Effects of reduced dialysis fluid flow in hemodialysis.

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 (QB), the dialysis fluid flow rate (QD), and the overall mass transfer area coefficient (K0A), an index of a dialyzer's performance. The flow ratio (QB : QD) to obtain a well-balanced dialysis efficiency is generally said to be 1 : 2. In Japan, the QB is controlled independently (from 200 to 250 mL/min) depending on individual conditions. However, the QD is usually set at around 500 mL/min regardless of the QB. MATERIALS AND METHODS To investigate the effect on dialysis efficiency of decreasing the QD from 500 to 400 mL/min, 12 patients were divided into two groups: one in which the QB was 150 mL/min, with 1.3-m(2) membranes; and another in which the QB was 200 mL/min, with 1.6-m(2) membranes. We defined the conditions with the QD of 500 mL/min as condition A, and that with the QD 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 QB 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 QB and a QD of 400 mL/min, and re-evaluated. RESULTS In condition B, a QB of 150 mL/min had no effect on the dialysis efficiency;whereas with a QB of 200 mL/min, slight yet significant differences were observed in the clearance of small molecular weight solutes. Condition B' (QB=210 mL/min) showed an equivalent or greater dialysis efficiency and demonstrated an association with theoretical values. CONCLUSIONS In hemodialysis, the flow ratio (QB : QD) should be maintained at 1 : 2 to obtain a well-balanced dialysis efficiency. The present study has shown that the QD can be decreased while maintaining this flow ratio. A well-balanced QD setting can be financially and environmentally conscious. In addition, use of the K0A equation is a highly effective method to calculate a QB that allows an expected dialysis efficiency to be achieved in case the QD needs to be decreased uniformly, as when dialysis fluid is in short supply during times of disaster.