Will the "short dialysis" of the eighties be adequate?

Almost 30 years have elapsed since the first successful attempts by Scribner and his associates of the Seattle Group to sustain life for an unlimited period of time in patients with end-stage renal failure. More than 250,000 patients are currently treated worldwide with various methods of maintenance dialysis, with survival rates reaching 75% at 10 years and 65% at 15 years reported by experienced groups. Such results are all the more remarkable (and initially unexpected) both because maintenance hemodialysis can replace only partially the numerous sophisticated regulatory functions of the normal kidney and despite our persistent ignorance of many factors involved in uremic toxicity. Moreover, an entirely new, multifaceted pathology has developed in the population of patients submitted to long-term hemodialysis as a consequence of the permanently incomplete correction of the uremic syndrome together with the multiple disorders and complications induced by dialysis and its related therapeutic procedures. In this context, the key question concerning the optimal duration of hemodialysis required to provide patients with a life as close to normal as possible, and in the highest conditions of safety and comfort, remains a matter of ongoing debate. The advances made through the years in understanding the mechanisms of many of the complications occurring in hemodialyzed patients have generated the concept of "adequate" dialysis. According to this concept, the weekly amount of dialysis delivered to a patient is the basic factor that must be considered in terms of a prescription; the weekly duration of dialysis represents only one variable among many that must be taken into account to define a "dialysis strategy" for a given patient. The large body of knowledge accumulated over time concerning the multiple aspects of the pathology arising in hemodialysis patients has contributed to the development of many technical advances; these have allowed ever more efficacious and safe control of the clinical and biologic disturbances caused by long-lasting terminal uremia. The average weekly dialysis time of 24 to 40 hours 25 years ago was reduced to less than 12 hours in the '70s and currently may be as few as 6 hours. Will the criteria for "adequate" dialysis be met in the long run despite this dramatic reduction in weekly dialysis time? That is the question to which this paper attempts to suggest at least a partial answer. We shall limit the scope of this study to the theoretical and practical problems relevant to maintenance hemodialysis therapy. Those specific to hemofiltration will not be discussed here.