Model‐Based Analysis of Potassium Removal During Hemodialysis

Abstract

Potassium ion (K(+)) kinetics in intra- and extracellular compartments during dialysis was studied by means of a double-pool computer model, which included potassium-dependent active transport (Na-K-ATPase pump) in 38 patients undergoing chronic hemodialysis. Each patient was treated for 2 weeks with a constant K(+) dialysate concentration (K(+)(CONST) therapy) and afterward for 2 weeks with a time-varying (profiled) K(+) dialysate concentration (K(+)(PROF) therapy). The two therapies induced different levels of K(+) plasma concentration (K(+)(CONST): 3.71 +/- 0.88 mmol/L vs. K(+)(PROF): 3.97 +/- 0.64 mmol/L, time-averaged values, P < 0.01). The computer model was tuned to accurately fit plasmatic K(+) measured in the course and 1 h after K(+)(CONST) and K(+)(PROF) therapies and was then used to simulate the kinetics of intra- and extracellular K(+). Model-based analysis showed that almost all the K(+) removal in the first 90 min of dialysis was derived from the extracellular compartment. The different K(+) time course in the dialysate and the consequently different Na-K pump activity resulted in a different sharing of removed potassium mass at the end of dialysis: 56% +/- 17% from the extracellular compartment in K(+)(PROF) versus 41% +/- 14% in K(+)(CONST). At the end of both therapies, the K(+) distribution was largely unbalanced, and, in the next 3 h, K(+) continued to flow in the extracellular space (about 24 mmol). After rebalancing, about 80% of the K(+) mass that was removed derived from the intracellular compartment. In conclusion, the Na-K pump plays a major role in K(+) apportionment between extracellular and intracellular compartments, and potassium dialysate concentration strongly influences pump activity.

Potassium kinetics during hemodialysis

“…It has previously been suggested by various investigators that approximately half of the potassium removed during hemodialysis comes from the intracellular compartment . The present observations are consistent with those previous reports since the total potassium mobilized from the inaccessible compartment during the hemodialysis treatment was roughly half of the total amount of potassium removed for all potassium dialysate concentration categories.…”

“…Two‐compartment kinetic models for potassium have been incorporated into simulation models of hemodialysis, but such models are complex. More recently, potassium kinetic models during acetate‐free biofiltration have been developed to optimize dialysate potassium profiling . Those models assume potassium distribution in intracellular and extracellular compartments and account for sodium‐potassium pump activity; however, they also contain several parameters that can be difficult to uniquely estimate from limited data during hemodialysis treatments when only measuring serum potassium kinetics.…”

Aerobic exercise increases phosphate removal during hemodialysis: A controlled trial

“…The efflux from the intracellular compartment follows passive diffusion, and the influx occurs through active transport because of the Na‐K‐ATPase transporter. The activity of this pump depends mainly on the extracellular potassium concentration, which significantly decreases in the course of the dialysis . Besides potassium serum concentration, insulin and catecholamines, which increase with exercise, cause the influx of potassium .…”

Integrated Monitoring for Personalized Renal Replacement Therapy

“…[4] Modelling urea distribution with two compartments was proven to be adequate, as well. As opposed to potassium, it is not influenced by active exchange processes.…”

“…The sodiumpotassium co-transporter establishes an active redistribution against concentration gradients, resulting in disequilibrium, which is essential for elementary physiological processes like excitation and neural activity. Equation 1 formulates the basic differential equation to describe a two compartment system following [4]. It describes the dependence of intra-and extracellular molar mass (dM ec /dt and dM ic /dt), of intra-and extracellular volumes (V ic and V ec ), diffusion coefficient (D c ), active trans-cellular transport coefficient (A C ), extracellular concentration for half-activation of active transport (K m ), ingestion (I) and removal (R).…”