You are the Medical director of a dialysis unit. A dialyzer manufacturing company is trying to sell you high efficiency dialyzers with a KoA of 2000ml/min. You are currently using dialyzers with a KoA of 1000ml/min. Having a great understanding of urea kinetics, you know that buying the high KoA dialyzer (albeit expensive) would be a great investment for your dialysis unit and would double the average Kt/V of your patients.
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Kt/V rises with increase in KoA. However, KoA >1000 ml/min are of marginal benefit especially with standard (Qb) blood flows of 400-500ml/min. Qb limits the benefit of dialyzers with excessively high KoA. Qb >500ml/min are difficult to achieve due to access flow limitations and needle resistance. Also higher blood flows may be un-physiologic and increase risk of access recirculation. Dialysis urea clearance can never exceed Qb. If all of the blood is cleared, clearance is the Qb.