Particulates formed in dialysis fluid: effect of silica in tap water

Background A fluid commonly used for dialysis in Japan is prepared from two dialysate concentrates and dialysis water. Silicon (Si) from tap water is reported in dialysis water as suspended insoluble particulate matters. We aimed to examine the source of insoluble particulate matters in the online prepared substitution fluid and to examine effects of the silica (SiO2) of tap water on the SiO2 of dialysis water. Method Based on the number of particles and particle size distribution in online prepared substitution fluid, we evaluated particle diameters and constituent elements of particles in online prepared substitution fluid. To identify sources of insoluble particulate matters in the online prepared substitution fluid, we measured particle diameters and constituent elements of particles adhering to the surface of hollow fiber of the final endotoxin-retentive filter (ETRF) and to the inner surface of the housing of the final ETRF and measured SiO2 in tap water, dialysis water, and commercial sterile substitution fluid. Results Si-containing particles accounted for 83% of 30 particles detected in the final ETRF (the hollow fibers and the housing) and the online prepared substitution fluid sampled from the final ETRF. The large variability in the SiO2 in tap water depending on the geographic regions. The SiO2 in dialysis water was 0.4-0.7 mg/L. Si was not detected in particles in the commercial sterilized substitution fluid, and the commercial sterile substitution fluids contained SiO2 at 0.1 mg/L. Conclusion We presume that insoluble particulates in online prepared substitution fluid were calcium and magnesium precipitated from dialysate and Si precipitated from dialysis water. Moreover, variation in the SiO2 in tap water is a factor affecting the SiO2 level in dialysis water. If the formation of silicates in the online prepared substitution fluid is considered and the target SiO2 in dialysis water is to be set <= 0.1 mg/L, SiO2 in tap water available in hospitals and dialysis centers should be known before specifications of instruments for dialysis fluid preparation are determined.