What is a fistula?
A fistula is a vein that has been attached to an artery. The increased pressure and flow in the vein generally causes it to grow larger and tougher. When the vein is big enough, is can be used for dialysis. There are several types of fistulas (see the gallery of accesses).
Can everyone have a fistula?
In order to have a fistula, you must have a vein that can be developed, a good enough artery to supply the blood flow necessary, and a surgeon who is able to put the two together. Patients with very bad hearts or bad circulation may not be able to tolerate the strain of a fistula.
What is a graft?
A graft is a teflon tube used to connect an adequate artery (one big and healthy enough to provide decent blood flow) and a healthy outflow vein capable of handling at least 1000cc of blood per minute. These artificial blood vessels are used to “bridge” the gap between artery and outflow when the patients other veins have been used up. Currently in the USA, about 40% of patients dialyze using graft.
Grafts are more prone to clotting and infection than fistulas, and the average lifespan of a graft (three years) is less than a fistula, so in general fistulas are more preferred when they are possible. However, a well-functioning graft may be preferable to a poorly functioning fistula. A well-functioning graft is much better than a catheter due to decreased risk of infection and lower risk of ruining the veins.
A graft in the forearm is sometimes used as a temporary option to help develop the veins in the upper arm for fistulas later (see the Gallery of medical photos for examples of fistulas created from the outflow veins of grafts). The graft can be used in short order (getting the catheter out before it can cause damage to be veins), and own the line a transition from graft to fistula may be possible.
What are the warning signs for grafts and fistulas?
- Prolonged bleeding from access after dialysis – over 20 minutes
- Change from a “buzz” or vibration felt over the graft or fistula to a pounding pulse
- More than one episode of infiltration or bruising around the graft or fistula
- Poor dialysis (insufficient clearance, recirculation) due to low flows
- A trend toward decreasing blood flows in a graft or fistula
- Elevated venous pressures on dialysis
- Swelling of the hand or arm on the side of the graft or fistula
- Development of “new veins” or popping out of old veins
- Pain in the graft or fistula
- Swellings in the graft or fistula
Call these signs to the attention of your nephrologist or dialysis center, or call Michigan Vascular Access (248-355-1100) for a prompt evaluation
DO NOT WAIT FOR YOUR GRAFT TO BLOW OR CLOT!!!!
The role of ultrasound in the creation of fistulas
The creation and maturation of fistulas for a greater percentage of dialysis patients has come to be understood as an important goal and a major quality advance. One contributing factor in allowing more fistulas to be created these days is ultrasound mapping – identifying veins that are not always readily apparent on clinical exam, and hence overlooked.
All too often I will examine a patient’s PTFE graft with ultrasound for some problem and find a large cephalic vein running underneath the graft. “Why didn’t they do a fistula?” I ask myself. Many times it is obvious that because of thick skin or chubby forearms, the vein was not palpable or visible, and so the opportunity was missed.
Many experts are recommending that ultrasound mapping be done prior to surgical consultation: that the nephrologist examine the patient, make a decision about the most appropriate vascular access, and then communicate that expectation to the surgeon. Certainly, there may be surgeons in most communities who can benefit from guidance regarding a procedure they do less frequently, and other surgeons whose care of the dialysis patient is improved by having their feet held in the fire by the nephrologist. Each nephrologist must make an assessment of the service their patients get from the local surgeons and adjust their practices accordingly. For many, more nephrological involvement in the access process may mean better results.
As the importance of vascular access for dialysis is increasingly recognized, however, more surgeons are becoming sophisticated in the assessment and treatment of the dialysis patient. In larger metropolitan areas there are even surgeons, like myself, focusing on this area as a large or exclusive part of our practices. For many of us, the office ultrasound is an essential extension of the physical examination, used in every new patient assessment and in the many of the follow-up visits.
In the new patient assessment, the office ultrasound is used to map the veins – measure the size, identify branches to be used in the anastomosis, identify or exclude clot from intravenous needle injury or other factors, follow the course of the vein, and identify the outflow. An attractive large vein at the wrist may lead to a long stenotic stretch in the mid forearm, dooming a wrist fistula, and setting up the patient for an early failure that will color his or her perception of access surgery. Futile operations can be predicted with better screening of the anatomy, and can thence be avoided. The high-yield procedure can be correctly identified in the initial office evaluation with the use of ultrasound in most instances.
Knowledge of the runoff allows long-term planning. A wrist fistula that does not mature sufficiently to be usable may still develop the antecubital veins. A forearm graft may then succeed where it would not have prior to vein growth. On the other hand, a graft in the forearm correctly placed can grow the cephalic vein in the upper arm, allowing an upper arm fistula at a later date. Or, an antecubital fistula useless for cannulation may grow a basilic vein to sufficient size and toughness to allow for transposition. All these stepwise approaches to providing vascular access are only made possible by an expanded knowledge of individual venous anatomy beyond what is easily visible.
We tend to focus on the veins, but arterial status can also be important. A huge vein at the wrist coupled with a two millimeter calcified radial artery in an older diabetic woman may be eagerly jumped on by the unwary surgeon who can be fooled by a “good pulse” in a superficial incompressible artery. This can be a recipe for intraoperative agony for the surgeon, early fistula failure, insufficient flows in any fistula that does develop, or digital ischemia due to steal. As another example, up to 15 or 20% of patients have a brachial artery that bifurcates in the upper arm rather than below the elbow, and a higher rate of access failures is noted in these patients. Forewarned is forearmed, as they say, and pre-operative knowledge of the anatomy derived from ultrasound examination may help identify the high-yield option for the patient without frustrating and time wasting exploratory surgery.
The precision of measurement achieved by a trained vascular lab technician will most often eclipse that of the surgeon, but in those practices where surgeons are adept enough to do a basic vascular ultrasound exam, a step can be eliminated, and time and money saved as the patient comes directly to the surgeon without stopping at the vascular lab. In my practice, I refer the patient for a formal vascular lab exam only if my exam precludes a fistula, for an ultrasound “second opinion”.
One important consideration is also the change in vascular tone that can occur due to room temperature, hydration status and other factors. A spastic vein invisible on one day may become a soda-straw on another. I routinely request an intrascalene block for my vascular access operations where possible not because it gives the best pain control (it doesn’t always), but because frequently the vasodilatory effects of the sympathetic block dilates the veins sufficiently to make the operation technically easier, to allow a fistula to be created at a lower level than previously thought possible, or even unveil a fistula option where a graft was planned. For this reason, the vascular access patient is almost invariably re-examined with a portable ultrasound in the operating room after the block is placed, and immediately before prepping the skin.
After the fistula is created, it will be reexamined with ultrasound on virtually every visit – measuring the size as the fistula develops over time, identifying branches that may need to be ligated to allow appropriate development of the fistula, or finding stenoses that indicate a need for balloon fistuloplasty. Measuring flow may be useful in the assessment of some fistulas. Measuring acceleration of flow may pinpoint an important stenosis. Tortuousity or depth-greater-than-width of a fistula on ultrasound may identify areas where cannulation will be difficult. Some deep fistulas will require superficialization or transposition prior to usability, and this assessment is aided by the ultrasound examination.
Once the fistula is judged usable, we frequently offer the patient the ultimate guide to cannulation. A digital photograph of the arm is taken and printed, then the fistula drawn on the printed photo with the assistance of an ultrasound examination. The course of the fistula is indicated, size at various points, depth below the skin at various points, location of branches, suggested areas for cannulation, and suggested areas to avoid are included. The photo-diagram is then xeroxed with several copies given the patient and one for the chart. Making the access more understandable for the Dialysis center personnel can reduce infiltration and make everyone’s day a little better.
Outflow veins of grafts are also ultrasound-examined when those patients are seen. The desirable result of having a graft placed is not just earlier usability, but the opportunity to develop a higher-level fistula option over time. When a patient understands that the long range plan is to abandon a forearm graft when it finally wears out and transit to an upper arm fistula, then eventual failure of the graft is not such a calamity, but a long expected opportunity to move on to something better.
In short, the availability of portable and affordable (less than $30,000) office ultrasound machines allows the surgeon to see under the skin more easily than before. Access planning and evaluation is improved, and so are results. Not all ultrasound examinations will be billable, but many will, and the machine pays for itself over time in a practice where it is used frequently. In my mind, office and intraoperative vascular ultrasound is an indispensable tool for the surgeon who wants to be effective in the management of the vascular access patient.
Creating forearm fistulas above the wrist!
The most well known location for AV fistulas is at the wrist. The so-called Brescia-Cimino fistula was the earliest described fistula and is still the gold standard for fistula creation. This fistula provides convenient and comfortable dialysis, preserves all the upper arm options, and should be the first choice where the patient’s anatomy permits.
Unfortunately, the vein at the wrist may be too small, or may be damaged from previous intravenous catheters during a hospital stay. In many people’s minds, the next option is a fistula at the elbow, so frequently a second forearm option is overlooked.
The cephalic vein receives an important branch from the back of the hand about two or three inches above the wrist. Like the Ohio River joining the Mississippi, the dorsal branch doubles the size of the cephalic vein, and this may be the only place a fistula is possible in the forearm. In my practice, I distinguish between a wrist fistula and a forearm fistula, the latter fistula being created at or above that dorsal branch.
This option may be missed because the veins are deep or otherwise not visible. Ultrasound in the doctor’s office (see “The role of ultrasound in the creation of fistulas”) or vein mapping in the Vascular Lab can prevent this mistake. Even if the vein is deep, it may become visible once it has grown, may be later moved to the surface (see “Superficialization of fistulas too deep to use”), or may succeed in building the veins in the upper arm.
The option may also be missed because a radial pulse palpable at the wrist may fade away further up the forearm. The artery may not be palpable two or three inches up from the wrist, but it is still there. Opening the fascia (connective tissue layer) next to the brachioradialis tendon reveals the artery. Dividing a couple of branches usually allows the artery to be mobilized enough to be used.
A fistula can even be performed in the mid-forearm by reflecting the brachioradialis muscle slightly to get at the artery. In this situation, only three or four inches of usable fistula develop in the forearm, and the second needle may need to be placed above the elbow.
Most often, both artery and vein are approached through the same 1 ½ inch incision, but occasionally they are far apart, and two incisions are required. In that case, the vein is brought through a tunnel between the two incisions.
The procedure is done as outpatient surgery, and healing is rapid. The patient is seen at one week, at one month, and at monthly intervals until the fistula is released for use. Forearm fistulas above the wrist are typically larger than standard wrist fistula and are frequently usable within a month of creation. Because the vessels are larger, the risk of failure in the hands of an experienced surgeon is less than with a wrist fistula, reducing futile operations and patient frustration. These forearm fistulas build the cephalic and basilic veins and preserve the options in the upper arm.
Disadvantages include a slightly more difficult surgery and slightly shorter length.
The forearm fistula may represent the best first step in vascular access for dialysis and should be considered before placing a forearm graft or creating a fistula at the elbow.
A strategy to utilize our hidden vascular assets!
The ideal fistula is straight, large, and in a location easy to cannulate for dialysis. Fistulas using the cephalic vein running from wrist to shoulder most often approach this ideal, but in many patients those veins are deep, tortuous, or impossible to cannulate. Too frequently, patients are told that the have “bad veins”, or that they cannot have a fistula. In the past, I myself have told patients with large arms and deep veins that they could not have a fistula. Fortunately I learned different, and now know better.
The cephalic vein in the forearm and the upper arm is associated with (bound down by) a layer of connective tissue from a point several inches above the wrist. Subcutaneous tissue (fat, “padding”, “insulation”) resides between that fascia and the skin. The more padding, the deeper the vein. We can ask the patient to lose weight to shrink this layer and bring the vein close to the skin, but this advice is often unreasonable.
The alternative is to move the vein closer to the skin and make it accessible for cannulation. Acceptance of this concept has allowed many people to have a fistula who were previously not thought to have that potential. Ordinarily, the vein is fistulized, and then superficialized later only if adequate growth is observed. Patients are happy to hear that a “bad” fistula can be moved and made usable.
The cephalic vein in the upper arm is the one most often superficialized. Whether the draining vein of a forearm graft or fistula, or a fistula created at the elbow, a long incision is made medial to the vein and the vein freed from elbow to shoulder. Branches are divided, stenoses fixed, and the arterialized vein divided just above the elbow. The mobilized vein is drawn through a tunnel created lateral to the incision so that the fistula will not be cannulated through a scar, and the two ends reattached. When the incision is healed, the fistula can be used – usually in a matter of just a few weeks.
If the vein is the draining vein of a forearm graft or fistula, it may not be necessary to place a catheter while the upper part heals, because the forearm portion continues to be usable. Eventually the forearm portion starts to fail, and the upper arm vein is connected to the brachial artery with abandonment of the forearm graft or fistula.
Superficializing the cephalic vein in the forearm is also possible, but is less common. If depth is the only reason that a forearm fistula is unusable, then bringing it to the surface not only can make it functional, but also preserve and develop the upper arm veins for future use.
Veins deep in the upper extremity can be usable no matter how big the arm, and should be considered a “hidden asset” for the dialysis patient. Superficialization of fistulas running too deep is a “high-yield operation” in the hands of an experienced Access surgeon. Every forearm graft should be considered a bridge to an upper arm fistula as a patient’s lifetime need for dialysis access is considered in a proactive fashion.
Transposing the basilic vein
Where possible, the cephalic vein is used for wrist or elbow level fistulas. It is usually located anteriorly, is relatively shallow, and is usually relatively straight with few branches. This is the vein most surgeons prefer to use for creation of an AV fistula. Unfortunately, the cephalic vein may be small, tortuous, and in many patients has been ruined by previous intravenous catheters.
Finding options for the patient beyond the standard wrist or elbow fistula requires that we consider using a previously underutilized resource – the basilic vein. The basilic is the biggest vein in the arm, but is placed far medially (making it an inconvenient location for cannulation), and deep. The vein runs under several layers of brachial fascia (connective tissue), is surrounded by nerves, and can be close to the brachial artery. To use it in its natural position is impractical, painful and possibly dangerous.
Since transposition of the basilic vein was described in the 1980s, experience has been growing in the use of this vein. In general, the basilic vein is mobilized through a long incision on the medial part of the arm from elbow to axilla. Branches are ligated and divided. The vein is divided near the elbow, drawn through a subcutaneous tunnel lateral to the incision, and connected to the brachial artery. Because the incision is long and creates a large raw surface that can ooze a large amount of tissue fluids, I always leave a drain in the wound and keep the patient in the hospital overnight.
In general, a basilic vein must be 4 millimeters to be usable in a first-time operation. Then, a month or more must pass before the fistula is considered for use. The one-year unassisted patency for basilic fistulas has been reported to be as low as 50%, reflecting in many studies relative inexperience with this technique.
Several strategies can be employed to increase the yield of this operation. Experience of the surgeon is important. I have done nearly 50 of these operations in the last three years, and I am still learning new tricks related to basilic fistulas. My one-year patency over the last two years is close to 90%. It is important to find a surgeon who is beyond the learning curve in this operation.
Secondly, it has been observed empirically that basilic transpositions done after previous access in the same arm are more successful. The basilic vein above a forearm graft or fistula may have been “built up” over time from receiving increased blood flow. Veins of seven, eight, ten millimeters or more are frequently seen in the outflow of forearm accesses. When the forearm access fails, the large and previously toughened basilic vein can be transposed and used for dialysis within weeks. This operation is a very high-yield procedure in the hands of an experienced access surgeon. The venous outflow of forearm grafts or failing fistulas should be examined with ultrasound to discover these options for transition to an upper arm fistula.
In patients whose median antecubital vein is patent and in continuity with the basilic vein, an antecubital fistula can be a useful first step to an upper arm fistula. The antecubital vein is fistulized in such a way to create flow to the cephalic and the median antecubital. If the cephalic vein develops, well and good. If not, frequently the median antecubital and basilic become large enough to use.
One advantage to a basilic fistula is that it always is transposed, and is usually tunneled right under the skin. Cephalic fistulas can be transposed (or superficialized), but are most often used in their native position, which is below a fascial layer, and usually deeper. A correctly tunneled fistula should be easy to palpate, visualize and cannulate.
The recent enthusiasm for PICC lines represents a threat to the basilic vein. Previously protected by depth, this vein is now being used more and more, and like the cephalic vein before it, is being ruined for use in creating dialysis access. Fortunately, experience in declotting basilic veins, or removing parts of it entirely for use as an autologous graft is growing. Nevertheless, it is my position that PICC lines in renal patients can lead to loss of fistula options, and should only be used when absolutely necessary.
In short, being able to use the basilic vein is an important option for dialysis patients whose cephalic veins are inadequate. Chances for creating a useful fistula are greatly increased when the access surgeon considers using the basilic vein and is familiar with the operation.
Maturation of fistulas once created
After an arteriovenous fistula is created, it must “mature”. In general, fistulas require a three-to-six month growth period as the vein subjected to higher pressure and blood flow becomes larger and tough enough to be cannulated in two places three times a week. As the goal of creating more fistulas has gotten more attention, actual performance in maturing fistulas to usefulness has been examined. Studies show a wide variance in maturation success rates, from 20 to 90%.
Generally accepted guidelines call for re-evaluation of a newly created fistula if it has not been deemed usable by 6 months. Assessment can include applying objective criteria to the fistula, such as protocolized ultrasound examinations and blood flow measurements, or a “gestalt” test can be administered by an experienced access surgeon or dialysis professional. My practice is to more aggressively re-evaluate fistulas when the patient is being dialyzed via a catheter, since the “clock is ticking” and it is only a matter of time until an infected catheter or central stenosis will occur. Slow growth is expected, and sometimes it is reasonable to give more time to achieve the goal, but frequently growth is stymied by anatomic problems which prevent further growth in a reasonable time. In these instances, action to correct the limitation will be necessary to restore the growth curve.
Many factors can interfere with the maturation of fistulas, and awareness of these factors should be included in the assessment process. The office ultrasound machine allows a better understanding of the developing anatomy of a fistula, and frequently identifies or suggests these limiting factors. A specific strategy for each type of problem is important. Waiting for the problem or difficult patient to go away is not a strategy.
Inflow stenoses are common in wrist and elbow level cephalic fistulas. The cephalic vein is frequently smaller between the wrist and the dorsal branch two inches up the forearm, and also between the antecubital fossa and the lateral branch several inches up from the elbow. Small clamps placed on the veins during surgery may injure the vein and create scarring and stenosis. In either location, a catheter can be placed in the fistula above the stenosis directed retrograde for contrast studies and balloon dilation of the narrow segment. A standard arterial angiogram from the leg out to the arm can also be useful in diagnosing and dilating inflow stenoses. This “minimally invasive” approach is frequently successful, and can be repeated as often as necessary.
An option for stenoses at the wrist is to abandon the venous segment between wrist and dorsal branch, and reattach the fistula at the dorsal branch where it is naturally larger to the radial artery slightly higher. The vessels are bigger, and more flow can be expected, but some length will be sacrificed, and the new fistula will be shorter.
Stenoses just above the elbow are more difficult to revise if venoplasty fails, as the brachial artery and cephalic vein tend to be further apart on opposite sides of the biceps muscle. Nevertheless, the cephalic can be freed and transposed across the biceps to meet the brachial artery several inches above the elbow, a larger lateral branch can sometimes be moved across in similar fashion, or a jump graft can bridge the gap.
Stenoses in mid-fistula or in the outflow are also known, and are generally signaled by pulsatility in all or part of the fistula. Stenoses in the “swing-zone” between the transposed and in-situ portions of the basilic vein in transposed basilic fistulas are very common. A swollen arm after placement of an AV fistula or graft frequently occurs due to central stenosis from catheters left in too long.
Again, fistulography, venoplasty, and (rarely) stenting are employed to diagnose and treat fistulas which are unusable because of pulsatility or other problems. Fortunately, venoplasty is usually successful in resolving the problem, although redilation may be necessary at intervals as scarring and stenosis recurs. The role of the “cutting balloon” recently approved by the FDA in reducing failure of venoplasty, or reducing the necessary frequency of dilations, remains to be defined. Revision can also be necessary, and the most rational course is sometimes to abandon a complicated and dysfunctional forearm fistula in favor of a surer upper arm fistula option.
Unlike grafts, fistulas can have branches which sometimes divert flow away from the desired “central channel” one wishes to develop for dialysis cannulation. One big vessel is far more usable than several smaller channels. Ligation of these branches through small incisions under local anesthesia can be safe and effective in redirecting blood flow in a more desirable direction. Caution should be exercised, however: multiple prominent branches should raise the question of whether there actually is a viable central channel, or whether there is an obstruction in what seems to be the main vessel. In this case, ligating multiple branches creates venous hypertension in the hand, and solves nothing. A careful ultrasound exam, or a concurrent fistulogram performed by the surgeon at the time of ligation provides maximum information, effectiveness and safety.
Once cleared for use, many patients experience a difficult phase as the dialysis personnel “learn the fistula”. Infiltrations and problems do occur. Too many problems over too long a time should prompt a re-evaluation of the fistula to smoke out overlooked adverse factors. Ultrasound exam or fistulography may be indicated.
Re-intervention to promote maturation of fistulas should not be regarded as a sign of failure, and no shame should be attached to a corrective procedure. Not all veins are ideal, and not all fistulas develop without help. The patient should be informed of these realities right up front before the first operation is done, and access surgeons should be proactive in monitoring new fistulas and acting appropriately to help them along. The end result – more useful fistulas for dialysis and less complications for the patients – is worth the added effort.
The myth of “permanent access” and when to arrange for a shuntogram
One of the great myths of vascular access is that of “permanent access”. In truth, there is no such thing – there is “long-term access” (a graft, fistula or cuffed catheter) and “short term access” (a temporary catheter). Patients and practitioners frequently find themselves frustrated when they encounter problems with “permanent access” and apply unrealistic expectations to the situation. A clear understanding of the natural history of grafts and fistulas, coupled with a plan to deal with the problems that inevitably occur, is necessary if we are to avoid loss of access and the disruption of our normal lives that can occur.
Having a fistula may be like owing a Mercedes, and having a graft may be like owing a Chevy, but in both cases the automobile owner is obliged to keep up with ordinary maintenance or the auto will turn into a piece of junk – the responsible owner does regular oil changes, routine maintenance, and tire rotation. Everyone takes their car to the shop when a “funny sound” in the engine or wobble in the wheels develops – otherwise you find yourself by the side of the road waiting for the AAA tow truck to turn up.
Why do we view our AV grafts and fistulas differently? Is dialysis access – a life-sustaining necessity – less important than basic transportation? Is dialysis access less important than the car that sits in our driveway? No, no, no……
No – dialysis access represents an important investment that we should monitor and protect, and the reality is that all access requires maintenance and regular repair. Industry figures show that patients with AV grafts require an average of 1-½ procedures a year to maintain dialysis access, AV fistulas less. As none of us likes the prospect of dreading and waiting for the next disaster to disrupt our lives, we would like a better way to monitor our vulnerabilities, predict our problems, and manage our lives.
How are we to know when to seek help with our dialysis access? Just as there are guidelines for auto maintenance, there are guidelines for monitoring the function of AV access. Sophisticated pressure monitoring, recirculation and clearance calculations, and flow measurements are being used in many units to identify patients in need of a diagnostic and corrective procedure. Monitoring of access performance and preemptive treatment of problems has been shown to lead to a reduction in hospitalizations, missed dialysis, and catheter placement.
The simplest measure is the clinical examination – something that can be done be the individual patient, his or her caretaker, the dialysis nurse or attending nephrologist. Evidence of problems with dialysis access should lead quickly to a fistulogram (needle puncture and x-ray of the shunt) and other corrective procedures, such as dilation of narrowings (venoplasty) or stent placement.
A change in mind-set that leads us to (1) expect a need for occasional intervention in our AV access, (2) watch for signs of graft or fistula problems, and (3) intervene electively and effectively to prevent loss of access will help “keep us on the road”, and keep us out of the hospital waiting for an emergency procedure.
No one wants to find him or herself standing on the side of the road waiting for the tow-truck.
Endovascular maintenance of dialysis access
“The myth of ‘permanent access’ and when to arrange for a shuntogram,” we discussed the reasons for referring patients for a shuntogram – to recognize that all access requires maintenance, that signs of failure allow us to predict when an access is about to fail, and the importance of taking care of our accesses without procrastination so we don’t find ourselves in an emergency situation.
A shuntogram may be urgent or elective depending on the severity of the “warning signs”, but generally can be arranged as an outpatient procedure at a time convenient to the patient. Because sedation may be used, the patient is generally asked not to eat anything after the evening before, and to have someone drive him or her.
Patients are advised to take their blood pressure medications with a sip of water. Diabetics are asked to hold their insulin dose the morning of the procedure. Most often, patients on coumadin, Plavix or aspirin are not required to stop their blood thinners prior to the procedure.
Patients with mild allergies to iodine contrast (hives, itching) are prepared with prednisone, zantac and benadryl to reduce the risk of allergic reaction. Patients who went into shock or had their airway close up due to iodine allergy should only have their procedure done under the supervision of an expert anesthesiologist who is prepared to manage this risk.
Once the patient is comfortable in the procedure room, the arm or leg with the problem access is cleaned and then walled off with sterile sheets. The graft or fistula is accessed with a needle, and a small tube placed for contrast injection. The graft or fistula is studied from its origin in the arm or leg all the way to the heart, with x-rays taken during contrast injection.
All narrowings in the circuit can cause failure of a graft or fistula, and all significant narrowings are stretched with a balloon from the central vessels out to the arterial anastomosis. Although the most common place for stenosis is at the venous anastomosis of a graft, narrowings in the central veins (from previous catheters), in the graft or at the arterial anastomosis are also very common, and may need to be treated to avoid thrombosis of the graft or fistula.
When all narrowings have been successfully stretched, a strong thrill (vibration) should be felt over the graft. A weak thrill can mean that an inflow problem has been missed. Continued pulsatility usually means that a significant outflow stenosis (narrowing) still exists.
The access is re-examined and retreated until a satisfactory result is obtained, or until nothing else can be done. Sometimes larger balloons are needed for a stubborn stenosis, or on occasion, a stenosis that does not respond to stretching alone may require a stent. Pressure or flow measurements may guide the surgeon in knowing when to quit, or when to keep working. Problem accesses that cannot be fixed endovascularly may require operative revision or replacement.
In conclusion, endovascular maintenance of dialysis access is guided by the appearance of signs that indicate the graft or fistula is beginning to fail (see “Warning signs for grafts and fistulas”. Endovascular treatment is less invasive, less costly, and less inconvenient than surgical revision. Since it is typically elective or only semi urgent, usually it can be scheduled at a time of the patient’s choosing.
Endovascular maintenance is the preferred way for patients with failing grafts or fistulas to keep their accesses functioning, and to avoid emergency trips to the hospital for clotted access.
Endovascular topics: Thrombolysis of AV grafts
It is estimated that 85% of graft and fistula failures are predictable, treatable and hence preventable.
Unfortunately, in the real world we live in, resources for monitoring are not currently funded by Medicare, the usual payor for most dialysis services. The units that do invest in monitoring must find the funds to provide monitoring at the expense of other needed services. Procrastination and denial on the part of the patients, combined with the many demands on dialysis providers, and uneven experience also contribute to a failure to catch the failing access before it clots.
And sometime they just clot, no matter how careful you are.
So – inevitably – in a dialysis population, a certain number of patients will clot their accesses every day. In the past, this usually meant spending hours in emergency, hours waiting for the surgeon, another and another surgery, and disruption to the personal schedule. Worse yet, the patient could find him or herself with a catheter, and weeks or months of delay until another access is successfully placed and the catheter removed. Fortunately, newer approaches now exist.
Endovascular thrombolysis of dialysis access is an extension of endovascular maintenance of access (see article). It is generally an outpatient procedure performed by Interventional radiologists, qualified surgeons, or Interventional nephrologists.
The procedure can take between 45 minutes and two hours, depending on the severity of the problem and the experience of the operator. In general, 85% of clotted grafts can be rescued without open surgery, and the graft is almost always usable the same day.
First, the clot in the graft must be removed or dissolved by one of several means. I prefer mechanical thrombolysis, which consists of grinding up the clot in the graft and then suctioning it out (think “Roto-rooter”), but some doctors prefer chemical thrombolysis, in which enzymes are dripped into the clot to dissolve it (think “Drano”). Once the clot is dissolved and removed, a small amount of x-ray dye is injected to examine the graft and find the reason for thrombosis.
Although the problem causing thrombosis of the graft is generally narrowing at the venous anastomosis (seen in 90% of clotted grafts), narrowing in the body of the graft due to frequent punctures, narrowing in the central veins due to previous catheters, and narrowing in the arterial inflow of the graft are also frequent problems, and must be corrected to achieve an acceptable result. Failure to recognize and correct all the problems can mean that the patient will return sooner than expected with a reclotted graft.
All narrowings are dilated with balloons inserted through the same small punctures used for the thrombolysis and x-ray examination. If necessary, a stent can also be placed if an acceptable result is not obtained (to prop open a stubborn narrowing), or if the graft ruptures during dilation (to patch the leak from the inside). Finally, the clot in the arterial end is removed, and flow restarted. When the result is judged acceptable, the punctures are sutured, and the patient can return to dialysis immediately with a usable graft.
In cases where the access cannot be saved, a catheter placement may be necessary, but valuable information to guide a revision may be gained, making the procedure worthwhile nonetheless.
Endovascular thrombolysis is not simple, and should be attempted only by trained and experienced providers, but it has been shown to reduce unnecessary surgery, provide more timely service and restoration of access, and should be the first resort in patients with clotted access.
Use of stents in hemodialysis access
In another article we briefly discussed thrombolysis of clotted hemodialysis access. We also noted that it is estimated that 85% of graft and fistula failures are predictable, treatable and hence preventable, yet sometimes they just clot, no matter how careful you are.
What we didn’t discuss is that no matter how careful you are, if you are in this field for long you will inevitably get a phone call telling you that the arm graft you declotted last week – the one that looked so good, the one you were so proud of – is clotted again. You will declot the graft again, look for overlooked problems, and hope to find a way to stop seeing that particular patient so often.
I tell my patients I want them to be just like “family”, which in my world means I prefer to see them only once a year. To accomplish that, I need to find ways to make my interventions more enduring.
The use of stents in repairing, restoring or normalizing hemodialysis access is controversial. In 1997, the DOQI committee found that the unassisted patency of stents in hemodialysis access was no better than venoplasty except in cases of elastic stenosis and suggested that stents be limited to surgically inaccessible lesions or where there is a contraindication to surgery (Guideline 19).
Since that time, stent technology has evolved, with dacron-covered stents, PTFE-covered stents, and drug eluting stents either now or soon to be available, and more extensive experience with the use of stents in hemodialysis access. There is now a general consensus that stents are indicated when there is rebound stenosis with more than 30% residual stenosis after balloon dilation, where there is restenosis within a short time period (one to three months) or where there is rupture of a vessel during dilation.
Stents are now being used in more innovative ways – patching pseudoaneurysms in grafts, providing a durable fix in venous anastomotic stenosis, and lining recannalized central venous occlusions with a PTFE-covered channel.
Results are mixed, and depend on many factors. My own experience includes patients whose recurring venous anastomotic stenoses were PTFE-stented up to several years ago, and when re-examined have been found to be completely clean in the stented areas. Central venous occlusions have also been effectively managed, with preservation of upper-extremity options for dialysis that would otherwise have been lost.
Dacron-covered and bare-wire stents have not faired so well and have required more frequent intervention, or have failed. Nevertheless, it is clear that we have managed to keep many grafts and fistulas functioning well beyond the point that they would have been abandoned or returned to the operating room.
Stents are another tool in the armamentarium of the vascular access provider, and as such can be used wisely in selected circumstances to achieve results impossible otherwise. The injudicious or profligate use of stents will not improve results, and may raise costs.
Where can I find additional resources on the internet?
- National Kidney Foundation of Michigan
- National Kidney Foundation
- National Kidney Foundation Advisory on KDOQI Clinical Practice Guidelines
The National Kidney Foundation has published 22 Clinical Practice Guidelines through its KDOQI process. These include recently revised and updated guidelines for the care of dialysis patients and a new guideline on anemia at all stages of CKD. At times, KDOQI guidelines have been utilized in the development of government policy to improve outcomes for dialysis patients.