Dialysis dose and frequency.

BACKGROUND: From the beginning of the dialysis era, the issue of optimal dialysis dose and frequency has been a central topic in the delivery of dialysis treatment.
METHODS: We undertook a discussion to achieve a consensus on key points relating to dialysis dose and frequency, focusing on the relationships with clinical and patient outcomes.
RESULTS: Traditionally, dialysis adequacy has been quantified referring to the kinetics of urea, taken as a paradigm of all uraemic toxins, and applying the principles of pharmacokinetics using either single- or double-pool variable volume models. An index of dialysis dose is the fractional clearance of urea, which is commonly expressed as Kt/V. It can be calculated from blood urea concentration and haemodialysis (HD) parameters, according to the respective urea kinetic model or by means of simplified formulas. Similar principles are applicable to peritoneal dialysis (PD), where weekly Kt/V and creatinine clearance are used. Recommended minimal targets for dialysis adequacy have been defined by both American and European guidelines (DOQI and European Best Practice Guidelines, respectively). The question of how to improve the severe outcome of dialysis patients has recently come back to the fore, since the results of two recent randomized controlled trials led to the conclusion that, in thrice weekly HD and in PD, increasing the dialysis dose well above the minimum requirements of current American guidelines did not improve patient outcome. Daily HD (defined as a minimum of six HD sessions per week), in the form of either short daytime HD or long slow nocturnal HD, is regarded as a possibility to improve dialysis patient outcome. The results of the studies published so far indicate excellent results with respect to all outcomes analysed: optimal blood pressure control, regression of left ventricular hypertrophy and amelioration of left ventricular performance, improvement of renal anaemia, optimal hyperphosphataemia control, improvement of nutritional status, reduction in oxidative stress indices and improvement in quality of life. The basis for these beneficial effects is thought to be a more physiological clearance of solutes and water, with reduced pre- and post-HD solute concentrations and interdialytic oscillation, compared with traditional HD. Apart from concerns regarding reimbursement and organizational issues, no serious adverse effects have been described with daily HD. However, the evidence accumulated is limited mainly to retrospective cohorts, with small patient numbers and no adequate controls in most instances. Therefore, large prospective studies with adequate controls are required to make daily HD accepted by reimbursing authorities and patients.
CONCLUSIONS: Given the available observational and interventional body of evidence, there is no reason to reduce arbitrarily dialysis dose, particularly dialysis treatment time in HD patients treated three times weekly. Daily HD represents a very promising tool for improving dialysis outcomes and quality of life, although its impact on patient survival has not yet been proven definitively.