As part of the CX Vascular Access Masterclass on Wednesday, Colin Deane (London, UK) considered the role of surveillance in thrombosis, asking whether there exists a test that is simple, safe, precise and timely. While it has been established that using angioplasty, stenting or surgery to treat thrombosis associated with stenosis is effective and that intervention is effective in reducing morbidity, questions remain regarding surveillance.
The focus of Deane’s presentation was measuring access flow by ultrasound, beginning with an overview of his early personal experience using this technique during his post-doctoral studies in Philadelphia, USA. This involved ultrasound measurement of flow in comparison with status and dynamic pressure and looked at it with a technique that used M-mode colour flow in grafts and fistulas at zero, five and 10 months.
Deane then went on to describe the King’s College London dialysis access surveillance programme using a Zonare Z-one scanner. He noted that flow was measured in the inflow artery, and then an ultrasound examination of the circuit was carried out for stenosis and thrombus in false and true aneurysms. Flow and stenosis were then graded on a traffic light system and e-mailed to the access team for action. Surveillance was then reset for the following intervention.
Deane elaborated on the traffic light grading system they used to grade the surveillance findings, noting that all ‘Green’ scans had six month follow up arranged, and represented flows either >600ml/min or which showed no reduction since the last scan, and in >50% of which no stenosis was identified. ‘Amber’ scans, representing a drop in flow rate >20% but flows still >1,000ml/min or unchanged flows of >600ml/min, had three month follow up arranged and finally, ‘red’ scans were assumed to require action and thus no follow up was arranged. These represented flows of <600ml/min with or without stenosis.
He noted a few issues which arose during the programme, namely flow measurement errors and changes, the interpretation of stenosis, practical problems such as whether the scan window was to fit in with dialysis or transport, and resource issues including having to stop the programme for two years due to a lack of funding.
According to Deane, the resolution of a large number of studies on this topic remains “elusive” and that due to the complexity of flow, surveillance remains “controversial”. He mentioned in particular two studies from 2019 which argued for and against the idea that vascular access surveillance in mature fistulas is worthwhile.
Deane posited that there are some questions that remain regarding surveillance of thrombosis. Firstly, the relationship of change in flow and degree of stenosis is complex and dependent on flow, site of stenosis and artery diameter. Additionally, he questioned whether there is an optimal interval for surveillance, and whether one-size-fits-all is effective. Finally, he remarked that costs remain a question related to surveillance.
After giving a brief overview of some “exciting” new technology in this field, Deane concluded: “This is going to be best where people are interested in it, trained and understand the clinical problem.”