Vascular and Interventional Radiology Review Shenoy and Darcy Ultrasound in Dialysis Interventions Vascular and Interventional Radiology Review FOUS ON: Surendra Shenoy 1 Michael Darcy 2 Shenoy S, Darcy M Keywords: arteriovenous fistula, arteriovenous grafts, dialysis interventions, ultrasound DOI:10.2214/JR.13.11277 Received May 22, 2013; accepted without revision May 23, 2013. 1 Department of Surgery, Living Donor Transplantation Program, Section of Transplantation, Washington University in St. Louis, St. Louis, MO. 2 Department of Radiology, Mallinckrodt Institute of Radiology, 510 S Kingshighway lvd, St. Louis, MO 63110. ddress correspondence to M. Darcy (darcym@mir.wustl.edu). WE This is a web exclusive article. JR 2013; 201:W539 W543 0361 803X/13/2014 W539 merican Roentgen Ray Society Ultrasound as a Tool for Preoperative Planning, Monitoring, and Interventions in Dialysis rteriovenous ccess OJETIVE. The rising prevalence of end-stage renal disease has resulted in increasing focus on delivery of vascular access care for hemodialysis. Duplex Doppler ultrasound, with its unique ability to reliably evaluate both structural and functional aspects of the peripheral vessels, is the preferred imaging modality for access planning and follow-up. ONLUSION. This article will review how ultrasound is currently used to evaluate patients pre-, intra-, and postoperatively for vascular access. T he rising prevalence of endstage renal disease (ESRD) and the consequent impact on health care economics has resulted in increasing focus on delivery of vascular access care, which is considered the chilles heel of hemodialysis. Duplex Doppler ultrasound (DDU), with its unique ability to reliably evaluate both structural and functional aspects of the peripheral vessels, is emerging as the preferred imaging modality for vascular access planning and follow-up. DDU is currently used to evaluate patients pre-, intra-, and postoperatively for vascular access. Use of Ultrasound for Preoperative Evaluation linical evaluation of a patient to plan vascular access starts with gathering the history pertaining to renal failure to assess the patient s longevity and the urgency with which the access is needed. Relevant history and clinical information, such as previous central and peripheral vein use and state of the arterial tree, are also recorded. This is followed by a thorough clinical examination to evaluate the patient s peripheral vasculature. Evaluation of the feeding artery and the outflow vein to create vascular access plays a major role in the success of this procedure [1, 2]. patient s body habitus can significantly impair the reliability of examining the venous anatomy. Reliability of the clinical examination is also limited in evaluation of the state of peripheral arteries. Ultrasound provides physicians with the ability to examine the vascular structures deep under the skin and overcome the shortcomings of physical examination. It is relatively inexpensive, is portable, and requires minimal space and setup. Hence, it is often performed by the examining physician. Such an approach has been shown to increase the success rate of arteriovenous fistula (VF) placement and maturation [3]. Vessel Mapping National Kidney Foundation Dialysis Outcomes Quality Initiative (NKF-DOQI) guidelines recommend that all patients being evaluated for vascular access should undergo vessel mapping [4]. With the creation of an arteriovenous anastomosis, the blood flow acutely increases five- to 10-fold, eventually leading to dilation of the outflow vein. Quality and caliber of the vessels play a key role in this response. Ultrasound vessel mapping is used to evaluate the arterial and venous anatomy and functionality [4, 5]. During mapping, the evaluator assesses the diameter and quality of the arterial wall and the anatomy and patency of the superficial and deep venous system in the extremities [6]. Vessel mapping is best performed using -mode ultrasound with a linear array probe with variable frequencies of 5 13 MHz. This provides excellent delineation of arterial and venous anatomy [7]. The entire arterial tree, starting from the axillary artery and following the brachial artery and its branching into radial and ulnar arteries, is examined for size and branching patterns. High branching of the radial artery can often be a cause for poor or slow maturation of an VF. Similar- W539
Shenoy and Darcy ly, a combination of narrow lumen and calcification in the artery is associated with poor maturation of the VF. During vessel mapping, the arterial tree is examined as distally as possible, and the most distal site used for access creation is the radial artery at the anatomic snuffbox region. olor Doppler is useful to establish the patency of the artery; however, its reliability to evaluate subtle stenosis in this low-flow setting is limited. Methods such as reactive hyperemia testing have been considered to evaluate the functionality of the artery; because of uncertainty associated with their clinical implications, these methods are not currently an integral part of vessel mapping [8]. The radial artery is the most common artery used to obtain the inflow for an VF, followed by the brachial artery. Vein mapping is done to study the venous anatomy [9]. The majority of VFs use the superficial veins (i.e., those superficial to the deep fascia). The most commonly used vein for fistula outflow is the cephalic vein in the forearm and in the upper arm. Reliability of venous mapping directly depends on the veins state of distention [10]. Hence, it is critical that techniques of venous distention [7], such as tourniquets, be used to ensure accurate assessment of the entire superficial and deep venous system. In the absence of adequate superficial venous anatomy in the forearm, deep veins at the elbow are considered as outflow veins to place a forearm graft. Similarly, when all superficial and deep veins in the forearm are absent, one can consider the upper arm deep veins, especially the basilic and axillary veins. Hence, vessel mapping involves the study of the entire superficial and deep venous system of the upper extremity. lthough ultrasound can provide information about the patency of the central venous system, the technique mostly relies on establishing indirect evidence on the basis of flow pattern [11]. If there is concern regarding central venous patency, catheter venography or T venography is preferred over ultrasound to evaluate the central venous system. VF Maturation Evaluation dequacy of dialysis depends on proper functioning of the VF. dequate blood flow and a good needle access segment are the two most important aspects of an VF [12]. lthough a flow of 600 ml/min is considered as the lower limit of normal, most well-functioning fistulas have flows of 800 1200 ml/min. DDU is reliable in measuring the velocity of the flow, and by use of a complex algorithm, time-averaged minute volume flow is calculated from the velocity and diameter of the blood vessel. rterial flow measurement is considered reliable and reproducible using DDU. The artery is thick walled, less compressible, and deeply situated and has long straight segments with similar diameter; these factors all make the flow measurement in the artery more reliable than trying to measure flow in the veins. For these reasons, inflow arterial flow measurement has evolved as the surrogate flow measurement of arteriovenous access. The needle access segment is the second important part of the access that determines its reliability to provide adequate dialysis. vein diameter of 6 mm or more is considered adequate. ecause of the need to withdraw the blood for the dialysis machine and return the cleaned blood to the patient, dialysis requires placement of two needles into the access outflow; for this reason, it is required to have a straight segment of at least 10 cm. Last, this needle access segment, along with being at least 6 mm in diameter and 10 cm long, is expected to be less than 5 6 mm deep relative to the skin. DDU can provide all this information in a noninvasive form. Thus, DDU has evolved as the imaging modality of choice to assess VF maturation. Role of Ultrasound in Long-Term ccess Monitoring Development of venous stenosis is the most common cause for arteriovenous access dysfunction. For arteriovenous grafts, the graft vein junction tends to be the most common place to develop stenoses that lead to arteriovenous graft dysfunction. In the setting of VF, a stenosis that develops up to 4 cm from the anastomosis is termed a juxtaanastomotic stenosis. Such stenosis tends to have significant impact on VF inflow. Stenosis can develop anywhere along the outflow vein all the way up to the central venous system in the setting of both VF and arteriovenous graft. These stenoses tend to have variable clinical manifestation based on location. It is not rare for the stenosis to manifest with problems during dialysis. Low access flow as determined by brachial artery flow measurement should prompt the clinician to examine the inflow area. Similarly, Fig. 1 Patient suspected of having venous outflow stenosis based on clinical history., Initial fistulogram shows juxtaanastomotic stenoses (arrows) that were not suspected. ntegrade access was obtained by palpation., Fistulogram after removal of initial access shows second retrograde access that was used to dilate stenoses. Had lesions been seen with ultrasound, retrograde access might have been chosen initially, which would have avoided extra puncture because study of rest of circuit revealed no central stenoses., Fistulogram shows good response to percutaneous transluminal angioplasty. W540
Ultrasound in Dialysis Interventions preserved brachial artery flow and strong pulsatility on the outflow vein should prompt the clinician to evaluate the venous outflow. DDU can provide both structural and functional information on such a stenosis. Whereas most inflow stenoses need further examination and intervention, it is often not so with venous outflow stenosis. In the outflow, the manifestation of a stenosis is relative to the blood flow. Intraprocedural Ultrasound Ultrasound is also invaluable for evaluating a dialysis access just before venography or an intervention. n initial look with ultrasound will increase the ease and efficiency of an intervention. For VFs, it is desirable to puncture somewhat near the anastomosis. This allows you to study the whole circuit from one access because it is easier to reflux contrast material to the anastomosis if the access is near the anastomosis. The location of the anastomosis is not always immediately evident because it may not be directly under the surgical scar and it may be remote from the needlestick segment. lso, the anastomosis is usually deeper than the outflow vein. Ultrasound allows you to choose a spot that is superficial enough for easy access but still somewhat close to the anastomosis. Fig. 2 Patient suspected of having juxtaanastomotic stenosis., Sonogram shows several centimeters of normal-caliber vein between anastomosis (small arrow) and stenosis (large arrow)., Venogram shows it was possible with ultrasound guidance to gain access pointing cephalad along outflow vein but with enough room to be able to treat proximal stenosis (arrow) that had been identified by ultrasound in., Venogram shows good result after percutaneous transluminal angioplasty of proximal stenosis. atheter was then able to be advanced to evaluate more central outflow veins. Ultrasound can detect stenoses near the anastomosis or in the planned access region. Without screening for stenoses, it is possible to inadvertently puncture too close to a stenosis to be able to perform angioplasty on it from that access (Fig. 1). Ultrasound allows you to pick an access that will ensure enough room to be able to deploy a balloon or stent (Fig. 2). lso, in patients with multilevel disease, it is sometimes difficult to know where the major stenosis is on the basis of clinical examination only. Thus, if the initial puncture is made in an antegrade direction (i.e., with the direction of blood flow in the outflow vein) and the major problem is actually a juxtaanastomotic stenosis, then it will be necessary to obtain a new, second access pointed toward the anastomosis. If the juxtaanastomotic stenosis is identified with ultrasound, then you may choose to start with a retrograde (i.e., toward the anastomosis) access. Even without a significant stenosis, the caliber of the outflow vein often varies. Ultrasound allows you to choose an access site where the vein is largest in caliber. The benefit of this is that the sheath is less likely to obturate the lumen of the outflow vein if a larger segment of vein is chosen for access. Maintaining flow around the sheath is important not only to prevent thrombosis but also to allow blood flow to push contrast material forward and more readily opacify central veins during venography. One of the downsides to percutaneous therapy is that you usually puncture some part of the outflow vein. This access has potential to cause spasm or stenosis. This problem can be eliminated by accessing the veins through a side branch that is not a part of the main outflow tract. This technique can be very useful when available. lthough they are not common, proximal side branches that are large enough to use for access can be identified and punctured with ultrasound guidance. ccess via a side branch has the added benefit that it may allow you to direct your catheters in either direction (Fig. 3), toward the arterial anastomosis or centrally. This is particularly useful when dealing with both a juxtaanastomotic stenosis and a more central outflow vein stenosis. fter treatment of one lesion, the catheter can then be redirected to treat the lesions in the other direction. This kind of redirection is usually not possible when directly accessing the outflow vein. Thus, treatment of both proximal and central lesions via access in the outflow vein requires two separate accesses point- W541
Shenoy and Darcy ing in opposite directions. ccessing a side branch may lead to stenosis or occlusion of that branch, but that is not necessarily bad. losure of a side branch may improve maturation of the fistula because side branches can divert flow from the main outflow vein. In loop arteriovenous grafts, ultrasound can be used to help confirm which is the venous and which is the arterial limb of the graft. ecause venous anastomotic stenoses and central stenoses are the most common causes of graft dysfunction, most often you will want to puncture pointing toward the venous outflow. lthough patients usually know which is the arterial and which is the venous limb, occasionally the patient is wrong and misleads your choice of access. With ultrasound, it is easy to identify which limb is which by tracing the graft limb back to its anastomosis. The vessel that the graft is hooked up to can easily be identified as an artery or vein. This is particularly useful when graft thrombosis prevents distinguishing the limbs by physical examination. n arteriovenous graft will sometimes develop intragraft stenoses from repeated access in an area. If you access the graft too close to a stenosis, you may not have enough room to inflate a balloon across the lesion without having the balloon extend out your puncture site. D Fig. 3 ccess via side branch., Initial fistulogram shows long juxtaanastomotic stenosis (small arrow). atheter had been introduced through side branch (large arrow) of outflow vein and extends up outflow vein at this point., Fistulogram shows catheter being redirected to treat juxtaanastomotic stricture., Fistulogram shows catheter being then redirected back up outflow vein (arrow) to treat mid upper arm outflow vein stenosis. D, Venogram shows 4.70-mm outflow vein stenosis (arrow) mentioned in. Identifying stenoses allows you to pick your access to allow treatment of these lesions. Not infrequently in VFs, venography reveals a stenosis near your access that may represent a real stenosis or just spasm; differentiation between the two is difficult using venography. If that segment was examined with ultrasound before the access and appeared normal, then you can be fairly sure that it is just spasm. Ultrasound may be useful in better defining pathology, which in turn might alter your intervention. One example is identifying thickened valves that may benefit from a valvulotomy rather than simple angioplasty. nother example is assessing the thrombus in an aneurysmal segment. n aneurysmal vein can harbor significant mural thrombus not readily apparent on contrast venography, and identifying this may have an impact on how a thrombectomy is performed. Finally, DDU can be useful in monitoring the response to angioplasty or stenting. The degree of residual stenosis after angioplasty can be measured with ultrasound [13]. acchnini et al. [14] found that after successful angioplasty of venous stenoses, access blood flow measured by ultrasound increased dramatically and returned to baseline flow values obtained before a stenosis had developed. Using this kind of physiologic measurement may potentially allow the operator to better assess the results of an intervention while at the same time reducing the use of contrast material and ionizing radiation. References 1. Davidson I, Gallieni M, Saxena R, Dolmatch. patient centered decision making dialysis access algorithm. J Vasc ccess 2007; 8:59 68 2. Nursal TZ, Oguzkurt L, Tercan F, et al. Is routine preoperative ultrasonographic mapping for arteriovenous fistula creation necessary in patients with favorable physical examination findings? Results of a randomized controlled trial. World J Surg 2006; 30:1100 1107 3. rimble KS, Rabbat G, Schiff D, Ingram J. The clinical utility of Doppler ultrasound prior to arteriovenous fistula creation. Semin Dial 2001; 14:314 317 4. [No authors listed]. III. NKF-K/DOQI clinical practice guidelines for vascular access: update 2000. m J Kidney Dis 2001; 37 (suppl 1):S137 S181 5. llon M, Lockhart ME, Lilly RZ, et al. Effect of preoperative sonographic mapping on vascular access outcomes in hemodialysis patients. Kidney Int 2001; 60:2013 2020 6. Ferring M, Henderson J, Wilmink, Smith S. Vascular ultrasound for the pre-operative evaluation prior to arteriovenous fistula formation for haemodialysis: review of the evidence. Nephrol Dial Transplant 2008; 23:1809 1815 7. Wellen J, Shenoy S. Ultrasound in vascular access. In: Wilson SE, ed. Vascular access: principle and practice. Philadelphia, P: Lippincott Williams and Wilkins, 2010:232 242 8. Malovrh M. The role of sonography in the planning of arteriovenous fistulas for hemodialysis. Semin Dial 2003; 16:299 303 9. Shenoy S. Surgical anatomy of upper arm: what is needed for VF planning. J Vasc ccess 2009; 10:223 232 10. Lockhart ME, Robbin ML, Fineberg NS, Wells W542
Ultrasound in Dialysis Interventions G, llon M. ephalic vein measurement before forearm fistula creation: does use of a tourniquet resources/guidelines/predialysisccess.pdf. Revised 2011. ccessed June 4, 2013 tion of duplex ultrasound-guided manual declotting and percutaneous transluminal angioplasty to meet the venous diameter threshold increase 12. harat, Shenoy S. ssessment and intervention in thrombosed native dialysis fistulas. Ren Fail the number of usable fistulas? J Ultrasound Med for arteriovenous fistula maturation. In: Wilson 2005; 27:713 719 2006; 25:1541 1545 11. IUM practice guideline for the performance of ultrasound vascular mapping for preoperative planning of dialysis access. www.aium.org/ SE, ed. Vascular access: principle and practice. Philadelphia, P: Lippincott Williams and Wilkins, 2010:196 205 13. Huang HL, hen, hang SH, et al. ombina- 14. acchini G, appello, La Milia V, ndrulli S, Locatelli F. olor Doppler ultrasonography imaging to guide transluminal angioplasty of venous stenosis. Kidney Int 2000; 58:1810 1813 W543