Coagulation within the dialyzer membrane fibres is an obvious biological sign of bio-incompatibility. To avoid clotting during extracorporeal treatment, an anticoagulant is added to the circuit, resulting in an increased risk for bleeding complications. In addition, there is evidence that a substantial number of fibers can become blocked before this is reflected in routinely observed parameters, or in termination of the dialysis session. Little is known about the impact of such subclinical clotting on dialyzer performance in terms of solute clearance. Membrane clogging may influence both the diffusive and convective transport characteristics of the dialyzer membrane before leading to complete dialyzer clotting. In 2018, we described a method to objectively count the number of blocked fibres inside a dialyzer using a micro-CT scanning technique. In the present trial, we use this method to assess the number of open fibers post dialysis, and this for three different dialysis durations and in two different dialyzer types. Just before the termination of the dialysis session, dialyzer clearance is assessed for different solutes from concentration measurements in blood samples as taken from the dialyzer inlet and outlet line.

The aim of this randomized cross-over study is to objectively quantify the impact of blocked fibers on the performance of different dialyzer membranes: ATA™ (asymmetric triacetate) membrane in the Solacea™ dialyzer, and polysulfone membrane in the FX800Cordiax dialyzer, and this with a decreased anticoagulation dose.

This single centre, randomized cross-over study includes ten consecutive stable chronic hemodialysis (HD) patients who experienced stable dialysis sessions during the last 4 weeks, and had no known coagulation disorder, active inflammation or malignancy. Double-needle vascular access is achieved through a native arterio-venous fistula or a well-functioning double lumen tunnelled central venous catheter. Patients are followed during 6 consecutive midweek dialysis sessions. At midweek, patients receive only 1/4th of their regular brand of Low-Molecular Weight Heparin anticoagulation at the beginning of the dialysis session. All test sessions are performed with blood flow at 300mL/min and dialysate flow at 500mL/min in post dilution hemodiafiltration (HDF) mode (substitution flow 75mL/min). Ultrafiltration rates are set according to the patient's interdialytic weight gain and clinical status.

Patients are randomized for hemodialyzer type and dialysis duration:

1. ATA™ Solacea 19H - 60min dialysis
2. ATA™ Solacea 19H - 120min dialysis
3. ATA™ Solacea 19H - 240min dialysis
4. polysulfone FX800Cordiax - 60min dialysis
5. polysulfone FX800Cordiax - 120min dialysis
6. polysulfone FX800Cordiax - 240min dialysis

Just before the termination of the 6 experimental midweek sessions, blood is sampled from the inlet and outlet blood lines. Blood samples are immediately centrifuged and serum vials are stored at -80°C until batch analysis. Post dialysis, dialyzers are rinsed and dried and scanned with micro computed tomography (CT) to count the number of open fibers.

Inclusion Criteria:

• 18 years or older
• experienced stable dialysis sessions during the last 4 weeks
• double needle/lumen well-functioning vascular access

Exclusion Criteria:

• known coagulation disorder
• active inflammation
• malignancy