Ouseph R, Ward R A
Department of Medicine, Division of Nephrology, University of Louisville, Louisville, KY, USA.
Am J Kidney Dis. 2001 Feb;37(2):316-20. doi: 10.1053/ajkd.2001.21296.
Dialyzer clearance depends on blood and dialysate flow rates and the product of the membrane surface area and mass transfer coefficient for the solute of interest, K(o)A. K(o)A is usually assumed to be constant for a given dialyzer and solute. Results of two recent studies challenge this assumption. Therefore, we examined the hypothesis that K(o)A depends on blood and dialysate flow rates during clinical dialysis. Urea clearances were measured for two different dialyzers at all four combinations of two blood flow rates (300 and 400 mL/min) and two dialysate flow rates (500 and 800 mL/min). Urea K(o)A was calculated by using standard equations for mass transfer in dialyzers operated with countercurrent flows. The impact of blood and dialysate flow rates on K(o)A was assessed by analysis of variance. Increasing dialysate flow rate from 500 to 800 mL/min significantly increased K(o)A (P = 0.018). Increasing blood flow rate from 300 to 400 mL/min did not significantly increase K(o)A (P = 0.083). Also, K(o)A decreased significantly with increasing hematocrit (P = 0.022). The results of this study extend previous in vitro findings by showing that increasing the dialysate flow rate increases urea K(o)A during clinical dialysis. However, the increase in K(o)A observed during clinical dialysis (5.7%) is less than that previously reported in vitro (14.7%), possibly because of the impact of blood cells and proteins on blood-side mass transfer resistance.
透析器清除率取决于血液和透析液流速以及膜表面积与目标溶质传质系数的乘积K(o)A。对于给定的透析器和溶质，通常假定K(o)A是恒定的。最近两项研究的结果对这一假设提出了挑战。因此，我们检验了K(o)A在临床透析过程中取决于血液和透析液流速的假设。在两种血流速率（300和400 mL/分钟）与两种透析液流速（500和800 mL/分钟）的所有四种组合下，对两种不同的透析器测量了尿素清除率。通过使用逆流操作的透析器中传质的标准方程计算尿素K(o)A。通过方差分析评估血液和透析液流速对K(o)A的影响。将透析液流速从500 mL/分钟提高到800 mL/分钟可显著提高K(o)A（P = 0.018）。将血流速率从300 mL/分钟提高到400 mL/分钟并未显著提高K(o)A（P = 0.083）。此外，K(o)A随着血细胞比容的增加而显著降低（P = 0.022）。本研究结果扩展了先前的体外研究结果，表明在临床透析过程中提高透析液流速可增加尿素K(o)A。然而，临床透析过程中观察到的K(o)A增加（5.7%）低于先前体外报道的增加（14.7%），这可能是由于血细胞和蛋白质对血液侧传质阻力的影响。
