Self-cannulation

Bill Peckham, the author of the excellent patient advocacy and home dialysis blog: dialysis from the sharp end of the needle has been on dialysis since 1990 and home dialysis since 2001 where self-cannulates using the buttonhole method. Last year he posted a video on Youtube that I only came across today. It shows his technique of needle insertion. I have often wondered how patients manage to cannulate themselves at home and this demonstrates it very nicely. I am full of admiration for my patients.

 

Bury it!

One of the issues that we come across repeatedly in the clinic is the timing of access insertion. We all want to avoid the use of catheters and so we refer patients early (when possible) for fistula formation. This is a bigger problem when your patient wants to start PD. You don’t want the patient to have the catheter placed too early because then they will be unnecessarily exposed to the risk of infection. At the same time, you don’t want to wait too long and get to the stage where the patient requires urgent HD (and often, once they start HD it is difficult to make the transition to PD). I saw a patient in the clinic a few weeks ago that fits this bill perfectly. He is an otherwise healthy man in his 60s who has a very active life and a full-time job. His creatinine had been stable for 2-3 years but climbed rapidly earlier this year and we thought he would need to start soon. However, his creatinine stabilized again and he is feeling well so we have him in a holding pattern with regard to the PD catheter insertion. Our surgeon suggested implanting a buried PD catheter, a technique that he has just started doing in our institution.

For this technique, the catheter is buried subcutaneously at the time of insertion. Then, when the patient is ready to start dialysis, the subcutaneous portion is externalized and the catheter can be used straight away. This can be done in the dialysis clinic and does not require a trip to the OR. Thus, a catheter can be inserted months (or even years) prior to use and the problem of timing is dealt with very elegantly. Recently, a paper was published which described the experience of the University of Denver where they have been using this technique as standard since 2000. In total, 134 catheters were implanted in that time. The period prior to externalization varied between 2 and 788 days with an average of 40 days. There was no relationship between catheter embedment time and the risk of catheter failure. 90% of catheters worked immediately and of the remaining 13 catheters, 12 were easily corrected laparascopically. Only 1 patient failed this technique and required transition to HD. This seems like a great technique and I look forward to seeing the results here over the next few months.

See also this earlier paper in KI about the experience with the use of buried catheters in Ottawa.

Femoral versus Jugular: part three

Previous posts have discussed various iterations of the cathedia study, a study comparing femoral and jugular placement of dialysis catheters in patients in the ICU. As mentioned before, the femoral route was not associated with a higher rate of infection than the jugular route, except in patients with a BMI>28.5, and catheter dysfunction rates were lower in the femoral and R jugular sites compared to the L jugular.

The same group has published another follow-up paper, this time in CJASN, analyzing patients who crossed over from a jugular to a femoral line or vice versa. 134 patients were included in total and again, using the patients as their own controls, there was no increased incidence of infections and no change in catheter dysfunction in the femoral group compared to the jugular. One major limitation of this study was that they did not use ultrasound to insert the lines which must be standard practice in most institutions these days. It should also be said that all three of these papers are from the same database, which adds a significant bias, and it has not yet been replicated. Still, for a fellow planning on inserting a line late at night and wondering what the best practice is, it provides further evidence that the femoral route is safe in most cases and that at least you are not doing any harm by utilizing this route for access.

Subclavian subterfuge and "Catheter Last"

While performing an electronic chart biopsy prior to examining a consult patient, I noticed a "nephrologic no-no," which can be seen on the patient's chest x-ray coursing under the right clavicle (see image). This finding was confirmed on my physical examination. The surgical team decided intra-operatively that the patient might need dialytic intervention so a right subclavian temporary dialysis catheter was placed. I had never seen one before, but I am sure many nephrologists who are no longer junior woodchucks like myself were around when subclavian dialysis catheter use was common. As my co-fellow Dr. McMahon pointed out in a previous post, the subclavian route was popular until an association was noticed between this route and subclavian thrombosis and stenosis.

Ted Steinman, one of our attendings at The Brigham, co-wrote a paper this year entitled, "Dialysis at a crossroads: 50 years later." In it, he and other pillars of nephrology propose a new path for dialysis therapy, and this is worth a read. One component of this path recommends changing the mantra "Fistula First" to "Catheter Last" given the unexplained augmented use of catheters and increased catheter-associated infections during the fistula first initiative. In other words, catheters should be the "last" choice for dialysis intiation given all of the complications caused by their use compared to grafts and fistulae. Furthermore, fistulae are not always attainable and cannot always be created in a timely fashion; thus, a graft is the next best thing and a very suitable alternative. The authors also propose that the Center for Medicare and Medicaid Services should consider catheter use to be sub-standard care. The overall premise behind the "Catheter Last" remains roughly the same, but this is an interesting way to think about our patients who are nearing the need for dialytic intervention that may motivate us more to prevent use of the dreaded catheter, especially when a subclavian one slips through the cracks.

Posted by Will Pendergraft

Seldinger Technique

One of the many pleasures of nephrology fellowship is learning how to put in temporary hemodialysis lines safely and efficiently using the Seldinger technique (the Swede is seen to the left). As an intern I constantly said to myself "don't let go of the wire, don't let go of the wire, don't let go of the wire." Having mastered this mantra I've now picked up a few more helpful tricks...

Always use the ultrasound. You just never know what the anatomy is going to look like and real time guidance really increases the number of single pass lines. Every central line I placed in residency used ultrasound localization but then landmarks without realtime guidance for placement. Realtime ultrasound definitely helps.

Lots of saline. It's great stuff. Really helpful if you're having a difficult time getting into the vein. The needle and syringe will sometimes become occluded with clotted blood from prior attempts. Flushing both the needle and syringe until the syringe plunger action is smooth helps avoid getting into the vessel but thinking you haven't because you can't aspirate due to clot. I like to keep the fresh and used saline pools separate so there's always some fresh saline handy.

Making sure the needle is in the venous lumen. Taking the syringe off and confirming the blood is dark and nonpulsatile is key to checking that the stick isn't arterial. If it's venous and your proceeding I've found it helpful to slightly drop the angle of the needle (to avoid going though the opposite wall of the vein "through and through") and advancing it 5mm or so further to get the needle tip fully within the lumen. Sometimes, if just the bevel has gotten in just a slight release of pressure moves it out of the vessel and you can't pass the wire.

Passing the guide wire. Not infrequently you'll be able to pass the guide wire to a point that clearly is beyond the tip of the needle and then encounter resistance (if it doesn't seem to have gotten past the needle tip you may be out of the vessel and need to start over). In the case of having gotten past the needle tip and then encountering resistance, sometimes flipping the circular plastic holder that houses the wire 180 degrees (which rotates the wire 180 degrees) will move the curled tip into a more favorable position and allow you to proceed.

The skin incision. Key to a smooth initial dilator insertion is a large enough skin incision along the trajectory of the wire. I've found that holding the guide wire steady along it's natural exit trajectory and then making the incision along this same angle is very helpful. The cutting edge of the scalpel should be directed away from the artery (cutting edge facing medial for the femoral, lateral for the internal jugular).

Trying not to kink the guide wire. Again, I've found that holding the guide wire firm and steady along it's natural exit trajectory then with the other hand advancing the dilator from as close to the skin as possible reduces the chances of kinking. If the wire does kink and you are unable to advance the dilator further, try pulling the guide wire back a centimeter or so while leaving the dilator in place. This will pull the kink into the dilator and then using the same techniques as above you can often complete the dilation.

Lots of 4x4s. When the dilator comes out, lots of blood. Having a 4x4 ready keeps the field clean and minimizes blood loss.

The catheter is in but now a port won't flush or pull back. Most catheters rotate freely in the wings used to suture them in place. If a port isn't functioning try rotating the catheter 180 degrees by twirling it in the wings, this will often move the distal port off the vessel wall and allow pull back and flush.

Hemodialysis Access Atlas

Here is a really excellent atlas covering all aspects of hemodialysis access function and malfunction which all renal fellows should read. We are indebted to Dr. Tushar Vachharajani, Marianne Neumann RN, and everyone at fistulafirst (www.fistulafirst.org/) for providing us with this wonderful resource. Please credit the authors if you intend to reproduce any of the content.

Click here to launch the atlas.

PD: Catheter outflow failure

I recently saw a patient in our peritoneal dialysis clinic who had been ultrafiltering about a liter a day but who was now consistently draining 100ml less than his instilled PD solution volumes despite extended drain times and multiple acrobatic contortions to try and recover additional fluid.

Peritoneal catheter outflow problems are common and many PD patients transfer to hemodialysis because of catheter related issues. Peritoneal outflow failure can be defined as the incomplete recover of instilled dialysate consistently within 45 minutes of beginning a drain.

So what are some of the things you can do when faced with a PD patient who is having difficulty recovering their dwells? Recently, an article in AJKD reviewed the topic and the salient points are outlined below.

1) Check for peritonitis – Start by looking for signs and symptoms then look at the dialysate to see if it’s overtly cloudy followed by a dialysate cell count and culture. During episodes of peritonitis the permeability of the peritoneal membrane to water, glucose and proteins is increased. This leads to rapid loss of the osmotic gradient as glucose moves from the dialysate into the blood resulting in reabsorption of fluid if dwell times are long enough.

2) Check a KUB – Useful for many reasons. The KUB can help you see catheter kinking, tip migration and constipation, which is very common culprit of outflow obstruction.

3) Examine the patient for signs of catheter leakage – Pericatheter leaks usually show up soon after catheter placement as wetness on the exit site dressing. Leakage of dialysate can also occur at any time into the abdominal wall, the pleural space (usually the right) and the genitals.

4) Is there resistance to dialysate or saline instillation? – If it’s tough getting fluid in in addition to getting fluid out something inside or outside the catheter is blocking it up. Inside kinks (which you might have seen on the KUB), fibrin and blood clots are potential culprits. Outside dilated stool filled intestine, and other intrabdominal organs in particular the omentum may be occluding the catheter. If fluid flows freely in, and the above options have been ruled out ultrafiltration failure should be considered.

In our patient, exam was unremarkable apart from trace lower extremity edema and saline was easily instilled into the peritoneal dialysis catheter by one of our RNs. The recovered PD dialysate was clear and cell count was zero. A KUB showed stable catheter position without kinking and copious stool. We started a trial of laxatives and were gratified to hear a few days later that our patient was now achieving his former ultrafiltration volumes.

Backflow

Recently we had a patient who, despite good adherence to dietary restrictions and 4 hour dialysis runs, had a high pre-dialysis potassium and an inadequate URR. She had an AVF with a history of multiple central stenoses and we suspected a recurrence. Her venous pressure wasn’t very high but we asked the nurses to check for recirculation.

Recirculation occurs when blood from the venous side of the circuit re-enters the arterial side thus reducing the efficiency of the dialysis. It is usually a result of poor flow in the access and the commonest cause is a venous stenosis leading to reduced outflow. It can also be caused by inappropriate needle placement and some recirculation is inevitable with the use of dialysis catheters, particularly when the lines are reversed. The calculation of recirculation is based on the idea that if none is occurring, the BUN in the peripheral circulation should be the same as the BUN in the arterial line. If recirculation is present, blood from the venous port mixes with blood entering the arterial port, thus reducing the BUN. The percentage recirculation is therefore calculated from the formula:

R = ([P - A] / [P – V]) x 100
where P= BUN periphery, A= BUN arterial line, V= BUN venous line and R= % recirculation

The issue that arises is from where to take the peripheral sample. Previously, the sample was taken from the contralateral arm. The problem with this is that mixing of blood returning from the AVF with returning systemic venous blood lowers the BUN in the heart relative to the periphery, leading to an overestimation of the BUN of the blood entering the AVF and therefore an overestimation of the percentage recirculation. This problem could be fixed by taking the sample from an artery but this is obviously impractical. Nowadays, most units use a protocol that involves stopping or slowing the blood flow through the dialyzer temporarily in order to take a sample from the arterial line which closely approximates the BUN of blood entering the AVF.

In our unit, the protocol involves taking arterial and venous samples, slowing the blood flow to 100mls/min for 30 seconds, withdrawing 10mls of blood and discarding it and then drawing the ‘peripheral’ sample from the arterial port. Although this technique probably underestimates recirculation slightly, it is sufficient to make the diagnosis. Recirculation of >15% is considered significant.

In this case, the % recirculation approached 50% and the patient had a fistulogram which showed a stenosis in the venous limb of the AVF and her clearances improved following angioplasty.

My head feels like it's about to explode

In a previous post I discussed the relative rates of infection and graft failure of femoral and jugular dialysis catheters. As a follow-on I wanted to talk about another potential complication of catheters.

Recently one of our patients had been having trouble with her AVF. She had it for 9 years and had multiple previous revisions and angioplasties of recurrent subclavian and brachiocephalic stenoses. She was admitted for insertion of a bovine interposition graft and the following day she had a tunneled RIJ catheter inserted as a bridge until the AVF could be used again.

The following day she presented to the ED with dyspnea, tongue and facial swelling. A laryngoscope found laryngeal swelling and she was intubated emergently. She had a CT neck which is shown below:





(Click image for larger view)

She previously had received radiotherapy to her neck for a SCC of unknown origin which had left her with no jugular vein on the left and chronic supraglottic edema. Shortly after insertion of the line, a clot formed in her RIJ proximal to the catheter which, in the absence of a LIJ led to a SVC-like syndrome. She was treated with intravenous heparin and eventually removal of the catheter.

Catheter-associated thrombosis is surprisingly common. Prior to the 1990s the most popular route for inserting temporary dialysis catheters was the subclavian vein but this was increasingly recognized to be associated with subclavian thrombosis and stenosis. As a result, most lines are now inserted into either the jugular (preferable) or femoral veins. Up to 25% of patients with femoral lines develop associated thrombus which can be asymptomatic but may also present with signs of DVT or PE. But what about jugular lines? According to this study of 143 prevalent dialysis patients with RIJ tunneled dialysis catheters, 26% were found to have a catheter-associated thrombus while 62% of these had a complete occlusion of their RIJ. None of these were symptomatic.

So what can you do about this? In one way, ignorance is bliss. Given that they are usually asymptomatic, in the absence of catheter dysfunction, we should probably do nothing as if you removed every line simply because of the presence of an asymptomatic thrombus, you would run out of access site very quickly. Perhaps the lesson is this. In patients with previous surgery/radiotherapy to the neck or with multiple previous catheter insertions, determine the anatomy prior to inserting a new line so that any future complications can be anticipated and dealt with promptly.

Femoral versus Jugular, part two

I have always been told that the jugular veins are preferable over the femoral veins when inserting temporary dialysis catheters. Various reasons are put forward for this including increased risk of infection and poor function of femoral catheters due to factors such as recirculation and frequent clotting. A previous post by Nate discussed the Cathedia study in which 750 bed-bound patients were randomized to receive a femoral catheter or a jugular catheter for dialysis. There was no difference in rates of infection as measured by catheter tip colonization or documented line-related bacteremia in the two groups. The authors’ only reservation was that in patients with a higher BMI, a jugular catheter was preferable. In contrast, in patients with a BMI less than 24.2, the use of a femoral catheter was associated with less infections. So much for the first complaint.

So, what about the risk of poor function associated with femoral catheters? In order to determine whether catheter site had any influence over dialysis performance, a paper was recently published in which the authors performed a secondary analysis of the data in the Cathedia trial. The primary endpoints were catheter dysfunction – defined as an inability to achieve adequate blood flow requiring catheter replacement, dialysis sessions delivered, URR and CRRT downtime. Overall, catheter dysfunction occurred in 10.3% of the femoral group and 11.1% of the jugular group. Comparing LIJ to RIJ, the risk of dysfunction was 6.6% on the right as opposed to 19.5% on the left, significantly higher then in the femoral group. There was no difference in URR, number of sessions or CRRT downtime between the two groups. The authors suggested that when choosing a site for vascular access, you should think – RIJ → Femoral → LIJ.

Nate in his previous post came to the conclusion that the original study would not necessarily change his practice although it made it easier to justify the use of femoral lines. This new paper seems like one more piece of evidence that might make me change mine

Achilles heel of dialysis

Vascular access is the Achilles tendon of hemodialysis. Just yesterday, I saw a patient with one of those lumbar catheters… Examining his arm revealed that he had failed 4 attempts of access creation (2 fistulas and 2 grafts). With that in mind, let’s start by reviewing the key components for a successful AVF creation: in our hospital, evaluation before placement of a fistula starts with:

*Dopplers of the upper extremities.
*The arterial lumen should have > 2.0mm at the point of anastomosis and the venous side should be at least 2.5mm.
*Ensuring that there are no proximal venous stenosis is also key, since some patients had lines before that increases the risk of subclavian stenosis, leading to inadequate maturation of the access.

Many of the diabetic patients have very small vessels, creating a special challenge for fistula maturation.

The order of preference for AVF creation once vessel size is confirmed is the following:

1. radial-cephalic
2. brachial-cephalic
3. brachial-basilic transposition.

Once the AVF is created, the rule of 6 apply in order to decide about usage (as discussed by Nate).

6 weeks after the AV fistula has been placed, the fistula should:
(a) be able to support a blood flow of 600 ml/min.
(b) be at a maximum of 6mm from the surface.
(c) have a diameter greater than 6mm.

There are multiple reasons for a fistula not to mature, but the main causes of early fistula failure can be classified as:

Inflow problems: pre-existing arterial anomalies (anatominally small, atherosclerotic disease) or acquired (juxta-anastomototic stenosis)

Outflow problems: pre-existing venous anomalies like anatomically small, fibrotic vein, proximal venous stenosis and accessory veins.

As you can see, an adequate evaluation with dopplers can usually ensure no pre-existing vascular conditions exist, leaving the 2 most common causes of early AVF failure as the presence of accessory branches and juxta-anastomotic stenosis. Early recognition is essential, since vascular interventions can save the fistula on both the above occasions.

Vas-cath exposure variability

How many vas-caths did you (the renal fellow) place during your clinical year (1 year)?

Poll results:

0-5 (IR does most of these) 4 (4%)
0-5 (Surgery does most of these) 2 (2%)
0-5 (IM residents do most of these) 3 (3%)
 0-5 (combination of IR, Surgery and IM) 12 (13%)

6-10            8   (9%)
11-25        17 (19%)
26-50        16 (18%)
51-100      12 (13%)
101-150    11 (12%)
151-200     2 (2%)
>201           4 (4%)

Total Respondents- 91

Looks like there is quite a bit of variability in the number of vas-caths performed by renal fellows. I was actually a little surprised by this. Looks like the majority of folks perform anywhere between 11-100 vas-caths in a year. However, 21 (23%) fellows actually placed fewer than 5 (majority were placed by a combination of VIR, Surgery & IM residents) in a year. 4 fellows placed >201 in a year, quite an impressive number for sure. I'm fairly confident that the number of vas-caths placed by fellows is decreasing somewhat each year. I bet this is from the rise of vascular interventional radiology gobbling up all of the procedure in the hospital. I wonder what this data would look in 4-5 years from now.

Ultrasound guided vas-cath placement

Much of the clinical year of the renal fellow is spent in the hospital rounding on patients admitted with access malfunction, catheter related infections or are in the ICU's with acute kidney injury. Many of these patients will require temporary dialysis access that in many cases will be life saving. Nate has already nicely discussed the debate between when to choose the femoral vs. the internal jugular vein in a previous post. These lines have the potential to pose many difficulties as patients with renal failure can have difficult and limited access sites. A difficult line can be avoided with appropriate training and imaging. We are fortunate to have an ultrasound readily available in our dialysis unit for vas-cath placement, but many hospitals do not.

An interesting article was published in the Feb 2010 CJASN by Prabhu et al in which 110 patients were randomized into two groups. One group had ultrasound guided femoral catheter placement and one group did not. The results, not surprisingly, showed that patients who had ultrasound guided vas-cath placement had a higher overall success rate (98.2% vs. 80%), better first attempt success rate (85.5% vs. 54.5%) and had few complications (5.5% vs. 18.2%). Furthermore, of the 11 patient who did not have a successful catheter placed without ultrasound guidance, 10 of these had success with use of the ultrasound in the exact same leg. This article also reviewed 3 other studies comparing ultrasound vs. standard landmark techniques. These studies show similar results.

Another interesting article was published in AJKD in 2009 by Barsuk et al from Nothwestern University. This study looked at the use of an ultrasound compatible central line simulator (like on the picture above) and deliberate practice before actually placing lines on patients. Again two groups were assessed in an unblinded fashion.

• Simulator Group- 12 first-year fellows were trained with the simulator and tested before and 2 weeks after the intervention with a 27 item clinical skills examinations checklist (available from the supplementary data).
• Traditional Group- 6 graduating second-year fellows were tested using the simulator once during the last 2 months of their fellowship.
  

Results from this study also showed benefit using the central line simulator. Interestingly, only one of the six graduating fellows met the minimum passing score. The simulator group improved dramatically from a score of 29.5% to a score of 88.6%. The course was highly rated by the attendees. It would be interesting to see if complications rates went down after the intervention. Also, I wonder if the higher scores would hold up over time. If I took the same test in a 2 week interval, I'm pretty sure I would score much higher on the second attempt. Especially after attending a 2 hour course.

I hope that more nephrology programs begin instituting programs like the simulator course. Likewise, ultrasound guided vas-cath placement needs to become standard practice. This can only help patient care and improve the competency of the graduating fellows. That being said, how many times do nephrologists in private practice put in temporary catheters? As the interventional radiology field continues to grow, this is surely decreasing.

Angiojet as a Cause of AKI??

The Angiojet Rheolytic Thrombectomy System is a medical device currently used to re-establish blood flow in a variety of settings. Briefly, a catheter is introduced into an area of thrombosis and a saline stream is directed towards the thrombus of interest. These saline jets generate a localized low pressure zone via the Bernoulli principle, leading to breaking up of the thrombus. The saline and clot particles are then sucked back into the catheter, avoiding potential embolic complications.

Angiojet has been primarily used for removing thrombus from arteries--for example, in acute myocardial infarction or acute graft thrombosis, for instance. It's also been useful in restoring flow in some dialysis accesses. More recently, however, efforts to use Angiojet in the treatment of venous clots--such as DVT or pulmonary emboli--have been attempted.

At a recent Renal Grand Rounds, one of the fellows presented an interesting case of a patient who developed acute renal failure shortly after undergoing attempted Angiojet therapy for a pulmonary embolus. In addition to a rising creatinine and oliguria, the patient developed red, heme-positive urine with only a few red blood cells, and labs reflecting intravascular hemolysis. Although it is not yet rigorously defined as a cause of acute renal failure, others have reported an association between Angiojet and AKI. It is possible that the Angiojet procedure is more likely to result in hemolysis if thrombectomy is attempted in a large, open space (e.g., for treatment of DVT/PE in a larger vein), as there have generally not been such complications when Angiojet has been used in restoring flow to arteries where the area of thrombus is relatively localized.

It will be interesting to see if there are further reports of this type of AKI with Angiojet.  I purposely put TWO questions marks in the title since I fully admit that much more work needs to be done in order to actually prove causality.  

Poll Results & Post-Boards Weariness

First things first:  last week's poll results showed that the majority of individuals were wary of using physician "Pay For Performance" as a strategy towards increasing AV fistula placement rates.  Proponents of this strategy (see editorial by Hakim and Himmelfarb in a 2009 KI article) would argue that linking AV fistula placement to some type of financial reward (or linking lack of AV fistula placement to some type of financial penalty, depending on your viewpoint) is the surest way to increase the AV fistula rate in the overall dialysis population.  Potential arguments against using a physician "Pay For Performance" strategy would include penalizing doctors who take care of patients with a lower success of achieving working AV fistulas and encouraging the placement of unnecessary AV fistulas, to name a few.  

So I took the boards yesterday, and I'm eager to hear what others thought of the exam.  Fair?  Frustrating?  Piece of cake?  My own view:  it's a hard exam, and not only because it requires 8 hours of concentration--like many of these ABIM exams, there are often 2-3 answers which seem like they could be right; the challenge comes in selecting the "Best Answer" according to whomever wrote the question.  Ever wonder how they come up with the questions?  Here is the ABIM's stated policy on how all their exams are developed.  This week's RFN Poll of the Week is Boards related.  

"Exotic" Hemodialysis Catheter Sites

You can probably tell that I am working my way through the most recent NephSAP on Vascular Access, as I keep on posting access-related posts. Today while leafing through the section on dialysis catheters, I was amused to read the following sentence:

"When all access sites have been exhausted, exotic sites such as transhepatic or translumbar locations can be used for placement of a tunneled dialysis catheter."

I found the phrase "exotic sites" somewhat amusing since for most people it should conjure up images of the Bahamas and South Pacific islands---definitely a scene involving palm trees, for me--rather than bizarre locations for dialysis catheters. It is a strange world nephrologists live in...

Besides transhepatic and translumbar locations, other "exotic sites" include the brachiocephalic vein (this case series by Falk describes 33 different patients who received a brachiocephalic catheter under ultrasound guidance with generally good results), the iliac vein (this report by Betz et al points out that while successful at providing dialysis, there exists the possibility of vascular damage which could make subsequent renal transplantation problematic), and even the great saphenous vein of the thigh (see article by Yates et al), which may be important in individuals who have stenosed or occluded central veins.

Preop Vascular Mapping for AVF/AVG

Current KDOQI Guidelines recommend the use of some type of vascular mapping studies in order to prepare for the creation of an AV fistula or an AV graft. While physical exam is useful--typically, application of a tourniquet around the upper extremity and gross measurement of veins which could potentially be used as targets--it is often unable to identify suitable targets in many individuals who are obese or have deeper veins.

Two other options are available for mapping: either duplex ultrasound or angiography, both of which have their benefits and drawbacks. Duplex ultrasound is attractive because it is non-invasive, and can be performed in both potential arterial and venous targets. There are also accepted ultrasound criteria which appear to predict, at least partially, the success of AVF maturation: in general, pre-op arterial diameter should be greater than 1.6mm and the venous diameter should be greater than 2.5mm at the site of anastamosis. Optimally, veins should be less than 0.5cm deep from the skin and should have an 8-10 cm straight segment for repeated cannulation. Duplex ultrasound is the preferred method of pre-op mapping according to KDOQI.

Angiography appears to be comparable to ultrasound in terms of pre-op AVF/AVG planning, but has the advantage of being able to more directly identify central stenoses--an all-too-common finding in individuals with previous dialysis catheters or central lines that can easily prevent the successful development of an AVF/AVG if present. The main disadvantage of angiography, of course, is that it is invasive and involves the injection of contrast dye--which may not be wise for individuals with advanced CKD whose renal function is so tenuous that dialysis planning is underway.

Secondary AV Fistulas

Since I'm presently trying to make it through the most recent ish of NephSAP--their first-ever issue of "Interventional Nephrology"--I'll do another access-related post.

A "secondary AV fistula" refers to a fistula created after a pre-existing graft or fistula has either outright failed or been determined to be suboptimal for continued dialysis. The creation of secondary fistulas represents an important way in which nephrologists might increase their overall percentage of patients dialyzing via AV fistula (see "Fistula First Campaign") rather than simply targeting incident CKD patients initiating dialysis.

From a terminology perspective, a "Type I secondary AV fistula" refers to when the outflow vein of a pre-existing AVF or AVG is able to be used as a target for a new "converted" AVF; the advantage of Type I AVFs are that they can often be used shortly after placement, not requiring lengthy maturation times and potentially avoiding the use of a transient dialysis catheter altogether. In contrast, a "Type II secondary AV fistula" refers to an entirely new AVF, which can occur either on the ipsilateral or contralateral side with reference to the failed fistula.

How well do secondary AVF perform? In one 2002 report by Ascher et al, 71 secondary fistulas demonstrated a 1-year and 2-year primary patency rate of 58% and 22%, respectively. These results are not suprisingly worse than the primary patency rates for primary AVFs (75% and 61%, respectively), but nonetheless demonstrate that in a few dialysis patients, the creation of a secondary AVF can give successful, long-term dialysis access. Hopefully, a better understanding of the process by which AV fistula fail could eventually lead to medications or surgical breakthroughs which might prolong the longevity of secondary access attempts.

When To Refer for AV Fistula Placement

The "Fistula First" initiative, which has as its goal the increase in % of dialysis patients who dialyze via an AV fistula rather than an AV graft or catheter, has been a controversial initiative.  Although few would debate that a working AV fistula is superior in terms of a decreased infection rate and improved graft longevity, there are many patients in whom attempted AV fistulas fail to mature, and delays in waiting for a functional AV fistula to develop have been suggested as a cause of patients who must start dialysis via catheter.  Due to this potential for delay in AV fistula maturation, it makes sense that we should perhaps err on the side of having the AV fistula placed earlier rather than later.  Which brings us to the question:  When should we refer CKD patients for AV fistula placement?

I don't think the answer is clear, but the present KDOQI recommendations are that access placement should occur once the GFR drops to less than 25 mL/min, if the serum creatinine goes greater than 4 mg/dL, or within 1 year of an anticipated need for dialysis.  It also states that a new primary fistula should be allowed to mature for a minimum of 1 month, and ideally for 3-4 months prior to cannulation (AV grafts, by comparison, require a maturation time of only between 3-6 weeks according to these guidelines).  

In this 2004 JASN article entitled, "Late creation of dialysis access for hemodialysis and increased risk of sepis" by Oliver et al, investigators from Canada performed a retrospective analysis of patients starting dialysis who had their access placed either "early" (defined as being placed greater than 4 months before initiating  HD), "just prior" (defined as being placed between 1-4 months before initiating HD), and "late" (defined as being placed 1 month before initiating HD).  Of note, the majority (3687 of 5924) were "late" access placements.  Early access creation was associated with a relative risk of sepsis of 0.57 and a relative risk of mortality of 0.76, both of which were predominantly explained by an increase in catheter use observed in the "late" group.  Granted, this is not a prospective trial, but it does seem to provide some rational evidence in support of early AV fistula placement.  

My personal (and still limited) experience in this area:  I think that many nephrologists know that early AV fistula placement is important, and this is discussed with patients at routine CKD office visits.  The challenges come from two main areas:  (1) actually convincing the patient to go ahead with it (there are often very powerful mechanisms of denial involved in a patient actually accepting the fact that they are eventually headed for dialysis), and (2) administrative delays in setting up a patient to be seen by a vascular surgeon.  If anybody has any tips on ways to increase early AV fistula placement, please share them!

Rule of 6s for Dialysis Access Placement

The "Rule of 6s" describes an easy way to evaluate the maturity of a recently-placed arteriovenous fistula for dialysis access--and is even mentioned by name in the most recent KDOQI Guidelines for Dialysis Access.  The Rule of 6s is as follows:

6 weeks after the AV fistula has been placed, the fistula should:

(a) be able to support a blood flow of 600 ml/min.

(b) be at a maximum of 6mm from the surface.

(c) have a diameter greater than 6mm.

Failure to achieve these goals warrants a further investigation, usually in collaboration with the access surgeon who placed the fistula, into why the fistula did not mature.  Ideally, the existing fistula can still be encouraged or modified to eventually achieve maturity; if not, a new access site can be attempted.