Point-of-care Vascular Ultrasound: Of Fistulas and Flows

Point-of-care ultrasound (POCUS) is increasingly being used in nephrology as a diagnostic tool, and there is a growing interest among physicians and nursing staff to learn how to use POCUS for the evaluation of the dialysis vascular access (DVA). The goal of POCUS is to extend the physical examination and more closely evaluate the DVA at bedside. Typically, POCUS quickly answers yes-no questions (ie, Is the vein too deep? Y/N). It is not the goal of POCUS of the vascular access to extensively investigate the entire fistula or graft. In conjunction with a good physical examination, brightness-mode ultrasound alone can answer most questions regarding the DVA, such as depth and diameter of the vessel. With some additional training, a limited color Doppler can be added to the standard evaluation to check flow direction and pseudoaneurysms. With more extensive training and an understanding of Doppler physics, access flow volumes can also be determined using spectral Doppler-mode ultrasound. Point-of-care ultrasound (POCUS) is increasingly being used in nephrology as a diagnostic tool, and there is a growing interest among physicians and nursing staff to learn how to use POCUS for the evaluation of the dialysis vascular access (DVA). The goal of POCUS is to extend the physical examination and more closely evaluate the DVA at bedside. Typically, POCUS quickly answers yes-no questions (ie, Is the vein too deep? Y/N). It is not the goal of POCUS of the vascular access to extensively investigate the entire fistula or graft. In conjunction with a good physical examination, brightness-mode ultrasound alone can answer most questions regarding the DVA, such as depth and diameter of the vessel. With some additional training, a limited color Doppler can be added to the standard evaluation to check flow direction and pseudoaneurysms. With more extensive training and an understanding of Doppler physics, access flow volumes can also be determined using spectral Doppler-mode ultrasound. Clinical Summary•Point-of-care ultrasound for the nephrologist should include dialysis vascular access (DVA) evaluation.•Training includes mastering the correct nomenclature of the DVA and proper physical examination technique.•Brightness-mode (with black and white images) ultrasound allows for evaluation of depth and diameter of the vessel as well as evaluation for extravasations and can be a guide for cannulation of the access.•Spectral Doppler-mode, although requiring more training and sufficient understanding of ultrasound physics, enables reliable flow volume measurements which adds essential information to the overall DVA evaluation. •Point-of-care ultrasound for the nephrologist should include dialysis vascular access (DVA) evaluation.•Training includes mastering the correct nomenclature of the DVA and proper physical examination technique.•Brightness-mode (with black and white images) ultrasound allows for evaluation of depth and diameter of the vessel as well as evaluation for extravasations and can be a guide for cannulation of the access.•Spectral Doppler-mode, although requiring more training and sufficient understanding of ultrasound physics, enables reliable flow volume measurements which adds essential information to the overall DVA evaluation. Point-of-care ultrasound (POCUS) is increasingly being used in medicine and its subspecialties.1Moore C.L. Copel J.A. Point-of-care ultrasonography.N Engl J Med. 2011; 364: 749-757Crossref PubMed Scopus (1079) Google Scholar Nephrology practitioners have recently shown increased interest in acquiring the necessary POCUS skills including the evaluation of the dialysis vascular access (DVA).2Koratala A. Teodorescu V. Niyyar V.D. The nephrologist as an ultrasonographer.Adv Chronic Kidney Dis. 2020; 27: 243-252Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar,3Niyyar V.D. O'Neill W.C. Point-of-care ultrasound in the practice of nephrology.Kidney Int. 2018; 93: 1052-1059Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar POCUS is an attractive tool because it is universally available, noninvasive, nontoxic, portable, and easily repeatable.1Moore C.L. Copel J.A. Point-of-care ultrasonography.N Engl J Med. 2011; 364: 749-757Crossref PubMed Scopus (1079) Google Scholar The goal of POCUS is to confirm and extend the DVA physical examination as well as allow real-time troubleshooting at the bedside. POCUS is an excellent tool for answering yes/no questions, ie, is the vessel too deep? It is not the goal of DVA POCUS to extensively investigate every possible characteristic of a given fistula or graft. These distinctions need to be kept in mind when setting trainee expectations and establishing rules and standards for teaching and competency. The objective of this article is to first describe the necessary knowledge base of nomenclature for the DVA, followed by a discussion of a thorough physical examination of the DVA combined with the proper technique of POCUS, and finally, a list of common applications of POCUS in a clinical setting. At present, POCUS of the DVA is neither commonly performed nor is it standardized for nephrology staff. Typically, nonnephrologists and vascular laboratory technologists perform ultrasound studies of the DVA using guidelines published by The American Institute of Ultrasound in Medicine.4AIUM practice guideline for the performance of a vascular ultrasound examination for Postoperative.Assess Dial Access. 2014; 33: 1321-1332Google Scholar This recommended examination format is complex and time-consuming and requires extensive training. Despite these guidelines, even when performed by expert vascular laboratories, data acquisition and its presentation and interpretation remain highly variable. One reason for this is that the nonnephrologists or technologists perform DVA examinations usually without practical knowledge of how DVAs are used in dialysis units, what surgical or endovascular procedures have been performed or are possible, and what cardiovascular consequences DVAs carry for individual patient's health. Experts in vascular access creation have published detailed protocols for dialysis access evaluation with Duplex ultrasound5Teodorescu V. Gustavson S. Schanzer H. Duplex ultrasound evaluation of hemodialysis access: a detailed protocol.Int J Nephrol. 2012; 2012: 508956-508962Crossref PubMed Scopus (42) Google Scholar; however, these are aimed at vascular surgeons or interventionalists. Nephrologists, dialysis nurses, and technicians, and as a result, their patients in clinic or the dialysis unit, would likely gain the greatest benefit from DVA POCUS training. However, practitioners often do not have the skills or specific ultrasound technical training to support and enhance the examination of the DVA. The first step is to be able to recognize and properly name the DVA using a standardized nomenclature for the dialysis access. According to the Society of Vascular Surgery guidelines, arterio-venous-fistulas and arterio-venous-grafts are named according to site of use (right/left, forearm/upper arm/thigh/chest-wall), the inflow artery used for arterial anastomosis (radial, brachial), the named vein used for the anastomosis (cephalic, basilic), and the indicator differentiating between an autogenous or a prosthetic access6Sidawy A.N. Gray R. Besarab A. et al.Recommended standards for reports dealing with arteriovenous hemodialysis accesses.J Vasc Surg. 2002; 35: 603-610Abstract Full Text Full Text PDF PubMed Scopus (664) Google Scholar (Table 1). Figure 1 depicts the most common types of access.Table 1Nomenclature of Dialysis AccessesType of AccessForearmUpper ArmAutogenous accessRadial-cephalic access (Snuff-box, Cimino, RADAR)Transposed ulnar-basilic (rare)Brachial-cephalic fistulaTransposed brachial-basilic fistulaTransposed brachial-brachial fistula (rare)Proximal radial—perforans fistula (Gracz or Endo-arterio-venous fistula)Proximal radial-cephalic bidirectional (Jennings) fistulaProsthetic accessRadial-cubital median/cephalic/basilic/brachial straight graftBrachial-cubital medial/cephalic/basilic/brachial forearm loop graftBrachial—axillary straight or loop graftAxillary-axillary loop graftAxillary-brachial loop graft (reverse)Abbreviation: RADAR = radial artery deviation and reimplantation (surgical technique for radial-cephalic autogenous access creation). Open table in a new tab Abbreviation: RADAR = radial artery deviation and reimplantation (surgical technique for radial-cephalic autogenous access creation). Step 2 is to use the same description of the access in terms of functional areas. The access circuit has an access inflow, the "stick zone" for needle insertions, and an access outflow (Fig 2). The access inflow encompasses the inflow arteries, the juxta-anastomotic segment, and an inflow segment of varying lengths between the juxta-anastomotic area and the visibly used needle-insertion segment. The "stick zone" can also be described as the body of the access and has an arterial needle and venous needle insertion area. The venous outflow encompasses peripheral and central veins leading to the right atrium. POCUS evaluation of the access is focused on the "stick-zone" and determines depth, diameter, and the location of side branches. Flow determination requires an additional evaluation of the inflow artery or a common single outflow vein segment. The final step before performing a POCUS is a standardized physical examination of the DVA.7Salman L. Beathard G. Interventional nephrology: physical examination as a tool for surveillance for the hemodialysis arteriovenous access.Clin J Am Soc Nephrol. 2013; 8: 1220-1227Crossref PubMed Scopus (46) Google Scholar This standardized physical examination described in the literature includes evaluating the following 5 criteria: thrill, bruit, pulsatility, augmentation, and the collapse of the vein during arm elevation.8Hentschel D.M. Hemodialysis vascular access Maintenance and Salvage.in: Darlin R.C. Ozaki K. Master Technique in Surgery. Lipincott Williams & Wilkins, Chicago/Turabian2015: 1-17Google Scholar The mastering of this comprehensive physical examination enables the understanding of flow, pressure, and difficulties that could arise during needle cannulation. Table 2 shows the 5 key elements of the physical examination with a description of a normal and abnormal examination. The absence of a bruit and thrill will typically be sufficient to determine that an access is completely thrombosed. Increased pulsatility, with no collapse of the body of the access, indicates a likely outflow obstruction. Poor augmentation with absent pulsatility indicates a likely inflow obstruction. Different types of accesses are predisposed to certain locations of stenoses as upper arm access and grafts often have outflow obstructions and forearm fistulas most often have inflow problems.9Turmel-Rodrigues L. Pengloan J. Baudin S. et al.Treatment of stenosis and thrombosis in haemodialysis fistulas and grafts by interventional radiology.Nephrol Dial Transplant. 2000; 15: 2029-2036Crossref PubMed Scopus (297) Google ScholarTable 2Physical Examination Components for Normal and Dysfunctional Dialysis AccessesExam ComponentNormalOutflow StenosisInflow StenosisThrillContinuous (juxta-anastomotic)Continuous (@stenosis)Discontinuous∗Depends on flow volume of the access. Bruit becomes discontinuous with lower flow volumes. (juxta-anastomotic)Discontinuous∗Depends on flow volume of the access. Bruit becomes discontinuous with lower flow volumes. (juxta-anastomotic)BruitContinuous (inflow/body)Continuous/Discontinuous∗Depends on flow volume of the access. Bruit becomes discontinuous with lower flow volumes.High pitch @stenosisContinuous/Discontinuous∗Depends on flow volume of the access. Bruit becomes discontinuous with lower flow volumes.High pitch @stenosisPulsatility (feel at body of access)NormalIncreased (retrograde to stenosis)Decreased (antegrade to stenosis)Augmentation (pulsatility while occluding outflow)NormalNormalWeakCollapse with arm elevation (observe at body of access while elevating arm over the heart level)Complete (forearm fistula)Partial (upper arm fistula)(This does not apply to grafts.)No collapse retrograde to stenosisComplete antegrade to stenosis∗ Depends on flow volume of the access. Bruit becomes discontinuous with lower flow volumes. Open table in a new tab In short, outflow stenoses will increase the intra-access pressure with increased bleeding propensity, infiltrations, and high venous pressure alarms while on the dialysis machine. Inflow stenoses are associated with difficult needle placement, arterial needle alarms, or collapse of the access around the venous needle. Inflow and outflow stenoses may decrease the overall access flow; therefore, measurement of flow volume alone does not allow one to determine where a stenosis is located. Ultrasound machines of any size, equipped with a high-frequency probe (7.5-12 MHz) are required. Brightness-mode (B-Mode) ultrasound is standard on any machine including hand-held ultrasound devices. For the utilization of Doppler, one has to differentiate between color Doppler and spectral Doppler. While color Doppler is available on nearly all types of machines, spectral Doppler may not be available on hand-held devices. In addition, the Doppler feature needs to include flow volume calculation software. As with any technical skill, adequate training and practice are a prerequisite. It is key to establish a comprehensive curriculum and enforce rigorous training criteria for the POCUS novice to ensure the resulting benefits for patients. This would include didactic training in principles of ultrasound and hands-on practice performing the particular examination. In addition, knowledge and application of standardized documentation, image storage, and report writing are equally important. A total of 50-100 training studies are often necessary to allow for competent and independent ultrasound evaluation of the DVA. These studies should include B-Mode images of the body of the access with measurement of depth and diameter. They should note if side-branches/hematomas are present and should measure access flow volumes in the brachial artery. To date, most training programs for vascular technologist apply criteria of the American Institute of Ultrasound in Medicine.4AIUM practice guideline for the performance of a vascular ultrasound examination for Postoperative.Assess Dial Access. 2014; 33: 1321-1332Google Scholar Currently, the American Society of Diagnostic and Interventional Nephrology is taking the lead in outlining criteria for vascular access ultrasound training and certification in the use of ultrasound throughout nephrology. These certification guidelines are presently under development. Ultrasound evaluation has been shown to be helpful in determining clinical maturation of the DVA while looking at diameter, depth, and flow volumes at 2 and 6 weeks after a newly created access.10Vascular Access 2006 Work Group. Clinical practice guidelines for vascular access.Am J Kidney Dis. 2006; 48: S176-S247https://doi.org/10.1053/j.ajkd.2006.04.029Abstract Full Text Full Text PDF PubMed Scopus (914) Google Scholar, 11Robbin M.L. Chamberlain N.E. Lockhart M.E. et al.Hemodialysis arteriovenous fistula maturity: US evaluation.Radiology. 2002; 225: 59-64Crossref PubMed Scopus (356) Google Scholar, 12Robbin M.L. Greene T. Allon M. et al.Prediction of arteriovenous fistula clinical maturation from Postoperative ultrasound measurements: findings from the hemodialysis fistula maturation study.J Am Soc Nephrol. 2018; 29: 2735-2744Crossref PubMed Scopus (62) Google Scholar A DVA is considered usable if the body of the access has a diameter of 4-6 mm and a depth of less than 5-6 mm, and the access has a flow volume of >500-600 mL/min.10Vascular Access 2006 Work Group. Clinical practice guidelines for vascular access.Am J Kidney Dis. 2006; 48: S176-S247https://doi.org/10.1053/j.ajkd.2006.04.029Abstract Full Text Full Text PDF PubMed Scopus (914) Google Scholar,13Lok C.E. Huber T.S. Lee T. et al.KDOQI clinical practice guideline for vascular access: 2019 Update.Am J Kidney Dis. 2020; 75: S1-S164Abstract Full Text Full Text PDF PubMed Scopus (544) Google Scholar In our experience, the rule of 6 (<6 mm depth, >6 mm diameter, and >600 mL/min flow) for defining access maturation is easier to remember and obtains better results in dialysis units. To date, vascular laboratories or radiology departments have been responsible for performing maturation studies of the DVA, but with proper training, nephrology practitioners can obtain the same parameters at the bedside or in the office using POCUS. It is important to note that several additional questions can also be answered using ultrasound at the bedside. Table 3 lists many of the questions, which may be addressed with POCUS applications.Table 3Appropriate Questions for Dialysis Vascular Access POCUSQuestionsB-Mode Diameter of access vein in needle insertion segment (body of access) Depth of access vein for needle insertion (body of access) Presence and location of side-branches (yes/no) Presence of extravasation/aneurysm/pseudo-aneurysm/fluid collection (yes/no) Presence of thrombus—partial or complete (yes/no) Guidance for needle insertionColor-mode Direction of flow Differentiate between hematoma vs pseudo-aneurysm (yes/no)Doppler (spectral) mode Flow volume measurementAbbreviation: POCUS = point-of-care ultrasound. Open table in a new tab Abbreviation: POCUS = point-of-care ultrasound. Rest the patient's arm comfortably on a pillow. Before beginning any DVA ultrasound study, it is of utmost importance to apply a liberal amount of ultrasound gel to the region of interest. Without adequate gel, the transmission of ultrasound waves, and therefore the image acquisition, will be incomplete. In addition, it is important not to apply too much pressure with the ultrasound probe. POCUS with B-Mode allows for a visual map of the DVA. It helps identify straight and curved sections. A transverse and longitudinal evaluation with B-Mode helps to determine if an access vein or graft is accessible with needles. If the vessel in the body of the access is at more than 5- to 6-mm depth, cannulation will be difficult or impossible. Figure 3 demonstrates a vessel that is sufficient in size and at appropriate depth for cannulation. If the vessel is not 5- to 6-mm wide, it will be difficult to cannulate without significant trauma and usually indicates that the access does not have the right flow and pressure balance. Tributary veins, known as side branches, can divert flow from the main access vein and can be a cause for poor augmentation observed during the physical examination. Side branches can occur in the presence and in the absence of stenoses of the access vein. In this situation, side branches can be located by performing a transverse sweep (sweeping of the ultrasound probe from the inflow to the outflow) over the access and subsequently drawn with a marker on the skin (Fig 4). A fascia overlying the vein can be another cause of poor augmentation and is again detectable using B-Mode ultrasound (Fig 4). Difficulty with cannulation in a patent access can be caused by a partially occluding thrombus. Thrombi are seen as echogenic, intraluminal filling defects. Any abnormal findings after a proper physical examination and POCUS should help determine whether a fistulogram with intervention (treating inflow or outflow stenosis) or vascular access surgery (superficialization of the vein, fasciotomy, or side-branch ligation) is required to make the DVA functional. Using ultrasound as guidance for cannulation is another highly useful application of POCUS. In the dialysis center, bedside ultrasound can be used to mark the arm for needle insertion. Alternatively, the needle can be inserted using real-time ultrasound.14Marticorena R.M. Mills L. Sutherland K. et al.Development of competencies for the use of bedside ultrasound for assessment and cannulation of hemodialysis vascular access.CANNT J. 2015; 25: 28-32PubMed Google Scholar,15Schoch M. Bennett P.N. Currey J. et al.Point-of-care ultrasound use for vascular access assessment and cannulation in hemodialysis: a scoping review.Semin Dial. 2020; 33: 355-368Crossref PubMed Scopus (12) Google Scholar Protocols using ultrasound-guided cannulations have been developed in several centers.16Niyyar V.D. Ultrasound-based simulation for cannulation in outpatient hemodialysis units: an educational protocol.J Vasc Access. 2019; (1129729819891530): 585-589Google Scholar,17Ward F. Faratro R. McQuillan R.F. Ultrasound-guided cannulation of the hemodialysis arteriovenous access.Semin Dial. 2017; 30: 319-325Crossref Scopus (20) Google Scholar Ultrasound-guided cannulation is particularly useful in low-flow, low-pressure accesses and fistulas with multiple outflow veins, a situation that is often encountered in percutaneously created arteriovenous fistulas. Occasionally, there is a lump or swelling over the access that requires evaluation and interpretation. Ultrasound can help determine whether the swelling is due to a dilation of the vein (aneurysm or pseudoaneurysm) or if there is a seroma, hematoma, or abscess overlying the access (Fig 5). Table 4 describes the ultrasonography appearance of commonly seen dialysis access–related pathologies.Table 4Ultrasonographic Appearance of Commonly Seen Pathologies Associated With the Dialysis AccessPathologySonographic Appearance of Access-Related PathologiesSeromaAn-echoic round structureHematomaHypoechoic/echo inhomogenous structure around the access veinAbscessHypoechoic/echo inhomogenous structure similar to a hematoma but with additional clinical signs of infectionAneurysmDilated segment of the access veinPseudoaneurysmOut pouching of the vessel with a pulsatile flow that appears on color and spectral DopplerTissue edemaCobblestoning pattern Open table in a new tab Partial and complete thrombosis of the access are seen as hypoechoic material within the lumen of the vein or graft. The application of color-mode Doppler (C-Mode) can be used to determine the presence and the direction of flow. As a general rule, flow moving toward the transducer will be coded red, and flow away from the transducer will be coded blue. For POCUS, it is best to limit the use of C-Mode as a tool to help answer simple questions, and not to map the entire access. While the physical examination alone can reveal that there is flow, the addition of color can be helpful to determine flow into a structure not related to the access, ie, pseudoaneurysm or continuous bleeding into the tissues (Fig 6). Spectral Doppler (D-Mode) allows for the measuring of flow velocities over time in a specific location and depicts them in graph form. While B- and C-Mode ultrasound are relatively easy to learn, several additional steps need to be mastered to correctly apply spectral Doppler. Spectral Doppler is required for flow volume determination. Timed average mean flow velocities (TAMVs) in a vessel as well as the diameter of the vessel for calculation of the area are the parameters needed for the flow volume calculation. TAMV needs to be obtained over several pulse cycles. The area of the vessel is calculated after measuring the diameter of the vessel. The following formula is used to measure flow volumes.Flow volume in ml/min = Mean velocity (TAMV) (cm/sec) × Area (cm2) × 60 (sec) This formula is preprogramed in ultrasound machines. Special attention is needed to make sure that the software is present and the settings are correct. To obtain accurate flow volume measurements in a vessel, several rules need to be strictly applied (Table 5).Table 5Step-by-Step Instruction for the Spectral Doppler Use for Flow Volume MeasurementsDialysis Access Flow Volume Measurement1)Measure in a region of straight, nontapering, nonturbulent flow (brachial artery at elbow or outflow vein at noncompressible site).2)Start D-Mode (do not use C-Mode).3)The Doppler gate is to be placed in the middle of the vessel.4)Adjust the angle of the incoming ultrasound waves using the steering function.5)Adjust gate to encompass at least 75% to 100% of the vessel lumen.6)Adjust the caliper for the angle correction to be parallel to the vessel (angle between incoming ultrasound wave and vessel < 60°).7)Start the spectral Doppler to obtain timed average flow velocities.8)Freeze image and Doppler and press Calculator.9)Time averaged mean velocity (TAMV) not time average peak velocities need to be preprogramed in calculation of flow volume.10)TAMV should be determined over a sequence of 3-4 cardiac cycles.11)The diameter of the vessel is measured perpendicular and with caution of not compressing the vessel.12)TAMV and diameter will allow the calculation the flow volume.13)Obtain 2-3 measurements to ensure accuracy and average.14)Document flow volume in conjunction with blood pressure measured at the same time. Open table in a new tab With the understanding that only a straight vessel with nonturbulent flow allows for correct flow measurement, it is best to measure access flow volumes in the brachial artery close to the elbow or in a singular outflow vein as opposed to the "stick zone".10Vascular Access 2006 Work Group. Clinical practice guidelines for vascular access.Am J Kidney Dis. 2006; 48: S176-S247https://doi.org/10.1053/j.ajkd.2006.04.029Abstract Full Text Full Text PDF PubMed Scopus (914) Google Scholar,12Robbin M.L. Greene T. Allon M. et al.Prediction of arteriovenous fistula clinical maturation from Postoperative ultrasound measurements: findings from the hemodialysis fistula maturation study.J Am Soc Nephrol. 2018; 29: 2735-2744Crossref PubMed Scopus (62) Google Scholar,18Ko S.H. Bandyk D.F. Hodgkiss-Harlow K.D. et al.Estimation of brachial artery volume flow by duplex ultrasound imaging predicts dialysis access maturation.J Vasc Surg. 2015; 61: 1521-1527Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar,19Zamboli P. Fiorini F. D'Amelio A. et al.Color Doppler ultrasound and arteriovenous fistulas for hemodialysis.J Ultrasound. 2014; 17: 253-263Crossref Scopus (49) Google Scholar Too often, the body of the access is tortuous and has varying diameters, and the flow is turbulent, resulting in inaccurate measurements. Also, it is of utmost importance to measure flow velocities at the proper angle (<60o), which is often impossible in a superficial vessel, such as the body of the access or the radial artery. Only a few studies compare the accuracy of ultrasound flow measurement with both the brachial artery and outflow vein with that of invasive flow measurement.20Bergmann M.H. Hentschel D.M. Toegel F. McMullan C. Voiculescu A. Measuring Access Blood Flow with Doppler: where should we measure? A cohort study comparing flow in the Brachial Artery and the Outflow Vein with invasive measurement with angioflow meter.J Vasc Access. 2017; 18: e84Google Scholar Figure 7 demonstrates the correct location for measuring flow volume in the brachial artery in a patient with a left forearm radial-cephalic autogenous access. Figure 8 demonstrates the images and measurements obtained for flow volume determination.Figure 8(A) B-Mode image of the brachial artery demonstrating the direction of ultrasound waves as compared to the artery and (B) the spectral Doppler for flow volume determination using the diameter and timed average mean velocities (TAMV) over several heart cycles.View Large Image Figure ViewerDownload Hi-res image Download (PPT) DVA flow volumes can be highly variable. Flow volumes can range from 200 to >3000 mL/min. The critical flow volume of an autogenous access has been determined to be around 400 mL/min. In a prosthetic access, the critical flow volume is approximately 600 mL/min.21Bay W.H. Henry M.L. Lazarus J.M. et al.Predicting hemodialysis access failure with color flow Doppler ultrasound.Am J Nephrol. 1998; 18: 296-304Crossref PubMed Scopus (124) Google Scholar,22Besarab A. Lubkowski T. Frinak S. et al.Detecting vascular access dysfunction.ASAIO J. 1997; 43: M539-M543Crossref Scopus (65) Google Scholar A fistula with a flow volume below 400 mL/min will not sustain efficient dialysis at pump speeds of 350-400 mL/min, and a graft with a flow volume below 600 mL/min is at risk for thrombosis. In the event where serial flow volume measurements are performed, a decrease in flow volume of more than 25% over 4 months points toward access dysfunction.10Vascular Access 2006 Work Group. Clinical practice guidelines for vascular access.Am J Kidney Dis. 2006; 48: S176-S247https://doi.org/10.1053/j.ajkd.2006.04.029Abstract Full Text Full Text PDF PubMed Scopus (914) Google Scholar Sometimes, DVA can have too much flow, ie, greater than 1.5 or 2 L/min. High flow puts the access at risk of bleeding, and high pressures, vein dilation with aneurysm formation. Patients with high flow are at risk to develop steal symptoms and/or heart failure. With diagnosis of high flow, it may be best to refer the patient for expert evaluation and possible treatment with flow reduction, ie, precision banding.23Beathard G.A. Jennings W.C. Wasse H. et al.ASDIN white paper: assessment and management of hemodialysis access-induced distal ischemia by interventional nephrologists.J Vasc Access. 2020; 21: 543-553Crossref Scopus (8) Google Scholar Spectral Doppler utilization for measurement of flow velocities and determination of stenosis of the DVA is difficult because of the aforementioned reasons, and the values are difficult to interpret. They also have limited clinical use. Therefore, measurement of flow velocities along the entire circuit is not recommended to be a standard for nonexpert vascular sonographers. After creation, a DVA should be carefully examined for patency and maturation. The 5 points of the physical examination can determine if there is any flow, if there is sufficient augmentation, and if there is an outflow problem. As long as there is bruit and thrill, the access is patent. If the vein itself is not well palpable and there is weak augmentation, POCUS can help determine depth, size, and presence of side branches or an overlying fascia. The additional measurement of flow volumes in the brachial artery will add pertinent information. A flow of less than 500-600 mL/min at 6 weeks after creation will require expert evaluation for further management.24Lomonte C. Casucci F. Antonelli M. et al.Is there a place for duplex screening of the brachial artery in the maturation of arteriovenous fistulas?.Semin Dial. 2005; 18: 243-246Crossref PubMed Scopus (83) Google Scholar POCUS can be used to check the diameter and depth of the access, which may have changed because of an infiltration. If the access is generally to deep, then the use of B-Mode for real-time needle insertion is another possible scenario. Additional flow volume measurement can help determine if the flows are too low or have decreased over time. Lumps or swelling over the access are frequent pathologies detected during dialysis. In these situations, the DVA can be assessed for pseudoaneurysms, hematoma, and extravasation with B- and C-Modes. Access flow volume measurement can help diagnose a high-flow access. Even though there is no standard definition of high flow, generally flow volumes greater than 1500-2000 mL/min are considered to put patients at risk for steal or congestive heart failure. POCUS represents a very valuable extension of the DVA physical examination. It is portable, noninvasive, easily repeatable, and can be performed efficiently at bedside by trained nephrology staff. Although the training may take several weeks, the trainee is more than compensated by the immediate availability of pertinent information describing the DVA and the resulting diagnosis based on the added data and the vascular visualization. Mastering B- and C-Mode ultrasound in conjunction with the skills for performing a detailed physical examination should be the first recommended steps for the novice ultrasonographer. More extensive training in the use of spectral Doppler is highly recommended for a more comprehensive understanding of the DVA. Ultimately, the use of POCUS by nephrology staff is of great benefit to them as well as to the patient and their access-related issues.