What determines the rate of toxin removal?
The rate of toxin removal is traditionally measured by the removal of urea. The removal of urea during the hemodialysis session is increased by any of these factors:
• Higher blood flow rate and dialysis flow rate: The higher the blood flow rate, the more urea diffusion that will occur per unit time. The limiting factor is the dialysis access, with a fistula usually being able to deliver the highest flow rates (up to about 550 mL/min) and a catheter usually being able to deliver the lowest flow rates (300 to 350 mL/min).
• Higher efficiency of the dialyzer: A higher-efficiency dialyzer typically has a large surface area, a thin membrane, and increased porosity. This efficiency is expressed as the dialyzer mass transfer area coefficient or KoA of the dialyzer.
• Longer time on dialysis: The longer the time for a single dialysis treatment, the more urea diffusion will occur. However, the urea removal per hour diminishes with each additional hour of dialysis provided.
• Frequency of dialysis: The standard form of in-center hemodialysis is three sessions per week, but increasing frequency increases the amount of urea and other uremic toxins that can be removed.
