Clinical relevance of abstruse transport phenomena in haemodialysis

Abstract

Haemodialysis (HD) utilizes the bidirectional properties of semipermeable membranes to remove uraemic toxins from blood while simultaneously replenishing electrolytes and buffers to correct metabolic acidosis. However, the nonspecific size-dependent transport across membranes also means that certain useful plasma constituents may be removed from the patient (together with uraemic toxins), or toxic compounds, e.g. endotoxin fragments, may accompany electrolytes and buffers of the dialysis fluids into blood and elicit severe biological reactions. We describe the mechanisms and implications of these undesirable transport processes that are inherent to all HD therapies and propose approaches to mitigate the effects of such transport. We focus particularly on two undesirable events that are considered to adversely affect HD therapy and possibly impact patient outcomes. Firstly, we describe how loss of albumin (and other essential substances) can occur while striving to eliminate larger uraemic toxins during HD and why hypoalbuminemia is a clinical condition to contend with. Secondly, we describe the origins and mode of transport of biologically active substances (from dialysis fluids with bacterial contamination) into the blood compartment and biological reactions they elicit. Endotoxin fragments activate various proinflammatory pathways to increase the underlying inflammation associated with chronic kidney disease. Both phenomena involve the physical as well as chemical properties of membranes that must be selected judiciously to balance the benefits with potential risks patients may encounter, in both the short and long term.

Impact of Hydrophilic Modification of Synthetic Dialysis Membranes on Hemocompatibility and Performance

“…This therapy can be performed at home with peritoneal dialysis or by extracorporeal treatments, such as low- and high-flux hemodialysis (HD), including low dialysate flow daily HD [ 3 ], or hemodiafiltration (HDF), which are the predominant treatment options for patients with ESKD [ 2 , 4 , 5 ]. In these extracorporeal treatments, a dialyzer replaces the function of the malfunctioning kidney, that is, elimination of a wide range of uremic toxins, e.g., ß2-microglobulin, urea, uric acid, or creatinine, and of excess fluid, while preventing loss of essential proteins, such as albumin [ 6 , 7 ]. This function of a dialyzer is called the performance and is generally described by clearance and sieving coefficient values in the instructions for use of the manufacturers.…”