Model-based analysis of Na-K+ pump influence on potassium depuration during Acetate Free Biofiltration (AFB)

Abstract

Potassium ion (K⁺) kinetics in intra and extracellular compartments during hemodialysis was studied by means of a double-pool computer model which included potassium-dependent active transport (Na-K-ATPase pump) in thirty-four patients (21M/13F; aged 66 plusmn 22 years old, dry weight 68 plusmn 18 kg, height 160 plusmn 15 cm) on renal replacement therapy with thrice weekly 4 hour double-needle hemodialysis. Each patient was studied during acetate free biofiltration (AFB) with a constant K⁺ dialysate concentration (K_CONST therapy) and with a time-varying (profiled) K⁺ dialysate concentration (K_PROF therapy). The two therapies induced different levels of K⁺ plasma concentration (K_CONST: 3.6plusmn0.8 vs. K_PROF: 4.0plusmn0.7 mmol/L, time-averaged values, p<0.01). The computer model was tuned to accurately fit plasmatic K⁺ measured in the course of 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 minutes of dialysis was mainly 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: 55+17% from the extracellular compartment in K⁺ _PROF vs. 41plusmn14% in K⁺ _CONST. These results suggest that the Na-K pump plays a major role in K⁺ apportionment between extracellular and intracellular compartments, and potassium dialysate concentration strongly influences pump activity. For this reason the computer-model here presented may represent a useful tool to quantitatively assess the impact of dialysate potassium on K⁺ kinetics in intra and extracellular compartments and to design dialysate potassium content tailored to the patient's needs.