Dialysis arteriovenous access monitoring and surveillance according to the 2017 Spanish Guidelines

Vascular access route venture of the chronic hemodialysis patient: A prospective cohort study

ObjectivesThis study aimed to collect evidence to improve the arteriovenous fistula practice by investigating vascular access routes and by identifying the factors influencing the preferred types of vascular access routes for the first-time hemodialysis in our center.MethodsWe performed an epidemiological, prospective, cohort study. The study included 308 patients, who underwent hemodialysis for the first time between March 2023 and August 2023 in our hemodialysis center. We evaluated biochemical parameters, preferred vascular access routes for the first-time hemodialysis, planned/emergency hemodialysis status, the qualifications of the healthcare provider, who inserted the central venous catheter, if applicable, the presence of hypervolemia, anticoagulant use, nephrology follow-up findings, and in-hospital mortality in all patients and in those, who continued with chronic hemodialysis.ResultsThe number of patients, who continued with chronic hemodialysis, was 167 (54.2%) and a temporary internal jugular central venous catheter was the most commonly preferred vascular access route for the first-time hemodialysis (47.3%). A central venous catheter was most commonly inserted by a nephrologist (53.7%) in chronic hemodialysis patients. Of the patients continuing with chronic hemodialysis, 45.5% were followed up in the nephrology outpatient clinic, 9.6% initiated hemodialysis on a planned basis, and 8.4% initiated hemodialysis with an arteriovenous fistula. A temporary internal jugular central venous catheter was commonly preferred when patients were followed up in the nephrology clinic and when the insertion was performed by a nephrologist; a transient femoral central venous catheter was commonly preferred in case of hypervolemia (p < .001, p < .001, and p = .028, respectively). Age, gender, etiology, anticoagulant use, or biochemical test results did not act on the selection of the access site for the insertion of central venous catheter at the time of the first hemodialysis treatment. The access site for central venous catheter was not associated with in-hospital mortality (p = .644). In the overall patient group, the in-hospital mortality was significantly low in patients followed up in the nephrology clinic (p = .014).ConclusionThe use of pre-emptive arteriovenous fistula for the first hemodialysis treatment occurs much less commonly than expected. Hemodialysis initiation rates with pre-emptive arteriovenous fistula lag behind nephrology outpatient follow-up rates.

Insights into the real-world practice of vascular access care pathways in Italy: data from a national survey

BACKGROUND

International guidelines issued recommendations for vascular access (VA) care for hemodialysis, but there are no registry data regarding this topic in Italy.

METHODS

A survey consisting of 17 items was sent to all Italian dialysis wards, via the Italian Society of Nephrology (SIN) website, from April to June 2021. The items were defined, discussed and approved by experts in vascular access management within the Italian Society of Nephrology. A total of 124 dialysis units answered, accounting for 14% of all dialysis units. The survey thus encompasses all regions within the country, with some regional variations in terms of adherence.

RESULTS

One hundred twenty-four facilities provided data, regarding 12,276 patients: 61% had an arteriovenous fistula (AVF), 34% had a central venous catheter (CVC), and 5% had an arteriovenous graft (AVG). Among them, two-thirds of the facilities reported having a vascular access care pathway, formally standardized in 79% of cases. Forty-six % of centers had a fully equipped vascular access care pathway, encompassing preoperative mapping (80%), vascular access setup (71%), arteriovenous fistula maturation monitoring (76%), first-level (80%) and second-level (78%) monitoring, and surgical and/or endovascular treatment of complications (66%). Vascular access monitoring was computerized in 39% of facilities. First-level monitoring (physical examination) was primarily done by nurses in two-thirds of facilities. Of note, 45% of centers had nurses who were skilled in ultrasound-guided cannulation. Quite surprisingly, facilities with less than 100 patients had a greater prevalence of arteriovenous fistulas than those with more than 100 patients (p = 0.0023). A protocolled vascular access care pathway was associated with a higher likelihood of having an arteriovenous fistula (70% AVF vs 42,1% CVC; p = 0.04). The presence in the facility of interventional nephrologists or nurses with ultrasound-guided cannulation skills significantly reduced the prevalence of central venous catheters.

CONCLUSION

These survey data further strengthen the need for formal and shared vascular access monitoring protocols.

Results of a hemodialysis vascular access routine ultrasound surveillance protocol and frequency of surveillance guided pre-emptive access maintenance interventions

BACKGROUND

To evaluate the implementation of routine surveillance using ultrasound on hemodialysis vascular access (VA) outcomes and determine the number and frequency of corrective, surveillance-guided procedures performed.

METHODS

Multicenter, prospective, observational study that includes consecutive hemodialysis patients receiving therapy from native arteriovenous fistulae (AVF) or grafts (AVG). Participants were assigned to a routine VA Color Doppler ultrasound surveillance (DUS) protocol from January 2019 to December 2021. Patients were referred for corrective procedures (endovascular or surgical) based on clinical or DUS findings (pre-emptive procedures; PEP). Primary endpoint was the estimation of primary unassisted (PUP) and secondary patency (SP) rates. Secondary endpoints were the determination of the number and frequency of PEP and VA survival rates.

RESULTS

In total, 223 patients with 243 VA (192 AVF and 51 AVG) were included. Access PUP and SP rates were 83% and 93% at 12 months, 75% and 88% at 24 months, and 72% and 83% at 36 months follow-up. Autologous fistulae PUP and SP were 89% and 96% at 12 months, 81% and 93% at 24 months, and 80% and 89% at 36 months, respectively. Graft PUP and SP were 56% and 80% at 12 months, 44% and 65% at 24 months, and 39% and 54% at 36 months, respectively. In total, 56 corrective procedures (38/56 PEP; 65.5%) were performed (0.13 procedures/year), of which 34 were in AVF patients (0.09 procedures/year) and 22 in AVG patients (0.40 procedures/year). Overall, 33 VA losses occurred (0.06 failures/year), 17 in AVF (0.04 failures/year), and 16 in AVG patients (0.20 failures/year).

CONCLUSION

The use of DUS resulted in the timely diagnosis of dysfunction, satisfactory overall VA survival, and patency rates, with a low PEP frequency. Randomized controlled trials are required to establish the value of DUS surveillance on access patency and whether DUS-guided interventions could improve VA outcomes.

US Volume Flow Assessment to Optimize Angioplasty of Dysfunctional Dialysis Access: The VOLA-II Multicenter Study

Background Digital subtraction angiography and thrill palpation demonstrate limitations when used to assess the outcomes of angioplasty in autologous arteriovenous fistulas (AVFs). Purpose To investigate a new functional quantifiable index of successful angioplasty for failing AVFs using intraprocedural percutaneous US volume flow (VF) measurements. Materials and Methods This prospective, multicenter, single-arm, cohort clinical trial included consecutive patients with indications for fluoroscopically guided balloon angioplasty due to AVF dysfunction between June 2020 and May 2022. Intraprocedural VF measurements were obtained before the procedure and after balloon dilation using transcutaneous duplex US. The primary end points were the quantification of VF-guided angioplasty outcomes and assessment of the association between postprocedural VF and freedom from target lesion reintervention (TLR) due to recurrence of access failure. Cox multivariate regression analysis was performed to identify predictors of TLR-free survival, which was estimated using Kaplan-Meier methods. Receiver operating characteristic curve analysis was used to determine the optimal cutoff VF value. Results In total, 100 participants (mean age, 67 years ± 12 [SD]; 84 male) were evaluated. The rate of freedom from TLR was 73% at 6 months. The mean pre- and postintervention VF values were 353 mL/min ± 199 and 1045 mL/min ± 413, respectively. Higher VF at completion of angioplasty (hazard ratio, 0.89 per 100 mL/min [95% CI: 0.82, 0.98]; P = .01) and forearm versus upper arm AVF (hazard ratio, 0.51 [95% CI: 0.27, 0.95]; P = .03) were independent predictors of increased freedom from TLR. A postprocedural VF of 720 mL/min (P < .001) was identified as the optimal cutoff point for predicting increased fistula freedom from reintervention and freedom of restenosis for radiocephalic AVFs, compared with an optimal cutoff point of 1120 mL/min (P = .03) for upper arm AVFs. Conclusion Intraprocedural VF measurement is a quantifiable functional index and postprocedural predictor of outcomes following angioplasty for failing dialysis AVFs. ClinicalTrials.gov identifier: NCT04694287 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Prince et al this issue.

Bedside 3D ultrasound fistula maturation assessment by non-expert sonographers provides equivalent accuracy to formal duplex sonography: A prospective clinical trial

BACKGROUND

EchoSure is an automated point-of-care 3D ultrasound (3DUS) designed to be used by dialysis technicians without advanced ultrasound training. The EchoMark/EchoSure System is a two-part system comprised of a bioresorbable implant, EchoMark, and a diagnostic ultrasound imaging platform, EchoSure. EchoSure was designed to enable any healthcare personnel in a dialysis clinic setting to obtain non-invasive, direct measurements of flow and vessel parameters that are critical quantifications used in the assessment of AVF maturation and readiness for hemodialysis cannulation.

OBJECTIVE

In this pilot feasibility study, we sought to explore whether use of an automated 3DUS could enable fistula assessment by non-experts and obtain measurement accuracy comparable to expert sonographer Duplex.

METHOD

This was a 20 subject prospective multicenter trial conducted at four sites in the United States. All subjects had an EchoMark implanted under their AVF during the fistula creation procedure. Subjects were evaluated at 2-weeks post-op with EchoSure and Duplex, followed by monthly assessments until either the 4-month visit or until radiographic maturation was achieved, whichever was longer. Beyond monthly ultrasound assessments, clinical follow-up continued every 6 months between months 6 and 24.

RESULT

Technical success of EchoMark implantation was demonstrated in 100% of subjects. Technical success of EchoSure was 99% across all scans. The mean percent difference in flow rate measurements between EchoSure and Duplex was -9.2% with a standard deviation of 38.1% compared to a mean percent difference of -15.7% with a standard deviation of 35.5% between Duplex measurements taken at the cannulation zone and brachial artery. Pearson correlation between EchoSure and Duplex was 0.708 versus 0.716 for the two Duplex measurements. Radiographic maturation was achieved in 70% of study subjects by 30 days and continued to rise to 90% through 90 days and 95% through 180 days after baseline.

CONCLUSION

This study demonstrates the feasibility and accuracy of an automated 3D ultrasound system for assessment of maturation at the dialysis bedside by non sonographers.

A review of the current recommendations and practices for hemodialysis access monitoring and maintenance procedures

The growing number of prevalent arteriovenous (AV) accesses has been associated with an increase in the incidence of procedures being performed to maintain patency. To reduce the rate of unnecessary procedures, the 2019 Kidney Disease Outcome Quality Initiative guidelines addended the AV access surveillance recommendations, which includes clinical monitoring and assessment of dialysis adequacy alone. Abnormal clinical findings would necessitate follow-up angiography with or without confirmatory duplex ultrasound. Due to poor patency, increased surveillance schedules have been proposed to identify stenosis early and potentially prevent acute thrombotic events and AV access failure. In this review, we outlined current AV access monitoring and maintenance procedure recommendations, as described by the Centers for Medicare and Medicaid Services and 2019 Kidney Disease Outcome Quality Initiative guidelines. In addition, we highlight the findings of recently published randomized controlled trials that have examined increased surveillance schedules.

Hemodialysis vascular access flow measurements by the novel DMed NephroFlow® device: A comparative study with Transonic®

INTRODUCTION

The current Spanish Clinical Guidelines on Vascular Access for Hemodialysis support the need for surveillance and monitoring of vascular access (VA) to avoid complications. Ultrasound dilution (UD) methods are accepted for the evaluation of VA flow and Transonic® has established the gold standard method for the measurement. The DMed NephroFlow (NIPRO®) device, based on UD method has recently been incorporated. We report a comparative study between the classic Transonic® versus the new NephroFlow® device.

MATERIAL AND METHODS

For two consecutive months, measurements of VA flow using both referred systems were performed in patients with a native arteriovenous fistula (AVF) or a graft (AVG) on hemodialysis (HD) in our unit. Both studies were undertaken according to the usual recommendations: VA flow of 250 ml/min, ultrafiltration rate without modifications, both needles in the same vein, and always in the first hour of the HD session.

RESULTS

Forty-five patients were included: 17 women and 28 men, mean age of 67 ± 12 years. Thirty patients were diabetic. The baseline meantime on HD was 51 ± 39 months (range: 3-163). Type of VA was: 17 patients radio-cephalic AVF, 17 brachiocephalic AVF, 7 brachiobasilic AVF, and 3 with a graft. The mean flow estimated by the Transonic® was 1222 ± 805 ml/min and the estimated flow by the NephroFlow® device was 1252 ± 975 ml/min. Good reliability between Transonic® and NephroFlow® was observed, with a reliability index of Cronbach's Alpha of 0.927 and an Intraclass Correlation Index of 0.928.

CONCLUSIONS

The NephroFlow® device seems comparable with the accepted gold standard UD method for estimating VA flow. More studies must be performed to verify these results. However, they should be considered for the surveillance and monitoring of VA flow, in agreement with the Spanish Guidelines.

Evaluation of arteriovenous fistula for hemodialysis with a new generation digital stethoscope: a pilot study

BACKGROUND AND AIMS

The management of complications of arteriovenous fistula (AVF) for hemodialysis, principally stenosis, remains a major challenge for clinicians with a substantial impact on health resources. Stenosis not infrequently preludes to thrombotic events with the loss of AVF functionality. A functioning AVF, when listened by a stethoscope, has a continuous systolic-diastolic low-frequency murmur, while with stenosis, the frequency of the murmur increases and the duration of diastolic component decreases, disappearing in severe stenosis. These evidences are strictly subjective and dependent from operator skill and experience. New generation digital stethoscopes are able to record sound and subsequently dedicated software allows to extract quantitative variables that characterize the sound in an absolutely objective and repeatable way. The aim of our study was to analyze with an appropriate software sounds from AVFs taken by a commercial digital stethoscope and to investigate the potentiality to develop an objective way to detect stenosis.

METHODS

Between September 2022 and January 2023, 64 chronic hemodialysis (HD) patients were screened by two blinded experienced examiners for recognized criteria for stenosis by Doppler ultrasound (DUS) and, consequently, the sound coming from the AVFs using a 3 M™ Littmann® CORE Digital Stethoscope 8570 in standardized sites was recorded. The sound waves were transformed into quantitative variables (amplitude and frequency) using a sound analysis software. The practical usefulness of the core digital stethoscope for a quick identification of an AVF stenosis was further evaluated through a pragmatic trial. Eight young nephrologist trainees underwent a simple auscultatory training consisting of two sessions of sound auscultation focusing two times on a "normal" AVF sound by placing the digital stethoscope on a convenience site of a functional AVF.

RESULTS

In 48 patients eligible, all sound components displayed, alone, a remarkable diagnostic capacity. More in detail, the AUC of the average power was 0.872 [95% CI 0.729-0.951], while that of the mean normalized frequency was 0.822 [95% 0.656-0.930]. From a total of 32 auscultations (eight different block sequences, each one comprising four auscultations), the young clinicians were able to identify the correct sound (stenosis/normal AVF) in 25 cases, corresponding to an overall accuracy of 78.12% (95% CI 60.03-90.72%).

CONCLUSIONS

The analysis of sound waves by a digital stethoscope permitted us to distinguish between stenotic and no stenotic AVFs. The standardization of this technique and the introducing of data in a deep learning algorithm could allow an objective and fast method for a frequent monitoring of AVF.

Quantitative physical examination indicators to detect patients with stenosis at a high risk of thrombosis at hemodialysis vascular access sites: A retrospective case-control study

BACKGROUND

Quantitative physical examination (PE) indicators, including palpable pulsatility length and outflow scores, can be used to quantify stenosis severity at hemodialysis vascular access sites. It is known that the risk of high-shear-related thrombosis is increased when the minimal luminal diameter (MLD) of stenosis decreases. At present, MLD is measured using sonography or angiography. This study sought to determine the relationship between quantitative PE indicators and MLD and report their diagnostic performance in detecting patients with stenosis at a high risk of thrombosis.

METHODS

We performed a retrospective case-control study using routinely collected data. We used the post-stenosis palpable pulsatility length (sPPL) and pulse-and-thrill based outflow score to assess the severity of AVF inflow and outflow stenosis, respectively. We recorded paired quantitative PE indicators and MLD before and after angioplasty in patients enrolled over a 4-month period.

RESULTS

A total of 249 paired PE indicators and MLD measurements were obtained from 163 patients. A receiver operating characteristic curve analysis showed that an MLD cutoff value of <1.55 mm and an MLD of <1.95 mm discriminated sPPL = 0 and PESOS (physical examination significant outflow stenosis)/1- of the outflow score, respectively, from all other measurements, with the area under the curve values of 0.8922 and 0.9618, respectively. With sPPL = 0 and PESOS/1- of the outflow score as diagnostic tools to detect inflow stenosis with an MLD of ⩽1.5 mm and outflow stenosis with an MLD of ⩽1.9 mm at vascular access sites, sensitivity = 86.00% and 88.46%; specificity = 97.67% and 92.11%; positive predictive values of 97.73% and 92.00% and negative predictive values of 85.71% and 88.61%, respectively, were observed.

CONCLUSIONS

Our preliminary results showed that physical examination can potentially be a diagnostic tool in detecting patients with stenosis who are at a high risk of thrombosis at hemodialysis vascular access sites with high diagnostic accuracy.

Oscillometric pulse wave analysis for detecting low flow arteriovenous fistula

BACKGROUND

Pulse wave analysis may be useful to assess fistula function. We aimed to prospectively evaluate if convenient oscillometric devices are applicable to detect flow below 500 ml/min in a real life clinical setting.

METHODS

Pulse waves were recorded ambilaterally with the vicorder® device at the brachial artery in 53 patients on haemodialysis with native fistula. Primary variables consisted of the mean slope between the systolic maximum and the diacrotic notch (Slope2), the sum of the mean slopes in the four characteristic sections of pulse waves (Slope∑) and the amplitude of relative volumetric change in the measuring cuff at the upper arm (AMP). Fistula flow was measured with the use of duplex sonography using a standardized approach.

RESULTS

Parameter values above or below the median indicated measurement at the non-fistula side, with sensitivities/specificities of 0.79/0.79 (p < 0.001) for Slope 2, 0.64/0.64 (p = 0.003) for Slope∑ and 0.81/0.81 (p < 0.001) for AMP if measurements at the fistula and non-fistula arm were considered. ROC-analyses of parameter values measured at the fistula to detect low flow demonstrated AUCs (with CI) of 0.652 (0.437-0.866, p = 0.167) for Slope2, 0.732 (0.566-0.899, p = 0.006) for Slope∑ and 0.775 (0.56-0.991, p = 0.012) for AMP. The point with maximal youden's index was regarded as optimal cut-off, which corresponded to sensitivities and specificities of 0.8/0.56 for slope2, 0.86/ 0.56 for Slope∑ and 0.93/0.78 for AMP.

CONCLUSION

Functional surveillance with oscillometry is a promising clinical application to detect a low fistula flow. Among all investigated pulse wave parameters AMP revealed the highest diagnostic accuracy.

Characterization of hemodialysis fistulas experienced abrupt thrombosis and determination of a proper follow-up protocol: A retrospective cohort study and an interventionist's perspective

Abrupt thrombosis is a form of thrombosis that occurs unexpectedly and without being preceded by hemodialysis fistula (AVF) dysfunction during dialysis. We found that AVFs with a history of abrupt thrombosis (abtAVF) appeared to have more episodes of thrombosis and required more frequent interventions than those without such history. Therefore, we sought to characterize the abtAVFs and examined our follow-up protocols to determine which one is optimal. We performed a retrospective cohort study using routinely collected data. The thrombosis rate, AVF loss rate, thrombosis-free primary patency, and secondary patency were calculated. Additionally, the restenosis rates of the AVFs under the follow-up protocol/sub-protocols and the abtAVFs were determined. The thrombosis rate, procedure rate, AVF loss rate, thrombosis-free primary patency, and secondary patency of the abtAVFs were 0.237/pt-yr, 2.702/pt-yr, 0.027/pt-yr, 78.3%, and 96.0%, respectively. The restenosis rate for AVFs in the abtAVF group and the angiographic follow-up sub-protocol were similar. However, the abtAVF group had a significantly higher thrombosis rate and AVF loss rate than AVFs without a history of abrupt thrombosis (n-abtAVF). The lowest thrombosis rate was observed for n-abtAVFs, followed up periodically under the outpatient or angiographic sub-protocols. AVFs with a history of abrupt thrombosis had a high restenosis rate, and periodic angiographic follow-up with a mean interval of 3 months was presumed appropriate. For selected populations, such as salvage-challenging AVFs, periodic outpatient or angiographic follow-up was mandatory to extend their usable lives for hemodialysis.

El documento Código fístula: un consenso histórico

El documento “Código fistula” ha sido elaborado por el Grupo Español Multidisciplinar del Acceso Vascular (GEMAV) en colaboración con las asociaciones españolas de pacientes renales ALCER y ADER. A imagen y semejanza de “Código infarto” y “Código ictus”, el “Código fístula” pretende ser un protocolo de atención urgente que permite identificar a las personas con enfermedad renal tratadas mediante hemodiálisis que presentan una patología aguda de su acceso vascular arteriovenoso, es decir, fístula nativa y fístula protésica, para trasladarlas, lo más rápidamente posible, a la Unidad Funcional del Acceso Vascular o al Hospital de referencia y efectuar el tratamiento mediante cirugía o procedimiento endovascular. Como la trombosis es la complicación más frecuente de la fístula, este evento será la causa más frecuente de activación del “Código fístula”. Dado que la trombosis incrementa la incidencia de hospitalización, el gasto sanitario y la morbimortalidad de la persona con enfermedad renal, el rescate de toda fístula trombosada debería ser una prioridad absoluta y considerarse una patología de manejo preferente que precisa de una solución lo más rápida posible. El documento “Código fistula”, además de GEMAV, ALCER y ADER, se ha consensuado por los siguientes grupos de trabajo y Sociedades Científicas españolas vinculadas a la atención de las persones con enfermedad renal (por orden alfabético): GEIRAS, SEACV, SEDEN, SEDYT, S.E.N. y SERVEI. Esperemos que pronto pueda aplicarse en todo el territorio español.

Is fetuin-A a biomarker of dialysis access dysfunction?

BACKGROUND

The arteriovenous (AV) access function of hemodialysis (HD) patients can be impaired by afferent artery stiffness due to preexisting microcalcification and by venous stenosis secondary to neointimal hyperplasia in whose development participates an upregulated local inflammatory process. Fetuin-A is a circulating potent inhibitor of vascular calcification and plays an important anti-inflammatory role. The aims of this prospective study were to investigate the relationship between baseline serum fetuin-A levels and: blood flow (Q_A) values at baseline, AV access failure (thrombosis or intervention for stenosis) during follow-up and primary unassisted AV access patency.

METHODS

We measured baseline serum fetuin-A levels and Q_A values of the AV access in 64 HD patients under routine Q_A surveillance for stenosis. Patients were classified into tertiles according to their baseline fetuin-A levels (g/L): <0.5 (tertile-1), 0.5-1.20 (tertile-2), and >1.20 (tertile-3).

RESULTS

Fetuin-A was positively correlated with Q_A (Spearman coefficient = 0.311, p = 0.012). Fourteen patients (21.9%) underwent AV access failure and they had lower fetuin-A (0.59 ± 0.32 g/L) and lower Q_A (739.4 ± 438.8 mL/min) values at baseline compared with the remaining patients (1.05 ± 0.65 g/L and 1273.0 ± 596.3 mL/min, respectively) (p = 0.027 and p < 0.001, respectively). The AV access failure rate was highest (34.8%) in tertile-1 (lowest fetuin-A level). Unadjusted Cox regression analysis showed a decrease in the risk of AV access patency loss by increasing fetuin-A concentration (hazard ratio 0.395 (95% confidence interval: 1.42-1.69), p = 0.044) but it was not confirmed in the adjusted model, although the hazard ratio was low (0.523). Kaplan-Meier analysis showed that patients in tertile-3 (highest fetuin-A concentration) had the highest primary unassisted AV access patency (λ² = 4.68, p = 0.030, log-rank test).

CONCLUSION

If our results are confirmed in further studies, fetuin-A could be used as a circulating biomarker to identify HD patients at greater risk for AV access dysfunction, who would benefit from much closer dialysis access surveillance.

The role of Doppler ultrasonography in vascular access surveillance-controversies continue

Chronic hemodialysis therapy required regular entry into the patient’s blood stream with adequate flow. The use of arteriovenous fistulas and grafts is linked with lower morbidity and mortality than the use of catheters. However, these types of accesses are frequently affected by stenoses, which decrease the flow and lead to both inadequate dialysis and access thrombosis. The idea of duplex Doppler ultrasound surveillance is based on the presumption that in-time diagnosis of an asymptomatic significant stenosis and its treatment prolongs access patency. Details of performed trials are conflicting, and current guidelines do not support ultrasound surveillance. This review article summarizes the trials performed and focuses on the reasons of conflicting results. We stress the need of precise standardized criteria of significant access stenosis and the weakness of the metaanalyses performed.

Utility of Blood Flow/Resistance Index Ratio (Qx) as a Marker of Stenosis and Future Thrombotic Events in Native Arteriovenous Fistulas

Objective: The resistance index (RI) and the blood flow volume (Q_a) are the most used Doppler ultrasound (DUS) parameters to identify the presence of stenosis in arteriovenous fistula (AVF). However, the reliability of these indexes is now matter of concern, particularly in predicting subsequent thrombosis. In this study, we aimed at testing the diagnostic capacity of the Q_a/RI ratio (Q_x) for the early identification of AVF stenosis and for thrombosis risk stratification.

Methods: From a multicentre source population of 336 HD patients, we identified 119 patients presenting at least one “alarm sign” for clinical suspicious of stenosis. Patients were therefore categorized by DUS as stenotic (n = 60) or not-stenotic (n = 59) and prospectively followed. Q_a, RI, and Q_X, together with various clinical and laboratory parameters, were recorded.

Results: Q_a and Q_x were significantly higher while RI was significantly lower in non-stenotic vs. stenotic patients (p < 0.001 for each comparison). At ROC analyses, Q_x had the best discriminatory power in identifying the presence of stenosis as compared to Q_a and RI (AUCs 0.976 vs. 0.953 and 0.804; p = 0.037 and p < 0.0001, respectively). During follow-up, we registered 30 thrombotic events with an incidence rate of 12.65 (95% CI 8.54–18.06) per 100 patients/year. In Cox-regression proportional hazard models, Q_x showed a better capacity to predict thrombosis occurrence as compared to Q_a (difference between c-indexes: 0.012; 95% CI 0.004–0.01).

Conclusions: In chronic haemodialysis patients, Q_x might represent a more reliable and valid indicator for the early identification of stenotic AVFs and for predicting the risk of following thrombosis.

Blood temperature monitoring-guided vascular access intervention improved dialysis adequacy

OBJECTIVES

The aim of this study was to investigate whether blood temperature monitoring-guided vascular access intervention could improve dialysis adequacy.

METHODS

We retrospectively evaluated all patients who received outpatient-based prevalent hemodialysis patients (n = 84) in our artificial kidney room between January 2019 and October 2019. Through blood temperature monitoring, access blood flow was calculated every month and Kt/V was calculated every 3 months. The reference point was set at the time of vascular intervention in the patients (n = 27) who underwent intervention or at the middle of the study period in patients (n = 57) who did not undergo intervention. The mean blood temperature monitoring-estimated access flow and Kt/V before and after the reference point were calculated and compared.

RESULTS

Among 84 patients, 30 (35.7%) showed access flow rates of <500 mL/min, calculated by blood temperature monitoring during the study period. Twenty-seven patients (32.1%) underwent vascular intervention, of whom 24 (28.6%) showed access flow rates of <500 mL/min, 2 (2.4%) showed weak bruit or thrill incapable of needling, and 1 (1.2%) presented acute occlusion. Six patients (7.1%) whose access flow rates were <500 mL/min refused to undergo intervention. All angiographies in the patients whose access flow rates were <500 mL/min who underwent intervention showed a significant stenosis. The mean change in blood temperature monitoring-estimated access flow and Kt/V before and after vascular intervention was 483.3 ± 490.6 and 0.19 ± 0.21, respectively, which showed significant differences (all p < 0.05). A weak positive correlation between the mean change in blood temperature monitoring-estimated access flow and Kt/V was shown in all study patients by Pearson's correlation analysis (r = 0.234, p = 0.033).

CONCLUSION

Access flow estimation by blood temperature monitoring might identify candidates who require vascular intervention. Blood temperature monitoring-guided vascular intervention significantly improved access flow and dialysis adequacy.

Quantification of the severity of outflow stenosis of hemodialysis fistulas with a pulse- and thrill-based scoring system

BACKGROUND

Hyper-pulsatility of hemodialysis arteriovenous fistula (AVF) is the basic physical examination finding when there is outflow stenosis. The arm elevation test can also be utilized to detect outflow stenosis. If there is no significant outflow stenosis, the AVF should collapse, at least partially, because of the effect of gravity when the AVF-bearing arm is elevated to a level above that of the heart. However, if there is significant outflow stenosis, the portion of the AVF downstream of the stenosis will collapse, while the portion upstream of the stenosis will remain distended (Clin J Am Soc Nephro 8:1220-7, 2013). In our daily practice, when performing the arm elevation test, we not only observe the collapsibility of the access outflow but also palpate the outflow to identify a background thrill that sometimes disappears with the arm at rest, only to reappear when the arm is elevated. If there is no thrill upon arm elevation, we assume that the outflow stenosis is severe and refer to this condition as "physical examination significant outflow stenosis" (PESOS). The aim of this study is to characterize PESOS using percentage stenosis and Doppler flow parameters.

METHODS

We performed a case-control study using data collected prospectively between June 2019 and December 2019. A pulse- and thrill-based score system was developed to assess the severity of AVF outflow stenosis. We recorded the outflow scores and Doppler measurements performed in 84 patients with mature fistulas over a 6-month period. Angiograms were reviewed to determine the severity of outflow stenosis, which was assessed by calculation of percentage stenosis.

RESULTS

Receiver operating characteristic analysis showed that a cutoff value of ≥74.44% stenosis discriminated PESOS from other AVF outflow scores, with an area under the curve of 0.9011. PESOS diagnosed cases with ≥75% outflow stenosis in an AVF, with a sensitivity of 80.39%, a specificity of 78.79%, a positive predictive value of 85.42%, and a negative predictive value of 72.22%.

CONCLUSIONS

PESOS can be used to diagnose ≥75% outflow stenosis in an AVF, with or without a significant collateral vein, and its diagnostic accuracy is high. The use of PESOS as an indicator for treatment implies that physical examination may represent a useful surveillance tool.

Predicting arterio-venous fistula failure by urea-method derived access blood flow in chronic hemodialysis patients

BACKGROUND

Dialysis access is an essential part of hemodialysis. Determining the access blood flow (Qa) can help predict arterio-venous fistula thrombosis. Qa determination by the urea method, which was previously described in the past is simple and is available in most of the dialysis units but was not be able to predict arterio-venous fistula thrombosis.

AIM

To compare the efficacy of Qa determination by the urea method and by ultrasound dilution methods in predicting arterio-venous fistula failure.

METHODS

Qa was measured by urea method and by ultrasound dilution simultaneously, every 3 months for a period of 1 year, in stable chronic hemodialysis patients with arterio-venous fistula. Arterio-venous fistula failure determined by clinical parameters and confirmed by Doppler ultrasound before sending the patient for interventional angioplasty.

RESULTS

This study enrolled a total of 16 patients, with 63% being male, 75% with lower-arm arterio-venous fistula and around 43% with previously done angioplasty. 59-Qa measurements were done, and 6 patients underwent angioplasty (one patient for severe upper limb edema, one for access thrombosis, and four for access dysfunction). Qa determination by the urea method had non-significantly lower Qa, (745 mL/min (interquartile range: 509-1143) and 779 mL/min (interquartile range: 530-1160), (p = 0.58)) and high correlation (r = 0.83, p < 0.001) to Qa by ultrasound dilution. The cut-off criteria with its sensitivity and specificity in predicting the access failure were 440 mL/min, 66.67%, and 96.15% for Qa determination by the urea and 400 mL/min, 66.67% and 90.38% for Qa by ultrasound dilution, respectively, with no difference in the area under the receiver operating characteristic curve.

CONCLUSION

Measurement of Qa determination by the urea method is well correlated with Qa by ultrasound dilution and can be used to predict vascular access failure.

Screening for hemodialysis graft stenosis and short-term thrombosis risk: A comparison of the available tools

INTRODUCTION

Guidelines recommend hemodialysis graft screening to identify and repair significant (>50%) stenosis at high risk of thrombosis, but there is insufficient evidence to prefer one or other screening tool due to the lack of studies comparing all available options.

METHODS

Seeking an optimal screening approach, we compared the performance of all currently used tools (duplex ultrasound to detect significant stenosis (StD) and measure access blood flow (QaD), ultrasound dilution access blood flow (QaU), static venous intra-access pressure ratio (VAPR), dynamic arterial and venous pressures measurement, and monitoring) for diagnosing significant angiography-proven stenosis (StA) and predicting incipient thrombosis (occurring within 4 months) in 62 grafts. All thrombotic and symptomatic acute hypotension episodes were recorded during follow-up.

RESULTS

VAPR > 0.70 and QaU < 1600 mL/min were the best indicators to angiography for those aiming to identify the majority of StA (91% sensitivity) and QaU < 1000 mL/min or StD for those aiming to avoid unnecessary angiograms (95%-93% positive predictive value). At Cox's analysis, the only significant thrombosis predictors were acute hypotension episodes (relative risk = 4.4 (95% confidence interval = 2.2-8.8), p < 0.0001) and QaU or QaD (14% (95% confidence interval = 8-21) or 16% (95% confidence interval = 6-25) increased risk per 100 mL/min drop in Qa, p < 0.003). Thrombosis risk (adjusted for acute hypotension) became significantly higher at QaU = 1000-700 mL/min (relative risk = 3.6 (95% confidence interval = 1.6-8.2), p < 0.001) and QaD = 1300-1000 mL/min (relative risk = 3.1 (95% confidence interval = 1.1-12.8), p = 0.031). The proportion of thromboses attributable to acute hypotension was 40% (95% confidence interval = 24-57).

CONCLUSIONS

Our comparative study showed that an effective screening for graft stenosis and short-term thrombosis risk can rely on Qa surveillance alone, and suggested that avoiding acute hypotension and correcting stenosis at QaU < 1000 mL/min or QaD < 1300 mL/min can contain thrombosis risk.

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.