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

Angioplasty of Long Venous Stenoses in Hemodialysis Access: At Last an Indication for Cutting Balloon?

PURPOSE

To compare the postintervention primary patency rates of cutting balloon angioplasty (CBA) with those of conventional percutaneous transluminal angioplasty (PTA) in the treatment of hemodialysis-related stenoses at least 2 cm long.

MATERIALS AND METHODS

This retrospective and controlled study included 29 patients with a hemodialysis-related stenosis at least 2 cm long. From August 2002 to August 2003, nine patients (PTA group, six upper-arm and three forearm fistulas) were treated with a conventional balloon (5-8 mm, 4 cm long). From September 2003 to December 2005, 20 patients (CBA group, 12 upper-arm and seven forearm fistulas; one polytetrafluoroethylene hemodialysis graft) were treated with a cutting balloon (5-7 mm, 1 cm long). The median follow-up was 22.1 months for the CBA group and 15.6 months for the PTA group. The Kaplan-Meier method was used to calculate the primary cumulative patency rates, and the log-rank test was used for comparison. Multivariate Cox models were generated by combining three variables: patient age, stenosis length, and treatment type (CBA or PTA).

RESULTS

In the CBA group, the postintervention primary patency was 85% +/- 16 at 6 months, 70% +/- 20 at 1 year, and 32% +/- 26 at 18 months. In the PTA group, the postintervention primary patency was 56% +/- 32 at 6 months and 21% (range, 0%-53%) at 1 year. When comparing PTA versus CBA with the log-rank test, there was a statistically significant difference (P = .009). With the multivariate Cox models, treatment was again a statistically significant (P = .007) determinant of primary patency; patient age and stenosis length were not.

CONCLUSION

The use of a cutting balloon as the first-line treatment for stenoses at least 2 cm long significantly improves the postintervention primary patency rate.

Mathematical model demonstrates influence of luminal diameters on venous pressure surveillance

BACKGROUND

The reliability of dialysis venous pressure (VP) in detecting stenosis is controversial. A mathematical model may help to resolve the controversy by providing insight into the factors that influence static VP.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

This study used inflow artery and outflow vein luminal diameters from duplex ultrasound studies of 94 patients. These diameters were applied to a mathematical model, and how they affect the relation among VP, mean arterial pressure (MAP), blood flow, and stenosis was determined. Whether VP/MAP is a valid adjustment for the influence of MAP on VP, and whether the standard VP/MAP referral threshold of 0.50 is valid, were also determined.

RESULTS

It was found that there is an approximate one-to-one relation between MAP and VP, so VP/MAP is a valid adjustment. Also, the 0.50 threshold successfully identifies most grafts with stenosis of 65% or more. However, the ratio of artery/vein diameters varied widely between patients, and the ratio independently influences VP/MAP. When the inflow artery is relatively narrow, the VP/MAP increase is delayed followed by a more rapid increase as critical stenosis is reached.

CONCLUSIONS

VP/MAP is a valid adjustment for the influence of MAP on VP, and the standard VP/MAP threshold of 0.50 warns of the transition to critical stenosis. However, relatively narrow arteries cause a delay followed by a rapid increase in VP/MAP that may not be detected before thrombosis unless measurements are very frequent. Clinical trials that emphasize trend analysis with frequent measurements are needed to evaluate the efficacy of VP surveillance.

Ultrahigh-pressure versus High-pressure Angioplasty for Treatment of Venous Anastomotic Stenosis in Hemodialysis Grafts: Is There a Difference in Patency?

PURPOSE

Ultrahigh-pressure (UHP) balloon catheters were compared with high-pressure (HP) balloon catheters to determine if there was a difference in patency after percutaneous transluminal angioplasty (PTA) of venous anastomotic stenoses.

MATERIALS AND METHODS

A retrospective study was conducted from January 2001 to September 2005 that included 22 patients with synthetic hemodialysis grafts who underwent 110 PTA procedures for venous anastomotic stenoses. Data collected included graft configuration and location, percent stenosis, balloon type used, residual stenosis, and total access blood flow before and after intervention. Patency from time of initial PTA to the next intervention was estimated with the Kaplan-Meier technique, with initial failures included in the analysis.

RESULTS

A total of 55 PTAs were performed in each group. Technical success rate was 96% (n = 106) and clinical success rate was 100%. Median survival times were 4.6 months for the UHP cohort and 5.4 months for the HP group. When each event was considered independent, the difference was significant (P = .014). However, when each PTA event was considered dependent on earlier PTA events, no significant difference in patency was observed (P = .64). The mean increases in access blood flow rate by ultrasound dilution (available for 71 events) after PTA were 264 mL/min with UHP and 524 mL/min with HP (P = .14, Student t test). One minor complication (0.9%) of focal extravasation after PTA occurred and resolved with prolonged balloon inflation.

CONCLUSION

Routine use of UHP for PTA of venous anastomotic stenoses in synthetic hemodialysis grafts was not associated with any significant change in patency compared with routine HP balloon angioplasty.

Current management of vascular access

Optimizing vascular access outcomes remains an ongoing challenge for clinical nephrologists. All other things being equal, fistulas are preferred over grafts, and grafts are preferred over catheters. Mature fistulas have better longevity and require fewer interventions, as compared with mature grafts. The major hurdle to increasing fistula use is the high rate of failure to mature of newly created fistulas. There is a desperate need for enhanced understanding of the mechanisms of failure to mature and the optimal type and timing of interventions to promote maturity. Grafts are prone to frequent stenosis and thrombosis. Surveillance for graft stenosis with preemptive angioplasty may reduce graft thrombosis, but recent randomized clinical trials have questioned the efficacy of this approach. Graft stenosis results from aggressive neointimal hyperplasia, and pharmacologic approaches to slowing this process are being investigated in clinical trials. Catheters are prone to frequent thrombosis and infection. The optimal management of catheter-related bacteremia is a subject of ongoing debate. Prophylaxis of catheter-related bacteremia continues to generate important clinical research. Close collaboration among nephrologists, surgeons, radiologists, and the dialysis staff is required to optimize vascular access outcomes and can be expedited by having a dedicated access coordinator to streamline the process. The goal of this review is to provide an update on the current status of vascular access management.

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.

Routine Surveillance in Vascular Access for Hemodialysis

There is increasing evidence that surveillance of AV access for haemodialysis prevents access thrombosis and improves the quality of care. This article reviews the evidence for surveillance and the various strategies and techniques available for detection of the failing access.

Vascular access and cardiac disease: is there a relationship?

PURPOSE OF REVIEW

Despite advances in hemodialysis technology, a stable and well functioning vascular access remains the bane of every hemodialysis patient. It is recognized that vascular access contributes to cardiovascular disease mortality through a number of mechanisms. This review describes the relationship between vascular access and cardiovascular disease by reviewing the relationships between infection risk, inflammation and cardiovascular disease, and the cardiovascular changes that occur as a consequence of vascular access. Improved understanding of these mechanisms and their interrelationship is warranted.

RECENT FINDINGS

The impact of arteriovenous fistula creation on cardiac structural and hemodynamic changes is described, as is vascular remodelling, which occurs in response to alterations in blood-flow properties. The development of central and peripheral vein stenosis is also a type of vascular remodelling and consequences of such events are not yet well understood. In addition, the contribution of vascular access to increased inflammation and atherosclerotic disease is reviewed. Finally, the hypothesis that vascular access dysfunction may be a predictor of vascular disease is explored.

SUMMARY

The relationship between vascular access and cardiac disease exists at different levels, ranging from inflammation promoting atherosclerotic disease to vascular remodelling changes of stenosis formation and left ventricular hypertrophy. Countless research opportunities abound.

Vascular access for hemodialysis

Establishing and maintaining adequate vascular access is essential to providing an appropriate dialysis dose in patients with end-stage renal disease. Complications related to vascular access have a significant role in dialysis-related morbidity and mortality. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) clinical practice guideline for dialysis access was last updated in 2000 and provides a framework for the optimal establishment and maintenance of dialysis access, and treatment of complications related to dialysis access. This paper reviews the 2000 K/DOQI dialysis access guideline as well as updated information published subsequently.

Influence of luminal diameters on flow surveillance of hemodialysis grafts: insights from a mathematical model

Randomized controlled trials have not shown that surveillance of graft blood flow (Q) prolongs graft life. Because luminal diameters affect flow resistance, this study examined whether the influence of diameters on Q can explain the limitations of surveillance. Inflow artery and outflow vein diameters were determined from duplex ultrasound studies of 94 patients. These diameters were applied to a mathematical model for determination of how they affect the relation between Q and stenosis. Also determined was the correlation between Q (by ultrasound dilution) and diameters, stenosis, and mean arterial pressure in 88 patients. Artery and vein diameters varied widely between patients, but arteries generally were narrower than veins. The model predicts that the relation between Q and stenosis is sigmoid: as stenosis progresses, Q initially remains unchanged but then rapidly decreases. A narrower artery increases flow resistance, causing a longer delay followed by a more rapid reduction in Q. In a multiple regression analysis of data from patients, Q correlated with artery and vein diameters, sum of largest stenoses from each circuit segment, and mean arterial pressure (R = 0.689, P < 0.001). This study helps to explain why Q surveillance predicts thrombosis in some patients but not others. Luminal diameters control the relation between Q and stenosis, and these diameters vary widely. During progressive stenosis, the delay and then rapid reduction in Q may impair recognition of low Q before thrombosis occurs. Surveillance outcomes might be improved by taking frequent measurements so that there is no delay in discovering that Q has decreased.

Does monthly native arteriovenous fistula blood-flow surveillance detect significant stenosis--a randomized controlled trial

BACKGROUND

Clinical practice guidelines recommend that the preferred method of surveillance for arteriovenous fistula (AVF) is the measurement of AVF blood flow (Qa). As these recommendations are based on observational studies, we conducted a randomized, prospective, double-blind, controlled trial to assess whether Qa surveillance results in an increased detection of AVF stenosis.

METHODS

A total of 137 patients were randomly assigned to receive either continuing AVF surveillance using current clinical criteria (control, usual treatment) or usual treatment plus AVF blood-flow surveillance by ultrasound dilution (Qa surveillance group). The primary outcome measure was the detection of a significant (>50%) AVF stenosis.

RESULTS

There were 67 and 68 patients assigned to the control and Qa surveillance groups, respectively. Patients in the Qa surveillance group were twice as likely to have a stenosis detected compared with the control hazard ratio (HR) confidence interval (CI) group (2.27, 95% 0.85-5.98, P = 0.09), with a trend for a significant stenosis to be detected earlier in the Qa surveillance group (P = 0.09, log rank test). However, using the Qa results alone prior to angiography, the area under the receiver operating characteristic curve demonstrated, at best, a moderate prediction of (>50%) AVF stenosis (0.78, 95% CI 0.63-0.94, P = 0.006).

CONCLUSION

This study demonstrates that the addition of AVF Qa monitoring to clinical screening for AVF stenosis resulted in a non-significant doubling in the detection of angiographically significant AVF stenosis. Further, large multi-centre randomized trials are feasible and will be necessary to confirm whether Qa surveillance and the correction of detected AVF stenosis will lead to a reduction in AVF thrombosis and increased AVF survival.

Randomized comparison of ultrasound surveillance and clinical monitoring on arteriovenous graft outcomes

Arteriovenous graft thrombosis is a frequent event in hemodialysis patients, and usually occurs in grafts with significant underlying stenosis. Regular surveillance for graft stenosis, with pre-emptive angioplasty of significant lesions, may improve graft outcomes. This prospective, randomized, clinical trial allocated 126 hemodialysis patients with grafts to either clinical monitoring alone (control group) or to regular ultrasound surveillance for graft stenosis every 4 months in addition to clinical monitoring (ultrasound group). The two randomized groups were closely matched with respect to demographic, clinical, and graft characteristics, with the exception of a lower frequency of diabetes in the ultrasound group. The primary outcome was graft survival, and the secondary outcome was thrombosis-free graft survival. The frequency of pre-emptive graft angioplasty was 64% higher in the ultrasound group than in the control group (1.05 vs 0.64 events per patient-year, P<0.001), whereas the frequency of thrombosis was not different (0.67 vs 0.78 per patient-year, P=0.37). The median time to permanent graft failure was similar between the two groups (38 vs 37 months, P=0.93). Likewise, the median time to graft thrombosis or failure did not differ (22 vs 25 months, P=0.33). There was no significant association between diabetes and time to graft failure (P=0.93) or time to graft thrombosis or failure (P=0.88). In conclusion, the addition of regular ultrasound surveillance for graft stenosis to clinical monitoring increases the frequency of pre-emptive angioplasty, but may not decrease the likelihood of graft failure or thrombosis.

Outcomes of thrombosed arteriovenous grafts: Comparison of stents vs angioplasty

The usual radiologic approach to thrombosed grafts is a combination of thrombectomy and angioplasty of the underlying lesion. However, the primary (unassisted) graft patency after thrombectomy is quite poor. We evaluated whether graft patency following thrombectomy is improved by placement of a stent in the stenotic lesion. Using a prospective, computerized vascular access database, we identified 14 patients with thrombosed arteriovenous (A-V) grafts treated with a stent at the venous anastomosis (stent group). The outcomes of these grafts was compared to those observed in 34 sex, age-, and date-matched control patients whose thrombosed A-V grafts were angioplastied (control group). Both groups were comparable in age, sex, race, diabetic status, graft age, and number of previous graft interventions. The immediate technical success, as indicated by the post-procedure graft to systemic pressure ratio, was similar in the stent and control groups (0.33+/-0.16 vs 0.41+/-0.17, P=0.14). The primary graft patency (time from thrombectomy to next intervention) was significantly longer for the stent group (median survival, 85 vs 27 days, P=0.02). Assisted or secondary patency (time from thrombectomy to permanent graft failure) was also longer for the stent group (median survival, 1215 vs 46 days, P=0.049). In conclusion, treatment of thrombosed grafts with a stenosis at the venous anastomosis with a stent results in longer primary and secondary graft survival, as compared to treatment with angioplasty. Stent placement may be a useful treatment modality in a subset of patients with thrombosed A-V grafts and stenosis at the venous anastomosis.

Monthly access flow monitoring with increased prophylactic angioplasty did not improve fistula patency

BACKGROUND

Regular access monitoring is recommended to detect and treat access stenosis in order to prevent access thrombosis and failure.

METHODS

In 1999, we instituted monthly access blood flow monitoring using the ultrasound dilution technique (UDT). In a sequential observational trial, 222 patients were studied for the impact of UDT monitoring on patency of their first arteriovenous autogenous fistula. Group 1, the historic group (before 1999), had 146 arteriovenous fistulas (50.7% upper arm), followed for 259 access-years. Group 2, the UDT-monitored group, had 76 arteriovenous fistulas (60.5% upper arm), followed for 123 access-years. Decision to refer for angiography was based on clinical criteria for group 1, and clinical criteria plus results of UDT flow monitoring in group 2.

RESULTS

Cumulative patency was longer (P < 0.01) and the thrombosis rate was lower (P < 0.05) in group 2. However, the improvement occurred prior to initiation of UDT flow monitoring. Comparing outcomes in group 2 patients whose fistula survived to start flow monitoring with group 1 patients whose fistula survived at least 160 days (the median time to starting UDT monitoring in group 2), there was a sevenfold increase in angioplasty procedures (0.67 vs. 0.09 per access-year) but no improvement in the thrombosis rate or cumulative fistula patency.

CONCLUSION

UDT monitoring increased the rate of angioplasty procedures and thereby shortened primary unassisted patency, but did not decrease the thrombosis rate or improve cumulative fistula patency.

Development of a sustained-release system for perivascular delivery of dipyridamole

Vascular access grafts implanted in dialysis patients are prone to failure in the long-term because of stenosis and occlusion caused by neointimal hyperplasia. Local delivery of antiproliferative drugs may be effective to prevent this consequence while minimizing the systemic side effects they cause. We developed a combination of poly(lactide-co-glycolide) (PLGA) microspheres with ReGel, an injectable copolymer, as a sustained-release system for perivascular delivery of an antiproliferative drug, dipyridamole. Dipyridamole-incorporated PLGA microspheres with various molecular weights (MWs) of PLGA were prepared by oil-in-water emulsion method. Encapsulation efficiency and surface morphology of microspheres were characterized. In vitro release kinetics of dipyridamole from ReGel or from microspheres/ReGel was experimentally determined. Without microspheres, 40% of the dipyridamole was released from ReGel as an initial burst in the first 3 days followed by continuous release in the subsequent 2 weeks. The use of PLGA microspheres decreased the initial burst and extended dipyridamole release from 23 to 35 days with increasing MW of PLGA. The highest MW PLGA showed a lag time of 17 days before consistent drug release occurred. Mixing microspheres and ReGel with two different MW PLGA achieved a continuous release for 35 days with little initial burst. In vivo release of dipyridamole from microspheres/ReGel exhibited a comparable release pattern to that seen in vitro. This injectable platform is a promising technique for sustained perivascular delivery of antiproliferative drugs.

Access Monitoring Is Worthwhile and Valuable

During the past several years, a limited number of small clinical trials have questioned the role of surveillance in the management of vascular accesses, since the prolongation of access longevity until replacement was not altered. Although prolongation of access life span is an important endpoint, it is not the only one. Reduction in thrombotic events reduces the risks to the patient resulting from loss of access patency. The body of evidence suggests that the detection of stenosis and prevention of thrombosis are valuable. When a test indicates the likely presence of a stenosis, venography or fistulography should be used to definitely establish the presence and the degree of the stenosis. In most cases, angioplasty should be performed if the stenosis is greater than 50% by diameter. The value of routine use of any surveillance technique for detecting anatomic stenosis alone without concomitant functional assessment by measurement of access flow, venous pressure, recirculation, or other physiologic parameter has not been established. Stenotic lesions should not be repaired merely because they are present. If such correction is performed, then intra-procedural studies of access flow or intra-access pressure prior to and following percutaneous transluminal angioplasty should be conducted to demonstrate a functional improvement with a 'successful' percutaneous transluminal angioplasty.

The morbidity and cost implications of hemodialysis clinical performance measures

Clinical performance measures, including dialysis dose, hemoglobin, albumin, and vascular access, are the focus of monitoring and quality improvement activities. However, little is known about the implications of clinical performance measures for hospital utilization and health care costs. We obtained clinical performance measures and hospitalization records for a national random sample of 10,650 hemodialysis patients and analyzed the relationship between changes in clinical performance measures and hospital utilization after adjustment for patient demographic and medical characteristics. Higher hemoglobin, higher albumin, and fistula or graft use were independently associated with fewer hospitalizations, fewer hospital days, and decreased Medicare inpatient reimbursement. For example, a 0.5 g/dL higher hemoglobin, a 0.25 g/dL higher albumin, fistula use, and graft use were associated with hospitalization rate ratios of 0.90 (95% confidence interval 0.85, 0.96), 0.64 (0.53, 0.77), 0.60 (0.52, 0.69), and 0.79 (0.71, 0.89), respectively. Moreover, there was a 2-3-fold variation in hospital utilization across end-stage renal disease networks that was still evident after adjustment for patient characteristics and clinical performance measures. Clinical performance measures, especially albumin and vascular access, are strongly associated with hospital utilization and health care costs. These results highlight the importance of targeting nutrition and vascular access in quality improvement efforts. The marked variation in hospital utilization across networks deserves further examination.

Stenosis detection in failing hemodialysis access fistulas and grafts: comparison of color Doppler ultrasonography, contrast-enhanced magnetic resonance angiography, and digital subtraction angiography

OBJECTIVE

Several imaging modalities are available for the evaluation of dysfunctional hemodialysis shunts. Color Doppler ultrasonography (CDUS) and digital subtraction angiography (DSA) are most widely used for the detection of access stenoses, and contrast-enhanced magnetic resonance angiography (CE-MRA) of shunts has recently been introduced. To date, no study has compared the value of these three modalities for stenosis detection in dysfunctional shunts. We prospectively compared CDUS and CE-MRA with DSA for the detection of significant (> or = 50%) stenoses in failing dialysis accesses, and we determined whether the interventionalist would benefit from CDUS performed before DSA and endovascular intervention.

METHODS

CDUS, CE-MRA, and DSA were performed of 49 dysfunctional hemodialysis arteriovenous fistulas and 32 grafts. The vascular tree of the accesses was divided into three to eight segments depending on the access type (arteriovenous fistula or arteriovenous graft) and the length of venous outflow. CDUS was performed and assessed by a vascular technician, whereas CE-MRA and DSA were interpreted by two magnetic resonance radiologists and two interventional radiologists, respectively. All readers were blinded to information from each other and from other studies. DSA was used as reference standard for stenosis detection.

RESULTS

DSA detected 111 significant (> or = 50%) stenoses in 433 vascular segments. Sensitivity and specificity of CDUS for the detection of significant stenosed vessel segments were 91% (95% CI, 84%-95%) and 97% (95% CI, 94%-98%), respectively. We found a positive predictive value of 91% (95% CI, 84%-95%) and a negative predictive value of 97% (95% CI, 94%-98%). The sensitivity, specificity, positive predictive value, and negative predictive value of MRA were 96% (95% CI, 90%-98%), 98% (95% CI, 96%-99%), 94% (95% CI, 88%-97%), and 98% (95% CI, 96%-99%), respectively. CDUS and CE-MRA depicted respectively three and four significant stenoses in six nondiagnostic DSA segments. The interventionalist would have chosen an alternative cannulation site in 38% of patients if the CDUS results had been available.

CONCLUSIONS

We suggest that CDUS be used as initial imaging modality of dysfunctional shunts, but complete access should be depicted at DSA and angioplasty to detect all significant stenoses eligible for intervention. CE-MRA should be considered only if DSA is inconclusive.

American Society of Diagnostic and Interventional Nephrology Section Editor: Stephen Ash: Stenosis Surveillance of Hemodialysis Grafts by Duplex Ultrasound Reduces Hospitalizations and Cost of Care

Most recent randomized controlled trials (RCTs) have found that hemodialysis graft surveillance combined with preemptive correction of stenosis does not prolong graft survival. Nevertheless, such programs may be justified if they reduce other adverse outcomes or decrease the cost of care. This study tested this hypothesis by applying a secondary analysis to our original RCT. This study of 101 patients evaluated correction of stenosis based upon blood flow (Q) and stenosis surveillance. Patients were randomly assigned to control, flow, or stenosis groups, and were followed for up to 28 months. Q was measured monthly by ultrasound dilution; stenosis was measured quarterly by duplex ultrasound. Stenosis of 50% was corrected by percutaneous transluminal angioplasty (PTA) after referral for angiography. Referral criteria were: control group, clinical criteria; flow group, Q < 600 ml/min or clinical criteria; stenosis group, stenosis > 50% or clinical criteria. We compared access-related hospitalizations and cost of care, and use of central venous dialysis catheters (CVCs), among the three groups. Hospitalization rates were higher in the control and flow groups than in the stenosis group (0.50, 0.57, 0.18/patient-year, respectively [p < 0.01]), and hospitalization costs were lowest in the stenosis group (p = 0.026). The stenosis group had a trend toward lowest CVC rates (0.44, 0.32, 0.20/patient-year, respectively [p = 0.20]). The costs of care were higher in the control and flow groups than in the stenosis group (dollar 3727, dollar 4839, dollar 3306/patient-year, respectively [p = 0.015]). The costs of stenosis (dollar 142/patient-year) and Q (dollar 279/patient-year) measurements were minimal compared to the total cost of access-related care. In conclusion, stenosis surveillance by duplex ultrasound combined with preemptive correction yielded reduced hospitalization rates and costs, reduced total cost of access-related care, and a trend of reduced CVC rates. In contrast, flow surveillance did not yield a significant benefit. Stenosis surveillance provides important benefits that may justify application of such programs.

American Society of Diagnostic and Interventional Nephrology Section Editor: Stephen Ash: Thresholds for Significant Decrease in Hemodialysis Access Blood Flow

During hemodialysis access surveillance, referral for evaluation and correction of stenosis is based upon determination that a significant decrease in blood flow (Q) has occurred. However, criteria for determining when a decrease is statistically significant have not yet been established. In this study we established such criteria by analyzing Q variation with the glucose pump test (GPT). We took nine Q measurements in each of 25 patients (18 grafts, 7 fistulas) during three dialysis sessions within a 2-week period (predialysis and during hours 1 and 3). We determined thresholds that define a significant percentage decrease in Q (deltaQ) for various p values. In order to confirm the general applicability of these thresholds, we computed the average within-patient Q variation during the three sessions (computed as a coefficient of variation and referred to as short-term variation). We then determined the relative influences of biological (true) variation and analytical error on short-term variation. We found that deltaQ must be > 33% to be significant at p < 0.05, whereas the threshold is > 17% for p < 0.20. Measuring Q at uniform versus different times during the sessions did not significantly reduce these thresholds. We also found that biological variation was nearly as large as short-term Q variation, whereas analytical error contributed minimally to short-term variation. In conclusion, this study defines thresholds for a significant deltaQ that have wide application in determining access referral for evaluation and correction of stenosis. Selection of a particular threshold should consider the relative importance of avoiding thrombosis versus avoiding unnecessary procedures. If avoiding unnecessary procedures is a priority, then we recommend a threshold of > 33%. These thresholds apply to other methods of measuring Q, provided analytical error is significantly less than biological variation.

Access Flow in Arteriovenous Accesses by Optodilutional and Ultrasound Dilution Methods

BACKGROUND

Most large studies evaluating the diagnostic properties of access blood flow (Qa) in arteriovenous (AV) accesses have used the Transonic HD01 (Transonic Systems Inc, Ithaca, NY) device, and recommended thresholds for angiography are based on data from these studies. There has been little exploration of how the use of other devices might affect the feasibility or performance of screening in AV accesses.

METHODS

We compared 2 devices for measuring Qa: the Transonic HD01 and the Crit-Line TQA III (Hemametrics, Salt Lake City, UT). We studied 124 adults with end-stage renal disease and a functioning AV access (fistula or graft). Qa was measured with both devices in immediate succession during a single dialysis treatment. The primary outcome was the technical feasibility of the Qa measurement. We also compared mean Qa values measured by the Crit-Line III and Transonic devices.

RESULTS

Qa measurements were less likely to be technically feasible when the Crit-Line III device was used compared with the Transonic device (86.3% versus 100%; P < 0.001). In patients with valid measurements, mean Qa measured using the Crit-Line III was significantly less than that measured using the Transonic HD01 device (886 +/- 557 versus 1,148 +/- 685 mL/min; P < 0.001). The mean difference was 261 mL/min (95% confidence interval [CI], 117 to 405) and was greater at higher levels of Qa. On average, Qa measured by means of the Crit-Line III device was 73% as high as that measured using the Transonic device (95% CI, 63 to 84). There was poor agreement between devices about whether criteria for angiography were met (kappa < 0.1). The proportion of patients for whom angiography was indicated (based on results from the Crit-Line device) was significantly greater than when only results from the Transonic device were considered (40.3% versus 7.3%; P < 0.001).

CONCLUSION

Consideration should be given to device-specific Qa thresholds for angiography or, alternatively, standardization of Qa results between manufacturers. Clinicians should be aware that Qa results cannot be compared directly between different devices, and access monitoring should be performed using a single technique in any given patient. Additional studies are required before the Crit-Line TQA device can be recommended for widespread use.

Survival and Complications of Indwelling Venous Catheters for Permanent Use in Hemodialysis Patients

BACKGROUND

The risk factors influencing the survival of indwelling central vein catheters and their potential complications have not been assessed in depth and on a large scale.

METHODS

We investigated the general characteristics of 245 single lumen cuffed tunneled catheters and analyzed their survival by Kaplan-Meier and Cox regression analysis. Risk factors for bacteremia and thrombosis were assessed by logistic regression analysis.

RESULTS

The incidence of exit-site infection, tunnel infection, bacteremia and thrombotic events was 0.35, 0.25, 1.71, and 1.94/1000 catheter days, respectively. The mean survival time per catheter was 276 days. After censoring for non catheter-related events leading to the removal of the catheter (n = 245 with 120 catheters censored and 125 events), the mean survival time of the catheter appeared to be 615 +/- 67 days (95% CI of 483-747) and the median survival time 310 +/- 50 days (95% CI of 212-408). The localization of the catheter into the right internal jugular vein results in significantly better survival as compared with other insertion sites both in Kaplan-Meier (mean survival of 650 days compared to a mean survival of 519 days, P value < 0.009) and in Cox regression analysis (relative risk of 0.537, P value < 0.001). Localization of the catheter into the right internal jugular vein seemed to increase the risk for bacteremia (relative risk of 1.798, P value of 0.063). The use of anticoagulant agents was not protective for thrombosis, although this might be due to lack of power (relative risk of 0.626, P value of 0.141).

CONCLUSION

We provide evidence of a mean survival in long-term hemodialysis catheter close to 2 years with an acceptable complication rate. If a long-term hemodialysis catheter is required, it is best placed in the right internal jugular vein.

A trial of detecting impending access-graft failure by simplified weekly flow monitoring

Access graft failure is a major problem in hemodialysis. Monitoring the flow through the access so that impending failure can be detected and prevented seems reasonable, but recent clinical trials have failed to show any benefit of such monitoring. Described here are plans for a clinical trial of a new flow monitoring procedure that measures access flow weekly instead of monthly and, being performed before dialysis, avoids the dialysis-induced changes in graft flow that may have affected earlier trials. The planned trial is to be carried out in two stages, the first to establish the sensitivity and specificity of the new method, and the second (if the results of the first stage warrant it) a controlled trial comparing access-costs and hospitalization days between a monitored group and a matched standard care control group. It is hoped that this trial of the new method will establish it as an effective means of extending access-graft life.

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.

Randomized controlled trial of prophylactic repair of hemodialysis arteriovenous graft stenosis

BACKGROUND

Previous nonrandomized studies suggest that prophylactic repair of hemodialyisis arteriovenous (AV) graft stenosis reduces thrombosis rates and increases cumulative graft survival. The present study is a randomized trial comparing prophylactic repair of AV graft stenosis with repair at the time of thrombosis.

METHODS

Sixty-four patients with elevated static venous pressure measured in an upper extremity AV graft were randomized to Intervention or Observation. Monthly static venous pressure/systolic blood pressure ratios (SVPR) were determined for all patients throughout the duration of study participation. Patients in the Intervention group underwent angiography and repair of identified stenoses if the monthly SVPR was elevated (>/=0.4). Patients in the Observation group underwent stenosis repair only in the event of access thrombosis or clinical evidence of access dysfunction. The primary end point was access abandonment.

RESULTS

Access abandonment occurred in 14 patients in the Intervention group and 14 patients in the Observation group during the 3.5-year study period. Time to access abandonment did not differ significantly between the treatment groups (hazard ratio for randomization to Intervention 1.75, 95% CI 0.80-3.82, P= 0.16). The proportion of patients with a thrombotic event was greater in the Observation group (72%) than in the Intervention group (44%) (P= 0.04), but overall thrombosis rates were similar in the groups.

CONCLUSION

Compared with a strategy of observation and repair of accesses only in the event of thrombosis, prospective static venous pressure monitoring with prophylactic stenosis repair did not prolong graft survival.

Establishment and maintenance of vascular access in incident hemodialysis patients: a prospective cost analysis

Despite the importance of hemodialysis vascular access, the cost of vascular access care has not been studied in detail. A prospective cost analysis was performed among incident hemodialysis patients to determine the cost of vascular access care overall and on the basis of access type. Detailed clinical and demographic information, as well as data on access type, was collected for all local incident hemodialysis patients between July 1, 1999, and November 1, 2001. A comprehensive measure of total vascular access costs, including surgery, radiology, hospitalization for access complications, physician costs, costs for management of outpatient bacteremia, and vascular access monitoring costs, was obtained. Costs are reported in 2002 Canadian dollars (1 CAN dollar = 0.69 US dollar). A total of 239 consecutive incident hemodialysis patients were identified, 49, 157, and 33 of whom were dialyzed exclusively with a catheter or had a native arteriovenous fistula or synthetic graft attempted, respectively. In year 1, 18.4% of all hospital admissions were for vascular access-related complications. The mean cost of all vascular access care in year 1 was 6890 CAN dollars(median 4020 dollars; interquartile range [IQR] 2440 dollars to 7540 dollars). The mean cost of access care per patient-year at risk for maintaining a catheter exclusively, attempting an arteriovenous fistula, or attempting a graft was 9180 dollars (median 3812 dollars; IQR 2250 dollars to 7762 dollars), 7989 dollars (median 4641 dollars ; IQR 3035 dollars to 8832 dollars), and 11,685 dollars (median 8152 dollars; IQR 3395 dollars to 12,908 dollars), respectively (P = 0.01). Vascular access care is responsible for a significant proportion of health care costs in the first year of hemodialysis. These results support clinical practice guidelines that recommend preferential placement of a native fistula.

Monitoring and maintenance of arteriovenous fistulae and graft function in haemodialysis patients

PURPOSE OF REVIEW

Several options exist for detecting and preventing stenosis in polytetrafluoroethylene grafts and arteriovenous fistulae for haemodialysis. Although observational studies show a significant benefit of such strategies, data from randomized trials are limited. This review describes recently published information that has helped to advance this field during the past year.

RECENT FINDINGS

A new method for the measurement of access blood flow is discussed. This technique does not require special apparatus, which may facilitate its use in settings where resources are limited. The utility and potential shortcomings of access blood flow monitoring in grafts and fistulae are discussed, focusing on three key controlled studies published during the past year. Although much additional research is needed, regular access blood flow monitoring may improve outcomes in fistulae. Although there is less evidence that access blood flow monitoring is beneficial in grafts, regular dynamic venous pressure monitoring seems reasonable, because it can detect stenosis at a low capital cost. Neither radiotherapy nor combination therapy with aspirin and clopidogrel are useful for the prevention of stenosis in grafts.

SUMMARY

Large randomized trials of screening appear feasible for both types of permanent vascular access. Given the adverse patient outcomes associated with access failure, as well as the high costs attributable to the implementation of ineffective screening strategies, such trials should be a high priority for nephrology researchers.

Vascular access for hemodialysis: 2004 and beyond

PURPOSE OF REVIEW

Developments in vascular access are accruing rapidly. The last systematic Kidney Disease Outcomes Quality Initiative guidelines review took place in 2000. The purpose of this review is to update several major areas in which clear progress has been made. A major 'Fistula First Initiative' in the USA is an attempt to increase markedly the fraction of patients receiving an autologous arteriovenous fistula as opposed to a graft. Preoperative mapping to evaluate veins and artery may permit construction of arteriovenous fistula in up to 70% of all patients, thereby reducing access thrombosis, infection, and perhaps increasing survival of patients.

RECENT FINDINGS

Although a number of different synthetic materials have been tried, none seems to have any definite advantage over plain expanded polytetrafluoroethylene for constructing synthetic bridge grafts. Two developments may influence practice: use of composite self-sealing grafts that can be used within hours may eliminate the need for temporary catheters; and use of nitinol surgical clips may reduce endothelial trauma and improve patency. Large-bore catheters can deliver blood flows of over 400 ml/min initially, but they are prone to progressive occlusion. Optimal means of using a fibrinolytic to preserve flow must be evaluated. Surveillance techniques are undergoing rapid re-evaluation. Finally, a variety of antibiotic lock techniques are being evaluated for their ability to prevent catheter-related infections.

SUMMARY

Greater efforts must be made to establish pre-end-stage renal disease programs to educate and prepare patients for hemodialysis and improve arteriovenous fistula placement rates, and to encourage clinicians to re-examine their current clinical practices and dedicate themselves to improving vascular access outcomes.

Determinants of native arteriovenous fistula blood flow

BACKGROUND

Determinants of native arteriovenous fistula (AVF) placement have been well studied. Little is known on whether these factors impact on subsequent blood flow (Qa) in the mature AVF.

METHODS

Arteriovenous fistula Qa and cardiac index (CI) were determined by ultrasound dilution. Multiple linear regression was used to assess independent predictors of AVF Qa.

RESULTS

Of the 148 patients available for the analysis, 68% were male, with 61% using a radiocephalic AVF. Aetiology of renal disease was: 38% glomerulonephritis (GN), 22% diabetes mellitus (DM), 9% hypertension/ischaemic (HTN) and 31% other. Thirty per cent had coronary artery disease (CAD), 10% cerebrovascular disease and 11% peripheral vascular disease (PVD). Median (iqr) Qa was 1185 mL/min (790-1650) and CI was 3.15 L/min per 1.73 m(2) (2.60-3.93). On univariable analysis, log CI (0.98, P < 0.001), age (-0.1 per 10 years, P = 0.002), access position (upper vs lower 0.26, P = 0.003, PVD (-0.35, P = 0.015), CAD (-0.25, P = 0.008), and primary renal disease (DM vs GN, -0.35, P = 0.003, HTN vs GN, -0.34, P = 0.04) were associated with Qa. On multivariable analysis, CI (0.84, P < 0.001), access position (upper vs lower, 0.17, P = 0.018) and primary renal disease (DM vs GN, -0.26, P = 0.005, and HTN vs GN, -0.26, P = 0.038) remained significant predictors of AVF Qa.

CONCLUSION

Once established, CI, AVF position and primary renal disease (hypertension/ischaemic and diabetes) are the major determinants of AVF Qa while female gender, CAD, PVD and body mass index were not significant determinants of Qa in this cohort.

Timing of first cannulation and vascular access failure in haemodialysis: an analysis of practice patterns at dialysis facilities in the DOPPS

BACKGROUND

Optimal waiting time before first use of vascular access is not known.

METHODS

Two practices-first cannulation time for fistulae and grafts, and blood flow rate-were examined as potential predictors of vascular access failure in the Dialysis Outcomes and Practice Patterns Study (DOPPS). Access failure (defined as time to first failure or first salvage intervention) was modelled using Cox regression.

RESULTS

Among 309 haemodialysis facilities, 2730 grafts and 2154 fistulae were studied. For grafts, first cannulation typically occurred within 2-4 weeks at 62% of US, 61% of European and 42% of Japanese facilities. For fistulae, first cannulation occurred <2 months after placement in 36% of US, 79% of European and 98% of Japanese facilities. Overall, the relative risk (RR) of graft failure in Europe was lower compared with the USA (RR = 0.69, P = 0.04). The RR of graft failure (reference group = first cannulation at 2-3 weeks) was 0.84 with first cannulation at <2 weeks (P = 0.11), 0.94 with first cannulation at 3-4 weeks (P = 0.48) and 0.93 with first cannulation at >4 weeks (P = 0.48). The RR of fistula failure was 0.72 with first cannulation at <4 weeks (P = 0.08), 0.91 at 2-3 months (P = 0.43) and 0.87 at >3 months (P = 0.31) (reference group = first cannulation at 1-2 months). Facility median blood flow rate was not a significant predictor of access failure.

CONCLUSIONS

Earlier cannulation of a newly placed vascular access at the haemodialysis facility level was not associated with increased risk of vascular access failure. Potential for confounding due to selection bias cannot be excluded, implying the importance of clinical judgement in determining time to first use of vascular access.

K/DOQI Guidelines: What Should an Interventionalist Know?

The Kidney Disease Outcomes Quality Initiative (K/DOQI) is an evolving, literature-based set of practice guidelines designed to improve measurably the quality of life for dialysis patients. As is characteristic of guidelines, they do not change as rapidly as the literature. The K/DOQI guidelines are not meant as the definitive document and should be not treated as such. Although the guidelines are not perfect, everyone caring for chronic renal patients should be very familiar with the guidelines. It is perfectly acceptable to adopt approaches that differ from the guidelines as long as they are supported by literature. An attempt is made in this article to review the aspects of the guidelines most pertinent to the interventionalist and outline deviations from the guidelines that are supported by literature.

Correlation of Intragraft Blood Flow with Characteristics of Stenoses Found During Diagnostic Fistulography

PURPOSE

To determine if intragraft blood flow measurements correlate with the anatomical characteristics of stenoses found during diagnostic fistulography.

MATERIALS AND METHODS

This investigation was a retrospective review of 40 patients with decreased intragraft blood flow (<600 mL/min) in patent polytetrafluoroethylene hemodialysis grafts who underwent diagnostic fistulography and angioplasty. Intragraft blood flow was measured with the ultrasonic dilution technique. The fistulogram images were reviewed and the anatomic characteristics of all stenoses were measured and recorded. These characteristics were correlated with the intragraft blood flow values.

RESULTS

The mean intragraft blood flow was 476 mL/min (range, 270-600 mL/min). Fistulography revealed a total of 71 stenoses and all 40 patients had at least one lesion with > 50% stenosis. There was no correlation between the intragraft blood flow and the location, length, or number of stenoses. There was a moderate inverse correlation between the intragraft blood flow and the degree of stenosis (P =.08). Fifty-nine stenoses were treated with angioplasty. The mean postangioplasty blood flow was 796 mL/min (range, 470-1565 mL/min). The mean change in blood flow after angioplasty was 311 mL/min (range, 15-1154 mL/min) There was no association between the change in blood flow after angioplasty and the number, length, or degree of residual stenosis.

CONCLUSION

Intragraft blood flow < 600 mL/min is an excellent predictor of the presence of at least one significant (>/=50%) stenosis. There was an inverse correlation between intragraft blood flow and the degree of stenosis. There was no association between the intragraft blood flow and the location, length, or number of stenosis.

Clinical validation of glucose pump test (GPT) compared with ultrasound dilution technology in arteriovenous graft surveillance

BACKGROUND

Blood flow (Qa) measurements are an important step in the surveillance protocol of haemodialysis vascular access (VA). The glucose pump test (GPT) is a new test for Qa measurement based on the dilution of a constant glucose infusion. The aim of this study is to verify the clinical accuracy of GPT in a graft surveillance protocol with sequential Qa measurements.

METHODS

In 30 chronic haemodialysis patients with graft, we compared monthly sequential Qa measurements performed with GPT in pre-dialysis and the ultrasound dilution technique (HD01 device Transonic Systems Inc., USA) during dialysis. The colour Doppler ultrasonography study (CDU) was our reference standard for the diagnosis of stenosis. The endpoints were the graft thrombosis or PTA treatment.

RESULTS

According to the K/DOQI guidelines we could identify the thrombosis high-risk grafts when Qa was <600 ml/min or <1000 ml/min with a decrease >25% in serial Qa measurements. HD01 yielded 27 of 112 high-risk Qa measurements (21 Qa <600 ml/min; mean 406+/-145 ml/min; 6 deltaQa >25%; mean 43+/-7%). In 12 of 27 cases the CDU control did not show haemodynamically significant stenoses (false positive); 15 of 27 cases were confirmed high-risk accesses by CDU and did PTAs (HD01 specificity 86%). GPT yielded 14 of 112 high-risk Qa measurements (8 Qa <600 ml/min; mean 404+/-135 ml/min; 6 deltaQa >25%; mean 38+/-8%) and all had severe stenoses and underwent PTA treatments showing a GPT specificity of 100%. The CDU study allowed us to correctly assess the Qa negative cases. HD01 method had 10 false negative cases (treated or clotted grafts with a Qa >600 ml/min and deltaQa <25%) with a sensitivity of 60%, while GPT had 11 false negative cases with a sensitivity of 56%. The diagnostic accuracy tested with the ROC curves was similar with both tests (area under the curve was 0.762 and 0.752 with GPT and ultrasound dilution, respectively; P = 0.985). The diagnostic efficiency (percentage of grafts with agreement between test result and factual situation) was 90 and 80% (P = 0.056) for GPT and HD01, respectively.

CONCLUSION

Compared with HD01, the GPT had a lower false positive rate and similar diagnostic accuracy and efficiency. The clinical implication is a smaller number of unnecessary, invasive procedures (angiographies or PTAs), without increasing the thrombosis risk. This study has shown that GPT is an accurate, quick and economic test for Qa monitoring.

The natural history of autogenous radio-cephalic wrist arteriovenous fistulas of haemodialysis patients: a prospective observational study

BACKGROUND

Clinical practice guidelines have supported vascular access surveillance programmes on the premise that the natural history of the vascular access will be altered by radiological or surgical interventions after vascular access dysfunction is detected. The primary objective of this study was to assess the actual risk of thrombosis of autogenous radio-cephalic (RC) wrist arteriovenous fistulas (AVFs) without any pre-emptive interventions.

METHODS

We enrolled 52 randomly selected adult Caucasian prevalent haemodialysis (HD) patients, all with autogenous RC wrist AVFs, into this prospective, observational study aimed to follow the natural history of their AVFs for 4 years. The protocol prescribed avoiding any surgical or interventional radiological procedures until access failure (AVF thrombosis or a vascular access not assuring a single-pool Kt/V > or =1.2). The subjects underwent yearly assessments of vascular access blood flow rate by means of a saline ultrasound dilution method.

RESULTS

All failures of vascular access were due to AVF thrombosis; none were attributed to an inadequacy of the dialysis dose. AVF thrombosis occurred in nine cases; a rate of 0.043 AVF thrombosis per patient-year at risk. A receiver operating characteristic curve, evaluating the diagnostic accuracy of baseline vascular access blood flow rate values in predicting AVF failure, showed an under-the-curve area of 0.82+/-0.05 SD (P = 0.01). The value of vascular access blood flow rate, identified as a predictor of AVF failure, was <700 ml/min with an 88.9% sensitivity and 68.6% specificity. When subdividing the population of AVFs into two groups according to the baseline vascular access blood flow rates, two out of the nine thromboses occurred among the AVFs that had baseline blood flow rates >700 ml/min (n = 31), whereas seven occurred among the AVFs that had baseline blood flow rates <700 ml/min (n = 21). The 4 year cumulative actuarial survival was 74.36 and 20.80%, respectively (log-rank test, P = 0.04). The 24 AVFs that remained patent at the end of the 4 years maintained a median blood flow rate > or =900 ml/min at all time points studied. Worth noting is that, five of them (20.8%) remained patent throughout the study with a blood flow rate consistently < or =500 ml/min.

CONCLUSIONS

This study shows a very low rate of AVF thrombosis per patient-year at risk and a high actuarial survival of autogenous RC wrist AVFs, particularly of those having a blood flow rate >700 ml/min. Thus, a vascular access blood flow rate <700 ml/min appears to be a reliable cut-off point at which to start a closer monitoring of this parameter-which may lead to further investigations and possibly interventions relevant to the function of the AVFs.