Ammonia toxicity appears to contribute to the genesis of
brain edema, a leading cause of death in
fulminant hepatic failure. Because dialysis has been recommended for acute
hyperammonemia in other conditions, we have conducted a study to analyze the determinants of
ammonia clearance with the use of a single-pass dialyzer. We have used an ionic
solution with a constant concentration of
ammonia to estimate clearance at different blood flow rates, at
dialysate flow rates, and with different dialyzer surfaces. Once
hemodialysis had been optimized, we estimated
ammonia,
glutamine, and
urea removal by using a single-compartment model. Our results show that the clearance of
ammonia is blood flow dependent and is also influenced by
dialysate flow rate and dialyzer surface. At clinically feasible conditions,
ammonia can be extracted by more than 80% by setting the
dialysate flow at a high rate. In addition to
ammonia removal,
hemodialysis allows the clearance of
urea and
glutamine, molecules that can be regarded as
ammonia equivalents and that also undergo flow-dependent elimination.