order feature and cooperative game-based embedded detector.

The bilateral photoplethysmography (PPG) analysis for arteriovenous fistula (AVF) dysfunction screening with a fractional-order feature and a cooperative game (CG)-based embedded detector is proposed. The proposed detector uses a feature extraction method and a CG to evaluate the risk level for AVF dysfunction for patients undergoing haemodialysis treatment. A Sprott system is used to design a self-synchronisation error formulation to quantify the differences in the changes of blood volume for the sinister and dexter thumbs' PPG signals. Bilateral PPGs exhibit a significant difference in rise time and amplitude, which is proportional to the degree of stenosis. A less parameterised CG model is then used to evaluate the risk level. The proposed detector is also studied using an embedded system and bilateral optical measurements. The experimental results show that the risk of AVF stenosis during haemodialysis treatment is detected earlier.

Functional diagnostic parameters for arteriovenous fistula.

The inability to detect the arteriovenous fistula (AVF) dysfunction in a timely manner under the current surveillance programs, which are based on either diameter (d), flow rate (Q), or pressure (p) measurements, is one of the major challenges of dialysis treatment. Thus, our aim is to introduce new functional diagnostic parameters that can better predict AVF functionality status. Six AVFs were created between the femoral arteries and veins of three pigs, each pig having two AVFs on either limb. Flow fields and pressure drop (Δp) in AVFs were obtained via numerical analysis utilizing the CT scan and Doppler ultrasound data at 2D (D: days), 7D, and 28D postsurgery. The dataset included 16 (two pigs [four AVFs] for three time points, and one pig [two AVFs] for two time points) repeated measurements over time, and the statistical analysis was done using a mixed model. To evaluate the nature of pressure drop-flow relationships in AVFs, the Δp was correlated with the average velocity at proximal artery (v) and also the corresponding scaled velocity (v*) by the curvature ratio of anastomotic segment. Based on these relationships, two new functional diagnostic parameters, including the nonlinear pressure drop coefficient (Cp ; pressure drop divided by dynamic pressure at proximal artery) and the linear resistance index (R; pressure drop divided by velocity at proximal artery), were introduced. The diagnostic parameters that were calculated based on scaled velocity are represented as R* and Cp *. A marginal (P = 0.1) increase in d from 2D (5.4 ± 0.7 mm) to 7D (6.8 ± 0.7 mm), along with a significant increase in Q (2D: 967 ± 273 mL/min; 7D: 1943 ± 273 mL/min), was accompanied by an almost unchanged Δp over this time period (2D: 16.42 ± 4.6 mm Hg; 7D: 16.40 ± 4.6 mm Hg). However, the insignificant increase in d and Q from 7D to 28D (d = 7.8 ± 0.8 mm; Q = 2181 ± 378 mL/min) was accompanied by the elevation in Δp (24.6 ± 6.5 mm Hg). The functional diagnostic parameters, R and Cp , decreased from 2D (R = 22.4 ± 2.8 mm Hg/m/s; Cp = 12.0 ± 2.6) to 7D (R = 20.8 ± 2.8 mm Hg/m/s; Cp = 8.1 ± 2.6), and then increased from 7D to 28D (R = 35.5 ± 5.7 mm Hg/m/s; Cp = 17.5 ± 3.6) with a marginal significance. However, when the scaled velocity was used to calculate R* and Cp *, the increase in diagnostic parameters from 7D to 28D achieved statistical significance (P < 0.05). In summary, although the differences in the hemodynamic parameters (d, Q, and Δp) from 7D to 28D were insignificant, changes in their combined effects in the form of diagnostic parameters were significant. Therefore, the functional diagnostic parameters are capable of better distinguishing changes in the hemodynamic variations, and thus, could be promising endpoints to diagnose the functionality of AVFs over time.

Prediction of Arteriovenous Fistula Dysfunction: Can it be Taught?

Physical examination (PE) is an excellent means of predicting arteriovenous fistula (AVF) dysfunction. Although quick and inexpensive, PE is seldom used as a tool to assess stenosis by general nephrologists, dialysis nurses, and dialysis technicians. Previous studies have demonstrated that PE can be taught to interventional specialists, but the perception remains that it is too complex to be performed by other health care professionals. We hypothesized that the physical exam can be taught to a nonmedical professional, and that, with time, it would be comparable to the physical exam performed by a full-time interventional specialist. An undergraduate student and an interventional specialist (MD) examined AVF for dysfunction in a tertiary care hospital over a 6-month period. PE was performed on patients who were suspected of having dialysis access dysfunction and were referred for angiography and intervention (n=49). Physical exam findings were categorized blindly by each examiner into four categories of lesion location: inflow, outflow, both, or neither. Data were privately recorded and compared to the gold standard of angiographic results. Potential confounding variables, including age, gender, diabetic status, and location of AVF were recorded. Weighted Cohen's kappa value was used as a measurement of the level of agreement beyond chance between the diagnoses made by physical exam and angiography. The full-time interventional specialist demonstrated correct prediction of lesion location of 89.8% (kappa=0.850), while the undergraduate student had a correct prediction of 77.6% (kappa=0.625). The student's performance, however, differed significantly over time. The student correctly predicted the location of the lesion in 6 (42.9%) of the first 14 patients (kappa=0.082), compared to 32 (91.4%) of the last 35 patients (kappa=0.855). We suggest that physical exam of AVF can be taught to a nonmedical professional in a short duration of time and the predictive value of the exam can be similar to that of an interventional specialist.

Combined functional and anatomical diagnostic endpoints for assessing arteriovenous fistula dysfunction.

Failure of arteriovenous fistulas (AVF) to mature and thrombosis in matured fistulas have been the major causes of morbidity and mortality in hemodialysis patients. Stenosis, which occurs due to adverse remodeling in AVFs, is one of the major underlying factors under both scenarios. Early diagnosis of a stenosis in an AVF can provide an opportunity to intervene in a timely manner for either assisting the maturation process or avoiding the thrombosis. The goal of surveillance strategies was to supplement the clinical evaluation (i.e., physical examination) of the AVF for better and earlier diagnosis of a developing stenosis. Surveillance strategies were mainly based on measurement of functional hemodynamic endpoints, including blood flow (Qa) to the vascular access and venous access pressure (VAP). As the changes in arterial pressure (MAP) affects the level of VAP, the ratio of VAP to MAP (VAPR = VAP/MAP) was used for diagnosis. A Qa < 400-500 mL/min or a VAPR > 0.55 is considered sign of significant stenosis, which requires immediate intervention. However, due to the complex nature of AVFs, the surveillance strategies have failed to consistently detect stenosis under different scenarios. VAPR has been primarily developed to detect outflow stenosis in arteriovenous grafts, and it hasn't been successful in accurate diagnosis of outflow lesions in AVFs. Similarly, AVFs can maintain relatively high blood flow despite the presence of a significant outflow stenosis and thus, Qa has been found to be a better predictor of only inflow lesions. Similar shortcomings have been reported in the detection of functional severity of coronary stenosis using diagnostic endpoints that were based on either flow or pressure. This limitation has been associated with the fact that both pressure and flow change in the presence of a stenosis and thus, hemodynamic diagnostic endpoints that employ only one of these parameters are inherently prone to inaccuracies. Recent attempts have resulted in development of new diagnostic endpoints that can combine the effects of pressure and flow. These new hemodynamic diagnostic endpoints have shown to be better predictors of functional severity of lesions as compared to either flow or pressure based counterparts. In this review article, we discussed the advantages and limitations of current functional and anatomical diagnostic endpoints in AVFs.