Author: Michael Vlessides
One of the first studies of its kind has found that primary and functional patencies of arteriovenous fistulas are significantly better when regional, rather than local, anesthesia is used. The study’s Scottish researchers thus recommended the use of brachial plexus block instead of local anesthesia as the anesthetic technique of choice for these procedures.
“There are over 100,000 arteriovenous fistulas performed in the [United States] every year,” said Alan Macfarlane, MD, an honorary clinical senior lecturer at the University of Glasgow, in Scotland. “It’s the best form of vascular access, but the problem with them is they fail, and they fail very commonly.
“We all know that regional anesthesia causes sympathetic effects and vasodilatation,” he continued. “So, we hypothesized that by increasing blood flow through the fistula, it might improve fistula outcome.” Nevertheless, there is little evidence that the mode of anesthesia influences long-term fistula patency, which led the researchers to conduct the observer-blinded, randomized controlled trial.
“Our initial, three-month data were published in the Lancet [2016;388(10049):1029-1030],” Dr. Macfarlane said. That study showed a clear survival advantage for patients who received the brachial plexus block. Furthermore, all of the secondary outcomes, such as arterial flow and venous dilatation, were superior in patients who received the brachial plexus block.
“Primary patency pertains to the fistula flow,” Dr. Macfarlane said. “But what you really want is a fistula that can be used effectively, and that’s functional patency.” Although there are several ways of determining functional patency, the investigators used a method called the “rule of 6’s.”
“The fistula has to be 6 mm wide; it’s got to have blood flow of 600 mL per minute; and it has to be less than 6 mm from the [skin] surface, so you can get the needle into it,” he said. “If it didn’t meet those criteria, it wasn’t functionally patent.”
Effect Not Seen With Brachiocephalic Fistulas
Presenting the study at the 2018 Joint World Congress on Regional Anesthesia and Pain Medicine and annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 4842), Dr. Macfarlane reported that while brachial plexus block resulted in vasodilatation and significantly increased brachial artery blood flow, local anesthesia did not.
Indeed, both primary and functional patencies at one year were significantly greater in the brachial plexus block group than the local anesthetic group (Table). The advantages of brachial plexus block for functional patency persisted in radiocephalic fistulas, but not brachiocephalic fistulas.
|Table. Patencies for Fistulas by Type of Anesthesia|
|Total Patient Population, N (%)||Brachial Plexus Block, n (%)||Local Anesthetic, n (%)||P Value|
|All Arteriovenous Fistulas|
|Primary patency at 3 months||92 (73)||53 (84)||39 (62)||<0.01|
|Functional patency at 1 year||86 (68)||51 (81)||35 (56)||<0.001|
|Primary patency at 3 months||32 (63)||20 (77)||12 (48)||0.03|
|Functional patency at 1 year||33 (65)||22 (85)||11 (44)||0.02|
|Primary patency at 3 months||60 (80)||33 (89)||27 (63)||0.05|
|Functional patency at 1 year||52 (69)||28 (76)||24 (63)||0.25|
“I imagine radiocephalic fistulas benefit more because they’re smaller vessels,” Dr. Macfarlane noted. “If you have bigger vessels, such as with brachiocephalic fistulas, then I think the flow is better anyway and it’s an easier operation for the surgeon.”
During the one-year follow-up, revisional procedures aimed at improving functional patency were also performed, where possible. Significantly more procedures were possible in patients who received the brachial plexus block (18 procedures in 14 patients) than in their counterparts given local anesthesia (six procedures in five patients) (P=0.005).
“A third of our patients had [a body mass index] over 35,” Dr. Macfarlane said. “Their fistula was working, but it wasn’t functionally patent because of the distance from the surface. But once we superficialized the fistula, then the functional patency became apparent and it worked.”
These results, he said, follow on the group’s three-month findings and demonstrate that both fistula maturation and revisional procedures can significantly improve patency rates at one year. “These results are quite exciting,” he added. “I don’t think there are any randomized controlled trials to show the effect of an anesthetic intervention on surgical outcome of fistulas.”
The investigators recommended the use of brachial plexus block over local anesthesia for all primary arteriovenous fistulas.
“Do you find that your vascular surgeons are recognizing the benefits of brachial plexus block, and therefore requesting it instead of local anesthesia in primary fistulas?” asked session moderator Jaime Baratta, MD, a clinical assistant professor of anesthesiology at Thomas Jefferson University, in Philadelphia.
“Yes,” Dr. Macfarlane replied. “At our hospital, they’re requesting more and more people who can perform these blocks.”
“It’s very interesting to think that something that is so short-lived can have such a long-term effect,” said Anahi Perlas, MD, an associate professor of anesthesia at the University of Toronto. “And there’s some evidence that some similar effects can occur, for example, in patients who undergo microvascular surgery. The thinking is that it’s likely related to the sympathetic block and increased vascular flow. It is possible that the same physiologic effect may be at play here.”