Nephrology Vascular Lab Maintains Health of Dialyzing Portals
What can be a fairly straightforward procedure in other patients takes on a new level of risk in a dialysis patient. "Keep in mind that in a normal patient, the flow in a vein is about .30 mL per minute. In the dialysis patient, it's one or two liters a minute. So ruptures take on new meaning," says Tom Watson, MD with Nephrology Associates.
That's part of why keeping accesses healthy in dialysis patients creates such gratifying work for Watson at the Nephrology Vascular Lab. Recently relocated to a new facility on I-65, the Lab performs about 2,000 procedures a year, serving about 1,000 of Nephrology Associates' patients, as well as referrals around the area.
"In areas without this kind of dialysis access center, patients have to be admitted to the hospital for all these procedures," Watson says. "But here, they come to our center, have the procedure and are home usually within an hour or two."
The most common procedure performed at the Lab is angioplasty. They do 30 to 40 a week. And now, besides using it to stretch scar tissue in existing constrictions, the Lab is using the procedure to help fistulas mature faster as well.
"If a fistula's not getting big enough, we can use the balloon to dilate the vessel," Watson says. But the dilation is done sequentially over several months to help the vessel expand to accommodate the needed flow of 600 to 1800cc per minute.
Coiling serves the opposite function. Rather than widening vessels, this newest procedure at the lab blocks them. The urologist places a metal coil in any collateral veins that are stealing blood from the portal. "It's pretty effective, but technically difficult getting the wires to make turns into those small veins. It's like a video game," Watson says.
Thrombectomies also present unique challenges when performed in an arteriovenous fistula. "They happen more with grafts than with fistulas. But with fistulas, it's more difficult," Watson says. In a graft, the synthetic tube makes navigation predictable. But in the enhanced blood vessel that forms a fistula, surgeons find erratic curves and abnormal turns with drastic variances in caliber.
"The gratifying part is that a fistula can last a dialysis patient a lifetime, but grafts have a predictable average lifespan of about two years," Watson says. "So being able to keep a fistula going is the most gratifying."
Besides fistulas and grafts, the lab also places and replaces tunneled catheters. These require a large bore IV into an internal jugular vein to form a permanent access.
Though catheters total about a third of the lab's procedures, they're the least favorite of the access options. "We view them as necessary evils for those without a permanent access yet or if they've used up all the sites for fistulas," Watson says. "We don't like them at all. They form nice tracts for bacteria to crawl up. Patients have a 250% greater mortality rate per year with catheters versus fistulas."
One edge the Lab offers patients when creating any dialysis portal stems from their vein mapping capability. Most places, hospitals included, use only ultrasounds for vein mappings. "But with ultrasounds, you can't see the central vein, because the lungs get in the way," Watson says.
At the Nephrology Vascular Lab, they also use venography. "An ultrasound gives you a static picture of the vein," Watson says. "With the video of a venogram, you can watch in real-time what the blood does. It's more complete. You can assess the flow into the chest and all the way back to the heart."
If a patient has had open-heart surgery or had ports before, they may have blockages in their central veins. "But you won't know that with an ultrasound until after you make the fistula that has to accommodate ten times more flow, and their arm swells," Watson says.
The Lab performs about 350 mappings a year. During the process, they map the whole arm and the chest. "So we know from wrist to heart, that the flow is as normal as can be," Watson says.
About 50 percent of their dialysis patients currently have fistulas, "and it's still getting better," Watson says. Recently, the Vascular Lab began making a concerted push to improve the use and health of fistulas over graphs and catheters.
"If you have a fistula, yearly mortality rates are in the 15 to 20 percent range, as opposed to 40 to 45 percent for patients with catheters," says Watson.
Because it can take six months or more for a fistula to mature, Watson recommends patients get mapped and the procedure done when their GFR reaches the 20 to 25 range.
"They may not use it for several years, but kidney failure can progress more rapidly in some patients," Watson says. "So whether they have a fistula or not, they have to go on dialysis when the GFR is in the 10 range. And, remember, fistulas are life-saving procedures."