Singapore General Hospital studies new treatment option for repeated episodes of blocked dialysis access.

For patients with kidney failure, undergoing regular haemodialysis to remove waste products and excess fluid in the blood is necessary for survival. Essential to this life-saving process is an entry point to access the blood vessels. It is usually created by connecting an artery and vein using a hollow tube (called an arteriovenous, or AV, graft), or by joining an artery and vein in the arm (AV fistula).

The access is so important that it is considered a patient’s “lifeline”. “Once it is blocked, there is no way the patient can do dialysis,” said Associate Professor Tan Chieh Suai, Senior Consultant and Head, Department of Renal Medicine, Singapore General Hospital (SGH).

Yet, an obstructed access is a common phenomenon. A blocked dialysis access is among the most common causes of hospitalisation in patients on haemodialysis.

At SGH, approximately 1,000 procedures are carried out to unclog blocked grafts and fistulas every year. About 70 per cent of patients with a history of a blocked graft require hospitalisation to unclog the dialysis access every six months.

“Understandably, it can be frustrating for patients, as the time and costs of repeated procedures to salvage a failing graft or fistula are on top of their thrice-weekly dialysis sessions,” said Prof Tan. A blocked graft or fistula typically takes around one to two hours to clear, and costs about $4,000 to $5,000 per treatment.

To explore more ways to keep a patient’s dialysis access viable for longer, a team of SGH clinicians from the Departments of Renal Medicine, Vascular Surgery, and Vascular and Interventional Radiology looked into a new treatment option that uses an angioplasty balloon coated with sirolimus, a drug that has been used successfully to prevent repeated narrowing of the coronary artery.

How the balloon works

The team recruited 20 patients with end-stage kidney failure with a blocked graft between October 2018 and October 2019 to evaluate the efficacy of the sirolimus-coated balloon.

The current treatment to salvage a blocked dialysis graft or fistula involves injecting clot-busting medications, known as thrombolytic agents, into the vessels to dissolve or soften the clot. The narrowed segment of the vessel, which is the root cause of the clotting, is then widened by inserting a plain angioplasty balloon into the affected area.

With the new treatment option, the balloon is coated with sirolimus and inserted under x-ray guidance into the blood vessel.

“When the balloon is inflated, the sirolimus is applied to the narrowed segment of the blood vessel. This prevents the narrowing from recurring, hence preventing the AV fistula or graft from failing again,” Prof Tan said.

Patients remain awake during the one-hour procedure performed under local anaesthesia.

Encouraging results

Prof Tan, the senior author of this pilot study, said that “results have been encouraging”, with only 50 per cent of patients who were treated with the sirolimuscoated balloon requiring a repeat procedure at six months.

The study was published in the peer-reviewed Journal of Vascular and International Radiology in December 2020.

SGH is currently on a one-year follow-up joint pilot study with Sengkang General Hospital and National University Hospital to determine if the sirolimus drugcoated balloon has similar efficacy in 170 patients with a failing AV fistula. According to Prof Tan, over 80 per cent of patients from this latest study did not require a repeat procedure at six months.

Prof Tan said that exploring new effective options to prevent repeated episodes of blocked dialysis access is important, as patients with kidney failure require lifelong dialysis treatment. A functioning access is key to successful therapy; without it, the consequences may be fatal.

“Effective therapy also means fewer procedures and hospital admissions, less pain, and more time for other activities,” he added.

Why does dialysis access get blocked?

When there is narrowing, or stenosis, due to cell growth within the blood vessel, it slows blood flow, and increases the chance of clotting and blockage.

It is not fully understood why some patients tend to experience such blockages more frequently than others, but such episodes of clotting can be time- and cost-consuming, and even potentially life-threatening to patients who require thrice-weekly haemodialysis.

The procedure carried out to salvage a failing graft (bottom diagram) or fistula (top diagram) also comes with risks, such as vessel rupture, bleeding and infection. It is also inconvenient for the patient to undergo repeated procedure and disruption to their dialysis schedule.

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