Effect of Dialysate-Side Mass Transfer Resistance on Small Solute Removal in Hemodialysis

Uremic toxicity is mediated by the retention of numerous types of solutes [1]. Characteristics which vary among uremic toxins include molecular weight, degree of protein binding, volume of distribution, and charge. The most widely studied group of uremic toxins is the low-molecular weight (MW) nitrogenous waste products. One of the most prominent characteristics of molecules in this toxin class is high diffusivity [2], largely explained by their low MW and lack of protein binding. Although not necessarily toxic per se in their free form, urea and creatinine serve as surrogate molecules for this class. The kinetic characteristics of urea during hemodialysis (HD) have been particularly widely studied and an abundant amount of recent clinical data from the United States indicates the extent of urea removal during HD, expressed as either treatment dose (Kt/V) or reduction ratio, is directly proportional to survival [3]. Therefore, a clear understanding by clinicians of the determinants of small solute mass transfer during HD is required. Overview of Diffusive Mass Transfer in Hemodialysis