Treatment modalities in comparison: when do clinical differences emerge?

Despite technological advances in dialysis equipment and modalities, the survival, morbidity and quality of life of uraemic patients undergoing regular haemodialysis treatment are still severely affected by acute intradialysis and long-term complications, possibly related to the treatment itself. Convective treatment modalities, such as haemodiafiltration and haemofiltration, are thought to be further improvements over standard diffusive haemodialysis. Moreover, several of the pathways activated in patients during dialysis have the potential to produce many side-effects. These occur three times a week, and are particularly intense in patients dialysed with so-called 'bio-incompatible' membranes. Thus the biocompatibility of dialysis membranes is increasingly recognized as one of the main factors in the improvement of dialysis treatment.

The main clinical studies to date are reviewed to highlight the clinical effects of different treatment modalities and membranes on the most important acute and long-term haemodialysis-related complications.

Epidemiological studies suggest that semisynthetic and synthetic membranes may reduce morbidity and mortality in dialysis patients. Despite the proven biological superiority of biocompatible membranes, we lack definitive evidence that thrice-weekly complement and cell activation over a period of years is detrimental to patients, because the results of prospective randomized studies are conflicting. However, it is important to remember that factors other than the dialysis membrane could influence the 'biocompatibility' of dialysis, including the dialysate, dialyser geometry, the distribution of blood in the dialyser, reuse, the sterilizant and materials used in reprocessing.

Further large-scale prospective and randomized trials with a long follow-up are needed in order to better clarify the clinical effect of different treatment modalities on the morbidity and mortality of patients on chronic renal replacement therapy. In particular, it must be clarified whether the possible clinical differences in treatment modalities are based on differences in the clearance of middle molecules or on biocompatibility, or, more generally, on the increasingly recognized clinical importance of high-flux treatments, and the possible interaction between membrane flux and biocompatibility.