Vascular access for hemodialysis

Successful use of a right atrial catheter for hemodialysis

Maintenance of patent hemodialysis access is a major issue in the chronic dialysis population. Patients on chronic hemodialysis are at risk of progressive loss of possible sites for permanent vascular access. This issue becomes increasingly important in patients who are not suitable candidates for any other mode of renal replacement therapy for a variety of clinical reasons. When all conventional access sites are exhausted, a creative approach is often needed to establish an alternative vascular access for dialysis to maintain life. We report the placement of a tunneled dialysis catheter in the right atrium in such a patient. After 14 months, this catheter is still being used to deliver hemodialysis without any complications.

Effect of Chymase Inhibition on the Arteriovenous Fistula Stenosis in Dogs

It was hypothesized that chymase may participate in hemodialysis vascular access dysfunction, as chymase has been known to be an effective enzyme in the conversion of angiotensin I (Ang I) to Ang II and in the latent TGF-beta1 to the active form. An arteriovenous (AV) fistula was created between the brachial artery and vein in dogs. In the AV anastomosis, when the walls of the venous and arterial sides were compared, the eccentric neointimal formation was most evident in the venous wall. Compared with the venous side downstream of the AV anastomosis, a severe neointimal hyperplasia was found in the venous side upstream of the AV anastomosis (intima/media, 153 +/- 25%). The chymase- and TGF-beta-positive mast cells were markedly accumulated in the proliferous neointima and media. In association with the reduction of chymase expression, a marked decrease in Ang II-, AT(1) receptor-, and TGF-beta-positive areas was achieved by NK3201 (a chymase inhibitor) treatment, and the neointima formation (intima/media: region A, 53 +/- 9%, P < 0.001; region B, 54 +/- 14%, P < 0.001) was also significantly suppressed in this group. Although lisinopril treatment also provided some beneficial effects with regard to the prevention of neointimal formation, the degree was less than that seen with chymase inhibition. These findings indicate that mast cell-derived chymase plays an essential role in the pathogenesis of the AV fistula access failure and that chymase inhibition may be a therapeutic target for the treatment of hemodialysis vascular access dysfunction in clinic settings.

Thrombophilia and the Risk for Hemodialysis Vascular Access Thrombosis

Vascular access thrombosis is the most common and costly complication in hemodialysis patients. The role of thrombophilia in access thrombosis is not established. A case-control study was conducted of 419 hemodialysis patients to determine whether thrombophilia was associated with arteriovenous fistula or graft thrombosis. Participants were enrolled from three in-center and five satellite dialysis units associated with a Canadian academic health science center that provides dialysis services in a catchment area of one million. Patients were tested for factor V Leiden, prothrombin gene mutation, factor XIII genotype, methylenetetrahydrofolate reductase genotype, lupus anticoagulant, anticardiolipin antibody, factor VIII, homocysteine, and lipoprotein (a) concentrations. Overall, 59 (55%) patients with access thrombosis had at least one thrombophilia compared with 122 (39%) patients without access thrombosis (unadjusted odds ratio [OR], 1.91; 95% confidence interval [CI], 1.23 to 2.98). After controlling for important risk factors, the association between any thrombophilia and access thrombosis remained (adjusted OR, 2.42; 95% CI, 1.47 to 3.99). For each additional thrombophilic disorder, the odds of access thrombosis increased significantly (adjusted OR, 1.87; 95% CI, 1.34 to 2.61). This study suggests that thrombophilia is associated with access thrombosis in dialysis patients. Large, multicenter, prospective cohort studies are needed to confirm the observations from this case-control study.

Percutaneous balloon cryoplasty: A new therapy for rapidly recurrent anastomotic venous stenoses of hemodialysis grafts?

Vascular access dysfunction is a major source of morbidity for end-stage renal disease patients on hemodialysis. The arteriovenous graft is a common access type for many of these patients. Frequent stenosis formation and thrombosis complicate this form of access. Patients may have a rapidly forming and recurrent venous stenosis at the graft-vein anastomosis that has been seen in both animal models and end-stage renal disease patients to be the result of neointimal hyperplasia. This venous lesion is particularly resistant and sometimes intractable to conventional angioplasty. As a result, new therapies have been developed to reduce the formation and/or recurrence of neointimal hyperplasia. These include special cutting balloons, drug-eluting stents, and endovascular brachytherapy. The authors present the cases of 5 patients with rapidly recurrent venous lesions at the graft-vein anastomosis that derived benefit from angioplasty with the cryoballoon. The time to stenosis or thrombosis in the arteriovenous grafts was increased from a mean of 3 weeks to more than 16 weeks with this technology. Cryotherapy with the cryoballoon (cryoplasty) may represent a useful therapy for patients with intractable stenoses at or near the venous anastomosis of arteriovenous grafts.

Prospective assessment of hemodialysis access patency after percutaneous intervention: Cox proportional hazards analysis

Vascular access failure is the greatest limitation of successful hemodialysis, but the factors associated with long-term patency have not been fully elucidated. Outcomes in a consecutive series of 294 thrombosed or failing accesses [128 fistulas (43.5%) and 166 grafts (56.5%) in 179 patients] were analyzed with life table and multivariable Cox proportional hazards analysis. Initial success was achieved in 275 of 294 accesses (95.6%). The median patency after intervention was 206 days (interquartile range, 79-457 days). Fistulas had longer median patency after intervention than grafts (286 vs. 170 days). Nonthrombosed accesses had longer median patency than thrombosed accesses (238 vs. 136 days), but thrombosed fistulas had similar median patency as thrombosed grafts (140 vs. 136 days). The selective use of stents as a bailout for failed balloon dilatation did not significantly reduce long-term patency (196 days for stented accesses vs. 210 days for unstented accesses). Long-term patency was inversely related to final access pressure, but access patency was not related to the presence of central venous occlusions, graft age, patient age, sex, or diabetes. Catheter-based intervention of thrombosed and failing dialysis accesses significantly prolongs patency and usefulness of dialysis accesses. The expanding use of fistulas, improved detection of early access failure, and selective use of bailout stents should enhance long-term access patency.

Arterial and venous smooth-muscle cells differ in their responses to antiproliferative drugs

Arteriovenous polytetrafluoroethylene (PTFE) grafts used for hemodialysis often fail as the result of myointimal hyperplasia with vascular smooth-muscle-cell (SMC) proliferation. The stenotic lesions occur primarily at the graft-vein anastomosis and less frequently at the graft-artery anastomosis. To explore the potentials of pharmacologic agents in preventing hemodialysis-graft stenosis, we first examined the susceptibility of venous and aortic SMCs to 3 antiproliferative drugs. Human aortic and saphenous-vein SMCs were cultured in a medium containing insulin, epidermal growth factor, fibroblast growth factor, and fetal bovine serum. Various concentrations of dipyridamole (0-100 microg/mL), paclitaxel (0-100 microg/mL), and tranilast (0-300 microg/mL) were added. After 72 hours, we subjected the cells to a mitochondrial enzymatic (methylthiazoletetrazolium; MTT) assay and a bromodeoxyuridine (BrdU)-incorporation assay as a means of assessing their proliferation. Dipyridamole, paclitaxel, and tranilast each inhibited the proliferation of aortic and venous SMCs in a dose-dependent manner ( P <.0001). Approximately 90% inhibition was achieved at dipyridamole concentrations of 75 microg/mL and greater in both MTT and BrdU assays; paclitaxel and tranilast were less effective. The venous SMCs were substantially more susceptible to inhibition by all 3 drugs than were the aortic SMCs in the MTT assay. The concentrations required to produce 50% inhibition (IC 50 ) in the venous cells were 5.8 microg/mL (11.5 micromol/L), 9.1 microg/mL (10.7 micromol/L), and 37.4 microg/mL (114.3 micromol/L), respectively, for dipyridamole, paclitaxel, and tranilast. These concentrations were approximately 4.2, 5.3, and 3.0 times lower, respectively, than the corresponding IC 50 values for the aortic cells. The differences in IC 50 between the aortic and venous cells for the 3 drugs were less pronounced in the BrdU assay. The results of this study suggest that strategies for the prevention of stenosis should take into account the fact that lesions at venous anastomoses of arteriovenous grafts may respond differently to drugs than do those at arterial anastomoses.

The salvage of graft occlusion in a maintenace hemodialysis patient with tuberous sclerosis by percutaneous transluminal angioplasty using intravascular ultrasound: case report

End-stage renal failure due to tuberous sclerosis is rare and there is no previous report of a patient with tuberous sclerosis undergoing long-term hemodialysis for over 18 years. The patency rate for a dialysis prosthetic graft is low, however, our patient's graft survived over 16 years. For thrombotic occlusion of a graft, we performed percutaneous thrombectomy and balloon angioplasty and salvaged graft occlusion. Moreover, this case is the first report in which the interventional procedure (mechanical thrombectomy and balloon angioplasty) could be observed by intravascular ultrasound in addition to angiography.

Long-term survival of arteriovenous fistulas in home hemodialysis patients

BACKGROUND

We report the outcome of arteriovenous (AV) fistulas created and managed by a multidisciplinary team in patients on hemodialysis (HD) over 20 years.

METHODS

We analyzed 432 AV fistulas in 301 home HD patients (12% diabetic; median age 47 years) followed for up to 161 months. Observed end points were spontaneous or surgical AV fistula closure, or construction of a new vascular anastomosis. Survival was analyzed for first and second AV fistulas and predictors of outcome for first AV fistulas.

RESULTS

One vascular surgeon constructed 58% of AV fistulas. Three hundred sixty-seven AV fistulas were in the forearm, 64 at or above the elbow, and 1 in the thigh. Four hundred fourteen AV fistulas used in situ vessels, and 18 were autografts. Two hundred thirty-one anastomoses were side-to-side. Only five grafts were placed during this time. There were 131 second and subsequent AV fistulas in 76 patients, 79 (60%) of which required primary construction, and 52 used arterialized vessels from a previous AV fistula. The median time from formation to use for first and second AV fistula, respectively, was 2.39 (SE 0.35) and 3.2 (SE 1.9) months. Assisted survival from first use for first AV fistula was 90% at 1 year, 66% at 5 years, 84% at 1 year, and 72% at 2 years for second AV fistula. AV fistula survival from creation was superior for side-to-side anastomoses (P < 0.0001) and in men (P= 0.05).

CONCLUSION

A multidisciplinary approach has been successful in providing durable AV fistulas for home HD for >95% of consecutive patients entering our program.

Local overexpression of C-type natriuretic peptide ameliorates vascular adaptation of porcine hemodialysis grafts

BACKGROUND

Outflow obstruction at the outflow tract of arteriovenous grafts contributes significantly to the poor patency rates of dialysis grafts in vivo. We addressed the potential of local periadventitial gene therapy at the outflow tract for improving access patency in a validated porcine model of arteriovenous grafts using an adenoviral vector encoding murine C-type natriuretic peptide (Ad.CNP).

METHODS

Gene transfer efficiency and optimal virus concentration were determined using Ad.LacZ on porcine jugular veins in vivo (N= 2). Next, in 14 pigs, arteriovenous grafts were implanted bilaterally between the carotid artery and the jugular vein, followed local venous transduction with Ad.CNP (right) and Ad.mock (left). Transduction efficiency of Ad.CNP was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and cyclic guanosine monophosphate (cGMP) measurements (N= 2). Fourteen days after gene transfer, arteriovenous grafts were excised for histologic analysis (N= 12).

RESULTS

Ad.LacZ transduction (1 x 10E10 IU) of porcine veins resulted in evident expression of beta-galactosidase, mainly in the adventitia. At termination, intima/media ratio was decreased by 37% in CNP-treated veins, predominantly due to medial thickening (Ad.CNP 3.1 +/- 0.6 mm(2) vs. Ad.mock 1.70 +/- 0.3 mm(2); P < 0.01) rather than decreased intimal hyperplasia (NS). Adventitial delivery of CNP resulted in increased external elastic lamina (EEL) (Ad.CNP 11.8 +/- 1.4 mm vs. Ad.mock 9.4 +/- 1.0 mm; P= 0.04) and luminal area (Ad.CNP 10.7 +/- 1.4 mm(2) vs. Ad.mock 8.8 +/- 1.7 mm(2); P= 0.05) at the venous anastomosis.

CONCLUSION

Overexpression of CNP enhances venous medial thickening and increases outward remodeling in the outflow tract of porcine arteriovenous grafts. These findings underscore the potential of local gene-therapeutic interventions in preventing luminal narrowing at the outflow tract of hemodialysis grafts.

Matrix metalloproteinase inhibition reduces intimal hyperplasia in a porcine arteriovenous-graft model

BACKGROUND

The patency of arteriovenous (AV) polytetrafluoroethylene grafts for hemodialysis is impaired by intimal hyperplasia (IH) at the venous outflow tract. IH mainly consists of vascular smooth muscle cells, fibroblasts, and extracellular matrix proteins. Because matrix metalloproteinases (MMPs) are enzymes able to degrade extracellular matrix proteins such as elastin and collagen and also stimulate migration of vascular smooth muscle cells, we hypothesized that BB2983 (a broad-spectrum MMP inhibitor) could reduce IH in AV grafts.

METHODS

In 12 pigs, AV grafts were created bilaterally between the carotid artery and the jugular vein. Six pigs received the oral MMP inhibitor (MMPi), and six pigs served as a control. Four weeks after AV shunting, the grafts and adjacent vessels were excised and underwent histologic analysis. Quantification of elastin content was performed on Elastin von Gieson-stained sections.

RESULTS

At the venous outflow tract, IH was strongly inhibited after MMPi when compared with the control group (1.02 +/- 0.26 mm(2) vs 2.14 +/- 0.38 mm(2); P =.027). The medial area did not differ significantly. In the control group elastin density decreased compared with nonoperated veins. This decrease was not observed in the MMPi group (nonoperated, 6.3% +/- 0.4%; MMPi, 7.2% +/- 0.7% vs untreated, 3.6% +/- 0.5%; P =.0004). Outward remodeling of the vein was not influenced by MMP inhibition.

CONCLUSION

MMPi reduces IH formation at the venous outflow tract of AV grafts in pigs, probably by inhibiting elastin degradation. These data suggest that MMP inhibitors might be useful for minimizing IH in AV grafts, thus prolonging patency rates of AV grafts in patients on hemodialysis.

Comparison of Arteriovenous Grafts in the Thigh and Upper Extremities in Hemodialysis Patients

ABSTRACT. Placement of a thigh graft is an option in hemodialysis patients who have exhausted all upper extremity sites for permanent vascular access. The outcome of thigh grafts has been reported only in retrospective studies. The outcomes of 409 grafts placed at a single institution during a 3.5-yr period were evaluated prospectively, including 63 thigh grafts (15% of the total). Information was recorded on surgical complications, dates of radiologic and surgical interventions, and date of graft failure. The technical failure rate was approximately twice as high for thigh grafts, as compared with upper extremity grafts (12.7versus5.8%;P= 0.046). Intervention-free survival was similar for thigh and upper extremity grafts (median, 3.9versus3.5 mo;P= 0.55). Thrombosis-free survival was also comparable for thigh and upper extremity grafts (median, 5.7versus5.5 mo;P= 0.94). Cumulative survival (time to permanent failure) was similar for thigh and upper extremity grafts (median, 14.8versus20.8 mo;P= 0.62). When technical failures were excluded, the median cumulative survival was 27.6 mo for thigh grafts and 22.5 mo for upper extremity grafts (P= 0.72). The frequency of angioplasty (0.28versus0.57 per year), thrombectomy (1.58versus0.94 per year), surgical revision (0.28versus0.18 per year), and total intervention rate (2.15versus1.70 per year) was similar between thigh and upper extremity grafts. Access loss as a result of infection tended to be higher for thigh grafts than for upper extremity grafts (11.1versus5.2%;P= 0.07). In conclusion, placement of thigh grafts should be considered a viable option among hemodialysis patients who have exhausted all options for a permanent vascular access in both upper extremities. E-mail mdallon@uab.edu

Regular Monitoring of Access Flow Compared with Monitoring of Venous Pressure Fails to Improve Graft Survival

ABSTRACT. Regular vascular access blood flow (Qa) surveillance is recommended to detect graft stenosis; however, there is little evidence that monitoring and correcting with angioplasty improves graft survival. This blinded, randomized, controlled trial of 112 patients studied time to graft thrombosis and graft loss, comparing monthly Qa plus standard surveillance (dynamic venous pressure and physical examination) (treatment group) to standard surveillance alone (control group). Only the treatment group was referred for angiogram if Qa <650 ml/min or a 20% decrease in Qa from baseline. Percutaneous angioplasty was performed for stenosis >50%. The rate of graft thrombosis per patient-year at risk was 0.41 and 0.51 in the control and treatment groups, respectively. Fifty-one interventions (0.93/patient-years at risk) were performed in the treatment groupversus31 interventions (0.61/patient-years at risk) in the control group. There was no difference in time to graft loss (P= 0.890). In a multivariate analysis, aspirin (ASA) therapy at baseline was associated with an 84% reduction in risk of graft thrombosis (odds ratio [OR], 0.14;P= 0.002). Higher baseline Qa (OR, 0.84;P= 0.05) and longer interval since graft insertion (OR, 0.97;P= 0.07) were associated with a decrease in graft thrombosis. Results reveal that graft surveillance that uses Qa increases the detection of stenosis, compared with standard surveillance; however, intervention with angioplasty does not improve the time to graft thrombosis or time to graft loss. E-mail: louise.moist@lhsc.on.ca

Hypercoagulable states and antithrombotic strategies in recurrent vascular access site thrombosis

Vascular access site thrombosis is a major cause of morbidity in patients receiving hemodialysis. The role of hypercoagulable states in recurrent vascular access site thrombosis remains poorly understood. Data are limited regarding systemic anticoagulation to improve access graft patency, because of concern about hemorrhagic complications. We determined the prevalence of hypercoagulable states and clinical outcome (thrombotic and hemorrhagic) after initiation of antithrombotic therapy in a series of patients with recurrent vascular access site thrombosis. We evaluated 31 patients who had sustained 119 thrombotic events that resulted in vascular access graft failure during the year before evaluation. Sixty-eight percent of patients tested had elevated concentrations of antibody to anticardiolipin or topical bovine thrombin, and 18% of patients tested had heparin-induced antibodies. More than 90% of patients had elevated factor VIII concentration, 62% had elevated fibrinogen concentrations, and 42% had elevated C-reactive protein concentrations. Twenty-nine patients were given antithrombotic therapy: 13 with warfarin sodium, 12 with unfractionated heparin (UFH), and 11 with low molecular weight heparin (LMWH). Seven patients received more than one antithrombotic agent, sequentially. Nineteen patients have had no thrombotic events since beginning antithrombotic therapy (10 with warfarin, 3 with UFH, 6 with LMWH). Mean follow-up was 8.6 months (median, 7 months). Eight patients sustained 10 bleeding complications (5 with warfarin, 3 with UFH, and 2 with LMWH). In conclusion, hypercoagulable states are common in patients with recurrent vascular access site thrombosis. Antithrombotic therapy may increase vascular access graft patency, but is associated with significant risk for hemorrhage. Prospective studies are needed to evaluate the role and safety of antithrombotic agents in improving vascular access graft patency.

Randomized controlled trial of clopidogrel plus aspirin to prevent hemodialysis access graft thrombosis

Thrombosis of hemodialysis vascular access grafts represents a major medical and economic burden. Experimental and clinical models suggest a role for antiplatelet agents in the prevention of thrombosis. The study was designed to determine the efficacy of the combination of aspirin and clopidogrel in the prevention of graft thrombosis. The study was a randomized, double-blind trial conducted at 30 hemodialysis units at Veterans Affairs medical centers. Participants undergoing hemodialysis with a polytetrafluoroethylene graft in the arm were randomized to receive either double placebos or aspirin (325 mg) and clopidogrel (75 mg) daily. Participants were to be monitored while receiving study medications for a minimum of 2 yr. The study was stopped after randomization of 200 participants, as recommended by the Data Safety and Monitoring Board because of a significantly increased risk of bleeding among the participants receiving aspirin and clopidogrel therapy. The cumulative incidence of bleeding events was significantly greater for those participants, compared with participants receiving placebos [hazard ratio, 1.98; 95% confidence interval (CI), 1.19 to 3.28; P = 0.007]. Twenty-three participants in the placebo group and 44 participants in the active treatment group experienced a bleeding event (P = 0.006). There was no significant benefit of active treatment in the prevention of thrombosis (hazard ratio, 0.81; 95% CI, 0.47 to 1.40; P = 0.45), although there was a trend toward a benefit among participants who had not experienced previous graft thrombosis (hazard ratio, 0.52; 95% CI, 0.22 to 1.26; P = 0.14). In the hemodialysis population, therapy with aspirin and clopidogrel was associated with a significantly increased risk of bleeding and probably would not result in a reduced frequency of graft thrombosis.

Coagulation: consultative hemostasis

Clinical hematologists are frequently consulted for the care of hospitalized patients with complicated coagulopathies. This chapter provides an update on the scientific and clinical advances noted in disseminated intravascular coagulation (DIC) and discusses the challenges in hemostasis consultation. In Section I, Dr. Marcel Levi reviews advances in our understanding of the pathogenic mechanisms of DIC. Novel therapeutic strategies that have been developed and evaluated in patients with DIC are discussed, as are the clinical trials performed in patients with sepsis. In Section II, Dr. Lawrence Leung provides an overview of the challenging problems in thrombosis encountered in the inpatient setting. Patients with deep vein thrombosis that is refractory to conventional anticoagulation and those with extensive mesenteric thrombosis as well as the evaluation of a positive PF4/heparin ELISA in a post-operative setting are discussed. Novel treatments for recurrent catheter thrombosis in dialysis patients is addressed as well. In Section III, Dr. Julie Hambleton reviews the hemostatic complications of solid organ transplantation. Coagulopathy associated with liver transplantation, contribution of underlying thrombophilia to graft thrombosis, drug-induced microangiopathy, and the indication for postoperative prophylaxis are emphasized. Dr. Hambleton reviews the clinical trials evaluating hemostatic agents in patients undergoing liver transplantation.

Perioperative topical bovine thrombin exposure is not associated with hemodialysis graft thrombosis

Arteriovenous (AV) graft use as hemodialysis access remains highly prevalent, with a consequent high thrombosis rate. The magnitude of this problem requires that all potentially modifiable risk factors for graft thrombosis be thoroughly investigated. During graft surgery, topical bovine thrombin is often administered, which can lead to the development of antibovine thrombin antibodies and subsequent hemostatic changes. A recent study correlated the presence of plasma antibovine thrombin antibodies with graft thrombosis in hemodialysis patients. We therefore hypothesized that perioperative topical bovine thrombin exposure would lead to the development of antibovine thrombin antibodies and graft thrombosis. We screened 314 hemodialysis patients and identified 73 patients who had 74 grafts placed for whom complete data on perioperative topical bovine thrombin exposure and subsequent graft outcomes was available. Sixty-one of these patients were available for retrospective measurement of antibovine thrombin antibodies, antihuman thrombin antibodies, and the thrombin activation markers thrombin activatible fibrinolysis inhibitor (TAFI) and thrombin precursor protein (TpP). In these grafts, there was no significant association between topical bovine thrombin exposure and primary assisted patency (P = 0.37). The presence of antibovine thrombin antibodies (P = 0.13), antihuman thrombin antibodies (P = 0.10), and increased TAFI (P = 0.18) were associated with trends toward reduced primary assisted patency which did not reach significance. There was a correlation between antibovine thrombin antibodies and antihuman thrombin antibodies (r = 0.30, P < 0.0001) and between TAFI and TpP trade mark (r = 0.30, P < 0.0001), but no significant correlation between topical bovine thrombin exposure and elevated levels of antibovine thrombin antibodies, antihuman thrombin antibodies, TAFI or TpP trade mark. We conclude that perioperative topical bovine thrombin exposure is not associated with subsequent graft thrombosis.

The role of hyperparathyroidism, erythropoietin therapy, and CMV infection in the failure of arteriovenous fistula in hemodialysis

BACKGROUND

Vascular access failure is the main cause of morbidity in hemodialysis. Venous stenosis and subsequent thrombosis, as the result of intimal hyperplasia, is the major cause of vascular access failure. Intimal hyperplasia of the arteriovenous fistula (AVF) closely resembles the main histopathologic feature of atherosclerosis. In addition to the classic atherogenic risk factors, recently, cytomegalovirus (CMV) infection and parathyroid hormone (PTH) have been suggested as a potential cause of vascular disease.

METHODS

In the present study, we evaluated the relationship between AVF dysfunction and mean plasma PTH, cholesterolemia, high titer anti-CMV immunoglobulin G (IgG) (>250 U/mL), hematocrit, and mean erythropoietin (EPO) dose in 36 cases and 51 controls matched for age, time on dialysis, and type of AVF.

RESULTS

A higher percentage of patients with AVF failure had a smoking habit and presented high anti-CMV IgG titer. Patients with AVF failure had significantly higher mean plasma PTH, whereas the groups did not differ for mean cholesterolemia and hematocrit. Mean EPO dose was slightly, but significantly, higher in the AVF failure group. Multiple logistic regression revealed that smoking, EPO dose, elevated mean plasma PTH and high titer anti-CMV antibodies, significantly increased the risk of AVF dysfunction.

CONCLUSION

Our data suggest that hyperparathyroidism, smoking habits, CMV infection and EPO, independently of the hematocrit achieved, represent independent risk factors for hemodialysis access thrombosis.

Rapid, arteriovenous graft failure due to intimal hyperplasia: a porcine, bilateral, carotid arteriovenous graft model

BACKGROUND

The loss of patency constitutes the major complication of arteriovenous (AV) polytetrafluoroethylene hemodialysis grafts. In most cases, this graft failure is due to intimal hyperplasia at the venous outflow tract, including proliferation of vascular, smooth muscle cells and fibroblasts with deposition of extracellular matrix proteins. Thus far, procedures developed for improving patency have proven unsuccessful, which can be partly explained by the lack of relevant animal models. For this purpose, we developed a porcine model for AV graft failure that will allow the assessment of promising therapeutic strategies in the near future.

MATERIALS AND METHODS

In 14 pigs, AV grafts were created bilaterally between the carotid artery and the jugular vein using expanded polytetrafluoroethylene. Two, 4 or 8 weeks after AV shunting, the grafts and adjacent vessels were excised and underwent histologic analysis.

RESULTS

From 2 weeks onwards, a thick neo-intima developed at the venous anastomosis, predominantly consisting of alpha-actin-positive vascular smooth muscle cells (VSMC). Intimal area increased over time, coinciding with a decreased graft flow. Grafts remained patent for at least 4 weeks. At 8 weeks, patency rates declined to less than 50% due to thrombus formation superimposed on progressive neo-intima formation.

CONCLUSIONS

Implantation of an AV graft between the carotid artery and jugular vein in pigs causes a rapid neo-intimal response, accompanied by a loss of patency of 50% at 8 weeks after surgery. This model offers a suitable tool to study local interventions aimed at the improvement of AV graft patency rates.

Saratin, an inhibitor of collagen-platelet interaction, decreases venous anastomotic intimal hyperplasia in a canine dialysis access model

Prosthetic dialysis access thrombosis and/or stenosis is the most common cause of graft impairment or loss and is primarily attributed to venous outflow stenosis due to intimal hyperplasia. Intimal hyperplasia is thought to result from interactions between areas of exposed subendothelial collagen in an injured vessel and platelets, resulting in platelet adhesion. Saratin, an inhibitor of the vWF-dependent binding of platelet to collagen interaction, has been shown in vitro to reduce the adhesion of platelets to collagen. In the current study, the authors investigated the effects of topical saratin administration in a canine dialysis access model in regard to intimal hyperplasia development at the venous anastomosis. Fourteen female mongrel dogs underwent placement of a femoral polytetrafluoroethylene (PTFE) dialysis access graft and were placed into 1 of 2 groups: 1) control or 2) experimental with topical saratin application. The experimental group had 600 microg of saratin (1 microg/microL) applied for 5 minutes directly onto the venous anastomosis before restoration of blood flow;control groups received vehicle control. At 4 weeks postoperative, a portion of the graft was removed along with a segment of the outflow vein. Veins were subsequently processed, sectioned, and analyzed along the length of the excised segment and divided into blocks that included the area of the graft toe, midanastomotic region and heel, and blocks A-E. Intimal hyperplasia was assessed by a computer-assisted morphometric analysis. Platelet counts and bleeding times were also measured. Vein segments in the control group (n=7) showed pronounced intimal hyperplasia in blocks B, C, and D as compared to the saratin group (n=6). Distribution of intimal hyperplasia by blocks between control and saratin groups were as follows: block [A] 8.6 +/- 1.9 vs 9.7 +/- 3.0% (p=NS), [B] 32.7 +/- 6.3 vs 10.7 +/- 3.5% (p=0.01), [C] 44.8 +/- 6.2% vs 10.3 +/- 1.5% (p=0.0004), [D] 40.8 +/- 11.0 vs 9.1 +/- 4.2% (p=0.02), [E] 7.5 +/- 5.5 vs 2.7 +/- 0.4% (p=NS). Intimal hyperplasia normalized to vein wall thickness also showed a significant reduction with saratin application. Bleeding times and platelet counts obtained at different time points during the experiment showed no difference between control and saratin groups. In a canine dialysis access model using PTFE grafts, topical application of saratin at the venous anastomosis decreased intimal hyperplasia development by as much as 77% when compared with control animals. Saratin provides for a method of substantially reducing intimal hyperplasia by direct local application without systemic side effects.

A randomized controlled trial of blood flow and stenosis surveillance of hemodialysis grafts

BACKGROUND

It is widely accepted that hemodialysis graft surveillance combined with correction of stenosis reduces thrombosis and prolongs graft survival. Nevertheless, few randomized controlled trials have evaluated this approach.

METHODS

In this randomized controlled trial, 101 patients were assigned to control, flow (Qa), or stenosis groups, and were followed for up to 28 months. All patients had monthly Qa measured by ultrasound dilution and quarterly percent stenosis measured by duplex ultrasound. Referral for angiography was based on the following criteria: (1) control group (N = 34), clinical criteria; (2) flow group (N = 32), Qa <600 mL/min or clinical criteria; and (3) stenosis group (N = 35), stenosis>50% or clinical criteria. Stenosis >or=50% during angiography was corrected by preemptive percutaneous transluminal angioplasty (PTA).

RESULTS

The preemptive PTA rate in the control group (0.22/patient year) was two thirds the rate in the flow group (0.34/patient year), and was highest in the stenosis group (0.65/patient year, P < 0.01). The percentage of grafts that thrombosed was similar in the control (47%) and flow groups (53%), but reduced in the stenosis group (29%, P = 0.10). Two-year graft survival was similar in the control (62%), flow (60%), and stenosis groups (64%) (P = 0.89).

CONCLUSION

Qa and stenosis surveillance were not associated with improved graft survival, although thrombosis was reduced in the stenosis group. The most important factors in this result may be that monthly Qa and quarterly stenosis measurements were not accurate or timely indicators of risk of thrombosis or progressive stenosis. This study does not support the concept that Qa or stenosis surveillance are superior to aggressive clinical monitoring.

Reducing vascular access morbidity: a comparative trial of two vascular access monitoring strategies

BACKGROUND

Thrombosis is the primary cause of access failure in polytetrafluoroethylene grafts and arteriovenous fistulas. It can lead to significant patient and access morbidity and mortality, and is difficult to prevent medically. Intervention is largely limited to maximizing access patency by detecting culprit lesions early and intervening with angioplasty or surgical revision. The most efficacious monitoring strategy is undetermined.

METHODS

This 3 year prospective study took advantage of a change in monitoring strategy used in a large dialysis centre to compare the efficacy of two methods used to monitor grafts and fistulas in order to prevent access thrombosis. Accesses were monitored using Duplex ultrasonography in year 1, while the saline ultrasound dilution technique (Transonic) became the primary monitoring strategy in year 3 (year 2 was a transition year). Risk factors for thrombosis were determined using multivariate survival analysis, and the performance of Duplex ultrasonography and Transonic monitoring was assessed.

RESULTS

A total of 303 656 access days at risk were assessed, with 344, 385 and 425 accesses in years 1, 2 and 3, respectively. The total thrombosis rate was 1.01/1000 access days in year 1 compared with 0.66/1000 access days in year 3. This was accomplished despite a reduction in procedure rates of 55% for angiograms, 13% for angioplasties and 31% for thrombolysis.

CONCLUSION

Low flow rates detected using Transonic monitoring were associated with increased thrombosis, while stenosis detected using Duplex ultrasonography was not a strong predictor of incipient thrombosis; however, these different access characteristics were compared using monitoring techniques that may be ideal in different clinical situations.

Increased venous proinflammatory gene expression and intimal hyperplasia in an aorto-caval fistula model in the rat

We hypothesized that the venous limb of an arteriovenous (AV) fistula would evince up-regulation of genes relevant to vascular remodeling along with neointimal hyperplasia and relevant histological changes. Using the aorto-caval model of an AV fistula model in the rat, we demonstrate marked up-regulation in such proinflammatory genes as monocyte chemoattractant protein-1, plasminogen activator inhibitor-1, and endothelin-1, 2 weeks after the creation of the fistula. Neointimal hyperplasia occurred in variable degrees by 5 weeks after establishing the fistula, and by 16 weeks, such neointimal hyperplasia was progressive and pronounced; at this time point, abundant extracellular matrix was also observed. Smooth muscle cells were present in the hyperplastic neointima as evidenced by staining for alpha-smooth muscle actin; ultrastructurally, smooth muscle cells with a synthetic as well as a contractile phenotype were readily observed. Accumulation of extracellular matrix in the model at 16 weeks was accompanied by increased expression of transforming growth factor-beta1 mRNA, the latter finding contrasting with the suppression of transforming growth factor-beta1 mRNA observed in this model at 2 weeks. In summary, we describe marked up-regulation in proinflammatory genes and progressive neointimal formation in the venous vasculature in an AV fistula model in the rat. We suggest that such alteration in gene expression and histological injury, in conjunction with the relative simplicity of this model, offer a new approach in the study of such timely biological and clinically relevant phenomena as differential gene expression in response to hemodynamic forces, processes involved in vascular remodeling, mechanisms of injury in venous bypass grafts, and mechanisms of dysfunction of AV fistulae used in hemodialysis.

Thrombosis in end-stage renal disease

Although renal failure has classically been associated with a bleeding tendency, thrombotic events are common among patients with end-stage renal disease (ESRD). A variety of thrombosis-favoring hematologic alterations have been demonstrated in these patients. In addition, "nontraditional" risk factors for thrombosis, such as hyperhomocysteinemia, endothelial dysfunction, inflammation, and malnutrition, are present in a significant proportion of chronic dialysis patients. Hemodialysis (HD) vascular access thrombosis, ischemic heart disease, and renal allograft thrombosis are well-recognized complications in these patients. Deep venous thrombosis and pulmonary embolism are viewed as rare in chronic dialysis patients, but recent studies suggest that this perception should be reconsidered. Several ESRD treatment factors such as recombinant erythropoietin (EPO) administration, dialyzer bioincompatibility, and calcineurin inhibitor administration may have prothrombotic effects. In this article we review the pathogenesis and clinical manifestations of thrombosis in ESRD and evaluate the evidence that chronic renal failure or its management predisposes to thrombotic events.

Basic steps for increasing the rate of autogenic vascular accesses for hemodialysis

The number of patients on chronic hemodialysis (HD) is steadily increasing worldwide. The creation of a well-functioning vascular access represents a critical aspect in their management. Autogenous arteriovenous fistulas (AVF) are considered the first choice vascular access in terms of lower morbidity and costs, and higher survival rates when compared with grafts. However, creating AVF at high rates is a complex task that requires a multidisciplinary approach, which includes nephrologists, access surgeons, dialysis nurses and radiologists. In the present work we review concisely the basic steps, for preserving all potential autogenic sites at both upper extremities for future AVF creation and, for prolonging the length of AVF survival. We feel that a more proactive involvement of nephrologists in the basic steps for AVF creation would substantially contribute to increase AVF rates among HD patients.

Aggressive venous neointimal hyperplasia in a pig model of arteriovenous graft stenosis

BACKGROUND

Vascular access dysfunction is the most important cause of morbidity and hospitalization in the hemodialysis population in the United States at a cost of well over one billion dollars per annum. Venous neointimal hyperplasia characterized by stenosis and subsequent thrombosis, is the major cause of polytetrafluoroethylene (PTFE) dialysis graft failure. Despite the magnitude of the problem, there are currently no effective therapies for the prevention or treatment of venous neointimal hyperplasia in PTFE dialysis grafts. We believe that this is partly due to the lack of a validated large animal model of arteriovenous stenosis that could be used to test out novel interventions.

METHODS

Seven-centimeter PTFE loop grafts were placed between the femoral artery and vein of domestic pigs. The grafts were removed at 2, 4, 7, 14 and 28 days after surgery and subjected to a detailed histological and immunohistochemical examination.

RESULTS

Significant neointimal hyperplasia and venous stenosis developed by 28 days at the graft-vein anastomosis. There was minimal neointimal hyperplasia at the graft-artery anastomosis. Venous neointimal hyperplasia (VNH) was characterized by (a) the presence of smooth muscle cells/myofibroblasts; (b) angiogenesis within both the neointima and adventitia; and (c) the presence of an active macrophage cell layer lining the PTFE graft material. These results are very similar to the human lesion previously described by us in dialysis patients.

CONCLUSIONS

We have developed and validated a pig model of venous neointimal hyperplasia that is very similar to the human lesion. We believe that this is an ideal model in which to test out novel interventions for the prevention and treatment of clinical hemodialysis vascular access dysfunction.

The impact of nasal carriage of methicillin-resistant and methicillin-susceptible Staphylococcus a ureus (MRSA & MSSA) on vascular access-related septicemia among patients with type-II diabetes on dialysis

BACKGROUND

Fairly higher nasal carriage rates among type-II diabetics place them at a greater risk of endogenous Staphylococcus aureus linked vascular access-related septicemia (VRS) that is also dependent on the type of vascular access used for hemodialysis (HD). The prevalence of nasal carriage of methicillin susceptible and methicillin-resistant S. aureus (MSSA and MRSA) and its impact on VRS was determined in order to identify most vulnerable group and plan potential prophylactic strategies, accordingly.

METHODS

Five standardized nasal swab cultures were performed in 208 patients enrolled for long-term HD through July 1996 to July 1999. Persistent nasal carriage was defined by two or more positive cultures for MSSA or MRSA. Peripheral blood cultures were collected on clinical suspicion of septicemia.

RESULTS

The prevalence of type-II diabetes of 28.0% with 72.4% of nasal carriage rate and three folds higher S. aureus related VRS (RR-3.19, p<0.0001) than diabetic non-carriers on HD, was observed. Type-II diabetics also had higher MSSA and MRSA nasal carriage rates (53.4% and 19.0%) than non-diabetic nasal carriers (18.6 and 6.0%) yet, carried a comparable (RR-4.0 vs. 4.5) risk of VRS between MSSA and MRSA nasal carriers. Among diabetic type-II S. aureus nasal carriers, central venous catheters (CVCs) carried 35 and 38 times higher collective risk of developing MSSA and MRSA nasal carriage-related VRS respectively than Arterio-venous fistula (AVF). The AVF recorded the lowest risk of developing MSSA and MRSA nasal carriage-related VRS (0.013 and 0.010 episodes/patient-year) in both diabetic type-II MSSA and MRSA nasal carrier groups.

CONCLUSIONS

Diabetic type-II S. aureus nasal carriers on HD through CVCs make an extremely high-risk group for MSSA and MRSA nasal carriage-related VRS. The incidence of S. aureus nasal carriage-related VRS could reasonably be reduced through a challenging obligation of optimizing AVF prevalence in this high-risk group, while limiting the use of CVCs, at the same time.

Diagnostic and interventional nephrology

The fragmented care of nephrology patients that results from referral to a radiologist for renal ultrasound (US) and biopsy, a surgeon for dialysis access placement, and an interventional radiologist for dialysis catheter placement and vascular access procedures often leads to delays in the treatment of these patients. Many specialists perform and interpret sonograms particular to their specialty rather than relying on technicians for performance and radiologists for interpretation, and nephrologists recently have begun to embrace this technology as an aid in the diagnosis and treatment of their patients. By combining an understanding of the pathophysiology of renal disease with the ability to perform clinical correlation and apply the laboratory data, the nephrologist is ideally suited to perform and interpret renal US and US guidance for percutaneous renal biopsies. Additionally, patients requiring peritoneal dialysis (PD) access have traditionally been referred to a general surgeon for catheter placement, which incurs additional delay in therapy and loss of decision-making control by the referring nephrologist. Recent data has emphasized that the peritoneal dialysis access procedure can be performed safely and effectively by a nephrologist trained in PD access procedures. Nephrologists also successfully perform tunneled hemodialysis catheter placement and vascular access procedures on an outpatient basis. The medical needs of patients with renal disease can be safely and efficiently delivered by a nephrologist trained in interventional nephrology (IN). This growing area of expertise will minimize delays, reduce cost, and allow physicians with training in the management of end-stage renal disease (ESRD) patients to be involved in the procedural aspects of their patients' care. An aggressive approach to the development of IN training programs at academic centers is warranted.

Improving dialysis access management

Renal replacement therapy requires either placement of a functional hemodialysis vascular access or peritoneal dialysis catheter. Early provision of a dialysis access improves patient care with reduction in morbidity and reduces the economic burden incurred as a result of delayed access placement. Vascular access dysfunctions (thrombosis and infection) pose the greatest burden on the end-stage renal disease population. This article reviews the current literature on the planning of dialysis access, with particular emphasis on issues pertaining to vascular access. Current concepts to maximize access patency and efficiently manage vascular access complications are highlighted.

Increasing arteriovenous fistulas in hemodialysis patients: problems and solutions

National guidelines promote increasing the prevalence of fistula use among hemodialysis patients. The prevalence of fistulas among hemodialysis patients reflects both national, regional, and local practice differences as well as patient-specific demographic and clinical factors. Increasing fistula prevalence requires increasing fistula placement, improving maturation of new fistulas, and enhancing long-term patency of mature fistulas for dialysis. Whether a patient receives a fistula depends on several factors: timing of referral for dialysis and vascular access, type of fistula placed, patient demographics, preference of the nephrologist, surgeon, and dialysis nurses, and vascular anatomy of the patient. Whether the placed fistula is useable for dialysis depends on additional factors, including adequacy of vessels, surgeon's experience, patient demographics, nursing skills, minimal acceptable dialysis blood flow, and attempts to revise immature fistulas. Whether a mature fistula achieves long-term patency depends on the ability to prevent and correct thrombosis. An optimal outcome is likely when there is (1) a multidisciplinary team approach to vascular access; (2) consensus about the goals among all interested parties (nephrologists, surgeons, radiologists, dialysis nurses, and patients); (3) early referral for placement of vascular access; (4) restriction of vascular access procedures to surgeons with demonstrable interest and experience; (5) routine, preoperative mapping of the patient's arteries and veins; (6) close, ongoing communication among the involved parties; and (7) prospective tracking of outcomes with continuous quality assessment. Implementing these measures is likely to increase the prevalence of fistulas in any given dialysis unit. However, differences among dialysis units are likely to persist because of differences in gender, race, and co-morbidity mix of the patient population.

Association between blood pressure, ultrafiltration, and hemodialysis graft thrombosis: a multivariable logistic regression analysis

Although a low blood flow (Q(a)) is the most important cause of graft thrombosis, several studies have shown that Q(a) measurements do not accurately predict thrombosis. This suggests that additional variables may influence thrombosis. Identification of such variables may be essential to designing surveillance protocols that accurately predict thrombosis. In this nested case-control study, we prospectively followed 105 patients for up to 2.5 years in order to test the association of a number of variables with thrombosis. These included Q(a) (monthly by ultrasound dilution), percentage stenosis (quarterly by duplex ultrasound), mean arterial pressure (MAP), percentage ultrafiltration (%UF) during dialysis (%UF = 100[liters]/[kilogram of weight]), and other variables that defined patient and graft characteristics. Patients were divided into patent (n = 53) and thrombosed groups (n = 52), and MAP and %UF from seven consecutive dialysis sessions were analyzed. In the thrombosed group, the last session was the final session before thrombosis. A multivariable logistic regression model showed that Q(a), MAP (the predialysis average of seven sessions), and %UF (from the last session) were independently associated with thrombosis, whereas all other variables were not. The model yielded the following odds ratios for thrombosis: for a single Q(a) value (reduction of 1,000 mL/min), 12.0 (P < 0.01); for %UF (increase of 4%), 5.3 (P < 0.01); for MAP (reduction of 30 mm Hg), 4.1 (P = 0.02); and for percentage decrease in Q(a) (> or =20% versus <20%), 2.4 (P = 0.12). We conclude that in addition to Q(a), both %UF at the last session before thrombosis and average predialysis MAP from seven sessions are independently associated with thrombosis. These results help explain why Q(a) alone does not accurately predict thrombosis. A prospective study is needed to determine whether %UF at each session and a moving average MAP from seven sessions improve the prediction of thrombosis. However, it should be recognized that a large %UF is a preterminal event that likely provides too short a warning for intervention before thrombosis.

External beam radiation attenuates venous neointimal hyperplasia in a pig model of arteriovenous polytetrafluoroethylene (PTFE) graft stenosis

PURPOSE

Hemodialysis vascular access dysfunction is an enormous clinical problem that causes great morbidity and costs well over one billion dollars per annum. The vast majority of hemodialysis vascular access dysfunction occurs as a result of venous stenosis and thrombosis at the graft-vein anastomosis. At a cellular level, this venous stenosis is the result of venous neointimal hyperplasia (VNH). There are, unfortunately, no effective therapies for VNH. The purpose of this study was to assess the role of external radiation therapy in preventing VNH and venous stenosis.

METHODS AND MATERIALS

Seven-centimeter polytetrafluoroethylene loop grafts were placed bilaterally between the femoral artery and vein of 12 Yorkshire Cross pigs. One side was treated with a single 16-Gy dose of external beam radiation with a linear accelerator, while the contralateral side served as an internal control. Swine were killed after 28 days, and the grafts were carefully dissected out and removed. Neointimal hyperplasia and luminal stenosis were then assessed morphometrically at the graft-vessel anastomoses.

RESULTS

External beam radiation therapy significantly reduced the amount of luminal stenosis at the graft-vein anastomosis, with minimal local and systemic toxicity.

CONCLUSIONS

External beam radiation therapy could be a useful and clinically relevant local treatment for venous stenosis in polytetrafluoroethylene dialysis grafts.

Elbow fistulas using autogeneous vein: patency rates and results of revision

BACKGROUND

The provision and maintenance of vascular access remains a major cost to end stage renal failure programmes. There are few reports regarding the surgical revision of the failing native elbow arteriovenous fistula (AVF).

PATIENTS AND METHODS

A retrospective case note review was performed on all patients identified from the hospital vascular access database as having undergone construction of an autogeneous vein elbow AVF. Over a seven year period 282 autogeneous vein AVFs were fashioned in 232 patients using the brachial artery as the in-flow conduit. Of these 208 were brachiocephalic fistulas, or a variant thereof, and 74 were fashioned using the transposed autologous basilic vein (136 male: 96 female; median age 60 years, range 14-94 years).

RESULTS

Of 282 elbow fistulas 197 were successfully used for dialysis (70%). Cumulative primary patency of elbow fistulas using autogeneous vein in this series was 68%, 54%, and 44% at one, two, and three years respectively. A further 34 revision procedures were performed on 28 fistulas to maintain fistula function, and cumulative secondary patency after surgical revision was 75%, 60%, and 46% at one, two, and three years. Overall 21 out of 34 procedures (62%) successfully restored fistula function and cumulative primary patency of the revised fistulas was 56% at one year. Eighteen AVFs (brachiocephalic, n=12; autologous basilar vein, n=6) required revision for access dysfunction secondary to a short stenoses within 4 cm of the arteriovenous anastomoses. Of these 18 AVFs eight were revised by excision of the stenosed segment and either primary anastomoses of the two cut ends of arterialised vein or reanastomoses of the proximal venous limb proximally on the brachial artery. In another nine fistulas the excised segment was replaced with a short interposition graft (polytetrafluoroethylene, n=7; native basilic vein, n=1; bovine carotid artery, n=1). One fistula with postanastomotic stenoses and a more proximal needle site stenoses was revised using two vein patches. Overall 100% were patent at 24 hours, 13 provided successful dialysis (72%), and cumulative primary patency was 67% and 50% at six months and one year respectively.

CONCLUSIONS

Successful surgical revision of failing native elbow fistulas can restore patency and improve cumulative secondary patency with potential benefits in terms of patient morbidity and mortality. These results compare favourably to published patency rates after fistula salvage using interventional radiological techniques.

Surveillance of fistula function by frequent recirculation measurements during high efficiency dialysis

Native fistulae are assumed to remain patent even with low access flows and are likely to cause access recirculation in high efficiency treatments done with high extracorporeal blood flows. We tested whether frequent recirculation measurements could be used to identify fistulae at risk to fail because of low access flow. High efficiency hemodialysis was delivered by 2008H machines equipped with blood temperature monitors (BTM) to measure recirculation within the first hour of every hemodialysis treatment. Access flow was measured when two consecutive BTM recirculation measurements exceeded a threshold of 15%. If access flow was < 500 ml/min, patients were referred for fistula revision. Eighty patients with native AV fistulae were studied for a period of 6 months. Nine of 11 interventions performed during the whole observation period were triggered by a BTM recirculation above the threshold. Two fistulae thrombosed in spite of a BTM recirculation below the threshold. One fistula with a BTM recirculation above the threshold had an access flow of 1,550 ml/min and was not referred for revision. BTM recirculation to detect fistulae for revision is sensitive (81.8%) and specific (98.6%) in the presence of cardiopulmonary recirculation and can be done with minimum intervention and without loss of efficient treatment time.

Tailoring the initial vascular access for dialysis patients

BACKGROUND

Creating a functioning initial arteriovenous (AV) access for aging and diabetic end-stage renal disease (ESRD) hemodialysis patients has been a challenge.

METHODS

This study describes 748 consecutive primary AV access creations and their primary (unassisted) and secondary (assisted) access survival at a single center. Twenty-four percent of the patients had diabetes as their cause of ESRD and the average age was 59.6 years. No patient receiving an initial AV access required synthetic graft material. All received an AV fistula. Three types of fistulae were created and their distribution varied significantly for diabetic and non-diabetic patients (respective percentages): forearm AV fistula (24%, 62%), perforating vein fistula (PVF) at the elbow (48%, 21%) and non-PVF at the elbow (29%, 17%).

RESULTS

Results of access survival for age groups <65 and 65+ years, male and female, diabetic and non-diabetic subgroups ranged from 51 to 75% for unassisted and from 75 to 96% for assisted two year access survival. PVF appeared to be advantageous over non-PVF access at the elbow. First intervention for peripheral steal syndrome was required at a rate of 7 and 0.6 per 100 patient-years at risk for diabetic and non-diabetic patients, respectively. The thrombosis rates per patient year of 0.03 for non-diabetics and 0.07 for diabetics are superior to previously published results for AV fistulae or for a combined AV fistula-AV graft approach.

CONCLUSIONS

Potential explanations for these excellent results among elderly and diabetic patients include preoperative evaluation, exclusive use of native vessels, a variable surgical approach including PVF, and the experience of a single operator.

Vascular access: anatomy, examination, management

A systematic approach to managing vascular access problems is the key to reducing current high rates of access thrombosis and failure. This approach begins with a thorough knowledge of vascular access anatomy that, when combined with the physical examination, can help optimize access planning and maintenance. Because of the high complication rate of synthetic grafts, there has been increased emphasis on creating autogenous arteriovenous (AV) fistulae, which, once established, are more trouble-free. The benefit of increased fistula creation will not be realized, however, until the high rate of early fistula failure is reduced. It is widely recommended that graft surveillance programs be implemented and that stenosis be corrected when accompanied by graft dysfunction. Graft blood flow (Q(a)) is the preferred surveillance method, but has a poor accuracy in predicting thrombosis. Most studies that have evaluated the benefit of Q(a) surveillance have used historical control groups, or have been retrospective or nonrandomized. Consequently, we believe it is not currently possible to make definitive, evidence-based recommendations concerning Q(a) surveillance. The most important factor in access survival may be a team approach with an organized commitment to access planning followed by recognition and treatment of access problems.

Value of static venous pressure for predicting arteriovenous graft thrombosis

BACKGROUND

Static venous pressure elevation has been shown to have both high sensitivity and high specificity for hemodialysis arteriovenous (AV) graft venous anastomosis stenosis. However, it is not known how well static venous pressure elevation predicts subsequent AV graft thrombosis.

METHODS

Monthly static venous pressure measurements were made during two consecutive dialysis sessions in all patients with a functioning upper extremity AV graft in two hemodialysis units during a 16-month period. Static venous pressure was normalized to systolic blood pressure and corrected for the height difference between the AV graft and the dialysis machine pressure transducer to yield the static venous pressure ratio (SVPR).

RESULTS

Fifty-four patients (38%) had a thrombotic event during the study period and thus were labeled as clotters. Among the clotters, SVPR just prior to thrombosis was 0.51 +/- 0.16 (mean +/- SD), and mean time to thrombosis following an elevated SVPR (> or =0.4) was 118 +/- 106 days. Receiver operating characteristic (ROC) curves were generated using the sensitivities and specificities of a range of SVPR values for access thrombosis within one, two, three and four months. The areas under the curve (AUCs) for the ROC curves ranged from 0.557 to 0.638, reflecting the absence of SVPR values with both high sensitivity and high specificity for access thrombosis. An increase in SVPR over time was not a better predictor of access thrombosis than absolute SVPR.

CONCLUSION

Static venous pressure measurement is not an optimal screening test for identifying AV grafts at risk for thrombosis.

Hemodialysis vascular access dysfunction from basic biology to clinical intervention

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population at a cost of over 1 billion dollars per annum. Venous stenosis and thrombosis as a result of venous neointimal hyperplasia are the major causes of hemodialysis vascular access dysfunction. Despite the magnitude of the clinical problem, there are currently no effective therapies for this condition. We believe that this could be because of an inadequate understanding of the pathogenesis of this condition. At a histological level, venous neointimal hyperplasia (both in human specimens and in a pig model) is characterized by the presence of smooth muscle cells/myofibroblasts, microvessel formation (angiogenesis), and the accumulation of extracellular matrix components, all of which could be potential targets for therapeutic intervention. In particular, polytetrafluoroethylene dialysis access grafts could be the ideal clinical model for testing out novel local therapies to block neointimal hyperplasia. The current review describes the lesion of venous neointimal hyperplasia in human samples and in a pig model and suggests possible future directions for the development of effective local therapies for this condition.

Salvage of poorly developed arteriovenous fistulae with percutaneous ligation of accessory veins

Many arteriovenous (AV) fistulae fail to achieve an adequate blood flow or size for successful cannulation because of accessory veins. We describe a simple technique to ligate accessory veins that does not require a surgical incision. In this retrospective study, 17 end-stage renal disease patients underwent ligation of accessory veins of poorly developed AV fistulae. There were 14 men and 3 women, and their average age was 50 +/- 13 years. There were 14 radiocephalic and 3 brachiocephalic fistulae. After identifying accessory veins with a fistulogram, two nonabsorbable 2-0 polypropylene (Prolene) sutures were placed percutaneously around each accessory vein in proximity to the AV fistula. Successful ligation was confirmed with a repeat fistulogram. This procedure was undertaken after 4 +/- 3 months following surgical placement. Successful maturation was defined as adequate blood flow to support effective hemodialysis and adequate caliber to allow for repeated cannulation with a 15G or 16G needle. Of 17 AV fistulae, 15 (88%) successfully matured 1.7 +/- 1 month (range, 0.3 to 6 months) after the procedure. The average number of accessory veins ligated was 1.7 +/- 0.8 (range, 1 to 3). All AV fistulae that matured after ligation of accessory veins were functioning at 44.5 +/- 12 weeks after first use. A technique for salvaging nonmaturing AV fistulae not requiring surgical cutdown for ligation of accessory veins is described. AV fistulae mature quickly after ligation of accessory veins. This is a rapid and safe procedure that can increase the prevalence of AV fistulae.

Superficialization of the wrist native arteriovenous fistula for effective hemodialysis vascular access construction

BACKGROUND

It is commonly known that the best type of vascular access for chronic hemodialysis, defined as the one with the lowest number of complications and longest use, is the primary (Brescia-Cimino) radiocephalic fistula. One reason for the impossibility of its creation is that the vein vessel on the forearm is located too deeply, which is primarily caused by the patients' obesity.

METHODS

In 24 obese patients the superficialization procedure of the venous part of fistula under the skin was performed.

RESULTS

In 23 patients of this group, an easy and uncomplicated fistula puncturing was achieved. One patient had the complication of fistula clotting.

CONCLUSION

Subcutaneous transposition of the arterialized median antebrachial vein is a simple and effective method of an adequate distal native fistula creation in patients with deeply located forearm veins.

Vascular access use in Europe and the United States: results from the DOPPS

BACKGROUND

A direct broad-based comparison of vascular access use and survival in Europe (EUR) and the United States (US) has not been performed previously. Case series reports suggest that vascular access practices differ substantially in the US and EUR. We report on a representative study (DOPPS) which has used the same data collection protocol for> 6400 hemodialysis (HD) patients to compare vascular access use at 145 US dialysis units and 101 units in five EUR countries (France, Germany, Italy, Spain, and the United Kingdom).

METHODS

Logistic analysis evaluated factors associated with native arteriovenous fistula (AVF) versus graft use or permanent access versus catheter use for prevalent and incident HD patients. Times to failure for AVF and graft were analyzed using Cox proportional hazards regression.

RESULTS

AVF was used by 80% of EUR and 24% of US prevalent patients, and was significantly associated with younger age, male gender, lower body mass index, non-diabetic status, lack of peripheral vascular disease, and no angina. After adjusting for these factors, AVF versus graft use was still much higher in EUR than US (AOR=21, P < 0.0001). AVF use within facilities varied from 0 to 87% (median 21%) in the US, and 39 to 100% (median 83%) in EUR. For patients who were new to HD, access use was: 66% AVF in EUR versus 15% in US (AOR=39, P < 0.0001), 31% catheters in EUR vs. 60% in US, and 2% grafts in EUR vs. 24% in US. In addition, 25% of EUR and 46% of US incident patients did not have a permanent access placed prior to starting HD. In EUR, 84% of new HD patients had seen a nephrologist for> 30 days prior to ESRD compared with 74% in the US (P < 0.0001); pre-ESRD care was associated with increased odds of AVF versus graft use (AOR=1.9, P=0.01). New HD patients had a 1.8-fold greater odds (P=0.002) of starting HD with a permanent access if a facility's typical time from referral to access placement was < or =2 weeks. AVF use when compared to grafts was substantially lower (AOR=0.61, P=0.04) when surgery trainees assisted or performed access placements. When used as a patient's first access, AVF survival was superior to grafts regarding time to first failure (RR=0.53, P=0.0002), and AVF survival was longer in EUR compared with the US (RR=0.49, P=0.0005). AVF and grafts each displayed better survival if used when initiating HD compared with being used after patients began dialysis with a catheter.

CONCLUSION

Large differences in vascular access use exist between EUR and the US, even after adjustment for patient characteristics. The results strongly suggest that a facility's preferences and approaches to vascular access practice are major determinants of vascular access use.

Catheter access for hemodialysis: an overview

The provision of hemodialysis requires repeated, reliable access to the central circulatory system. Long-term hemodialysis has best been provided by arteriovenous fistulae and arteriovenous grafts. In recent years, more and more patients have been chronically dialyzed with tunneled dialysis catheters. These catheters, which were originally developed as a short-term bridge to permanent vascular access, have made up an increasing percentage of maintenance vascular access. While these catheters have the advantage of ease of placement and are immediately ready for use, they substantially increase the risk of bacteremia, stenosis of central veins, and even mortality.

Clinical consequences of infected arteriovenous grafts in hemodialysis patients

Arteriovenous (AV) graft infection is a serious adverse event in hemodialysis patients; however, there is little published literature describing its consequences. We identified prospectively all AV graft infections occurring at our institution during a 4.5-year period. We analyzed immediate complications, as well as long-term consequences, including the need for subsequent vascular-access procedures and duration of catheter-dependent dialysis therapy. Ninety graft infections were identified in 78 patients, yielding a rate of 8.2 infections/100 graft-years. Patients with graft infection were much more likely to have a low serum albumin level (<3.5 g/dL) in the month preceding the infection compared with noninfected controls (73% versus 18%; P < 0.001). Infections occurred within 1 month of graft placement in 15%, at 1 to 12 months in 44%, and longer than 1 year from surgery in 41%. The pathogen was a gram-positive coccus in 97% of cases, particularly Staphylococcus aureus (60%) and Staphylococcus epidermidis (22%). The initial graft infection entailed hospitalization for a mean of 7.5 days. Eleven patients (12%) developed a total of 17 major complications, including death (5 patients), clinical sepsis requiring vasopressors (4 patients), septic arthritis (3 patients), epidural abscess (1 patient), endocarditis (1 patient), osteomyelitis (1 patient), myocardial infarction (1 patient), and cerebrovascular accident (1 patient). After removal of an infected graft, patients were catheter dependent for a median of 3.8 months. The duration of catheter dependence was less than 3 months in 36%, 3 to 6 months in 38%, 6 to 12 months in 14%, and greater than 1 year in 12%. During the period of catheter dependence, patients required a mean of 9.7 access procedures, including graft removal (1.0 procedure), nontunneled dialysis catheters (4.4 procedures), tunneled dialysis catheters (3.0 procedures), and new permanent accesses (1.4 procedures). In addition, patients averaged 0.85 episodes of bacteremia while they were catheter dependent. In conclusion, graft infection results in substantial morbidity, prolonged dependence on dialysis catheters, and multiple vascular-access procedures.