Expanded hemodialysis: what's up, Doc?

In recent years there has been an increasing interest in expanded hemodialysis (HDx), an emerging renal replacement therapy based on the use of medium cut-off membranes (MCO). Thanks to the internal architecture of these types of membranes, with a higher pore size and smaller fiber inner diameter to favor internal filtration rate, they can increase the removal of larger middle molecules in conventional hemodialysis. Secondarily, several reports suggest that this therapy potentially improve the outcomes for end-stage renal disease patients. However, HDx has not been defined yet and the characteristics of MCO membranes are not well stablished. The aim of this narrative review is to define HDx and summarize the dialyzers that have been used so far to perform this therapy, collect the evidence available on its efficacy and clinical outcomes compared with other hemodialysis techniques and settle the bases for its optimal prescription.