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Sorry it's taken a while to get back to you.
The answer is a bit multi-faceted. In regards to forearm fistulae you are completely right, retrograde radial artery flow beyond the anastomosis is perfectly normal in instances where the palmer arch is intact, and depending on where you read this retrograde distal radial flow can make up to 25% of the overall volume flow. Some papers even suggest that in some fistulas the retrograde flow alone is actually sufficient to provide effective dialysis.
Being that you mostly see upper arm AVFs you are likely exposed to a higher proportion of patients with distal ischemia due to a higher prevalence of this symptom in this variety of AVF. This is because brachial artery anastomoses tend to be larger which create lower vascular resistance, that pull more blood through the fistula and away from the hand, which is a problem that’s compounded by the fact that this is the only inflow artery to the forearm, as opposed to a RCAVF where only one of three arteries to the hand is affected.
We also need to discuss the differentiation between steal and steal syndrome. Most BCAVF will demonstrate physical steal whether that’s a bit of bi-directional flow in the brachial artery beyond the anastomosis or a retrograde radial/ulnar artery. This can be totally asymptomatic but becomes steal syndrome when symptoms of ischemia are present which is, like you say, a purely clinical diagnosis.
These symptoms can often be worse during HD which for sonographers obviously isn’t great because we can’t scan them during this period to see if there is any haemodynamic change. In answer to your actual question though - the only useful information we can provide via ultrasound is the status of the fistula (functional? Volume flow? Stenoses?),forearm arteries (all patent?) and the palmer arch (intact?).
Hope this helps
Hi Lauren,
We had a good chat about your question in our SIG meeting last night. It's a great question and we aim to get back to you with a full answer with reference papers by the end of next week.
Thanks for posting and feel free to ask any other vascular related questions.
Matt