A new approach to evaluate vascular access in hemodialysis patients

Reassessing the utility of access recirculation and Kt/V for the prediction of arteriovenous fistula failure using online clearance monitoring: the SHUNT STUDY

BACKGROUND

The arteriovenous fistula (AVF) is prone to thrombosis which can be avoided by use of monitoring and surveillance programmes. Although surveillance imaging techniques have been shown to be more sensitive and specific than clinical monitoring during dialysis, monitoring may have significant advantages in terms of cost and time saving. In this study we evaluate the yield of two monitoring techniques [blood temperature monitoring (BTM) access recirculation (AR) and Kt/V via online-clearance-monitoring (OCM)].

METHODS

In this single-centre prospective observational study, 101 patients were followed-up for one year. The primary outcome measure was a composite of AVF failure. OCM-Kt/V and BTM-AR were recorded at every dialysis session.

RESULTS

Of all baseline characteristics only a prior history of percutaneous transluminal angioplasty (PTA) to the AVF conferred a significant change in AVF survival (failure events/100 pt years with prior PTA vs. without = 64.0 vs. 17.3, log-rank p = 0.0014; unadjusted hazard ratio (HR) 3.74 (95% CI 1.56-8.94) p = 0.003). Participants with baseline AR < 10% vs. > 15% had poorer AVF survival (p = 0.0002) and HR for baseline AR 10-15% group vs. AR > 15% group = 4.5 (95% CI 1.55-13.05). There was no combination of change in (Δ) AR, ΔKt/V or its presence over any number of dialysis sessions that provided an acceptable combination of sensitivity and specificity or discrimination for AVF failure.

CONCLUSIONS

BTM-AR and OCM-Kt/V are specific but insufficiently sensitive tools for the prediction of AVF failure. BTM-AR and OCM-Kt/V use at every dialysis session appears to add little to the traditional, infrequent use of these evaluations.

Weight-Based Assessment of Access Flow Threshold to Predict Arteriovenous Fistula Functional Patency

Introduction

The 2019 Kidney Disease Outcome Quality Initiative (K/DOQI) guideline recommended evaluating arteriovenous fistula (AVF) malfunction risks primarily based on clinical monitoring, which can be assisted with the value of vascular access flow (Qa). Nevertheless, Qa thresholds recommended by different guidelines vary, ranging from 300 to 500 ml/min. This study investigated the optimal Qa threshold to predict future functional patency in AVFs with Qa <500 ml/min.

Methods

Both the clinical indicators of access dysfunction and the Qa value were monitored in patients receiving hemodialysis by the radiocephalic AVF. Routine access flow surveillance was performed by the ultrasound dilution method (HD03, Transonic Inc.). The development of clinically significant indicators of access dysfunction, which necessitated percutaneous transluminal angiography (PTA) to maintain functional patency, was analyzed in this cohort.

Results

Among the enrolled 302 patients, Qa of 52 patients was under 500 ml/min. These 52 patients received 2 Qa measurements during the follow-up period. Of these 52 patients, serial Qa of 17 patients varied trivially and their AVF remained functional. Multivariable logistic regression analysis revealed that a low Qa per ideal body weight (IBW) is an independent predictor of AVF functional loss. Receiver operating characteristic curve analysis of Qa/IBW in predicting future AVF functional loss revealed that the best cutoff value of Qa is 7.1 times the IBW.

Conclusion

For radiocephalic AVFs with Qa <500 ml/min, the minimally required Qa to maintain access function is associated with individual IBW. The IBW-based Qa threshold assessment would allow more flexibility in the treatment of patients and reduce unnecessary invasive measures.

Early Detection of Arteriovenous Fistula Stenosis in Hemodialysis Patients through Routine Measurements of Dialysis Dose (Kt/V)

BACKGROUND

Monitoring of arteriovenous (AV) fistula to detect hemodynamically important stenosis is crucial for the prevention of AV fistula thrombosis. The aim of our study was to analyze the importance of dialysis dose (Kt/V) during online postdilution hemodiafiltration (HDF) for early detection of AV fistula stenosis.

METHODS

Hemodialysis patients with AV fistula were included in this study. We compared a group of 44 patients who have undergone fistulography and subsequently percutaneous transluminal angioplasty (PTA) of significant AV fistula stenosis (active group) with a group of 44 age- and sex-matched patients without PTA (control group). Observational time in both groups was the same.

RESULTS

All patients had postdilution online HDF using a F5008 dialysis machine, which can measure online single-pool Kt/V. All data were analyzed during the performance of 2056 HDF procedures. In the active group, we found statistically significantly lower values of Kt/V, all 8 weeks before PTA. In the active group, there was a significant improvement in Kt/V in the first (p < 0.001) and second week (p = 0.049) after PTA. Three and 8 weeks after PTA, we did not find any statistically significant difference in Kt/V between both groups (p = 0.114; p = 0.058). Patients in the active group had statistically significantly lower substitution volumes and blood pump flow rates during HDF over the whole observation period before and after PTA. In contrast, there were no differences in venous pressure in the dialysis circuit between both groups throughout the observation period.

CONCLUSION

In hemodialysis patients with AV fistula, treated with online HDF, routine measurements of Kt/V during each HDF are a beneficial, quick, and straightforward method for early detection of hemodynamically significant AV fistula stenosis.

Getting the basics right: the monitoring of arteriovenous fistulae, a review of the evidence

PURPOSE OF REVIEW

Despite being the preferred vascular access for haemodialysis, the arteriovenous fistula (AVF) remains prone to a number of complications, the most common of these being thrombosis secondary to stenosis. This has resulted in the widespread use of monitoring and surveillance programmes. Surveillance uses more resources than monitoring and has not been convincingly shown to improve outcomes. The evidence supporting the use of the various monitoring tools has been relatively neglected and has not been the focus of literature review. This narrative review is the first to appraise the evidence for the use of physical examination, access recirculation, Kt/V and dynamic venous pressures (DVP) as monitoring tools in mature AVF.

RECENT FINDINGS

The vastly increased number of data points for access recirculation, Kt/V and DVP produced as standard by online clearance monitoring (OCM) on modern dialysis machines is likely to have significantly changed the utility of these metrics in the prediction of AVF failure. Algorithms have been developed to highlight those of highest risk of failure.

SUMMARY

The evidence supporting the use of monitoring in the prediction of AVF failure is predominantly observational, underpowered and more than 20 years old. Access recirculation and Kt/V appears to have higher utility in AVF than in arteriovenous grafts. We suggest that the development of OCM necessitates the reevaluation of these tools.

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.

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.

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.

Dysfunctional autogenous hemodialysis fistulas: outcomes after angioplasty--are there clinical predictors of patency?

PURPOSE

To determine the primary and secondary patency rates for fistulas treated with angioplasty, as well as clinical predictors of fistula patency after angioplasty.

MATERIALS AND METHODS

The authors reviewed their institutional experience with autogenous fistulas from June 1997 to June 2002. A total of 104 men and 36 women were treated. Mean age +/- standard deviation of patient cohort was 62.4 years +/- 15.6. Patient age and sex, age of fistula at initial intervention, presence of diabetes, side and location of fistula, location of stenosis, and number of venous stenoses dilated were examined. Patency after angioplasty was estimated by using the Kaplan-Meier method, and predictors of patency were examined by using a Cox proportional hazards model.

RESULTS

One hundred fifty-one dysfunctional fistulas (94 radiocephalic and 57 brachiocephalic) were treated with angioplasty initially. Clinical success rate was 98.0% (297 of 303 interventions). At 3, 6, and 12 months, respectively, primary patency rates +/- standard errors of the estimate were 73% +/- 6, 51% +/- 7, and 39% +/- 7 for brachiocephalic fistulas and 85% +/- 4, 75% +/- 5, and 62% +/- 5 for radiocephalic fistulas; secondary patency rates were 96% +/- 2.4, 89% +/- 4, and 85% +/- 5 for brachiocephalic fistulas and 91% +/- 3, 88% +/- 3, and 86% +/- 4 for radiocephalic fistulas. For all time points, there was a significant difference in primary (P =.004) but not secondary (P =.45) patency between radiocephalic and brachiocephalic fistulas. Stenosis was most prevalent within 3 cm of the arteriovenous anastomosis in 74 (64%) of the 116 dysfunctional radiocephalic fistulas and at the cephalic arch in 22 (30%) of the 74 dysfunctional brachiocephalic fistulas. The clinical variables examined did not influence outcome. Complications occurred in seven (2.3%) of 303 interventions.

CONCLUSION

Patency after angioplasty in dysfunctional autogenous hemodialysis fistulas exceeds that observed in hemodialysis grafts. None of the clinical or anatomic variables examined affected patency outcome.

Best threshold for diagnosis of stenosis or thrombosis within six months of access flow measurement in arteriovenous fistulae

Canadian clinical practice guidelines recommend performing angiography when access blood flow (Qa) is <500 ml/min in native vessel arteriovenous fistulae (AVF), but data on the value of Qa that best predicts stenosis are sparse. Because correction of stenosis in AVF improves patency rates, this issue seems worthy of investigation. Receiver-operating characteristic curves were constructed to examine the relationship between different threshold values of Qa and stenosis in 340 patients with AVF. Stenosis was defined by the composite outcome of access failure or angiographic stenosis occurring within 6 mo of the first Qa measurement. The Qa value was then classified as true negative, true positive, false negative, or false positive for stenosis. An additional analysis was performed in which Qa was corrected for systolic BP before assigning it to one of the four diagnostic categories. The area under the curve for the composite definition of stenosis was 0.86. Graphically, Qa thresholds of <500 and <600 ml/min had similar efficacy for detecting stenosis or access failure within 6 mo, and both seemed superior to <400 ml/min. However, the frequency of the composite definition of stenosis among AVF with Qa between 500 and 600 ml/min was only 6 (25%) of 24, as compared with 58 (76%) of 76 when Qa was <500 ml/min. This suggests that most lesions that would be found using a threshold of <600 ml/min occurred in AVF with Qa <500 ml/min and that the small gain in sensitivity associated with the <600-ml/min threshold would be outweighed by the reduced specificity compared with <500 ml/min. Correcting Qa for BP did not improve diagnostic performance or change these results, which were consistent in several sensitivity analyses. Qa measurements seemed to predict stenosis or incipient access failure equally well in groups defined by diabetic status, gender, and AVF location. In conclusion, it was found that Qa <500 ml/min seems to be the most appropriate threshold for performing angiography in patients with native vessel AVF. It is recommended that clinicians arrange angiography when Qa is <500 ml/min in AVF.

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.

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.

Access flow measurement during surveillance and percutaneous transluminal angioplasty intervention

The introduction of routine access flow measurement methodology has enabled accurate identification of problematic accesses and provided a means for follow-up evaluation. These methods have uncovered, in some cases, that interventions are either immediately unsuccessful or that they fail within 3 months to maintain flow above preintervention levels. The purpose of this article is to analyze the main problems that occur at each step in the loop of flow surveillance-intervention-follow-up and to provide suggestions for improving outcomes. Analysis of published access flow data suggests that the main problems lie in the areas of inadequate analysis of flow surveillance data, lack of objective technology for quantifying intervention effectiveness, and lack of follow-up flow measurements in the hemodialysis (HD) unit after the intervention. The following three recommendations may improve surveillance outcomes: 1). using a reliable access flow technology combined with analysis of all hemodynamic data (including mean arterial pressure) before referring patients for angiography to decrease surveillance false positives; 2). performing intra-access blood flow measurement during angioplasty, which may improve outcomes by giving warning of errors before the patient leaves the intervention suite. Success achieved in restoring flow as measured during the intervention usually predicts good immediate outcomes in the HD unit; 3). measuring access flows during the next week after angioplasty. If the results are unsatisfactory, the patient should be further evaluated to avoid a potential thrombotic event.

Prevalence and treatment of cephalic arch stenosis in dysfunctional autogenous hemodialysis fistulas

PURPOSE

Cephalic arch stenosis (CAS) is a recently recognized cause of dysfunction in autogenous hemodialysis fistulas. The prevalence of this lesion among dysfunctional autogenous fistulas is described, as are outcomes after percutaneous therapy.

MATERIALS AND METHODS

A cohort of 177 dysfunctional autogenous fistulas treated over a 48-month period was retrospectively analyzed for the presence of CAS. Of these, 116 (66%) were radiocephalic fistulas and 61 (34%) were brachiocephalic fistulas. CAS was identified in 26 fistulas among 24 patients. Fifty dilations and three stent placements in the cephalic arch were performed. Surveillance was conducted after percutaneous therapy by means of ultrasound dilution technique and measurement of dialysis flow rates. Patency rates were estimated with use of the Kaplan-Meier method. No patients were lost to follow-up.

RESULTS

The prevalence of CAS was 15% (26 of 177). There was a significant difference in the prevalence of CAS between brachiocephalic and radiocephalic fistulas (39% vs 2%; P <.001). High-pressure noncompliant balloon catheters were required in 29 of 50 dilations (58%) to efface the lesion. Primary patency rates (+/-SE) at 3, 6, and 12 months were 76% +/- 8, 42% +/- 10, and 23% +/- 9, respectively. Primary assisted patency rates (+/-SE) at 3, 6, and 12 months were 96% +/- 4, 83% +/- 8, and 75% +/- 10. Complications occurred in three cases (6%). A major complication with rupture of the cephalic arch resulted in thrombosis and fistula loss (n = 1); two minor complications of cephalic arch rupture were salvaged with placement of a Wallstent (n = 1) or prolonged balloon inflation (n = 1).

CONCLUSIONS

CAS is common among failing brachiocephalic arteriovenous fistulas. With aggressive percutaneous intervention and surveillance, favorable primary assisted patency rates can be achieved.

Prospective evaluation of the intra-access flow of recently created native arteriovenous fistulae

BACKGROUND

The aim of this study is to assess the evolution of intra-access flow (Q(ac)) in recently created native arteriovenous fistulae (AVFs) during the first few months of use.

METHODS

All AVFs were monitored by means of ultrasound dilution using Transonic (Transonic Systems Inc, Ithaca, NY). First Q(ac) measurements were obtained between 6 to 10 weeks after creation and subsequently every 3 to 6 weeks during the following 4 months. Per routine, AVFs are cannulated 6 weeks after their creation in our unit. Fifty-seven patients with new AVFs were initially enrolled, but 12 patients were lost at follow-up. There was a 69% to 31% ratio of brachiocephalic (BC) to radiocephalic (RC) AVFs, and diabetes affected an equal proportion of patients in both subtypes.

RESULTS

Mean initial and final Q(ac)s were 1,132 +/- 681 and 1,097 +/- 644 mL/min, respectively; there was no significant difference during the study period. However, the Q(ac) of BC AVFs remained approximately twice as high as the Q(ac) of RC AVFs during the observation period (initial Q(ac), 1,336 +/- 689 versus 645 +/- 332 mL/min; final Q(ac), 1,285 +/- 652 versus 647 +/- 331 mL/min, respectively). Male sex was associated with a greater Q(ac) throughout the evaluation (1,263 +/- 754 versus 852 +/- 375 mL/min for women). No significant difference was noted between different age groups, and diabetes did not significantly affect Q(ac). Finally, the initial Q(ac) of a BC AVF was influenced by the presence of a previously functioning RC AVF on the same arm. The initial Q(ac) in BC AVFs was 1,800 +/- 919 mL/min in that subgroup (and decreased to 1,302 +/- 733 mL/min by the end of the study, therefore becoming similar to the mean Q(ac) of other BC AVFs).

CONCLUSION

From these results, we conclude that newly created native AVFs have an initial Q(ac) that does not vary significantly during the first 6 months and may already be maximal at 6 weeks or at the time of first needle puncture in our hands. Among demographic factors, sex influences the Q(ac) of native AVFs, whereas age and diabetes do not.

Hemodialysis access imaging: comparison of flow-interrupted contrast-enhanced MR angiography and digital subtraction angiography

PURPOSE

To compare flow-interrupted contrast material-enhanced magnetic resonance (MR) angiography with conventional digital subtraction angiography (DSA) for hemodialysis access imaging.

MATERIALS AND METHODS

Twenty-two accesses (14 arteriovenous grafts [AVGs], eight arteriovenous fistulas [AVFs]) in 18 consecutive patients were imaged with flow-interrupted contrast-enhanced MR angiography and subsequent conventional DSA. MR image quality was assessed as excellent, good, or nondiagnostic. Anastomotic diameters in AVGs and postanastomotic diameters in AVFs were measured in consideration of an adjacent normal segment. Reductions in the diameter of the lumen and interobserver differences were analyzed with method comparison as described by Bland and Altman and expressed as the mean difference with its 95% confidence limits (CLs) (mean +/- 2 SDs).

RESULTS

Image quality obtained with flow-interrupted contrast-enhanced MR angiography was considered excellent in 73% (16 of 22) and good in 23% (5 of 22). Method comparison analysis between MR angiography and DSA indicated a mean difference of 3.2% (95% CLs: -26.7%, 33.1%) for observer 1 and 4.1% (95% CLs: -23.8%, 32.1%) for observer 2. Interobserver analysis at MR angiography indicated a mean difference of 3.2% (95% CLs: -28.8%, 35.2%), and that at DSA indicated a mean difference of 3.6% (95% CLs: -9.4%, 16.7%).

CONCLUSION

Image quality and anatomic depiction with flow-interrupted contrast-enhanced MR angiography and with DSA were comparable.

Hemodialysis vascular assessment by an ultrasound dilution method (transonic) in patients older than 65 years

Malfunction of vascular access is one of the most frequent causes of morbidity and mortality in hemodialysis patients (HD). Early diagnosis makes possible the most frequent vascular access (VA) used in HD patients. The arteriovenous fistula (AVF), both autologous or heterologous, is the appropriate correction by an interventional radiologist or by surgery, before thrombosis appears. For this purpose, a follow-up of VA is mandatory. New technologies offer non-invasive methods for this purpose. In HD sessions ultrasound 'on line' and ultrasound-dilution techniques permit us to monitor vascular access in HD patients. Also transonic technology has been validated for this purpose, although the limitations of its use among elderly patients is unknown. Using the Transonic HD01 monitor, we studied vascular access in 45 patients in HD older than 65 years, and compared them with 47 patients who were younger than 65 years. The parameters analyzed were: effective flow Qt, recirculation, venous pressure and access flow. We found no significant differences between these parameters but in both groups found that the effective flow measure by Transonic was lower than that measured by a blood pump. Both groups contained patients who had no recirculation but had an access flow that was lower than expected. To rule out stenosis of VA in those patients, we performed an Eco Doppler confirming that all patients had stenosis. With this method, one can determines the access flow and thus predicts the possibility of future thrombosis.

CONCLUSION

Our data confirm that one can evaluate VA in patients older than 65 years with Transonic HD01 monitor, and also in patients younger than 65 years. Due to the special characteristics of the vessels in elderly patients, Transonic HD01 monitor is a good method by which to monitor VA in them.

Optimizing dialysis dose by increasing blood flow rate in patients with reduced vascular-access flow rate

Dialysis efficacy indexed by Kt/V can generally be augmented by increasing the dialyzer blood flow rate. However, increasing the dialyzer blood flow rate may lead to vascular-access recirculation (AR) in patients with a compromised vascular-access flow rate. This can have an attenuating effect on dialysis efficacy. The aim of the present study is to investigate the effect of dialyzer blood flow rates of 200, 300, and 400 mL/min on AR and Kt/V in 8 patients with low (<600 mL/min) and 13 patients with normal (>600 mL/min) vascular-access flow rates. AR and vascular-access flow rate were determined using an ultrasound saline dilution technique, and session-delivered Kt/V was computed using an on-line dialysate urea monitor. AR was minor and only observed in 4 patients in the low vascular-access flow rate group (0.9% +/- 0.6%) at dialyzer blood flow rates of 200 mL/min (1 patient), 300 mL/min (2 patients), and 400 mL/min (3 patients) and 4 patients in the normal vascular-access flow rate group (1.2% +/- 1.1%) at dialyzer blood flow rates of 200 mL/min (3 patients) and 300 mL/min (1 patient). Kt/V increased with increasing dialyzer blood flow rates in both groups, and in individual cases, there was no decrease in Kt/V at greater dialyzer blood flow rates in either group. Also in those patients with minor AR, Kt/V increased at greater dialyzer blood flow rates, except in 1 patient in the low-flow group, in whom Kt/V remained unchanged at a change in dialyzer blood flow rate from 300 to 400 mL/min, whereas AR increased. From this study, it is concluded that even in patients with low access flow, increasing dialyzer blood flow rate in general leads to an increase in delivered Kt/V regardless of vascular access flow rate.

Screening for subclinical stenosis in native vessel arteriovenous fistulae

Guidelines recommend the use of ultrasound dilution techniques (UDT), including measurement of access recirculation (AR) and access blood flow (Q(a)), to screen for subclinical vascular access dysfunction. Although these techniques are efficacious in polytetrafluoroethylene grafts, data in native vessel arteriovenous fistulae (AVF) are lacking. A prospective observational study was conducted to evaluate the utility of UDT screening in AVF. Q(a) and AR were measured bimonthly. Positive studies required fistulograms and were defined by Q(a) < 500 ml/min, DeltaQ(a) > 20% from baseline or AR > 5%. Accesses with stenosis underwent percutaneous angioplasty. After 1 yr, there were 1355 mo of follow-up in 177 patients. There were 44 positive studies in 40 patients. Q(a) was <500 ml/min in 36 (82%), DeltaQ(a) was >20% in 5 (11%), and AR was >5% in 6 (14%). Of patients with Q(a) < 500 ml/min, 29 (81%) had stenosis. Only two patients (40%) with DeltaQ(a) > 20% but Q(a) > 500 ml/min had stenosis. No patient with AR > 5% had stenosis unless Q(a) was also <500 ml/min. Immediate patency rate was 93% post-PTA. Mean Q(a) increased from 303 +/- 154 ml/min to 602 +/- 220 ml/min (P < 0.0001), and mean urea reduction ratio increased from 70.4 +/- 8.4% to 74.6 +/- 6.5% (P = 0.003) post-PTA. The results demonstrate that UDT could detect subclinical stenoses in AVF, and most lesions were amenable to angioplasty. AVF that underwent PTA delivered higher Q(a) and urea reduction ratio, and immediate patency rates were acceptable. Access failure after negative UDT was unusual. Measuring AR increases the time required to perform UDT but does not improve utility. Serial measurements of Q(a) alone may be the best strategy for screening AVF.