Simplified measurement of intra-access pressure

Intradialytic techniques for automatic and everyday access monitoring

Vascular access dysfunction is associated with reduced delivery of dialysis, unplanned admissions, patient symptoms, and loss of access, making assessment of vascular access a fundamental part of routine care in dialysis. Clinical trials to predict the risk of access thrombosis based on accepted reference methods of access performance have been disappointing. Reference methods are time-consuming, affect the delivery of dialysis, and therefore cannot repeatedly be used with every dialysis session. There is now a new focus on data continuously and regularly collected with every dialysis treatment, directly or indirectly associated with access function, and without interrupting or affecting the delivered dose of dialysis. This narrative review will focus on techniques that can be used continuously or intermittently during dialysis, taking advantage of methods integrated into the dialysis machine and which do not affect the delivery of dialysis. Examples include extracorporeal blood flow, dynamic line pressures, effective clearance, dose of delivered dialysis, and recirculation which are all routinely measured on most modern dialysis machines. Integrated information collected throughout every dialysis session and analyzed by expert systems and machine learning has the potential to improve the identification of accesses at risk of thrombosis.

Expression of Defensin Antimicrobial Peptides in the Peritoneal Cavity of Patients on Peritoneal Dialysis

Objective

To investigate the expression and regulation of defensins in the peritoneal cavity of peritoneal dialysis (PD) patients.

Design

The presence of defensins in the peritoneal cavity was assessed using reverse transcription polymerase chain reaction (RT-PCR). In vivo defensin expression was analyzed in human peritoneal membrane biopsies and in peritoneal cavity leukocytes isolated from spent dialysate. Defensin expression in vitro was assessed in cultured human peritoneal mesothelial cells (HPMC) and confirmed with PCR Southern blot and DNA sequencing. The effect of tumor necrosis factor alpha (TNFa) and epidermal growth factor (EGF) on b2 defensin expression in HPMC was analyzed by Northern blot analysis and RT-PCR respectively.

Results

Both a and b classes of defensins are expressed in the peritoneal cavity of PD patients. Messenger RNA for the a-defensin human neutrophil peptide 3 and for b-defensin-1 (hbD-1) were found in preparations containing predominantly peritoneal leukocytes, whereas b-defensin-2 (hbD-2) is expressed by HPMC. HPMC isolated from different individuals displayed variability in both basal hbD-2 expression and in response to stimulation by TNFa. Conversely, EGF consistently downregulated the level of hbD-2 message in HPMC.

Conclusion

a- and b-defensins are expressed in the peritoneal cavity, and hbD-2 is the main defensin present in the peritoneal membrane. Variable levels of expression of hbD-2 by mesothelial cells were seen, with evidence of regulation by cytokines and growth factors. This provides evidence for a previously unknown mechanism of innate immunity at that site.

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.

A systematic follow-up protocol achieving a low hemodialysis graft thrombosis rate

INTRODUCTION

Graft is an alternative to native arteriovenous fistula to ensure permanent vascular access in hemodialysis patients. The most common complication is significant stenosis, which frequently causes thrombosis and graft loss. Periodic monitoring and surveillance with elective correction of stenotic lesions can prolong graft survival.

OBJECTIVE

To describe the effect of early diagnosis of significant stenosis on the rate of thrombosis and graft patency.

METHODS

Retrospective, observational study of a cohort of 86 prevalent patients undergoing hemodialysis with a graft as their vascular access. We applied a systematic follow-up protocol of 115 grafts based on various screening methods of monitoring (clinical monitoring, pre-pump arterial pressure, dynamic venous pressure, percentage of recirculation, and dose of dialysis) in conjunction with surveillance (normalized intra-access venous pressure and access flow). The annual rates of thrombosis, and primary, primary-assisted, and secondary patency were assessed.

RESULTS

The incidence of significant stenosis and thrombosis was 57.4% (65/115) and 39.0% (45/115), respectively. Of all screening procedures, normalized intra-access venous pressure was the best predictor of significant stenosis (hazards ratio, 7.71; 95% confidence interval, 3.06-19.46). The annual rate of thrombosis fluctuated from 0 to 0.26 thromboses/patient/year, with an average rate of 0.14 thromboses/patient/year. Primary, primary-assisted, and secondary patency were 74%/79%/82%, 50%/60%/66%, and 23%/35%/37% at 1, 2, and 5 years, respectively.

CONCLUSION

The implementation of a systematic graft follow-up protocol combined with monitoring and surveillance enabled early diagnosis and elective correction of significant stenosis, prolonged graft patency, and a low thrombosis rate.

Prediction of vascular access stenosis: Blood temperature monitoring with the Twister versus static intra-access pressure ratio

Background

The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend intra-access flow (Qa) measurement as the preferred vascular access surveillance method over static intra-access pressure ratio (SIAPR). Recently, it has become possible to perform Qa measurement during hemodialysis using thermodilution method called blood temperature monitoring (BTM) with the Twister device. The aim of this study was to investigate the correlation between Qa by BTM and SIAPR and to compare the performance of two tests in prediction of vascular access stenosis.

Methods

The study was performed from January 2016 to November 2017 and included 97 patients with arteriovenous fistulas (AVF). Qa by BTM and SIAPR were simultaneously measured every 1~3 months with a total of 449 measurements during study period.

Results

In our study population, mean age was 59.9±10.0 years and 61.9% were diabetes. The mean Qa obtained by BTM was 1186±588 mL/min. There was no correlation between Qa by BTM and venous SIAPR (r = 0.061, P = 0.196). Angiography identified 36 stenotic AVFs (37.1%) among the study subjects. They included 13 cases with only inflow stenosis, 6 with only outflow stenosis, and 17 with stenosis on both sides. Receiver-operating characteristic (ROC) curve analysis showed that Qa by BTM had higher discriminative ability to diagnose vascular access stenosis compared to SIAPR (P <0.001). The Qa less than 583 mL/min showed the highest diagnostic accuracy in vascular stenosis prediction.

Conclusion

Intradialytic measurement of Qa by BTM showed better diagnostic power over venous SIAPR in prediction of vascular access stenosis.

Spanish Clinical Guidelines on Vascular Access for Haemodialysis

Vascular access for haemodialysis is key in renal patients both due to its associated morbidity and mortality and due to its impact on quality of life. The process, from the creation and maintenance of vascular access to the treatment of its complications, represents a challenge when it comes to decision-making, due to the complexity of the existing disease and the diversity of the specialities involved. With a view to finding a common approach, the Spanish Multidisciplinary Group on Vascular Access (GEMAV), which includes experts from the five scientific societies involved (nephrology [S.E.N.], vascular surgery [SEACV], vascular and interventional radiology [SERAM-SERVEI], infectious diseases [SEIMC] and nephrology nursing [SEDEN]), along with the methodological support of the Cochrane Center, has updated the Guidelines on Vascular Access for Haemodialysis, published in 2005. These guidelines maintain a similar structure, in that they review the evidence without compromising the educational aspects. However, on one hand, they provide an update to methodology development following the guidelines of the GRADE system in order to translate this systematic review of evidence into recommendations that facilitate decision-making in routine clinical practice, and, on the other hand, the guidelines establish quality indicators which make it possible to monitor the quality of healthcare.

Improved Measurement of Vascular Access Pressure

Vascular access stenosis and thrombosis is one of the key problems for hemodialysis patients. Prospective monitoring of static venous dialysis pressures can be applied to detect outflow stenoses in a vascular access. However, the location of stenoses within the access may influence the diagnostic value of venous pressure measurements. Whereas a decrease in access flow occurs with all types of stenosis, strictures within the arterial anastomosis or between arterial and venous dialysis needle cannot be detected with venous pressure measurements alone.

A new approach is discussed, which bases on the improved measurement of static venous and arterial extracorporeal pressures. Extracorporeal pressure at zero blood flow depends on both the position of the heart relative to the extracorporeal blood circuit and the vertical offset between access site and fluid level in the bloodline. After hydrostatic correction of each pressure signal the normalized arterial and venous intra-access pressure ratio AP/MAP can be calculated. A venous stenosis leads to an increase in both arterial and venous pressure ratio. In case of access stenosis between arterial and venous needle the ratio of venous pressure to mean arterial pressure is normal, and only the arterial pressure ratio is elevated. In summary, a combination of arterial and venous pressure measurement is more sensitive and allows differentiation between mid-access and venous stenosis. Hydrostatic correction of the dialysis pressure signal is inevitable. To minimize the rate of access thrombosis, venous and arterial intra-access pressure should be considered when evaluating dialysis pressures as part of any access monitoring program.

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Monitoring and Surveillance of Hemodialysis Vascular Access Using StenTec and Physical Exam

Hemodialysis vascular access surveillance for hemodynamically significant stenosis can be a challenge because no universal gold standard exists. The StenTec Gauge measures static intra-access peak pressure and graphically displays the ratio of this pressure to systemic systolic (peak) arterial pressure (PIA ratio). In combination with careful physical exam (PE), the StenTec Gauge is an acceptable and cost-effective way of detecting hemodynamically significant stenosis in arteriovenous fistulas (AVF) or grafts (AVG). In a selected population of 21 hemodialysis patients with mature arteriovenous access, a StenTec reading and physical examination was measured on a weekly basis. Interventional procedures for suspected access dysfunction were performed if there was a greater than 25% increase of the PIA ratio from baseline in two consecutive readings, along with correlating clinical suspicion from physical examination findings. StenTec independently had a sensitivity of 56% and a specificity of 99% in detecting clinically significant stenosis. PE alone had a sensitivity of 89% and a specificity of 100%. StenTec combined with PE had a sensitivity of 100% and a specificity of 99% for predicting hemodynamically significant stenosis. StenTec detected 4 of 10 patients who had a PIA ratio value of ≥0.5, which correlates with current National Kidney Foundation Disease Outcomes Quality Initiative (KDOQI) criteria for mean intra-access pressure ratios indicating a clinically significant outflow stenosis. PE predicted 9 of 10 patients with stenosis, and the combination of StenTec and PE predicted all 10 patients with clinically significant stenosis using the KDOQI criteria for PIA ratio. Hemodynamically significant access stenosis can be detected with excellent accuracy using both StenTec and PE measurements combined for monitoring and surveillance methods.

Diagnosis of arteriovenous fistula dysfunction

Arteriovenous fistula (AVF) dysfunction remains a major contributor to the morbidity and mortality of hemodialysis patients. The failure of a newly created AVF to mature and development of stenosis in an established AVF are two common clinical predicaments. The goal is to identify a dysfunctional AVF early enough to intervene in a timely manner to either assist with the maturation process or to prevent thrombosis. The currently available tools in our armamentarium include clinical evaluation, physical examination of the AVF, and surveillance tests. Physical examination has been recognized as a simple and cost-effective tool, but is often not implemented either because of lack of training or time constraints. Surveillance tests include measurement of access flow or pressure as a surrogate marker of AVF dysfunction. Surveillance tests often require expensive equipment, additional personnel, and are controversial. Currently, there are guidelines and recommendations to include all of these measures while evaluating an AVF. Implementing judicious use of these tools in clinical practice can facilitate early diagnosis for timely intervention in the appropriate population. Furthermore, this strategy may avoid unnecessary interventions and assist with healthcare cost containment.

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.

Hemodialysis vascular access monitoring: current concepts

Most arteriovenous grafts fail due to irreversible thrombosis, and most clotted grafts have an underlying stenotic lesion. These observations raise the plausible hypothesis that early detection of graft stenosis with preemptive angioplasty will reduce the likelihood of graft thrombosis. A number of noninvasive methods can be used to detect hemodynamically significant graft stenosis with a high positive predictive value. These tests include clinical monitoring, as well as surveillance by static dialysis venous pressures, flow monitoring, or duplex ultrasound. However, these surveillance tests have a much lower positive predictive value for graft thrombosis in the absence of preemptive angioplasty. In other words, none of the currently available surveillance tests can reliably distinguish between stenosed grafts destined to clot, and those that will remain patent without intervention. As a consequence, any program of graft surveillance necessarily results in a substantial proportion of unnecessary angioplasties. Moreover, a substantial proportion of grafts thrombose despite a normal antecedent surveillance test. Numerous observational studies have found an impressive reduction of graft thrombosis after implementation of a stenosis surveillance program. In contrast, 5 of 6 randomized clinical trials failed to show a reduction of graft thrombosis in patients undergoing graft surveillance, as compared with those receiving only clinical monitoring. The lack of benefit of surveillance is largely attributable to the rapid recurrence of stenosis after angioplasty. Thus, routine surveillance for graft stenosis, with preemptive angioplasty, cannot be recommended for reduction of graft thrombosis. Future research should be directed at pharmacologic interventions to prevent graft stenosis.

A method for monitoring vascular access function during hemodialysis

We tested a new bedside method to determine the function of native arteriovenous fistula in 16 patients performed during hemodialysis without stopping the treatment. We initially measured vascular access flow (Q(a)) in each patient using the Transonic HD01(plus) device. We then measured the pressure in arterial and venous drip chambers at different blood pump flow rates (Q(bset)=0, 50, 100, 250, 300, 350 ml/min). The intravascular blood pressure gradient (P(f)) between arterial and venous puncture sites was estimated by a mathematical model. P(f) was positive for low Q(bset), but became negative when Q(bset) overcame the threshold value (Q(Inv)). Such critical flow showed a high correlation with Q(a), even if it was systemically lower. Computer analysis of fluid dynamics showed that when the blood pump flow overcame the Q(Inv) threshold, a critical transition from laminar flow to vortex circulation took place downstream of the venous needle, causing a dangerous shearstress on the vessel wall. Our results show that Q(Inv) provides an indication of the maximal blood pump flow rate needed to be reached to maximize blood flow supply in order to limit hemodynamic stress on the vascular access.

Vascular access thrombosis prophylaxis

Vascular access thrombosis in the hemodialysis patient leads to significant cost and morbidity. Fistula patency supersedes graft patency, therefore obtaining a mature functioning fistula in patients approaching end-stage renal disease (ESRD) by early patient education and referral needs to be practiced. Current methods to maintain vascular access patency rely on early detection and radiologic or surgical prevention of thrombosis. Study of thrombosis biology has elucidated other potential targets for the prophylaxis of vascular access thrombosis. The goal of this review is to examine the current available methods for vascular access thrombosis prophylaxis.

Static intra-access pressure ratio does not correlate with access blood flow

BACKGROUND

Access flow (Qa) measurement is recommended by Kidney Disease Outcomes Quality Initiative (K/DOQI) as the preferred method for access surveillance. Static intra-access pressure ratio (SIAPR) measurement is the second surveillance method of choice. The purpose of this prospective multicenter study was to investigate the relationship between SIAPR and Qa and to examine the premise upon which SIAPR surveillance is based-namely, that high SIAPR is a surrogate for low Qa associated with hemodynamically significant stenosis.

METHODS

SIAPR and Qa (HD01; Transonic Systems, Inc., Ithaca, NY, USA) were simultaneously measured monthly in 242 patients [146 prosthetic arteriovenous bridge grafts (AVG), 96 autogenous arteriovenous fistulas (AVF)] from three centers. SIAPR was measured according to the K/DOQI protocol.

RESULTS

There was no correlation between Qa and venous or arterial SIAPR in AVGs (R(2)= 0.0037 and R(2)= 0.006, respectively, N= 730), or in AVFs (R(2)= 0.0247 and R(2)= 0.0329, respectively, N= 431). Of the high SIAPR measurements in AVGs, 81% and 50% were associated with Qa > or =600 and Qa > or =1000 mL/min, respectively. Of the AVGs studied, 41% (60/146) had consistently high Qa > or =1000 mL/min. Seventy percent (42/60) of these high-Qa AVGs had at least two consecutive sessions with high SIAPR measurements, thereby meeting the K/DOQI SIAPR criteria for referral. In addition, 78% (14/18) of new AVGs with Qa > or =1000 mL/min, and 86% (6/7) of AVGs with the highest Qa (> or =2000 mL/min), had high SIAPR. As a result, these high-Qa AVGs, which represented the best functioning AVGs by K/DOQI Qa standards, were erroneously targeted for referral based on SIAPR measurements.

CONCLUSION

SIAPR does not correlate with Qa or discriminate between high and low Qa. Therefore, because the utility of SIAPR surveillance for detection of clinically significant stenosis depends on a correlation with Qa, the current use of absolute K/DOQI SIAPR thresholds for intervention based on the presumption that such thresholds are indicative of low Qa is not justified, and should be discontinued. Studies need to be done to examine the utility of SIAPR for trend analysis.

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.

Slow-flow venous pressure for detection of arteriovenous graft malfunction

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Vascular access surgery managed by renal physicians: the choice of native arteriovenous fistulas for hemodialysis

BACKGROUND

After decades of success in dialysis research and treatment, prompt availability of a well-functioning vascular access for dialysis remains a disturbing problem. On the basis of a single-center experience in which nephrologists are responsible for access surgery, we sought to identify predictors of catheter use at the start of hemodialysis (HD) therapy and risk factors affecting first permanent access survival.

METHODS

Demographics, comorbid conditions, predialysis follow-up, and access-related procedures of the 197 consecutive patients beginning extracorporeal treatment between 1995 and 2001 were prospectively entered into our database.

RESULTS

Despite the high prevalence of comorbidities (diabetes, 22%; cardiovascular disease, 50%; neoplasm, 15%), all subjects received a native fistula as a first permanent access, but almost 60% initiated HD therapy using a catheter. The latter showed more comorbidities and were referred later. According to the Kaplan-Meier method, median primary and secondary survivals of the first fistula were 38.1 months and more than 70 months, respectively. The Cox model indicated that diabetes and previous catheter use were independently associated with 85% and 63% greater relative risks for first failure, but only diabetes led to a greater risk for final failure (relative risk, 2.38; P = 0.05).

CONCLUSION

Both the absence of predialysis care and presence of comorbidity influence access type at HD therapy initiation and fistula survival. Earlier intervention strategies can increase the use and durability of a native fistula for HD. Direct involvement of nephrologists in the management of access surgery can be helpful in this respect.

Vascular access: anatomy, examination, management

A systematic approach to managing vascular access problems is the key to reducing current high rates of access thrombosis and failure. This approach begins with a thorough knowledge of vascular access anatomy that, when combined with the physical examination, can help optimize access planning and maintenance. Because of the high complication rate of synthetic grafts, there has been increased emphasis on creating autogenous arteriovenous (AV) fistulae, which, once established, are more trouble-free. The benefit of increased fistula creation will not be realized, however, until the high rate of early fistula failure is reduced. It is widely recommended that graft surveillance programs be implemented and that stenosis be corrected when accompanied by graft dysfunction. Graft blood flow (Q(a)) is the preferred surveillance method, but has a poor accuracy in predicting thrombosis. Most studies that have evaluated the benefit of Q(a) surveillance have used historical control groups, or have been retrospective or nonrandomized. Consequently, we believe it is not currently possible to make definitive, evidence-based recommendations concerning Q(a) surveillance. The most important factor in access survival may be a team approach with an organized commitment to access planning followed by recognition and treatment of access problems.

Value of static venous pressure for predicting arteriovenous graft thrombosis

BACKGROUND

Static venous pressure elevation has been shown to have both high sensitivity and high specificity for hemodialysis arteriovenous (AV) graft venous anastomosis stenosis. However, it is not known how well static venous pressure elevation predicts subsequent AV graft thrombosis.

METHODS

Monthly static venous pressure measurements were made during two consecutive dialysis sessions in all patients with a functioning upper extremity AV graft in two hemodialysis units during a 16-month period. Static venous pressure was normalized to systolic blood pressure and corrected for the height difference between the AV graft and the dialysis machine pressure transducer to yield the static venous pressure ratio (SVPR).

RESULTS

Fifty-four patients (38%) had a thrombotic event during the study period and thus were labeled as clotters. Among the clotters, SVPR just prior to thrombosis was 0.51 +/- 0.16 (mean +/- SD), and mean time to thrombosis following an elevated SVPR (> or =0.4) was 118 +/- 106 days. Receiver operating characteristic (ROC) curves were generated using the sensitivities and specificities of a range of SVPR values for access thrombosis within one, two, three and four months. The areas under the curve (AUCs) for the ROC curves ranged from 0.557 to 0.638, reflecting the absence of SVPR values with both high sensitivity and high specificity for access thrombosis. An increase in SVPR over time was not a better predictor of access thrombosis than absolute SVPR.

CONCLUSION

Static venous pressure measurement is not an optimal screening test for identifying AV grafts at risk for thrombosis.

Extracorporeal pressure monitoring and the detection of vascular access stenosis

Prospective monitoring of static venous pressure is an established tool to detect outflow stenoses in a vascular access. However, with this method it is not possible to identify vascular stenoses which are localized between the arterial and venous dialysis needle. We describe a new approach based on both static arterial and venous extracorporeal pressures. Pressure data of 9 dialysis patients with normal vascular access function and 9 patients with stenotic access were analyzed. Extracorporeal pressure was found to depend on the position of the heart relative to the extracorporeal blood circuit. All patients with venous outflow stenoses had an elevated ratio of arterial and venous intra-access pressure to mean arterial pressure. In case of access stenosis between arterial and venous needle the ratio of venous pressure to mean arterial pressure was normal, and only the arterial pressure ratio was elevated. We conclude that combined arterial and venous intraaccess pressure measurement normalized by mean blood pressure detects venous stenosis as well as stenosis between the arterial and venous dialysis needle. To minimize the rate of access thrombosis both arterial and venous intra-access pressure should be monitored.

Effects of systemic hemodynamics on flow within vascular accesses used for hemodialysis

Absolute value of access flow (QA) and change in flow (deltaQA) over time are major determinants of access patency. However, QA may change in response to variation in systemic hemodynamics among dialysis sessions. We examined the effect of mean arterial pressure (MAP), cardiac output (CO), and segmental resistances (R) on QA. Access flow and CO (L/min) were determined by Transonic ultrasound dilution. Static intra-access pressures (mm Hg) at the arterial segment (AS) and venous segment (VS) were determined with the access unoccluded. During access occlusion (O), the AS pressure was equated to arterial pressure (MAPo), whereas the VS pressure reflected venous pressure (VP). Total and segmental vascular resistances (mm Hg-min/L) were calculated as deltaP/Q. We studied 58 arteriovenous (AV) grafts and 35 autologous AV fistulae (AVF) with measurements on two or more occasions in 43 grafts and 25 AVF. MAPC differed from MAPo by >20 mm Hg in 22% of patients. AS (58 +/- 2 vs. 31 +/- 2) and VS (40 +/- 1 vs. 25 +/- 2) were greater in grafts than in AVF, whereas VP was equal. Access flow (0.91 +/- 0.03 vs. 0.91 +/- 0.05 L/min), cardiac output (5.1 +/- 0.1 vs. 5.5 +/- 0.2 L/min), and total access resistance (115 +/- 5 vs. 11 +/- 6) were equal in grafts and AVF, but non-access systemic R was lower in patients with AVF that those with grafts (26 +/- 1 vs. 30 +/- 1). AS and VS resistances were greater in AVF than grafts (87 +/- 6 vs. 54 +/- 3 and 37 +/- 3 vs. 16 +/- 3). Multivariate analysis indicated that CO and ipsilateral MAPo affected flow in both access types. In grafts, all three access resistance elements, AS, VS, and total independently influenced flow, whereas in AVF, the VS did not. Unexpectedly, the ratio of systemic to access resistance also influenced access flow. The pressure in the venous system draining the access affected access flow in AVF but not grafts. We conclude that the hemodynamics of grafts and AVF differ. Cardiac output, MAP, and the arterial segment resistance influence QA in both access types and need to be considered when evaluating QA as part of the trend analysis for detecting access dysfunction.

Vascular access blood flow monitoring reduces access morbidity and costs

BACKGROUND

Vascular access morbidity results in suboptimal patient outcomes and costs more than $8000 per patient-year at risk, representing approximately 15% of total Medicare expenditures for ESRD patients annually. In recent years, the rate of access thrombosis has improved following the advent of vascular access blood flow monitoring (VABFM) programs to identify and treat stenosis prior to thrombosis. To define further both the clinical and financial impact of such programs, we used the ultrasound dilution method to study the effects of VABFM on thrombosis-related morbid events and associated costs, compared with both dynamic venous pressure monitoring (DVPM) and no monitoring (NM) in arteriovenous fistulas (AVF) and grafts.

METHODS

A total of 132 chronic hemodialysis patients were followed prospectively for three consecutive study phases (I, 11 months of NM; II, 12 months of DVPM; III, 10 months of VABFM). All vascular access-related information (thrombosis rate, hospitalization, angiogram, angioplasty, access surgery, thrombectomy, catheter placement, missed treatments) was collected during the three study periods.

RESULTS

During the three study phases, graft thrombosis rate was reduced from 0.71 (phase I), to 0.67 (phase II), to 0.16 (phase III) events per patient-year at risk (P < 0.001 phase III vs. phases I and II). Similarly, hospital days, missed treatments, and catheter use related to thrombotic events were significantly reduced during phase III compared to phases I and II. Hospital days related to vascular access morbidity and adjusted for patient-year at risk were 1.8, 1.6, and 0.4 and missed dialysis treatments were 0.98, 0.86, and 0.26 treatments per patient-year at risk for phases I, II, and III, respectively (P < 0.001 for phase III vs. phases I and II). Catheter use was also significantly reduced during phases II and III, from 0.29 (phase I) to 0.17 and further to 0.07 catheters per patient-year at risk, respectively (P < 0.05 for phase III vs. phase I). Percutaneous angioplasty procedures increased during phases II and III from 0.09 to 0.32 to 0.54 procedures per patient-year at risk for phases I, II, and III, respectively (P < 0.01 for phase III vs. phase I). When the total cost of treatment for thrombosis-related events for grafts was estimated, it was found that during phase III, the adjusted yearly billed amount was reduced by 49% versus phase I and 54% versus phase II to $158,550. Similar trends in reduced thrombosis-related morbid events and cost were observed for AVFs.

CONCLUSIONS

VABFM for early detection of vascular access malfunction coupled with preventive intervention reduces thrombosis rates in both polytetrafluoroethylene (PTFE) grafts and native AVFs. While there was a significant increase in the number of angioplasties done during the flow monitoring phase, the comprehensive cost is markedly reduced due to the decreased number of hospitalizations, catheters placed, missed treatments, and surgical interventions. Vascular access blood flow monitoring along with preventive interventions should be the standard of care in chronic hemodialysis patients.

Clinical performance characteristics of hemodialysis graft monitoring

BACKGROUND

Regular monitoring of dialysis grafts is recommended, but the value of dialysis graft blood flow monitoring and venous pressures in predicting subsequent outcomes are controversial.

METHODS

Over a period of one month, we performed simultaneous flow and venous pressure monitoring in 71 dialysis patients with polytetrafluoroethylene (PTFE) grafts. These patients were prospectively followed for one year. Receiver operating characteristic (ROC) curves were constructed to evaluate the performance of the various monitoring techniques.

RESULTS

During the period of follow-up, there were 71 graft failures (30 angioplasty alone and 41 thrombosis followed by interventional or surgical revisions). Failed grafts had a lower blood flow rate [799 +/- 452 (SD) mL/min] when compared with those without failure (1019 +/- 485 mL/min, P = 0.05) Single static or dynamic venous-pressure monitoring were not predictive of graft failure. ROC analysis showed poor performance of graft flows in predicting graft failures over the short (30 days, AUC = 0.726, 95% CI, 0.509 to 0.942) and long term (one year, AUC = 0.630, 95% CI, 0.499 to 0.761). An adjustment of graft flows for systolic blood pressure or classification of graft based both on flows and venous pressure did not improve test performance.

CONCLUSIONS

Although dialysis graft blood flow rates are statistically different in patients who have graft failure (graft angioplasty and surgery or thrombosis) versus those who do not, the performance characteristics preclude clinical decision-making from an isolated blood flow or venous pressure study.

Vascular access problems in dialysis patients: pathogenesis and strategies for management

Repetitive hemodialysis was made possible through the development of a chronic means of accessing the circulation. This was accomplished through the use of arteriovenous fistulae or grafts, using autologous veins or synthetic materials. Although the arteriovenous fistula remains the access of choice, synthetic arteriovenous grafts are used in most patients because of problems with late referral to a nephrologist and poor vasculature. This article describes the means of accessing the circulation for hemodialysis, the pathogenesis of access failure through progressive stenosis followed by thrombosis, methods of detecting access dysfunction before thrombosis, and therapeutic options. Although angiographic or surgical intervention remain the mainstays of management, medical treatments to decrease stenosis and delay thrombosis are currently under investigation.

Flow in hemodialysis grafts after angioplasty: Do radiologic criteria predict success?

BACKGROUND

The anatomic success of percutaneous angioplasty of venous stenosis is determined by the improvement in cross-sectional diameter of the vessel. A successful outcome is defined as a residual stenosis of <30%. The purpose of this study was to determine whether the angiographic assessment of a venous stenosis correlates with the change in graft blood flow following angioplasty.

METHODS

Twenty-two hemodialysis patients with decreased intragraft blood flow (<700 mL/min) underwent diagnostic fistulography and angioplasty. All grafts were patent at the time of the procedure. Intragraft blood flow was measured before and after angioplasty using the ultrasonic dilution technique. Change in graft blood flow after angioplasty was correlated to the morphologic changes of the treated stenosis.

RESULTS

The mean preangioplasty and postangioplasty graft blood flows were 457 +/- 136 and 818 +/- 202 mL/min, respectively. The mean degree of stenosis before angioplasty was 74 +/- 15% and 18 +/- 14% after dilation (P < 0.001). The only variable that significantly correlated with postangioplasty blood flow was preangioplasty flow (r2 = 0.22, P < 0.001). The postangioplasty blood flow was not significantly different than the highest recorded blood flow measured in that graft (798 +/- 213 mL/min, P = NS). There was no significant correlation between the change in blood flow and the change in percentage of stenosis.

CONCLUSION

Following angioplasty of a venous stenosis, the graft blood flow is most closely predicted by the preprocedural blood flow and is similar to the highest recorded blood flow ever measured in that graft. Angiographic criteria to assess the success of angioplasty are not predictive of changes in blood flow.

Graft surveillance: venous pressure, access flow, or the combination?

BACKGROUND

Increased venous pressure (VP) and decreased access flow (Qa) are predictors of dialysis access graft thrombosis. VP is easily obtainable. Qa assessment requires a special device and takes more time. The aims of our randomized multicenter studies were to compare outcome in patients with grafts monitored by VP or Qa (study A) or monitored by VP or the combination of VP and Qa (study B).

METHODS

We performed VP measurements consisting of weekly VP at a pump flow of 200 mL/min (VP200) and the ratio of VP0/MAP. Qa was measured every eight weeks with the Transonic HD01 hemodialysis monitor. Threshold levels for referral for angiography were VP200> 150 mm Hg or VP0/MAP> 0.5 (both at 3 consecutive dialysis sessions) or Qa <600 mL/min. Subsequent therapy consisted of either percutaneous transluminal angioplasty (PTA) or surgery.

RESULTS

Total follow-up was 80.5 patient-years for 125 grafts. The vast majority of a total of 131 positive tests was followed by angiography and corrective intervention. In study A, the rate of thromboses not preceded by a positive test was 0.19 and 0.24 per patient-year (P = NS), and in study B, it was 0.32 versus 0.28 per patient-year (P = NS). Survival curves were not significantly different between the subgroups.

CONCLUSIONS

These data demonstrate that standardized monitoring of either VP or Qa or the combination of both and subsequent corrective intervention can reduce thrombosis rate in grafts to below the recommended quality of care standard (that is, 0.5 per patient-year, NKF-DOQI). These surveillance strategies are equally effective in reducing thrombosis rates.

Hemodialysis arteriovenous access: detection of stenosis and response to treatment by vascular access blood flow

BACKGROUND

Hemodialysis access to the circulation is best provided by native and synthetic arteriovenous fistulae (AVF and AVG). Thromboses caused by venous outflow stenoses prevent the long-term use of AV access. This pilot study was performed to evaluate the ability of ultrasound dilution-derived access blood flows to detect AV access stenosis and to evaluate the response to treatment.

METHODS

This pilot study was a single-center, prospective observational intervention trial. The monitoring technique used was ultrasound dilution access blood flow measurements performed monthly and after any intervention. Screening criteria for interventions were decrements in access flow of 20% when the flow value fell under 1000 mL/min or absolute flow of <600 mL/min. The primary intervention when flow criteria were met was biplanar venography of the access with percutaneous transluminal angioplasty (PTA) of detected stenoses. Stenoses unresponsive to PTA were sent for surgical revision. Access thrombosis was considered a study ending event.

RESULTS

Baseline access flow at study entry for AVF was 919 and 1237 mL/min for AVG. Sequential measurement of AV access flow detected AV access stenosis. PTA and surgical revision significantly restored AV access flow back toward the baseline flow measurement. Failure to restore access flow by at least 20% following intervention occurred in 14% of AVF and 21% of AVG PTA attempts. Transluminal angioplasty, once successfully performed, was required at a mean of 5.8-month intervals in order to maintain AVG flow. In contrast, AVF flow was restored for a much longer period of time following angioplasty (11.4 month follow-up at the time of study end). Compared with historic controls, which used venous dialysis pressure as the primary monitoring technique, the overall (AVF-AVG) thrombosis rates improved from 25 to 16% per patient year, and AVF thrombosis rates improved from 16 to 7% per patient year. When flow was not successfully restored, thrombosis ensued. Eight of 10 thrombosis episodes were predicted based on inability to improve access flow either as a result of stenosis treatment failure or unsuccessful referral for treatment.

CONCLUSION

Sequential measurement of AV access flow is an acceptable means of both monitoring for the development of access stenoses and assessing response to therapy. PTAs of AVF are more durable than PTAs of AV grafts.

Assessment of sonographic venous peak systolic velocity in detecting hemodialysis arteriovenous graft stenosis

There is no single effective means of assessing arteriovenous access function, although monitoring hemodialysis venous pressure (VP) or measuring access recirculation may be of some benefit. The present study assesses prospectively the efficacy of following the peak systolic velocity (PSV) as a single measure to detect arteriovenous graft (AVG) stenosis. PSV was measured in 12 patients after new AVG placement and at approximately 2-month intervals. Angiography was also performed after new graft placement and when PSV was elevated to greater than 200 cm/sec, hemodialysis access VP increased to greater than 150 mm Hg on three consecutive readings, or access recirculation increased to greater than 11%. PSV was then compared with results from angiography, VP monitoring, and access recirculation. The 12 patients underwent 34 PSV studies, followed by angiography on 25 occasions. Each patient underwent at least one angiogram. Each abnormal PSV value was confirmed with the finding of stenosis on angiogram, except for two patients with PSVs greater than 400 cm/sec and normal angiography results. VP and recirculation were not elevated. During this period, two patients developed thrombosis of the AVG, and two patients underwent angioplasty with improvement in PSV. We conclude that elevations in PSV measured at the venous anastomosis are an effective means of screening for AVG stenosis, AVG stenosis can occur early after AVG placement, and elevated VP and recirculation are late findings in AVG dysfunction.

Antibodies to topical bovine thrombin correlate with access thrombosis

Bovine thrombin is often used topically to promote hemostasis during vascular surgery, including dialysis-access placement. Patients frequently develop antibodies to bovine thrombin preparations, and some may develop antiphospholipid antibodies. We evaluated 88 hemodialysis patients for the presence of antibodies to topical bovine thrombin to determine if elevated antibody levels correlated with vascular access thrombosis. Twenty-seven patients (30.7%) had elevated antibody levels to topical bovine thrombin. More patients with elevated antibody levels had prior vascular access thrombosis than patients with normal antibody levels (13 of 27 versus 5 of 61 patients; P < 0.001). This difference was almost entirely the result of greater levels of thrombosis in patients with polytetrafluoroethylene (PTFE) grafts and elevated antibody levels. In these patients, 11 of 13 patients (84.6%) with elevated antibody levels had a previous thrombosis compared with 2 of 15 patients (13. 3%) with normal antibody levels (P < 0.001). Patients with elevated antibody levels and PTFE grafts also had more prior thromboses (1.92 +/- 1.60 versus 0.133 +/- 0.35 thromboses; P < 0.01) and a greater thrombosis rate (66.89 +/- 63.71 versus 4.65 +/- 12.05 thromboses/100 patient-years; P < 0.01) than patients with normal antibody levels. There were no differences in the frequency of myocardial infarction, coronary artery bypass, access age, presence of diabetes mellitus, platelet counts, anticardiolipin antibody, albumin, lactate dehydrogenase, or C-reactive protein levels. In conclusion, patients with PTFE grafts and elevated antibody levels to topical bovine thrombin had significantly more vascular access thrombosis.

Glucose degradation product methylglyoxal enhances the production of vascular endothelial growth factor in peritoneal cells: role in the functional and morphological alterations of peritoneal membranes in peritoneal dialysis

Peritoneal membrane permeability deteriorates in peritoneal dialysis (PD) patients. We test whether glucose degradation products (GDPs) in PD fluids, glyoxal, methylglyoxal and 3-deoxyglucosone, stimulate the production of vascular endothelial growth factor (VEGF), a factor known to enhance vascular permeability and angiogenesis. VEGF increased in cultured rat mesothelial and human endothelial cells exposed to methylglyoxal, but not to glyoxal or 3-deoxyglucosone. VEGF also increased in peritoneal tissue of rats given intraperitoneally methylglyoxal. VEGF and carboxymethyllysine (CML) (formed from GDPs) co-localized immunohistochemically in mesothelial layer and vascular walls of the peritoneal membrane of patients given chronic PD. By contrast, in the peritoneum of non-uremic subjects, VEGF was identified only in vascular walls, in the absence of CML. VEGF production induced by GDPs may play a role in the progressive deterioration of the peritoneal membrane.

Haemodialysis access: the case for prospective monitoring

Thrombosis in haemodialysis accesses remains a major problem. It is associated with stenosis that causes haemodynamic and anatomical changes. By prospective monitoring it is possible to identify patients at risk of thrombosis. Those patients should be referred for corrective intervention. This approach can result in a thrombosis rate below the advised quality of care standard of 0.5 thromboses/patient-year.

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

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