Department of Nephrology, Dialysis and Transplantation, San Bortolo Hospital, Vicenza, Italy.
Blood Purif. 2013;35(1-3):106-11. doi: 10.1159/000346093. Epub 2013 Jan 22.
BACKGROUND/AIMS: Continuous renal replacement therapy (CRRT) is commonly used for critically ill patients with acute kidney injury. During treatment, a slow dialysate flow rate can be applied to enhance diffusive solute removal. However, due to the lack of the rationale of the dialysate flow configuration (countercurrent or concurrent to blood flow), in clinical practice, the connection settings of a hemodiafilter are done depending on nurse preference or at random.
In this study, we investigated the effects of flow configurations in a hemodiafilter during continuous venovenous hemodialysis on solute removal and fluid transport using computational fluid dynamic modeling. We solved the momentum equation coupling solute transport to predict quantitative diffusion and convection phenomena in a simplified hemodiafilter model.
Computational modeling results showed superior solute removal (clearance of urea: 67.8 vs. 45.1 ml/min) and convection (filtration volume: 29.0 vs. 25.7 ml/min) performances for the countercurrent flow configuration. Countercurrent flow configuration enhances convection and diffusion compared to concurrent flow configuration by increasing filtration volume and equilibrium concentration in the proximal part of a hemodiafilter and backfiltration of pure dialysate in the distal part. In clinical practice, the countercurrent dialysate flow configuration of a hemodiafilter could increase solute removal in CRRT. Nevertheless, while this configuration may become mandatory for high-efficiency treatments, the impact of differences in solute removal observed in slow continuous therapies may be less important. Under these circumstances, if continuous therapies are prescribed, some of the advantages of the concurrent configuration in terms of simpler circuit layout and simpler machine design may overcome the advantages in terms of solute clearance.
Different dialysate flow configurations influence solute clearance and change major solute removal mechanisms in the proximal and distal parts of a hemodiafilter. Advantages of each configuration should be balanced against the overall performance of the treatment and its simplicity in terms of treatment delivery and circuit handling procedures.
背景/目的：连续肾脏替代疗法（CRRT）常用于治疗急性肾损伤的危重症患者。在治疗过程中，可以应用较慢的透析液流速以增强弥散溶质清除。然而，由于缺乏透析液流配置（逆流或与血流并行）的基本原理，在临床实践中，血液透析器的连接设置取决于护士的偏好或随机进行。
在这项研究中，我们使用计算流体动力学模型研究了连续静脉-静脉血液透析过程中血液透析器中的流型对溶质清除和液体传输的影响。我们通过求解动量方程来耦合溶质输运，以预测简化血液透析器模型中的定量扩散和对流现象。
计算模型结果表明，逆流流型的溶质清除（尿素清除率：67.8 比 45.1ml/min）和对流（滤过体积：29.0 比 25.7ml/min）性能更好。与并行流型相比，逆流流型通过增加滤过体积和血液透析器近端的平衡浓度以及在远端回灌纯透析液，增强了对流和扩散作用。在临床实践中，血液透析器的逆流透析液流型可增加 CRRT 中的溶质清除。然而，虽然这种配置可能对高效治疗成为强制性要求，但在缓慢的连续治疗中观察到的溶质清除率差异的影响可能不太重要。在这种情况下，如果规定进行连续治疗，那么在回路布局和机器设计更简单方面，并行配置的一些优势可能会超过溶质清除率方面的优势。
不同的透析液流型会影响溶质清除，并改变血液透析器近端和远端的主要溶质清除机制。应根据治疗的整体性能及其在治疗输送和回路处理程序方面的简单性来平衡每种配置的优势。
