Hemodynamic screening and early percutaneous intervention reduce hemodialysis access thrombosis and increase graft longevity

Surveillance and monitoring of dialysis access

Vascular access is the lifeline of a hemodialysis patient. Currently arteriovenous fistula and graft are considered the permanent options for vascular access. Monitoring and surveillance of vascular access are an integral part of the care of hemodialysis patient. Although different techniques and methods are available for identifying access dysfunction, the scientific evidence for the optimal methodology is lacking. A small number of randomized controlled trials have been performed evaluating different surveillance techniques. We performed a study of the recent literature published in the PUBMED, to review the scientific evidence on different methodologies currently being used for surveillance and monitoring and their impact on the care of the dialysis access. The limited randomized studies especially involving fistulae and small sample size of the published studies with conflicting results highlight the need for a larger multicentered randomized study with hard clinical end points to evaluate the optimal surveillance strategy for both fistula and graft.

Optimizing function and treatment of hemodialysis grafts and fistulae

We are entering a new era for the management of hemodialysis grafts and fistulae. The hallmark of this new era will be the use of quantitative, hemodynamic parameters to optimize vascular access function and improve the results of our endovascular interventions. The implementation of vascular access surveillance programs has not only decreased the incidence of vascular access thrombosis, but also has provided new insights into the hemodynamic performance of grafts and fistulae. The measurement and analysis of intra-access blood flow has proven useful for the early detection of developing stenosis, and also provides a quantitative method to assess the results of our endovascular interventions. In the future, the use of quantitative hemodynamic measurements will play an increasingly important role in our evaluation and treatment of hemodialysis grafts and fistulae.

Arterial line pressure control enhanced extracorporeal blood flow prescription in hemodialysis patients

Background

In hemodialysis, extracorporeal blood flow (Qb) recommendation is 300–500 mL/min. To achieve the best Qb, we based our prescription on dynamic arterial line pressure (DALP).

Methods

This prospective study included 72 patients with catheter Group 1 (G1), 1877 treatments and 35 arterio-venous (AV) fistulae Group 2 (G2), 1868 treatments. The dialysis staff was trained to prescribe Qb sufficient to obtain DALP between -200 to -250 mmHg. We measured ionic clearance (IK: mL/min), access recirculation, DALP (mmHg) and Qb (mL/min). Six prescription zones were identified: from an optimal A zone (Qb > 400, DALP -200 to -250) to zones with lower Qb E (Qb < 300, DALP -200 to -250) and F (Qb < 300, DALP > -199).

Results

Treatments distribution in A was 695 (37%) in G1 vs. 704 (37.7%) in G2 (P = 0.7). In B 150 (8%) in G1 vs. 458 (24.5%) in G2 (P < 0.0001). Recirculation in A was 10.0% (Inter quartile rank, IQR 6.5, 14.2) in G1 vs. 9.8% (IQR 7.5, 14.1) in G2 (P = 0.62). IK in A was 214 ± 34 (G1) vs. 213 ± 35 (G2) (P = 0.65). IK Anova between G2 zones was: A vs. C and D (P < 0.000001). Staff prescription adherence was 81.3% (G1) vs. 84.1% (G2) (P = 0.02).

Conclusion

In conclusion, an optimal Qb can de prescribed with DALP of -200 mmHg. Staff adherence to DLAP treatment prescription could be reached up to 81.3% in catheters and 84.1% in AV fistulae.

Results of aggressive graft surveillance and endovascular treatment on secondary patency rates of Vectra Vascular Access Grafts

OBJECTIVE

The aim of the present study was to determine the effect of an aggressive graft surveillance and endovascular treatment protocol on secondary patency rates of a polyetherurethaneurea vascular access graft, specially designed to provide early access and rapid hemostasis.

METHODS

One hundred and ninety Vectra Vascular Access Grafts (C. R. Bard, Inc, Murray Hill, NJ) were placed in 176 patients (78 females and 98 males, mean age 61.7 years). There were 41 forearm grafts, 145 upper arm grafts and four thigh grafts. Graft surveillance was performed by using clinical and hemodialysis parameters to detect a failing/failed graft and followed by endovascular treatment, rheolytic thrombectomy (AngioJet, Possis Medical Inc, Minneapolis, Minn) and/or angioplasty +/- stenting of the anatomical lesion (arterial anastomosis, graft, venous outflow, draining or central veins).

RESULTS

Hemodialysis started after a median of 15.5 days, as soon as from the day of the operation in some cases. Bleeding complications occurred in six patients (3.2%), venous hypertension in seven (3.7%), steal syndrome in two (1.1%), neurological complications in two (1.1%), while late infection (range 2.7-14.6 months) was seen in six patients (3.2%). Thrombectomy and angioplasty (median number of sessions 1, interquartile range 1-2) was performed in 43 grafts. Isolated angioplasty, not associated with thrombosis (median number of sessions 1, interquartile range 1-2), was performed in 50 grafts. These interventions increased primary assisted patency from 69% and 63% at 12 and 18 months, respectively to a secondary patency rate of 86%. Taking into account grafts removed for late infection, functional secondary patency rate dropped to 83% and 81%, at 12 and 18 months, respectively. Arterial anastomosis angioplasty was performed more frequently in thrombosed grafts (28.6%) than failing grafts (6.7%), P < .001 and had a significant negative predictive value on secondary patency rates at 12 and 18 months, which were 60.5% compared with 89% for grafts that had no interventions performed (P = .007) and 90.9% for grafts that had any intra-graft, venous outflow, or draining or central vein stenosis treated with angioplasty at any stage (P = .002). Multivariate analysis identified the presence of arterial anastomosis stenosis as the single predictor of secondary patency (relative risk 0.247, P = .002).

CONCLUSIONS

Aggressive graft surveillance and endovascular treatment increases significantly secondary patency rates of Vectra Vascular Access Grafts. Longer follow-up will determine the effectiveness of this policy. The role of inflow stenosis on graft longevity and alternative treatment options warrant further investigation.

Effects of omega-3 fatty acid supplementation on vascular access thrombosis in polytetrafluorethylene grafts

OBJECTIVE

The purpose of this study was to investigate the effects of orally administered over-the-counter omega-3 (n-3) fatty acid supplements on primary patency of polytetrafluoroethylene (PTFE) grafts.

DESIGN

This study was conducted with a triple-blind, permuted-block, randomized, placebo-controlled experimental design.

SETTING

Dialysis clinics with patients who, in accordance with physician diagnosis, needed a new PTFE graft.

PATIENTS AND OTHER PARTICIPANTS

Patients on long-term hemodialysis with newly placed PTFE grafts who were unable to receive a native arteriovenous fistula.

INTERVENTION

Patients were followed prospectively for 8 months after they had been placed into an n-3 fatty acid or control group and were monitored for primary patency.

MAIN OUTCOME VARIABLE

Primary patency of the PTFE graft.

RESULTS

The n-3 fatty acid group had a mean PTFE graft primary patency rate of 254.2 days (SEM = 51.8), and the control group had a mean PTFE graft primary patency rate of 254.1 days (SEM = 34.6), revealing no significant difference in survival time between groups.

CONCLUSIONS

No significant differences in primary patency rates were noted in the experimental and control groups.

Use of Stent Grafts to Repair Hemodialysis Graft–related Pseudoaneurysms

PURPOSE

To review the author's early experience with stent grafts to repair hemodialysis graft-related pseudoaneurysms.

MATERIALS AND METHODS

Eleven patients had undergone insertion of a stent graft to repair a pseudoaneurysm arising from a PTFE hemodialysis graft. The study group consists of seven women and four men with a mean age of 50.7 years. The primary indications for stent graft placement were: rapid enlargement of a pseudoaneurysm in four patients, difficulty with cannulating the graft in two patients, high risk of acute rupture in three patients, persistent bleeding from the pseudoaneurysm in one patient, and one was incidentally discovered during diagnostic fistulography. In 10 of the 11 patients, the pseudoaneurysm arose from the arterial limb of a loop-configuration graft. A stent graft was successfully deployed in all patients. The radiological and surgical records were reviewed.

RESULTS

The Viabahn endoprosthesis was successfully inserted and deployed in all 11 patients. Six patients underwent subsequent interventions, which ended primary patency at 39 days, 40 days, 63 days, 104 days, 120 days, and 327 days after insertion of the stent graft. However, no additional interventions have been performed in five patients and primary patency continues. In these five patients the interval of continuing primary patency is 55 days, 92 days, 103 days, 139 days, and 196 days. In this small group of patients the primary patency rate is 71% at 3 months and 20% at 6 months.

DISCUSSION

Early experience has demonstrated that a stent graft can successfully exclude a pseudoaneurysm from a hemodialysis graft and may prevent further enlargement and decrease the likelihood of rupture. However, in two of these 11 patients, the large pseudoaneurysm remained problematic and required subsequent surgical repair.

Homocysteine and vascular access thrombosis in a cohort of end-stage renal disease patients

BACKGROUND

Maintaining successful hemodialysis services is dependent upon an access to circulation that is reliable and stable. Complications of vascular access such as dysfunction, thrombosis, or infection are major causes of hospitalization with thrombosis being the most common reoccurring problem. Initial prospective evidence supports an independent association between total homocysteine (tHcy) levels and access thrombosis. The purpose of this study was to determine if significant associations exist between tHcy, age, gender, and vascular access thrombosis in patients with end-stage renal disease (ESRD).

SUBJECTS AND METHODS

One hundred eighty-five (N=185) patients undergoing dialysis were selected as subjects. The retrospective sample was divided into a one or less vascular access thrombosis (VAT) (VAT) group (n= 133) and more than one (VAT II) VAT group (n= 52). The data was collected during a 16-month period (January 2000 to April 2002). Additional subgroup analyses included gender and age.

RESULTS

The Mann-Whitney U nonparametric t-Test for variance between groups revealed no significant difference in tHcy values between VAT groups (U=1841.50, p=0.284). A two-sample t-Test for variance between tHcy and age revealed no significant differences (F-ratio = 0.832, p = 0.32). A chi-square analysis revealed no significant differences in gender and VAT groups (chi2=0.246, p=0.62). A Kolmogorov-Smirnov test for normality was calculated for tHcy with a p-value of 0.859 revealing insufficient evidence that the distribution is not normal. Spearman Rank Correlations were calculated, revealing low to moderate associations among variables.

CONCLUSIONS

While some studies have demonstrated a relationship between tHcy and VAT, this study found that chronically high homocysteine levels in patients with ESRD were not associated with incidence of VAT. There were no significant differences in the number of VATs across additional variables of age and gender.

Colour Doppler ultrasound assessment of well-functioning mature arteriovenous fistulas for haemodialysis access

BACKGROUND

A well-functioning mature arteriovenous fistula is essential for the maintenance of haemodialysis in patients with chronic renal failure. The Brescia-Cimino arteriovenous fistula has the best survival characteristics and low rate of complications. The most common reason of fistula failure is thrombosis caused by stenosis. Colour Doppler ultrasonography has proven to be effective in the assessment of anatomical vascular features. The majority of studies were done in patients with clinically presumed arteriovenous fistula complications. However, only limited data are available about the well-functioning mature arteriovenous fistulas. The purpose of the present study was to evaluate completely asymptomatic, mature arteriovenous fistulas with colour Doppler ultrasound.

MATERIALS AND METHODS

From July 2001 to April 2003, we examined 139 patients with the end-stage renal disease. They were in the range of 19-79 years of age (mean, 46.7 years). The study included only the patients who met the following criteria: (1) no difficulties with haemodialysis (as reported by nurses); (2) normal venous diastolic blood pressure (<150 mmHg) at monthly evaluation; (3) normal urea clearance x time/urea volume of distribution; (4) blood cells count, plasma electrolytes, and liver function at monthly evaluation. The mean fistula age was 26 months (S.D.=21.9). The mean time of dialysis therapy was 49 months. Thirty-eight percent patients had primary fistulas, 23%--secondary, 11%--third and 11%--fourth, 4%--fifth, 5%--sixth, and 8% patients had more than sixth.

RESULTS

There was no correlation between: (1) patient's age and fistula age; (2) patient's age and number of fistulas in one patient; (3) fistula age and number of fistulas in one patient; (4) localization of fistula and fistula age. There was a strong correlation between dialysis therapy period and number of fistulas in one patient. The mean flow volume was 1204.1 ml/min (S.D.=554). It was significantly higher in the fistulas with aneurysms, calcifications and tortuous vessels and lower in those with stenosis. There was no correlation between the flow volume or presence of stenosis and fistula age. Stenosis was detected in 64% fistulas. Fifty-seven percent of stenoses were located in the anastomotic region, 22% stenoses were in vein junction, 19% were at one or both ends of aneurysm, and 2% in the remaining region of the efferent vein. Perivascular colour artefacts were present at the 94% fistulas with stenosis. Chronic venous occlusion with collateral veins was detected in 6% of fistulas. The aneurysms were observed in 54% fistulas. The mean diameter of aneurysms was 12.4 mm. Ninety-six percent of aneurysms were located at puncture sites. Ten patients had a small thrombus in an aneurysm and at puncture sites.

CONCLUSIONS

We conclude that there was a high level of abnormalities present in well-functioning mature arteriovenous fistulas. However, these abnormalities were not sufficient to affect the functioning of the dialysis fistula.

Physical Examination versus Normalized Pressure Ratio for Predicting Outcomes of Hemodialysis Access Interventions

PURPOSE

The ratio of intragraft venous limb pressure (VLP) to systemic pressure (S) has been proposed to help determine the endpoint of hemodialysis access interventions. It was hypothesized that physical examination of the access could be used in the same way and these techniques were compared as predictors of outcome.

PATIENTS AND METHODS

With use of a quality-assurance database, records from 117 hemodialysis access interventions were retrospectively reviewed. Only interventions in grafts were included. The database included physical examination (to establish thrill, thrill with slight pulsatility [TSP], pulse with slight thrill [PST], and pulse) at three locations along the graft (proximal, midportion, and distal), normalized pressure ratio calculated with S from a blood pressure cuff (S(cuff)) and S within the graft with outflow occluded (S(direct)), graft configuration and location, indication, operator, and time to next intervention (outcome of primary patency). Only procedures with complete follow-up data were included in the analysis (n = 97; declotting, n = 51; prophylactic percutaneous transluminal angioplasty [PTA], n = 46). Statistical analysis was performed with use of Cox proportional-hazards regression.

RESULTS

Graft configuration, location, side, VLP, S(direct), and S(cuff) did not affect outcomes. An operator effect was noted for two physicians and was adjusted for in all analyses. Pressure ratios were weak predictors of outcome (VLP/S(direct), P =.07; VLP/S(cuff), P =.08) and suggested that patency increased with increasing pressure ratio, contrary to earlier studies. Procedure type predicted outcome (declotting, median patency of 50 days; PTA, median patency of 105 days; P =.01). Thrill at distal physical examination was predictive of outcome (P =.04) and even more so when thrill and TSP combined were compared with PST and pulse combined (P =.03). Similar but less-pronounced effects were seen at midportion and proximal physical examinations.

CONCLUSIONS

The presence of a thrill or slightly pulsatile thrill at the distal (venous) end of a dialysis graft is the best predictor of outcome after percutaneous intervention. Based on the present study, the authors believe that physical examination of dialysis access should supplant pressure measurements as an endpoint of intervention and should serve as an essential component of quality assurance of access interventions.

Slow-flow venous pressure for detection of arteriovenous graft malfunction

BACKGROUND

Early detection with elective intervention of malfunctioning arteriovenous (AV) grafts improves access viability. Herein, we evaluated outlet venous pressure (OP), normalized by mean arterial blood pressure (MABP), at varying blood flow (Qb) rates in the detection of venous outlet stenosis.

METHODS

This single-center, observational study included stable dialysis patients with polytetrafluoroethylene (PTFE) AV grafts. Phase I involved the determination of the optimal Qb (0, 50, 250, or 400 mL/min) and threshold OP/MABP. Sixty-one patients were followed up for 6 months. The primary end point was graft thrombosis. Phase II assessed serial slow-flow pressure (SFpr = OP/MABP at Qb of 50 mL/min) in a larger sample size (N = 152). The primary end point was graft thrombosis. Phase III implemented the use of SFpr monitoring in the detection and correction of outlet lesion(s).

RESULTS

In phase I, 21 patients developed graft thrombosis. The most significant difference in pressure between the functioning and thrombosed grafts was at Qb of 0 mL/min and SFpr. The threshold of OP/MABP at Qb 0 (>0.53) and SFpr (>0.6) were predictive of graft thrombosis. In phase II, 37 of 42 patients with graft thrombosis had SFpr>0.6 (sensitivity 88.1%; specificity 97.2%; positive and negative predictive values were 90.2% and 95.5%, respectively). In phase III, 13 patients with SFpr>0.6 had outlet lesions on angiography.

CONCLUSION

Serial SFpr used in conjunction with angiography and angioplasty provides a strategy for reducing the incidence of thrombosis. This technique has comparable sensitivity and specificity to other existing methods. This technique is both time-efficient and cost-effective.

Hemodialysis access assessment with intravascular ultrasound

Reliable identification and treatment of specific hemodialysis access complications may improve access patency and result in significant cost reduction. Angiography is the gold standard for the evaluation of vascular access; however, it has significant limitations. Intravascular ultrasound (IVUS) is a relatively new technique capable of detecting subtle vascular abnormalities. To investigate the safety, feasibility, and accuracy of IVUS imaging to detect hemodialysis access complications, including stenoses, graft deterioration, and thrombus, we performed 31 IVUS imaging studies in 22 hemodialysis patients. Nineteen studies were performed in the dialysis unit, and 12 studies in the angiography suite. The IVUS catheter was inserted into the graft through the access used for hemodialysis. Findings of 21 studies (17 patients) imaged on the same day by both angiography and IVUS were compared. Grafts and vessels were successfully imaged using IVUS in 29 of 31 studies. There were no adverse effects caused by IVUS. Angiography assessed 17 of 54 vessel segments as normal versus 9 of 54 segments by IVUS (P < 0.001). Angiography detected lesions in 25 segments as opposed to 33 segments by IVUS (P < 0.001). A thrombus was detected in 32 of 54 vessel segments by IVUS, but in only 1 of 54 segments by angiography (P < 0.001). In conclusion, IVUS imaging is feasible and safe to assess hemodialysis access in the angiographic suite and dialysis unit. IVUS detected more vascular abnormalities than angiography. IVUS may be a useful independent imaging and screening modality in the assessment of dialysis access complications, which may help increase graft patency and reduce cost.

Brachial arterial access: endovascular treatment of failing Brescia-Cimino hemodialysis fistulas--initial success and long-term results

PURPOSE

To evaluate safety and efficacy of endovascular interventions in failing antebrachial Brescia-Cimino hemodialysis fistulas in consecutive patients.

MATERIALS AND METHODS

Altogether, 103 interventions were performed in 53 Brescia-Cimino shunts in 51 patients by means of antegrade brachial arterial access. Twelve interventions were initiated with pharmacomechanical thrombolysis and/or thromboaspiration. All interventions included balloon angioplasty that was completed with stent placement in eight cases and with endovascular brachytherapy with an iridium 192 source in five cases.

RESULTS

The technical success rate of the primary interventions was 92% (49 of 53) and that for all interventions was 95% (98 of 103). The rate of major complications was 4% (four of 103). Clinical success was achieved in 92% (95 of 103) of the interventions. By including the initial failures, 58% +/- 7 (standard error of the estimate), 44% +/- 8, 40% +/- 8, and 32% +/- 10 primary and 90% +/- 5, 85% +/- 5, 79% +/- 7, and 79% +/- 7 secondary clinical patency rates were registered at 6 months and 1, 2, and 3 years, respectively, by means of Kaplan-Meier analysis. The location of the main treated lesion at the arteriovenous anastomosis (P =.03) was a predictor of poorer long-term patency.

CONCLUSION

Endovascular interventions with antegrade brachial arterial access are highly effective in restoring function in failing Brescia-Cimino fistulas.

New hemodynamic test for assessment of failing hemodialysis grafts: the saline infusion test

PURPOSE

To validate the saline infusion test, a new hemodynamic test for assessment of failing hemodialysis access grafts.

MATERIALS AND METHODS

Over a 12-month period, 31 procedures were performed in 25 patients with synthetic forearm loop grafts for hemodialysis. Pre- and postangioplasty measurements of static graft pressures and infusion pressures were obtained. For the saline infusion test, graft pressure was measured while saline was infused at a rate of 600 mL/min for 10 seconds with arterial inflow occluded. Comparison was made to percent outflow stenosis as determined with pre- and postangioplasty angiograms.

RESULTS

There was no correlation between either the static intragraft pressure (r = .085, P = .654) or the normalized pressure ratio (r = .136, P = .4676) and venous outflow stenosis in the preangioplasty group. When pressure was measured during infusion, a significant Pearson correlation was observed between infusion pressure and percent of angiographic stenosis (r = .60, P = .0002). All three pressure tests were significantly correlated to the percent stenosis identified after angioplasty.

CONCLUSIONS

Pressure measured in the graft during the saline infusion test at a standard rate that simulates optimal graft flow correlates with the angiographic degree of stenosis and warrants further investigation as a useful adjunct to the assessment of revascularization results.

Early detection and treatment of hemodialysis access dysfunction

PURPOSE

To assess the usefulness of a program for the early detection of hemodialysis graft dysfunction and the impact on graft survival of percutaneous transluminal angioplasty (PTA) and stent implantation to correct venous stenosis.

METHODS

A program for the early detection of hemodialysis access graft dysfunction was carried out in 110 patients over a period of 80 months. Detection was based on physical examination, flow rate measurements, venous pressure, and analytical determinations performed at dialysis. The stenoses detected were treated by PTA or PTA plus stent deployment. Survival curves compared primary and assisted patency rates for the different graft types.

RESULTS

The most important indicators of dysfunction were increased venous pressure and difficulty in cannulation of the graft. Significant stenoses were revealed by 227 (92.2%) of the 246 fistulography procedures performed. PTA results were satisfactory in 100% of the Thomas grafts, 74% of the Brescia-Cimino (BC) grafts, and 53% of the polytetrafluoroethylene (PTFE) grafts. Technical success rates for stent deployment were 92% for BC grafts and 100% for PTFE grafts, while functional success rates were 96% and 97%, respectively. The difference in the primary patency (P1) and assisted patency (AP) values was statistically significant for all three graft types. There was no significant difference in the patency rates for grafts treated by PTA alone or by PTA and stent deployment.

CONCLUSION

A surveillance program helped prevent graft thrombosis, and intervention as required achieved excellent primary and assisted patency rates. Stent deployment salvaged a considerable number of accesses but did not significantly extend access survival time.

Monitoring interposition graft venous pressures at higher blood-flow rates improves sensitivity in predicting graft failure

Monitoring the patency of hemodialysis interposition grafts is recommended to improve graft survival. Which blood flows best predict graft survival is not known. We monitored venous pressures in 32 dialysis patients over a median of 252 days at variable flow rates of the blood pump (Qb). Venous pressure trends (VPTs), maximum venous pressure (MVP), and the variability of venous pressure (percent coefficient of variation) were calculated. Kaplan-Meier curves were constructed from the time of the end of VPT monitoring to time to failure, defined as angioplasty, clotting, or surgical revision. Risk for graft failure for each 10-mm Hg increase in venous pressure was calculated by the Cox proportional hazards model. There were 12 graft failures, but no failures in 12 fistulas over the course of the study. The variability in venous pressure was less at greater Qbs. For grafts, VPTs were predictive of event only when calculated for Qbs greater than 100 mL/min. At Qbs of 400 mL/min, there was a 70% risk for graft failure with each 10-mm Hg increase in VPT. The risk for graft failure increased between 28% and 44% for each 10-mm Hg increase in MVP at all Qbs. MVP of 230 mm Hg at a Qb of 400 mL/min provided the best efficiency of test performance. Dialysis venous chamber pressure monitoring is a useful test to predict graft stenosis or thrombosis. There is a substantial variability in venous pressures in the same patient that reduces with increasing Qbs. Venous pressure monitoring at greater Qbs provides a more sensitive method for predicting access failure.