Background: Hemodialysis is a treatment in which uremic toxins and excess water content are removed from the blood with a dialyzer and dialysis fluid. The efficiency of hemodialysis is strongly influenced by the following 3 parameters: the blood flow rate (Q_B), the dialysis fluid flow rate (Q_D), and the overall mass transfer area coefficient (K₀A), an index of a dialyzer's performance. The flow ratio (Q_B : Q_D) to obtain a well-balanced dialysis efficiency is generally said to be 1 : 2. In Japan, the Q_B is controlled independently (from 200 to 250 mL/min) depending on individual conditions. However, the Q_D is usually set at around 500 mL/min regardless of the Q_B.
Materials and Methods: To investigate the effect on dialysis efficiency of decreasing the Q_D from 500 to 400 mL/min, 12 patients were divided into two groups: one in which the Q_B was 150 mL/min, with 1.3-m² membranes; and another in which the Q_B was 200 mL/min, with 1.6-m² membranes. We defined the conditions with the Q_D of 500 mL/min as condition A, and that with the Q_D of 400 mL/min as condition B. Each operating condition was assigned for 2 weeks as crossover trials. To evaluate solute removal, we calculated clearance, reduction rate, removal amount, clear space, the clear space rate, and albumin leakage. Furthermore, when dialysis efficiency decreased in condition B, we performed a supplementary test: we calculated the Q_B with the K₀A equation to achieve a dialysis efficiency equivalent to that in condition A, defined as condition B', as the operating condition with the calculated Q_B and a Q_D of 400 mL/min, and re-evaluated.
Results: In condition B, a Q_B of 150 mL/min had no effect on the dialysis efficiency;whereas with a Q_B of 200 mL/min, slight yet significant differences were observed in the clearance of small molecular weight solutes. Condition B' (Q_B=210 mL/min) showed an equivalent or greater dialysis efficiency and demonstrated an association with theoretical values.
Conclusions: In hemodialysis, the flow ratio (Q_B : Q_D) should be maintained at 1 : 2 to obtain a well-balanced dialysis efficiency. The present study has shown that the Q_D can be decreased while maintaining this flow ratio. A well-balanced Q_D setting can be financially and environmentally conscious. In addition, use of the K₀A equation is a highly effective method to calculate a Q_B that allows an expected dialysis efficiency to be achieved in case the Q_D needs to be decreased uniformly, as when dialysis fluid is in short supply during times of disaster.