Simple model of intra-extracellular potassium kinetics and removal applied to constant and potassium-profiled...

The incidence rate for sudden death in hemodialysis patients ranges between 2% and 7%. This phenomenon is frequently due to cardiac arrhythmias. In particular, the process of potassium (K(+)) depuration performed during hemodialysis has been found to be related to arrhythmia onset. The main aim of this study was to introduce a simple double-pool mathematical model of K(+) kinetics to investigate the effects of dialysate K(+) concentration on intracellular and extracellular K(+) removal. The secondary aim was to evaluate the K(+) removed from the different body pools in 2 different types of K(+) dialysate: constant and profiled.

Our model evaluated K(+) removal and body water in the intracellular and extracellular spaces using plasma, erythrocytes and spent dialysate K(+) concentration, and intracellular and extracellular volume (t=0) in 6 patients (4 females and 2 males). All patients were treated with acetate-free biofiltration with a constant K(+) dialysate concentration (AFB) and with a profiled one (AFB-K). Moreover, the electrolyte concentration (sodium, calcium and bicarbonate) and pH were analyzed in all sessions.

A similar total potassium removal was evaluated by the model, starting from a similar final K(+) plasma reduction. At 10 minutes, the model assessed a higher K(+) removal in the extracellular space during AFB (26.6% vs. 7.7%, p<0.001) involving a lower K(+) concentration (5.0 +/- 0.5 in AFB and 5.2 +/- 0.6 in AFB-K, p<0.05) and consequently a higher cell hyperpolarization (-73.4 +/- 3.9 mV vs. -72.1 +/- 2.4 mV, p=0.05). No differences in pH, intracellular and extracellular Na+ or plasma Ca(2+) were highlighted between AFB and AFB-K.

The model we developed allows us to evaluate K(+) removal and body water in the intracellular and extracellular spaces during treatment. The assessment of this information may have a relevant role toward an understanding of the causes of the Nernst potential changes during hemodialysis that are often related to the onset of arrhythmias.