Removal of Phosphorus by Hemodialysis

Abstract

The control of serum phosphorus by dialysis is made difficult by the fact that intradialytic blood levels tend to be low, and because phosphorus is removed almost exclusively from the plasma during its passage through the dialyzer. The most practical way to increase phosphorus removal is to extend dialysis time, although attention to dialysis efficiency (surface area, advanced membrane, and higher blood and dialysate flow rates) also plays a role. Benefits of hemodiafiltration in helping control serum phosphorus have been claimed, but not found in all studies. Because serum phosphorus levels tend to plateau during the later parts of a dialysis session, extending weekly dialysis time is of greater benefit for phosphorus removal than for urea removal. Increasing dialysis frequency also probably has a small benefit. It appears that 18-30 hours of dialysis per week are required to obviate the need for phosphorus binders. Several promising models of phosphorus kinetics are under development. These may help predict the change in treatment on serum phosphorus levels, but their ability to do so has not yet been critically assessed.

Is Expanded Hemodialysis an Option to Online Hemodiafiltration for Small- and Middle-Sized Molecules Clearance?

“…One of the few approaches that have shown a reduction in serum phosphorus concentrations is increasing dialysis time [20]. In one study, the overall phosphorus clearance and total mass of phosphorus removed was significantly larger by using medium cutoff membranes compared to high-flux HD [17].…”

A Pseudo‐One Compartment Model of Phosphorus Kinetics During Hemodialysis: Further Supporting Evidence

“…The kinetics of phosphorus in HD patients is complex, and mathematical models of phosphorus kinetics are inexact representations of complex physiological transport mechanisms within patients. Several models of phosphorus kinetics during HD are under development ; each model has different objectives and practicality. A pseudo‐one compartment kinetic model has been previously shown to describe phosphorus kinetics during short and conventional HD treatments , during a week on thrice weekly HD , and in a large cohort of patients treated by conventional HD .…”

“…Further, it has been proposed to assist in the prescription of high dose HD for improved control of serum phosphorus levels . It cannot, however, describe certain phenomena observed clinically in some reports, such as differences in serum phosphorus concentration on different days of the week or intradialytic increases in serum phosphorus . If these latter phenomena are of clinical interest, other kinetic models may be more relevant .…”

“…It cannot, however, describe certain phenomena observed clinically in some reports, such as differences in serum phosphorus concentration on different days of the week or intradialytic increases in serum phosphorus . If these latter phenomena are of clinical interest, other kinetic models may be more relevant . On the other hand, a pseudo‐one compartment model is the simplest model and therefore, by Occam's razor, most desirable for many applications.…”

“…The control of serum phosphorus concentrations in patients treated by dialysis modalities is limited by low clearances, such as during continuous peritoneal dialysis , or by short weekly treatment times, such as during conventional thrice‐weekly hemodialysis (HD) . Consequently, many dialysis patients have significantly elevated serum concentrations of phosphorus despite liberal prescription of oral phosphorus binding agents and dietary restriction of phosphorus‐containing foods.…”