To investigate the haemolysis in haemodialysis cannulae, an in-vitro set up is built, using a unipuncture dialysis system. This system is connected to a bag with fresh calf's blood, by the cannula under test, mounted in a large bloodline (5mm diameter). The blood characteristics are kept constant by means of a bicarbonate dialysate in the dialyser. During a 6h period, haematological parameters are regularly sampled. Flow through the cannulae is recorded, which is about 500mUmin. Four different cannulae are tested and compared to the results obtained without any cannula in the circuit. In all cases a linear increase in plasma free haemoglobin levels is found after 6h. The cannulae can be ranked from 8F catheter over 13G, 14G to 16G cannula, the latter producing the highest degree of haemolysis. When using plastic cannulae at high blood flows, their haemolytic effect may not be neglected.

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Some studies found that the removal of middle molecules has a long-term effect on mortality and, even more, is enhanced by high-flux dialysis. In order to enhance middle molecule removal in a low-flux dialyzer, the present study aimed at investigating the combined impact of dialyzer flows and membrane surface area. Blood and dialysate flows were varied within the clinical range 300-500 and 500-800 mL/min, respectively, while the ultrafiltration rate was kept constant at 0.1 L/hr. Single-pass tests were performed in vitro in a single Fresenius F6HPS dialyzer (3 tests) and serially (5 tests) and parallel (3 tests) connected dialyzers. The blood substitution fluid consisted of dialysis fluid in which radioactive-labeled vitamin B12 (molecular weight 1355 Da) was dissolved. Dialyzer clearance as well as whole-body clearance was calculated from radioactivity concentrations of samples taken from the inlet and outlet bloodline. Adding a second dialyzer in series or parallel ameliorated the overall dialyzer and whole-body clearance significantly, except for the highest applied blood flows of 500 mL/min. Better solute removal was also obtained with higher dialysate flows, while the use of higher blood flows seemed advantageous only when using a single dialyzer. Analysis of the ultrafiltration profiles in the different configurations illustrated that enhancing the internal filtration rate ameliorates convective transport of middle molecules. Adequate solute removal results from a number of interactions, as there are blood and dialysate flows, membrane surface area, filtration profile and concentration profiles in the blood and dialysate compartment.

The existence of a sheet around a single lumen dialysis catheter tip, which provokes a valve mechanism, is proved by the observation that several times during the replacement procedure of a dialysis catheter, a sheet surrounding the surface of the catheter is removed with the dialysis catheter. This sheet is grey, approximately 1 mm thick and 30 mm long and consists of fibrin and thrombocytes. Bacteriological examinations were always negative. The existence of the sheet in vivo is demonstrated by digitalized angiography during the removal procedure for single lumen dialysis catheters. Rarely, only the sheet is removed with the catheter. It all other instances, the sheet is stripped off and remains in the subcutaneous tunnel or in the vascular bed without causing much clinical discomfort in most patients. Occasionally an episode of cough, dyspnea, hypotension, retrosternal oppression or hemoptae after removing the single lumen dialysis catheter, suggest pulmonary embolism or lung infarction.

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