Although remarkable progress has been made, chronic kidney disease still poses a major burden on both individual patients, as well as on society as a whole. There is a strong inverse relationship between decreasing renal function, as estimated by glomerular filtration rate, and mortality rate, especially death due to cardiovascular disease. The exact cause(s) remain to be elucidated. Uremic toxins might play an important role.

In the course of decreasing renal function the concentration of numerous intracellular and extracellular compounds vary from the non-uremic state. But still increasing number of uremic retention solutes are being identified. Renal replacement strategies aim to remove potentially harmful substances from the body. Traditionally much attention has been paid to small water-soluble molecules such as urea nitrogen and creatinine. Based on the results of the recent HEMO and ADEMEX studies, increases of small water-soluble solute removal above the level reached with modern dialysis techniques - hemodialysis, peritoneal dialysis (HD, PD) - seem not to be advantageous with regard to patient outcome. These findings may point to the importance of other distinct groups of uremic retention solutes. In view of the data described above, protein-bound solutes might be good candidates.

Several advantages of long duration hemodialysis have been observed, including a better control of blood pressure by decreasing extracellular fluid volume, lowering peripheral vascular resistance and improving endothelium-dependent and -independent vasodilation. A normalization of heart rate variability and improvement of left-ventricular function was noted as well. Furthermore, anemia control has been shown to be easier and several nutritional parameters improved in patients treated with long duration HD. The therapy results in higher small water-soluble solute removal, phosphate removal and greater elimination of larger molecules (e.g. β2-microglobulin).

It seems an appealing question whether a better control of the serum levels of protein-bound solutes can be achieved by long duration (nocturnal) hemodialysis. This might be another advantage of this therapeutic modality, or may even in part explain the better outcome of patients treated this way.

The study compares intermittent hemodialysis with long nocturnal hemodialysis with respect to serum concentrations of several protein bound uremic toxins, as well as solute removal.