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Patient Selection for EndoAVF
Lauren Fang • Dec 28, 2020 • 481 hits
Long-lasting vascular access for dialysis can be achieved via the creation of an arteriovenous fistula using an endovascular approach. However, not every patient is a good candidate for percutaneous endoAVF creation. Interventional nephrologist Dr. Neghae Mawla discusses types of vascular access for dialysis, collaboration with vascular surgery, endovascular AV fistula patient selection, and patient referral patterns for endoAVF.
We’ve provided the highlight reel in this article, but you can listen to the full podcast below.
The BackTable Brief
• EndoAVFs are upper arm fistulas that utilize either the cephalic or the basilic vein. Endo candidates are determined with ultrasound vessel mapping, which screens for a perforating vein as well as continuity between the cephalic and/or basilic surface veins with the radial and/or ulnar veins. Preprocedural ultrasound also evaluates vessel flow. Dr. Mawla states that the rule of thumb is a cephalic or basilic outflow size of 2.5 mm, which is the general criteria for a surgical fistula. He also looks for a minimum 2.0 mm for the median cubital, cubital cephalic, and perforating veins.
• Some patients may have more than one potential site of vascular access. For example, they may have forearm radial cephalic and endo upper arm options. In these cases, there is no standard answer for which vascular access site to select, according to Dr. Mawla. Patient preference helps guide the decision. Ultimately, patients who fail EndoAVF can still go back to get a radial cephalic fistula surgically and the same applies vice versa.
• With EndoAVF, there are opportunities to collaborate with vascular surgeons. Dr. Mawla states that even when the fistula, vessel sizes, and flows are good, there may not be enough room for two dialysis needles. Often, a vascular surgeon can elevate a median cubital vein that dives down steep as it crosses over. A vascular surgeon can also perform a basilic vein transposition to allow for easier dialysis access.
• For EndoAVF creation, Dr. Mawla receives patient referrals from external dialysis clinics and nephrologists as well as internal referrals through his private practice.
Table of Contents
(1) Endovascular AV Fistula Compared to Other Types of Vascular Access for Dialysis
(2) Collaborating with Vascular Surgery
(3) EndoAVF Patient Selection
(4) Patient Referrals for EndoAVF
Endovascular AV Fistula Compared to Other Types of Vascular Access for Dialysis
There are many options when it comes to vascular access for dialysis, including AV grafts, catheters, endovascular AV fistulas and open surgical fistulas. According to Dr. Mawla, the quality of dialysis with a catheter is always lower due to higher infection rates, however, they are good for immediate use. Because outcomes for fistulas are better than grafts in terms of lifespan and infection, the Fistula First initiative started. EndoAVF came along as an innovation for creating anastomosis in a simpler way. Although EndoAVF can be a great option for some patients, the current guidelines for hemodialysis vascular access have changed to “right access for the right patient at the right time.”
Can you provide our listeners the broad view of dialysis and need for fistula creation?
The thing about vascular access or dialysis access in particular is these patients are hooked at the machine, and the machine is running at about, on average, 400 ml per minute. You've got to have a large caliber access, and something that will support pulling the blood at 400, running it through, and returning it all back. That's where just a plain, old access doesn't work. I explain to my patients, "Put an IV in, it's not going to run fast enough." So that's really where the concept of vascular access came in, and if I remember correctly in the early days, they were doing femoral artery puncture. They were using the arterial blood pressure to actually pump through the entire circuit. We're 50-60 years out now from the original Cimino fistula. The arteriovenous fistula allowed us to use venous access for both needles instead of an arterial access and a venous access. The first innovation has been this EndoAVF in terms of how to create the anastomosis in a simpler way.
For some people who don't know anything about this procedure, can you talk about the difference between what a standard surgically created fistula looks like versus an EndoAVF?
So if you look at an upper arm fistula, the surgical fistula is usually anastomosed to the brachial artery above the cubital fossa. So, you've got a cephalic alpha, and it's an end-to-side anastomosis, and so either you will have a cephalic outflow or you will have a basilic outflow. The basilic vein gets transposed and elevated as well because as it travels up the arm, it tends to dive in underneath the bicep's muscle. Just the way it courses, it's hard for the patient to sit there on dialysis with the needles on the inside of the arm. So, the surgeon will elevate it, and transpose it, bringing it more to the front, so the dialysis nurses can access it. Because the endo-anastomosis is actually in the proximal forearm, you get a little bit more real estate in terms of cannulations on… For dialysis I actually utilize the median cubital vein for my cannulation site. So if I've got an endo basilic, meaning that there's no cephalic outflow, I will plan on cannulating across the median cubital vein, and I have been able to get almost most of my patients cannulated without a basilic elevation or transposition. One of the really nice advantages of an endo option is if the patient only has a basilic vein, then it doesn't absolutely require an elevation and transposition because that's actually a pretty big surgery sometimes, especially on these elderly patients.
We have a lot of trainees who are listeners, can you talk about what people mean when they say Fistula First, and why fistula creation is so important for the dialysis population? Why not just put catheters in everybody?
It's all about outcomes in terms of infection rates and quality. The quality of dialysis with a catheter is always lower, and the only reason catheters are still around is because of immediate use. Even then immediate use graft still takes two or three days to let the soft tissue swelling to calm down before you can access it. The graft is immediate use, but the tissue may not allow immediate use, and a lot of times that's okay, but the infection rates for catheters are higher. The outcomes with catheters at the dialysis level are clearly lower, so that's why we made a big push to avoid catheters. The outcomes for fistulas are better than graft in terms of lifespan, and infection, so that's why this initiative came out with Fistula First, to really try to get a fistula in someone who's a candidate because that's where the better outcomes were. Now, the newest guidelines have gone away from a Fistula First on everybody to more of a right access for the right patient at the right time. We recognize that a 90-year old patient who starts on dialysis, whose lifespan is a year and a half or two years, may not need to go through the hassle of getting a fistula in and struggling to get mature. Maybe a graft is better for a patient, or maybe the catheter is better for a patient. Now the algorithm is starting to change, and the question of where does EndoAVF come into this algorithm is also unclear at this time. The idea behind the Fistula First initiative was really based on the fact that a mature fistula is better than a mature graft, which is better than a catheter.
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Collaborating with Vascular Surgery
Dr. Mawla discusses collaboration with vascular surgeons for basilic vein transposition and elevation for easier dialysis access. A single stage endo basilic anastomosis followed by a surgical elevation can be a great option for patients wanting to avoid a two-stage procedure.
There is an option though, if you did need a basilic vein transposition, to collaborate with maybe vascular surgeons on this procedure. You could still do the endo AV fistula, and then they could participate in the transposition portion.
Absolutely, and I've done that. The patients that have required an elevation, I reached out to my surgeon and said, "Look, I've got enough, fistula is great, the vessels sizes are great, flows are great. I just don't have enough room for two needles." I can get one needle in if I needed to, but that second one it's just not going to take. The median cubital vein just dives down really steep as it crosses over, so I've had one of my surgeons elevate that. Another patient actually came to me because the surgeon saw the patient and said, "We're going to do a two-stage basilic transposition.” The basilic vein is of a marginal size, and the surgeon may opt to do it as a two-stage procedure, one, just to create the anastomosis, wait for it to develop, and then after it's matured, do the basilic elevation. The patient was a little apprehensive about two surgeries, went back and told the nephrologist, who says, "Maybe we could do stage one endovascular.” A stage one endo basilic anastomosis followed by a surgical elevation I think is a great option for some of these patients.
EndoAVF Patient Selection
EndoAVF candidacy is determined via ultrasound vessel mapping. In order for EndoAVF to be an option, Dr. Mawla states that the perforating vein, typically antecubital fossa, must communicate between the cephalic and/or basilic surface veins down to the radial and/or ulnar veins. Some individuals lack a perforator or do not have cephalic or basilic outflow. Dr. Mawla’s EndoAVF capture rate is around 50% after ultrasound screening. Patients who are not endoAVF candidates can still be candidates for a surgical brachiocephalic or brachiobasilic fistula.
Regarding EndoAVF fistula, can you talk about, first, who is a candidate, and what does the pre-procedure or evaluation look like to tease apart who and who is not a candidate for the EndoAVF?
Everything is done with ultrasound screening for me in my center, so the first question is to figure out, "Are they an upper arm fistula candidate or not?" So your EndoAVFs are an upper arm fistula either utilizing the cephalic vein or the basilic vein. There's no forearm EndoAVF options. If they are an upper arm fistula candidate, then it's a matter of additional screening of the perforating vein to figure out, "Are they an endo candidate?" A lot of patients are not an endo candidate, but can be a surgical brachiocephalic or a brachiobasilic fistula for example. It really boils down to the anatomy of the perforating vein, which is typically antecubital fossa. It’s really identifying where does that perforating vein go? The perforating vein really just communicates the deep veins and the surface veins. If you look at your surface veins, meaning the cephalic and the basilic as your fistula outflow for cannulation for dialysis, if that perforating vein will communicate between one of those or both of those down to the radial veins and/or ulnar veins, then that gives you an EndoAVF option.
It seems like whether or not you have a perforating vein and maybe the position or connection of that perforating vein is very important, but is there anything else regarding vessel diameter or arterial inflow that you look for on the preprocedural ultrasound?
The general rule of thumb is a cephalic or basilic outflow of two and half millimeters, which is your general criteria for a surgical fistula. That's where I start with. In addition to just the basilic, I also look at the median cubital vein because that comes into play for the EndoAVF. I look at a 2.0 mm for a median cubital vein or the cubital cephalic, perforating veins are 2.0 mm, and then the artery dimensions are all at the minimum of 2.0 mm. So really, it's two and half at the outflow, and 2.0 everywhere else is really the threshold in terms of your vessel criteria. If you're looking at Ellipsys, it's really looking at radial, proximal radial artery perforating vein, and your outflow. If you're looking at a WavelinQ, you're looking at ulnar artery, in addition to ulnar veins in that proximal territory, and your radial veins in that proximal territory as well for your anastomosis.
For those who don't know, or may not have any experience with this, when you say proximal territory, will just clarify?
Sure. Everything is at the proximal forearm, so we're looking right at the bifurcation of the brachial artery into the radial and the ulnar. Typically right around the range of the recurrent radial artery is where that perforator comes down and communicates just adjacent to the radial artery. On the ulnar side, we look to keep it in the common ulnar artery before the interosseous take off.
In your experience, what are the most common things that you're evaluating for in EndoAVF? What are the most common veins you see that exclude them from being a candidate for the procedure?
It all boils down to vessel anatomy. I've tended to notice patients that have a high bifurcation of the brachial artery in the upper arm sometimes don't have a perforator, and sometimes it doesn't communicate very well because it just seems like their superficial outflows are not that good, and they stay small. Some people have large cephalic, basilic drainage. It's a matter of which highway am I going to take home. For dialysis I need that large cephalic and basilic drainage, and I've noticed that high bifurcations tend to have very big radial veins, and very big ulnar veins, but their superficial veins are not that big, or they just don't communicate well into the deep level. It's not that I haven't done any [like that], but they are less common of a catch. Then, it's just those variants where everything drains into the brachial veins, and they have no cephalic or basilic outflow. A lot of people don't have perforators. My capture rate is right around 50% I think, in terms of my screenings to those that are a candidate for EndoAVF.
In your mind, who is the patient that comes in that is an ideal candidate for the procedures completely based on the anatomy that you find on the ultrasound?
It is all based off anatomy really. Then, it's just a matter of talking to the patient and saying, "Okay, which way do you want to go?" In general, the dilemma is not so much when it's an endo versus an open option. You can tell them, "Look, we can do this endo or we can do it open." Most of them choose the endo option. The dilemma in terms of discussions is if they have a forearm radial cephalic option, and they also have an endo upper arm option, then what's the right access for them? I don't know that there is an answer, a good answer or a standard answer yet because our standard algorithm always says just to really start in the forearm, and then work your way up for surgical fistula. But now, this endo anastomosis is at the deep level, and if an endo fistula doesn't take or goes down, it usually goes down at the deep level near at the anastomosis or at the perforating vein. I've had a couple of patients that failed my EndoAVF that went back later and got a radial cephalic fistula surgically, and they're doing fine. Those are the ones that I have discussions with the patients to say, "Hey, which way do you want to go? Do you want to start with the forearm, or do you want to start with the upper arm?" The question is, if an EndoAVF takes, and lasts them five years, then can you go back and do a radial cephalic fistula when that goes down? It depends on, again, where it fails.
If the patient goes just on radial cephalic fistula, and that fails, can you do Endo AV fistula subsequently?
Yes, you can. I've noticed there's almost a bimodal curve towards EndoAVF. The elderly patients, even if they have a radial cephalic option, will choose an EndoAVF just to avoid the surgical open, just to avoid anesthesia. Someone who's 75, we'll look at lifespan. If you get them one good access, that may be the only one they need to get their access for the remainder of their time on dialysis. So, the elderly patients will preferentially choose an upper arm EndoAVF over a radial cephalic fistula. The young patients who are in their 20s and 30s will do the same, choosing upper arm for the cosmetic reasons more than lifespan reasons. But, the patients who are in their middle age, that are more in their 40s, 50s, and even early 60s, it's a 50-50 split. A lot of them say, "I want to preserve all the access choices I can." I say, "Okay, then start with the Cimino." Some of them say, "No, let's go ahead and start up here."
Patient Referrals for EndoAVF
Dr. Mawla receives patient referrals from external dialysis clinics and internal referrals through his practice, Dallas Nephrology Associates. He notes that some physicians are hesitant in sending every patient for endovascular AV fistula until they are able to see the results of the entire procedure from anastomosis to cannulation to catheter removal.
How do patients end up in your clinic for the pre-procedural evaluation? What are the referral patterns for this procedure?
I'm unique in the sense because my practice, Dallas Nephrology Associates, has 90 plus nephrologists, and so most of my referrals are internal. I didn't have to do a lot of effort into the marketing side of it. Not all of my partners refer to me because the geography is obviously so big. I'm in North Dallas, and so the patients from the South, it's a waste for them to get up to me, so not all of them are able to. Some of the patients still will make that drive up there just for the screening, but really I've kept it all internal. I do have some patients that come from other physicians and other practices, and I think part of that is driven by dialysis clinics because the dialysis clinics are also taking care of these patients. So, if they get a patient that initiates on dialysis, they say, "What's your access plan?" Then the dialysis clinics will send them over for the vein mapping as well. They obviously check with the referring physician, but if the referring physician says, "Yeah, that's fine, I don't have preference. Send it to whoever you want,” then the dialysis clinics will send them over. A lot of education is also spent at the dialysis clinic level for the referral practice, in addition to your nephrologist that would be referring to you.
Were there any people who were reluctant or had some reservations about sending patients for this procedure?
There are. I think it's really mainly they just want to see how it develops and how it goes, and they want to provide the best care for their patients. They want to make sure EndoAVF is a good option, not only in terms of the anastomosis, but you have to see it through all the way to cannulation and catheter removal. A lot of them are waiting to see this whole process and how it goes before they really start sending all their patients over.
Dr. Neghae Mawla
Dr. Neghae Mawla is an Interventional Nephrologist with Dallas Nephrology Associates in Texas.
Dr. Christopher Beck
Dr. Chris Beck is a practicing interventional radiologist with Regional Radiology Group in New Orleans.
Cite This Podcast
BackTable, LLC (Producer). (2020, August 17). Ep. 77 – Endovascular AV Fistula Creation [Audio podcast]. Retrieved from https://www.backtable.com
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