Model‐Based Analysis of Potassium Removal During Hemodialysis

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.