大剂量前稀释CVVH治疗中血流量对溶质清除的作用

目的：通过前稀释持续静脉-静脉血液滤过(CVVH)治疗的体外实验，研究血流量和超滤率在前稀释模式CVVH时对溶质清除的影响。方法：建立等容、前稀释CVVH体外实验装置，置换液流量(Qs)等于超滤率(Quf)，采用高通透性膜血滤器，测定不同Quf和血流量时尿素、肌酐的滤器清除率(Kf)和患者获得的清除率(Kt)以及溶质的筛系数(SC)。每个Qb和Quf组合重复实验3次(n=3)。结果：该实验条件下，尿素、肌酐SC接近1．00，滤器清除率(Kf)等于SC；Qb或Quf增加，其SC无明显变化。在前稀释模式时，CVVH患者获得的溶质清除率(Kt)比滤器的清除率(Kf)低，增加Qb可使患者获得的清除率和清除效率增加。增加血流量的这种作用在超滤率=100mL／min时尤其显著。结论:CVVH在前稀释时，小分子溶质Kf与Quf基本相等，Quf可作为治疗剂量的指标。在前稀释时，患者Kf低于Kf，增加血流量(Qb)可显著提高治疗效率，特别是在大剂量前稀释CVVH治疗时。

Effect of blood flow rate on solute clearance in high-dose pre-dilution continuous venovenous hemofiltration

Objective Since the dose range recently shown favorably to influence the outcome in the patient treated with continuous venovenous hemofiltration (CVVH) is very difficult to deliver in the post-dilution mode, the pre-dilution mode is typically prescribed for high-dose therapy. However, the relatively low blood flow rate (Qb) that has been traditionally prescribed in CVVH may limit the ability to deliver such therapy. On this study we try to determine the influence of blood flow rate on clearance efficiency and treatment clearance at a fixed ultrafiltration rate. Methods In an experimental isovolemic pre-dilution CVVH system employing Quf of 33 , 67 and 100 mL/min ( substitution fluid rates, Qs equal to Quf) , we determined the variable Qb(150, 250, 350 and 450 mL/min; bovine blood, hematocrit 30% ) on urea and creatinine clearance by a 1.2 m2 polysulfone hemofilter (HF1200, Minntech) , for each Qb/Quf combination( n =3). Results For small solutes, the sieving coefficient (SC) was close to 1.0 at all Qb/Quf combinations; filter clearances ( Kf ) were thus equal to Quf; increasing Quf did not significantly modify SC. Solute clearances delivered to patients (Kt) were lower than the clearances of filter itself with this pre-dilution CVVH. Both the clearance efficiency and the clearances delivered to patients ( Kt) increased with increase in Qb . The Qb effect was especially pronounced at Quf= 100 mL/min. Conclusion In pre-dilution CVVH , filter clearance for small solutes equaled Quf at evaluated rates; Quf can be used as a surrogate of treatment dose. Solute clearances delivered to the patients were lower than the clearances of filter itself. For a given ultrafiltration rate, increase in the blood flow rale will significantly improve treatment efficiency in the predilution mode. Delivery of high-dose predilu-tion CVVH is enhanced by use of Qb values that are significantly greater than those traditionally employed.