[Sodium kinetics in peritoneal dialysis: from theory to clinical practice]

Cardiovascular disease (CVD) is the leading cause of death in dialysis patients. Among the main risk factors for CV mortality, hydro-saline retention is frequently observed in peritoneal dialysis (PD) patients, due to the transport mechanisms occurring within the peritoneal cavity. The analysis of sodium (Na) kinetics is a useful method to understand better the transport of fluids and solutes in PD. In the absence of peritoneal ultrafiltration (UF), Na removal by diffusion during a peritoneal dwell is extremely low. Therefore, to increase peritoneal Na removal, the attainment of peritoneal UF is a basic requisite; however, achieving this goal requires the use of solutions with hypertonic glucose concentrations. On the other hand, such a type of convective transport induces the transport of free-water, by aquaporin-1 channels located on the endothelial side of the peritoneal membrane; therefore, leading to a disproportionate removal of plasmatic water as compared with the removal of plasmatic Na (hyponatric removal). PD solutions containing icodextrin at 7.5% concentration determine UF with a different mechanism (colloid-osmotic), without inducing any free-water transport. However, clinical studies have failed to show a benefit of icodextrin solution in reducing blood pressure (BP) values and increasing Na removal. Therefore, the use of PD solutions with low Na concentrations (102-120 mmol/L) has been recently proposed as another available therapeutic strategy to prevent the development and reduce the prevalence of hydro-saline retention and hypertension in PD patients.