Computer modelling of haemodialysis/ultrafiltration explaining the pathogenesis of the disequilibrium syndrome.

Based on the hypothesis that rapid corrections of pH, Na+ and osmolality give rise to disequilibrium (DES) during efficient haemodialysis (HD), a 14 compartment model has been designed for dynamic analysis of the induced fluid shifts and the resulting haemodynamic reactions. Simulated HD and ultrafiltration (UF) on the model were based on data from 11 steady state dialysis (RDT) patients (diffusion coefficients for urea, body fluid compartments, haemodynamic monitoring by Swan-Ganz catheters). The model reactions correlated remarkably with clinical findings and indicate how far a patient's haemodynamic compensation can prevent circulatory collapse and hypovolaemia, mainly through lowering the mean pressure in a major portion of the capillaries. Steady weight dialysis causes reduction of blood volume up to 65 per cent before circulatory collapse occurs.