Although clinical benefits associated with low sodium dialysate in CAPD such as higher removal of sodium and water have been reported elsewhere, its mechanism is still speculative.
To assess mass transport characteristics by this unique dialysate composition we utilized mathematical model being reported previously. In this computer simulation 8.3ml/min, 9.4ml/min and 10ml/min of mass transfer area coefficients (MTAC) for sodium, chloride and glucose were cited from the literatures. Sodium concentrations in dialysate were varied from 76mEq/l to 129mEq/l, compensating its associated decreases of osmolarity by glucose.
An increase of approximately 22ml of net ultrafiltration volume at 6hr dwell time could be achieved by reduction of 1mEq/l of serum sodium concentration in the range of 130mEq/l-150mEq/l of serum sodium concentration while only 2.3-0.5ml of net UF volume increase per 1mEq/l of dialysate sodium concentration decrease could be estimated in the range of 76mEq/l-129mEq/l of dialysate sodium concentration. 20% and 41% of sodium were transported by diffusion in standard dialysate (129mEq/l) and LNaD (102mEq/l), respectively.
It is clearly indicated that diffusive transport becomes dominant in sodium removal as sodium concentration in dialysate decreases, while both increase of reflection coefficient and decrease of MTAC of sodium tend to reduce water removal.