Do not forget to individualize dialysate sodium prescription

Sodium mass balance is primarily dependent on two factors: dietary salt intake and sodium removal during haemodialysis (HD). Salt intake during the interdialysis period is dependent on patient behaviour and is a strong driver of volume overload [1]. The average American consumes ∼149 mmol/day [2]; most Western societies consume between 150 and 250 mmol/day [3]. There is evidence that HD patients ingest similar amounts of sodium. A small series of Spanish HD patients showed baseline sodium intake of ∼173 mmol/day [4]. Likewise, a study of 28 English HD patients showed an average estimated sodium intake of 251 mmol/day [5]. Sodium load in HD patients is associated with thirst, fluid retention, interdialysis weight gain (IDWG) and hypertension [6]. Therefore, one of the most important goals of the dialysis therapy is to remove exactly the mass of sodium that has been accumulated in the interdialysis period in order to reach a zero sodium mass balance. Sodium removal during HD can occur through convection and diffusion. Current prescribing practices for chronic intermittent HD rely primarily on convective losses (∼78%) and less on diffusive losses (∼22%) [5]. This relative distribution, however, is dependent on the amount of ultrafiltration occurring during any given HD session (i.e. convective losses) and the prescribed dialysate sodium concentration and its relationship with patient’s own plasma sodium (i.e. diffusive losses). The diffusive gradient between plasma and the inlet dialyser sodium concentration is an important factor in the ‘fine tuning’ of sodium balance in bicarbonate HD [1].