Native arteriovenous fistula blood flow and resistance during hemodialysis

Guidelines on vascular access for hemodialysis from the Brazilian Society of Angiology and Vascular Surgery

Chronic kidney disease is a worldwide public health problem, and end-stage renal disease requires dialysis. Most patients requiring renal replacement therapy have to undergo hemodialysis. Therefore, vascular access is extremely important for the dialysis population, directly affecting the quality of life and the morbidity and mortality of this patient population. Since making, managing and salvaging of vascular accesses falls within the purview of the vascular surgeon, developing guideline to help specialists better manage vascular accesses for hemodialysis if of great importance. Thus, the objective of this guideline is to present a set of recommendations to guide decisions involved in the referral, evaluation, choice, surveillance and management of complications of vascular accesses for hemodialysis.

KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update

The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) has provided evidence-based guidelines for hemodialysis vascular access since 1996. Since the last update in 2006, there has been a great accumulation of new evidence and sophistication in the guidelines process. The 2019 update to the KDOQI Clinical Practice Guideline for Vascular Access is a comprehensive document intended to assist multidisciplinary practitioners care for chronic kidney disease patients and their vascular access. New topics include the end-stage kidney disease "Life-Plan" and related concepts, guidance on vascular access choice, new targets for arteriovenous access (fistulas and grafts) and central venous catheters, management of specific complications, and renewed approaches to some older topics. Appraisal of the quality of the evidence was independently conducted by using a Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, and interpretation and application followed the GRADE Evidence to Decision frameworks. As applicable, each guideline statement is accompanied by rationale/background information, a detailed justification, monitoring and evaluation guidance, implementation considerations, special discussions, and recommendations for future research.

The effect of vascular access type on intra-access flow volume during hemodialysis

INTRODUCTION

Previous studies have revealed that vascular access resistance is constant during hemodialysis, but differs according to vascular access type. It is possible that intra-access flow volume (Qac) variation during hemodialysis may also differ according to vascular access type. We conducted this study to investigate whether there are differences in Qac according to vascular access type during hemodialysis.

METHODS

A total of 58 lower-arm arteriovenous fistula, 14 lower-arm arteriovenous graft, 27 upper-arm arteriovenous fistula, and 45 upper-arm arteriovenous graft cases were studied. Three consecutive Qac values (at 30, 120, and 240 min after the start of hemodialysis) were measured in each patient by the ultrasound dilution technique. Variations in Qac over time were analyzed using repeated measures analysis of variance and multivariate regression analyses, to assess the impact of different factors on Qac variation.

RESULTS

The repeated measures analysis of variance revealed that a significant interaction exists between time and vascular access type (p < 0.001). This suggests that vascular access type affects Qac change (%) variation over time during hemodialysis. In a multivariate analysis, mean arterial pressure change during hemodialysis (p = 0.009), access type (p < 0.001), and access location (p < 0.001) were independent variables causing Qac change variation.

CONCLUSION

This study showed that there is a significant difference in Qac variation according to vascular access type during hemodialysis and that arteriovenous graft (vs arteriovenous fistula) and the lower-arm location (vs upper arm) were associated with a decrease in Qac during hemodialysis. This suggests that consideration of vascular access type is required to minimize Qac variation during hemodialysis.

Sentinel vascular access monitoring after endovascular intervention predicts access outcome

BACKGROUND AND OBJECTIVES

The vascular access pressure ratio test identifies dialysis vascular access dysfunction when three consecutive vascular access pressure ratios are >0.55. We tested whether the magnitude of the decline in vascular access pressure ratio 1-week post-intervention could alert of subsequent access failure.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

The retrospective study included all vascular access procedures at one institution from March 2014 to June 2016. Data included demographics, comorbidities, vascular access features, %ΔVAPR = ((Pre-Post)/Pre] × 100% assessed within the first 2 weeks post-percutaneous transluminal balloon angioplasty, time-to-next procedure, and patency. The log-rank test compared the area under the curve, receiver operating curve, Kaplan-Meier arteriovenous graft and arteriovenous fistula survival curves. A multivariable Cox proportional hazard (CP) model was used to determine the association of %ΔVAPR with access patency.

RESULTS

Analysis of 138 subjects (females 51%; Black 87%) included 64 arteriovenous fistulas with 104 angioplasties and 74 arteriovenous grafts with 134 angioplasties. The area under the receiver operating characteristic curve for fistula failure at 3 months was 0.59, with optimal screening characteristics of 33.3%, sensitivity of 56.1%, and specificity of 63.2%. Arteriovenous fistula with <33.3% decline compared to >33.3% required earlier subsequent procedure (136 vs 231 days), lower survival on Kaplan-Meier analysis (P = 0.01), and twofold greater risk of failure (P = .006). Area under the receiver operating characteristic for arteriovenous graft failure at 3 months had a sensitivity of 52.3% and specificity of 67.4%. Arteriovenous graft with a post-intervention vascular access pressure ratio decline of <28.8% also required earlier subsequent procedure (144 vs 189 days), lower survival on Kaplan-Meier (P = 0.04), and a 59% higher risk for failure. The area under the receiver operating characteristic curve for combined access failure (arteriovenous fistula + arteriovenous graft) at 3 months had an optimal cut-point value of 31.2%, a sensitivity of 54.6%, and a specificity of 63.1%. Access with a <31.2% drop had a 62% increase in the risk of failure (hazard ratio 1.62; confidence interval 1.16, 2.27; P = 0.005).

CONCLUSION

The magnitude of post-intervention reduction in vascular access pressure ratio provides a novel predictive measure of access outcomes.

A Dedicated Vascular access Program can Improve Arteriovenous Fistula Rates without Increasing Catheters

Purpose

We describe the development and implementation of a comprehensive multidisciplinary vascular access (VA) program and describe its impact on VA distribution rates.

Methods

A retrospective review of all incident and prevalent patients in our hemodialysis (HD) unit was conducted in September 2001 to determine baseline data including: type of VA along with patient characteristics and comorbidities. Similar data was extracted from the database in 2005 for incident and prevalent patients.

Results

The VA program had a significant impact on arteriovenous fistulae (AVF) rates in both incident and prevalent HD patients: incident AVF rates increased from 14 to 39% (p=0.04) and prevalent AVF rates from 60 to 64% (p=0.015). Multivariate analysis revealed that male gender (OR 1.79 [CI 0.85–0.98, p=0.006]) and year of dialysis initiation 2005 vs. 2001 (OR 1.65 [CI 1.09–2.5, p=0.017]) were associated with AVF use among prevalent HD patients. Furthermore, age (per 5 years over 70) is associated with a decreased likelihood of having an AVF (OR 0.91 [CI 0.85–0.98, p=0.009]) whereas comorbidities of cardiovascular disease and diabetes had no impact.

Conclusion

We demonstrate that a structured VA program can increase the number of functioning fistulas without a corresponding increase in catheters in incident and prevalent HD patients.

Evolution of Hemodialysis Access Resistance: A Longitudinal 5-Year Model using Functional Principal Components Analysis

Purpose

Arteriovenous fistulae (AVF) and grafts (AVG) are the preferred accesses in hemodialysis (HD). By monitoring Access Resistance (AR) one can potentially identify problems with an established HD access, but little is known about how these changes in AR occur, or the variations between the two access types as they mature longitudinally. We postulated that AR evolves differentially between AVF and AVG, a critical aspect to further understanding of the natural history of HD accesses. To describe these changes, we applied a novel statistical methodology of Functional Principal Component (FPC) analysis.

Methods

Using ultrasound dilution flow studies, we retrospectively studied 479 functional HD accesses in which a total of 4573 assessments were made. Accounting for patient factors of age, race, gender and diabetes mellitus (DM) status, we employed a multivariate, mixed-effects model. Using the mean effects of those covariates, we then applied FPC analyses to assess the longitudinal, time-dependent changes between AVFs and AVGs over a 5-year period.

Results

Both types of upper-arm access were associated with a lower initial AR. Older age and DM were associated with a higher AR. Longitudinal AR varied significantly for both AVF and AVG, between the upper arm and lower arm. As a function of time, AVG was associated with an increasing AR. Conversely, AVF, especially upper-arm ones, demonstrated a longitudinal drop in AR.

Conclusions

Evolutionally AR can be predicted not only by the type of access, but also by the location along the arm of that access and by clinical patient factors. Longitudinal change in AR does differ between AVG and AVF. Our report provides the foundation of observed changes over time and provides insight as to how these variations are affected. We endorse ongoing surveillance to screen for clinical sequelae, even years from initial placement.

The rise and fall of access blood flow surveillance in arteriovenous fistulas

Vascular access blood flow (Qa) surveillance has been described as a typical false paradigm, an example of how new tests are sometimes adopted even without good-quality evidence of their benefits. This may be true for grafts, but not necessarily for arteriovenous fistulas. We reviewed the literature on Qa surveillance in fistulas to see whether it complies with the World Health Organization's criteria for screening tests. Measuring Qa has a fairly good reproducibility. Qa shows an excellent-to-good accuracy for stenosis being the only bedside screening test that achieves a very high sensitivity while retaining a fair-to-good positive predictive value for Qa thresholds of 600 ml/minute or higher associated with a >25% drop in Qa, or findings suggesting stenosis on physical examination. The accuracy of Qa in predicting thrombosis is hard to establish because of the heterogeneity of published studies, though a Qa of 300 ml/minute seems the most reliable cutoff. Qa surveillance affords a significant 2- to 3-fold reduction in the risk of thrombosis by comparison with clinical monitoring alone when Qa criteria highly sensitive to stenosis are considered, regardless of the study design (randomized controlled trials, cohort studies with concurrent or historic controls). Using highly sensitive Qa screening criteria also halves the risk of access loss, although this effect is not statistically significant. Our analysis strongly suggests that Qa surveillance is an effective method for screening mature fistulas, though further, appropriately designed studies are needed to fully elucidate its benefits and cost effectiveness.

Should current criteria for detecting and repairing arteriovenous fistula stenosis be reconsidered? Interim analysis of a randomized controlled trial

BACKGROUND

The vascular access guidelines recommend that arteriovenous fistulas (AVFs) with access dysfunction and an access blood flow (Qa) <300-500 mL/min be referred for stenosis imaging and treatment. Significant (>50%) stenosis, however, may be detected in a well-functioning AVF with a Qa > 500 mL/min, too, but whether it is worth correcting or not remains to be seen.

METHODS

In October 2006, we began an open randomized controlled trial enrolling patients with an AVF with subclinical stenosis and Qa > 500 mL/min, to see how elective stenosis repair [treatment group (TX)] influenced access failure (thrombosis or impending thrombosis requiring access revision), or loss and the related cost compared with stenosis correction according to the guidelines, i.e. after the onset of access dysfunction or a Qa < 400 mL/min [control group (C)]. An interim analysis was performed in July 2012, by which time the trial had enrolled 58 patients (30 C and 28 TX).

RESULTS

TX led to a relative risk of 0.47 [95% confidence interval (CI): 0.17-1.15] for access failure (P = 0.090), 0.37 [95% CI: 0.12-0.97] for thrombosis (P = 0.033) and 0.36 [95% CI: 0.09-0.99] for access loss (P = 0.041). In the setting of our study (in which all surgery was performed as in patient procedure) no significant differences in costs emerged between the two strategies. The mean incremental cost-effectiveness ratio for TX was €282 or €321 to avoid one episode of thrombosis or access loss, respectively.

CONCLUSIONS

Our interim analysis showed that elective repair of subclinical stenosis in AVFs with Qa > 500 mL/min cost-effectively reduces the risk of thrombosis and access loss in comparison with the approach of the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines, raising the question of whether the currently recommended criteria for assessing and treating stenosis should be reconsidered.

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.

Blood Flow Measurements during Hemodialysis Vascular Access Interventions - Catheter-Based Thermodilution or Doppler Ultrasound?

Purpose

To test the clinical performance of catheter-based thermodilution and Doppler ultrasound of the feeding brachial artery for blood flow measurements during hemodialysis vascular access interventions.

Methods

Thirty patients with arteriovenous fistulas who underwent 46 interventions had access blood flow measured before and after every procedure. Two methods, catheter-based thermodilution and Doppler ultrasound, were compared to the reference method of ultrasound dilution. Catheter-based thermodilution and Doppler ultrasound were performed during the endovascular procedures while flow by ultrasound dilution was determined within three days of the procedure. The methods were compared using regression analysis and tested for systematic bias.

Results

Failure to position the thermodilutional catheter correctly was observed in 8 out of 46 (17%) pre-intervention measurements. Post-intervention measurements and ultrasound measurements were feasible in all patients. The average level of agreement was good when comparing catheter-based thermodilution to ultrasound dilution. However, blood flow by ultrasound dilution may differ by ±130 mL/min (±22%) at a flow level of 600 mL/min by thermodilution. Results from Doppler ultrasound displayed a moderate level of agreement on average when compared to ultrasound dilution. Blood flow by ultrasound dilution may differ by ±160 mL/min (±27%) at a flow level of 600 mL/min by Doppler ultrasound. No systematic bias was detected by either method.

Conclusions

On average, results from catheter-based thermodilution were more in agreement with results from the ultrasound dilution technique compared to Doppler ultrasound. However, considering the cost and the high technical failure rate of the thermodilutional system, we recommend the use of ultrasound.

Epidemiology and blood flow surveillance of the native arteriovenous fistula: a review of the recent literature

Vascular access placement is a key management issue for hemodialysis patients. Despite being well regarded as the access of first choice, the native arteriovenous fistula (AVF) remains underutilized in the United States. The first part of this review examines recent epidemiology studies addressing patient factors associated with the use of the synthetic arteriovenous graft as opposed to the native fistula. Female gender and older age are consistently associated with a higher frequency of graft use. Diabetes, peripheral vascular disease, and body mass index were associated with graft use in some but not all of the studies. Recent evidence also suggests an independent survival advantage for patients dialyzing via native fistulae especially for infection-related mortality. The second part reviews evidence surrounding the recommendations for blood flow surveillance of the native fistula. The hemodynamic features of the native fistula are examined and differences from synthetic grafts are highlighted. Clinical studies assessing the use of blood flow surveillance to prevent the sudden thrombosis of native fistulae are reviewed. Blood flow thresholds for further investigation are yet to be determined definitely for AVF and randomized studies should be performed to assesses the impact on AVF thrombosis rates.

Comparison of classical and non-classical cardiovascular risk factors influencing the patency of native arteriovenous fistulas after percutaneous transluminal angioplasty therapy among haemodialysis patients

OBJECTIVE

To evaluate the classical and non-classical cardiovascular risk factors that effect patency of native arteriovenous fistulas (AVF) in end stage renal disease (ESRD) patients who are undergoing regular haemodialysis treatment and have a percutaneous transluminal angioplasty (PTA) procedure.

METHODS

All PTAs performed between 1 October 2002 and 30 September 2004 were identified from case notes and the computerised database and follow up to 31 March 2005. The definition of patency of AVF after PTA was including primary or secondary patencies. Risks were analysed to assess the influence on survival following PTAs of age, sex, serum cholesterol, serum triglyceride, diabetes, use of aspirin, current smoking and hypertension, serum albumin, serum calcium-phosphate product, intact parathyroid hormone (I-PTH), and urea reduction ratio (URR).

RESULTS

The patency rate of AVFs of all interventions was 65% at 6 months. Factors with poor patencies of AVFs after PTA procedures were higher serum calcium-phosphate product (p = 0.033), higher URR (p<0.001), lower serum albumin (p<0.001), non-hypertension (p = 0.010) and "non-smoker + ex-smoker group" (p = 0.033). The hypertensive patients and current smokers had lower patency failure after PTAs (p<0.01 and p<0.05, respectively).

CONCLUSIONS

Unfavourable cumulative patency rates are observed in haemodialysis patients with higher URR, higher serum calcium-phosphate product and hypoalbuminaemia (lower serum albumin before the PTA procedure). Hypertension and current smoking were associated with better patency rates of AVF after PTA.

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.

Within-session and between-session variability of haemodialysis shunt flow measurements

BACKGROUND

Knowledge of the variability of a measurement method is essential for its clinical application. We investigated the variability of shunt flow measurements, since this is a relatively neglected area in the literature. In particular, no direct comparison of between-session and within-session variability was available until now.

METHODS

During two consecutive dialysis sessions, shunt flow was measured three times with the ultrasound dilution method in 24 chronic haemodialysis patients with various types of shunts. Needle orientation and blood pressure at the time of flow measurement were recorded. In these patients, shunt flow was also measured three times by duplex ultrasound before the first dialysis session.

RESULTS

The within-session variation coefficient (VC) of shunt flow measured with ultrasound dilution was 7.7%, whereas the between-session VC was 14.2% (n.s.). The within-session VC of Doppler shunt flow was 11.6% which was not significantly different from the corresponding figure of ultrasound dilution. Analysis of subgroups showed that changes in needle orientation caused large differences between sessions in radiocephalic fistulas but not in brachiocephalic fistulas: in the radiocephalic fistulas with the same needle orientation, VC was 6.7%, but with different needle orientation it was 23.5% (P = 0.02); the corresponding figures for brachiocephalic fistulas were 14.6% (same direction) and 11.4% (different direction, n.s.).

CONCLUSION

Reproducibility of shunt flow measurements between dialysis sessions in radiocephalic fistulas is critically dependent on similar needle orientation. With similar needle position and correction for blood pressure differences, flow changes of more than 20-25% are likely to reflect true flow changes. The variability of duplex flow measurements is at least as large as that of the ultrasound dilution method.

Prediction of failure of native arteriovenous fistulas using 'on-line' fistula flow measurements

BACKGROUND

Measurement of blood flow within native arteriovenous fistula during haemodialysis is recommended to detect incipient fistula failure. In the present study the value of such flow measurements was assessed in a group of patients on maintenance haemodialysis, with access via native arteriovenous fistulas.

METHODS

Flow was measured using the 'on-line' thermodilution technique, on three separate occasions, and correlated with subsequent fistula failure within 6 months.

RESULTS

Of the 53 patients studied, there were six failures (three thromboses and three inadequate dialysis filtration rates). Flow rates in patients who progressed to fistula failure were significantly less than flow rates in patients whose fistulas did not fail (U = 13.0, P < 0.0003). Failure was no more common in one type of fistula than another (type fistula: F = 0.29, P = 0.88; flow predicting failure: F = 7.22, P = 0.010). Receiver operating characteristic (ROC) curve analyses confirmed flow measurement to be a useful predictor of fistula failure (area under ROC curve 0.91). The optimal threshold of 576 mL/min flow gave a sensitivity of 89% and a specificity of 81%. Measurement of access resistance was less useful in predicting failure (area under ROC curve 0.87). Measurement of fall in flow from the previous measurement was of no use (area under ROC curve 0.535).

CONCLUSION

On-line thermodilution measurement of flow within established native arteriovenous fistula is useful in surveillance and early prediction of fistula failure. Fistula flow <576 mL/min may indicate incipient native fistula failure, and should prompt further investigation.

Arteriovenous fistula-associated high-output cardiac failure: a review of mechanisms

High-output cardiac failure can be a rare complication of high-output arteriovenous fistula. The authors present a case in which a hemodialysis patient with a high-flow arteriovenous fistula has cardiac failure that improves with fistula closure. The hemodynamic effects of a fistula are reviewed, and the hemodialysis literature regarding high-output cardiac failure is summarized. To gain insight into the problem of high-output cardiac failure, research efforts should focus on the prospective monitoring of high-access flows.

Factors associated with access blood flow in native vessel arteriovenous fistulae

BACKGROUND

Access blood flow (Qa) identifies stenosis in patients with native vessel AV fistulae (AVF), but data on factors that are associated with Qa in normally functioning accesses are sparse. Such factors could be used in conjunction with Qa to improve the diagnostic performance of screening. We examined the relationship between Qa and certain clinical characteristics in a large group of patients with AVF.

METHODS

This was a retrospective study of incident and prevalent haemodialysis patients treated at a single institution, all of whom had a functioning AVF during the study period. Qa was measured bimonthly using ultrasound dilution in all subjects. Mixed models were used to explore the relationship between Qa and a group of independent variables, including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), diabetes mellitus, patient age, sex, height, body mass index (BMI) and AVF location (forearm vs upper arm).

RESULTS

A total of 4084 Qa measurements was made in 294 patients. Univariate analysis found that younger patient age, non-diabetic status, higher blood pressure (SBP, DBP, MAP, all at the time of Qa measurement), upper arm AVF location and overweight status (BMI >/=25) were significantly associated with Qa. SBP appeared to be more strongly associated with Qa than either DBP or MAP. Patient sex, height and interval between access creation and Qa measurement were not significantly associated with Qa. Tests for interaction suggested that the association between SBP and age and Qa varied significantly by access location. In a multivariate model, SBP, overweight status and diabetic status were independently associated with Qa. The strength of the association between these characteristics and Qa appeared to be clinically relevant.

CONCLUSIONS

Our findings suggest that a single Qa threshold for angiography in all patients may be simplistic, and that the optimal threshold might vary by patient subgroup. The strong association between SBP and Qa suggests that adjusting Qa for SBP may improve the specificity of access screening. Further work is required to determine whether such modifications to current practice would improve the predictive power of Qa measurements for detection of stenosis in AVF.

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.

Diagnostic accuracy of ultrasound dilution access blood flow measurement in detecting stenosis and predicting thrombosis in native forearm arteriovenous fistulae for hemodialysis

BACKGROUND

Vascular access surveillance by ultrasound dilution blood flow rate (Qa) measurement is widely recommended; however, optimal criteria for detecting stenosis and predicting thrombosis in arteriovenous fistulae (AVFs) are still not clearly defined.

METHODS

In a blinded trial, we evaluated the accuracy of single Qa measurement, Qa adjusted for mean arterial pressure (Qa/MAP), and decrease in Qa over time (dQa) in detecting stenosis and predicting thrombosis in an unselected population of 120 hemodialysis subjects with native forearm AVFs (91 AVFs, located at the wrist; 29 AVFs, located at the midforearm). All AVFs underwent fistulography, which identified greater than 50% stenosis in 54 cases.

RESULTS

Receiver operating characteristic curve analysis showed that dQa, Qa, and Qa/MAP have a high stenosis discriminative ability with similar areas under the curve (AUCs), ie, 0.961 +/- 0.025, 0.946 +/- 0.021, and 0.912 +/- 0.032, respectively. In the population as a whole, optimal thresholds for stenosis were Qa less than 750 mL/min alone and in combination with dQa greater than 25% (efficiency, 90%); however, the best threshold depended on anastomotic site; it was Qa less than 750 mL/min for an AVF at the wrist and Qa less than 1,000 mL/min for an AVF in the midforearm. Qa was the best predictor of incipient thrombosis (AUC, 0.981 +/- 0.013) with an optimal threshold at less than 300 mL/min (efficiency, 94%). Pooled intra-assay and interassay variation coefficients were 8.2% for MAP, 7.9% for Qa, and 11.2% for Qa/MAP.

CONCLUSION

Our study shows that ultrasound dilution Qa measurement is a reproducible and highly accurate tool for detecting stenosis and predicting thrombosis in forearm AVFs. Neither Qa/MAP nor dQa improve the diagnostic performance of Qa alone, although its combination with dQa increases the test's sensitivity for stenosis.