Vascular Access Monitoring and Surveillance
In the late 1980s and early 1990s, frequent hemodialysis (HD) access complications, particularly with arteriovenous grafts (AVG), lead to the development of vascular access monitoring protocols1. The universal goal of access monitoring is to identify access stenosis and enable intervention prior to thrombosis; thereby, maximizing access longevity and minimizing morbidity2. The advent and use of techniques including dynamic and static venous pressure monitoring, physical examination, access flow measurement, imagining and combined imaging and flow monitoring by duplex ultrasound demonstrate that it is possible to predict which accesses are at high risk for future thrombosis3. When vascular access monitoring is coupled with a program of elective stenosis correction, access thrombosis rates decline approximately 50-75%4. However, the long-term impact on access survival remains undetermined due to a lack of high powered randomized trials4.
The publication of the Dialysis Outcomes Quality Initiative (DOQI) and Kidney Disease Outcomes Quality Initiative (KDOQI) vascular access guidelines marked a major step in improving and standardizing a comprehensive approach to vascular access management5. The updated 2019 KDOQI Clinical Practice Guidelines for Vascular Access recommend that each dialysis facility have in place an organized program for the prospective diagnosis of venous stenosis by means of monitoring and surveillance6. The KDOQI guidelines recommend routine access monitoring and maintenance in conjunction with the adoption of standard criteria and an access surveillance plan for each patient6.
Preferred methods of vascular access surveillance vary according to the access type. For surveillance of arteriovenous fistulae (AVF), the 2019 KDOQI work group prefers6:
- Direct access flow measurements
- Physical examination to evaluate for findings of persistent swelling of the arm, presence of collateral veins, prolonged bleeding after needle withdrawal, or altered characteristics of pulse or thrill in the outflow vein
- Duplex ultrasound
Acceptable AVF surveillance methods include recirculation using a non–urea-based dilutional method and static pressures, direct or derived.
For surveillance of grafts, the 2019 KDOQI guidelines prefer6:
- Intra-access flow using sequential measurements with trend analysis
- Directly measured or derived static venous dialysis pressure
- Duplex ultrasound
Physical examination is the cornerstone of clinical monitoring. The elements of access physical examination include inspection (arm, shoulder, breast, neck, and face), palpation (from artery graft anastomosis to chest wall), and auscultation. Pulse augmentation and arm elevation tests, to evaluate the inflow and outflow tract, is also recommended7. Performing physical examination during an angioplasty procedure can assist in assessing the hemodynamics of the access and gauging the response to balloon dilatation7. KDOQI recommends physical examination, at least monthly by a qualified individual, to detect dysfunction in AVF and AVG6. Physical examination of the vascular access is simple to perform and readily available6; however, it does require training. A report involving only AVF, demonstrated the impact of training upon the accuracy of physical examination between an experienced interventionalist (IN) and a nephrology fellow (NF) with one month of training in physical examination of dialysis access8. Forty-five and 142 consecutive cases of AVF dysfunction were examined by the NF and IN, respectively8. Evaluation of the data revealed that the differences between NF and IN were not significant for outflow or inflow stenosis. However, the NF performed significantly better than the IN regarding central vein stenosis. Nephrology fellow [strong agreement (79%), Kappa value = 0.44]; IN [weak agreement (11%), Kappa value = 0.17] 8.
Access flow measurement
The best validated and most widely recommended method of access surveillance for detecting hemodynamically significant stenoses4,9 is monthly access blood flow (Qa) measurement. A prospective study of 91 HD patients assessed the correlation between thrombosis and changes in Qa over a period of 18 months; Qa was assessed every six months via the ultrasound dilution technique10. Only accesses with flows of more than 800ml/min were included. Among the accesses that thrombosed, a 22 and 41% decrease in Qa was found during the first and second observation periods, respectively10. By comparison, a 4% decrease and a 15% increase in Qa were observed among accesses that did not thrombose. Accesses with a greater than 35% decrease in Qa had an approximate 14-fold increased risk of thrombosis compared to those without change10.
In a recent controlled cohort study, adding Qa surveillance to unsystematic clinical monitoring of mature AVF, increased the rate of stenosis detection and elective treatment, thereby reducing the need for temporary central venous catheters. This resulted in decreased thrombosis and access-related costs, and improved access patency rates in the first 3 years after fistula maturation9.
The measurement of Qa should be considered early in the HD treatment to eliminate error caused by decreases in cardiac output related to ultrafiltration. In one series of 32 patients, serial Qa measurements were performed within 30, 90 and 150 minutes after the start of the HD treatment11. The mean Qa decreased significantly over time: 1,344 ± 486 mL/min (range, 600 to 2,525 mL/min), decreased to 1,308 ± 532 mL/min (range, 560 to 2,905 mL/min) at 90 minutes, and decreased further to 1,250 ± 552 mL/min (range, 465 to 2,905 mL/min) at 150 minutes11. There was a statistically significant difference between first and final measurements (p = 0.03), corresponding to an overall decrease of 7% in Qa between initial and final measurements during HD11.
Several techniques are available for Qa measurement. These include ultrasound dilution (UD), conductivity dialysance, and duplex ultrasound. The most common indirect technique for Qa is UD. In this technique, an indicator (saline) is infused distally into the dialysis access after line reversal. Ultrasonic sensors measure changes in the protein concentration producing dilution curves used for the calculation of Qa4. Sands et al12 demonstrated a tight correlation (r=.83) between Qa measured by duplex ultrasonography and UD. Studies have shown that AVG with an access flow of <700 cm3/min have a 59% increase in the relative risk of developing thrombosis within the subsequent 3 months4. This technique has been available commercially for the past decade. However, the challenges of the UD technique are multiple. There needs to be at least 1 available UD machine, a trained technician, a quality assurance and maintenance program, provisions for travel as well as a backup plan if the trained technician becomes unavailable13.
In the early 1990s, Gotch et al14 developed a novel method for long-term serial measurement of Qa. This method used online (real-time) conductivity (OLC) dialysance. Conductivity dialysance measures the dialysance of sodium which can be considered equivalent to the dialysance of urea14. A recent study by Lacson et al13 has found a highly significant correlation between paired measurements of OLC dialysance and UD. In this 50 patient (27 AVG; 23 AVF) single center pilot study, mean UD access flow was 1086 ± 629 mL/min, whereas mean OLC access flow was 951± 575 mL/min, with significant correlation (0.93; p<0.0001) for all accesses combined13. OLC is an attractive and practical alternative to UD measurement. OLC is readily available within the HD machine which allows for measurement within the patient’s HD treatment. It can be repeated in successive HD treatments without the pre-planning necessary for specific technicians. Any trained clinical staff can perform the measurement. Using OLC may overcome the barriers posed by the cost and program requirements of instituting a UD vascular access surveillance program13.
Color-flow duplex ultrasound provides anatomic imaging in addition to physiologic data (Qa measurement) reflecting the function of the dialysis access12. In the late 1980s, Tordoir et al15 compared imaging of 64 accesses by color flow duplex ultrasound and angiography. Color flow Doppler ultrasound accurately identified significant stenosis in polytetrafluoroethylene (PTFE) grafts (accuracy 86%, sensitivity 92%, specificity 84%) and in AVF (accuracy 81%, sensitivity 79%, specificity 81%)12. Identification of venous outflow stenosis, the most common site of graft pathology, was even more impressive (accuracy 96%, sensitivity 95%, specificity 97%)12. Abbreviated Doppler ultrasound limited to measurement of Qa and imagining of the graft venous anastomosis is also an effective means of graft surveillance. In over 1300 cases, abbreviated studies identified over 85% of PTFE grafts with a significant abnormality on a complete Doppler ultrasound examination and had a 79.7% sensitivity and an 88.6% specificity for > 50% stenosis anywhere in the PTFE graft or venous runoff12. Color flow Doppler ultrasound has proven accuracy in the identification of patients at high risk for thrombosis, is mobile and noninvasive. Yet, direct QA measurements by means of Doppler ultrasound or magnetic resonance are expensive and can be impractical to perform routinely during HD treatment16.
Venous pressure monitoring
Dynamic venous pressure (DVP) is measured by the dialysis machine pressure transducer at the beginning of hemodialysis using 15-gauge needles at a blood flow of 200. Measurements > 125-150 mmHg (different on each brand of hemodialysis machine) on 3 consecutive treatments are considered abnormal17. Although DVP is relatively simple and inexpensive to perform, static venous pressure is more predictive than DVP because it eliminates many of the confounding variables of needle size, machine type and blood flow associated with DVP measurement18. In the mid to late 1990’s, Besarab and colleagues19,20demonstrated that elevated static venous pressure was highly sensitive and specific for detecting venous stenosis in AVG. This was questioned by a more recent study by Dember et al21 which found that static venous pressure measurement had a poor sensitivity and specificity for predicting AVG thrombosis and was therefore not an optimal screening test for identifying AVG at risk for thrombosis.
With static pressures, analysis of trends is more informative than any one measurement6. Overall, recent trials have shown that dynamic and static venous pressures are less effective than access flow-based monitoring protocols4.
Signs and symptoms of access dysfunction
Other indicators that may be suspect in pending access failure include22:
- Edema: Indicative of potential infection or venous outflow impairment
- Palpable graft pulsation: May be predictive of venous anastomotic stenosis and stenosis in fistula
- Decreases in delivered dialysis dose: May be indicative of either insufficient blood flow or high recirculation possibly due to stenosis
- Excessive negative pressures (below -200 mm Hg with 15-gauge needles and a blood flow of 400ml/min): May indicate a failure of the fistula to provide the flow demanded by the blood pump due to a potential inflow stenosis in the fistula
- Prolonged bleeding time after needle withdrawal (without excessive anticoagulation): Should be measured and documented as a potential indicator for graft or fistula stenosis. Prolonged bleeding of > 10 minutes or a change from current baseline with no change in anticoagulation may indicate stenosis particularly in PFTE grafts and requires evaluation
Prolongation of access survival
Although regular Qa surveillance is recommended to detect graft stenosis, there is little evidence that monitoring and correcting with angioplasty improves AVG survival23. Moist et al23 studied time to graft thrombosis and graft loss, comparing monthly Qa plus standard surveillance (DVP and physical examination) (treatment group) to standard surveillance alone (control group). In this blinded, randomized, controlled trial of 112 patients, there was no difference in time to graft loss (p = 0.890) 23. However, monitoring Qa in AVF does show promise. Tessitore et al 8 demonstrated that regular Qa surveillance is associated with significantly more access imaging, stenosis detection and elective repair, and significantly fewer temporary central venous catheter placements.
Despite the varying data regarding access monitoring techniques, early identification of failing accesses does provide the opportunity for elective repair of vascular access sites. Access monitoring allows planning, coordination of effort, and elective intervention for the correction of access dysfunction, rather than as urgent procedures with the potential need for hospitalization or catheter placement or access replacement6. Furthermore, some studies have reported that access flow-based surveillance programs are cost effective24. Additional prospective studies are necessary to further clarify these issues.
- Sands JJ. Vascular access 2007. Minerva Urol Nefrol. 2007;59(3):237-249. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17912221.
- Sirken GR, Shah C, Raja R. Slow-flow venous pressure for detection of arteriovenous graft malfunction. Kidney Int. 2003;63(5):1894-1898. Available from: https://pubmed.ncbi.nlm.nih.gov/12675869/.
- Waniewski J, Debowska M, Wojcik-Zaluska A, Ksiazek A, Zaluska W. Quantification of Dialytic Removal and Extracellular Calcium Mass Balance during a Weekly Cycle of Hemodialysis. Sands JM, ed. PLoS One. 2016;11(4):e0153285. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27073861.
- Sands JJ. Vascular Access Monitoring Improves Outcomes. Blood Purif. 2005;23:45-49.
- Sands JJ. Vascular access: the past, present and future. Blood Purif. 2009;27(1):22-27. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19169013.
- Lok CE, Huber TS, Lee T, et al. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update. Am J Kidney Dis. 2020;75(4):S1-S164. Available from: https://pubmed.ncbi.nlm.nih.gov/32778223/.
- Leon C, Orozco-Vargas LC, Krishnamurthy G, et al. Accuracy of physical examination in the detection of arteriovenous graft stenosis. Semin Dial. 2008;21(1):85-88. Available from: https://pubmed.ncbi.nlm.nih.gov/18251963/.
- Leon C, Asif A. Physical examination of arteriovenous fistulae by a renal fellow: Does it compare favorably to an experienced interventionalist? Semin Dial. 2008;21(6):557-560. Available from: https://pubmed.ncbi.nlm.nih.gov/18764788/.
- Tessitore N, Bedogna V, Poli A, et al. Adding access blood flow surveillance to clinical monitoring reduces thrombosis rates and costs, and improves fistula patency in the short term: A controlled cohort study. Nephrol Dial Transplant. 2008;23(11):3578-3584. Available from: https://pubmed.ncbi.nlm.nih.gov/18511608/.
- Neyra NR, Ikizler TA, May RE, et al. Change in access blood flow over time predicts vascular access thrombosis. Kidney Int. 1998;54(5):1714-1719. Available from: https://pubmed.ncbi.nlm.nih.gov/9844149/.
- Rehman SU, Pupim LB, Shyr Y, Hakim R, Ikizler TA. Intradialytic serial vascular access flow measurements. Am J Kidney Dis. 1999;34(3):471-477. Available from: https://pubmed.ncbi.nlm.nih.gov/10469857/.
- Sands JJ, Ferrell LM, Perry MA. The role of color flow Doppler ultrasound in dialysis access. Semin Nephrol. 2002;22(3):195-201. Available from: http://www.ncbi.nlm.nih.gov/pubmed/12012305.
- Lacson E, Lazarus JM, Panlilio R, Gotch F. Comparison of hemodialysis blood access flow rates using online measurement of conductivity dialysance and ultrasound dilution. Am J Kidney Dis. 2008;51(1):99-106. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18155538.
- Gotch FA, Buyaki R, Panlilio F, Folden T. Measurement of blood access flow rate during hemodialysis from conductivity dialysance. ASAIO J. 1999;45(3):139-146. Available from: http://www.ncbi.nlm.nih.gov/pubmed/10360712.
- Tordoir JHM, de Bruin HG, Hoeneveld H, Eikelboom BC, Kitslaar PJEHM. Duplex ultrasound scanning in the assessment of arteriovenous fistulas created for hemodialysis access: Comparison with digital subtraction angiography. J Vasc Surg. 1989;10(2):0122-0128. Available from: https://pubmed.ncbi.nlm.nih.gov/2668564/.
- Astor BC, Eustace JA, Powe NR, Klag MJ, Fink NE, Coresh J. Type of vascular access and survival among incident hemodialysis patients: The choices for healthy outcomes in caring for ESRD (CHOICE) study. J Am Soc Nephrol. 2005;16(5):1449-1455. Available from: https://pubmed.ncbi.nlm.nih.gov/15788468/.
- Schwab SJ, Raymond JR, Saeed M, Newman GE, Dennis PA, Bollinger RR. Prevention of hemodialysis fistula thrombosis. Early detection of venous stenosis. Kidney Int. 1989;36(4):707-711. Available from: https://pubmed.ncbi.nlm.nih.gov/2530385/.
- Whittier WL. Surveillance of hemodialysis vascular access. Semin Intervent Radiol. 2009;26(2):130-138. Available from: /pmc/articles/PMC3036423/.
- Besarab A, Al-Saghir F, Alnabhan N, Lubkowski T, Frinak S. Simplified measurement of intra-access pressure. ASAIO J. 1996;42(5).
- Besarab A, Sullivan KL, Ross RP, Moritz MJ. Utility of intra-access pressure monitoring in detecting and correcting venous outlet stenoses prior to thrombosis. Kidney Int. 1995;47(5):1364-1373. Available from: https://pubmed.ncbi.nlm.nih.gov/7637266/.
- Dember LM, Holmberg EF, Kaufman JS. Value of static venous pressure for predicting arteriovenous graft thrombosis. Kidney Int. 2002;61(5):1899-1904. Available from: https://pubmed.ncbi.nlm.nih.gov/11967043/.
- MacRae JM, Dipchand C, Oliver M, et al. Arteriovenous Access Failure, Stenosis, and Thrombosis. Can J kidney Heal Dis. 2016;3:2054358116669126. Available from: http://www.ncbi.nlm.nih.gov/pubmed/28270918.
- Moist LM, Churchill DN, House AA, et al. Regular monitoring of access flow compared with monitoring of venous pressure fails to improve graft survival. J Am Soc Nephrol. 2003;14(10):2645-2653. Available from: https://pubmed.ncbi.nlm.nih.gov/14514744/.
- McCarley P, Wingard RL, Shyr Y, Pettus W, Hakim RM, Alp Ikizler T. Vascular access blood flow monitoring reduces access morbidity and costs. Kidney Int. 2001;60(3):1164-1172. Available from: https://pubmed.ncbi.nlm.nih.gov/11532113/.
P/N 101052-01 Rev A 03/2021