Canaud B, Bosc J Y, Cabrol L, Leray-Moragues H, Navino C, Verzetti G, Thomaseth K
Nephrology, Lapeyronie University Hospital, Montpellier, France.
Kidney Int Suppl. 2000 Aug;76:S28-40. doi: 10.1046/j.1523-1755.2000.07604.x.
"Dialysis dose," a concept developed by Sargent and Gotch based on urea kinetic modeling, is a useful and recognized tool that is used to quantitate and optimize a dialysis-efficacy program. However, it has been shown that oversimplification of the "dialysis adequacy" concept to the Kt/V index might lead to dramatic underdialysis and subsequent deleterious consequences on morbidity and mortality of dialysis patients. With this perspective, the determination of Kt/V must be very cautious and rely on accurate measurement of postdialysis urea concentration and its use integrated as a tool in a quality-assurance process.
In this study, we analyzed urea dynamics by means of a blood side (ultrafiltrate) continuous online urea monitoring system interfaced with a two-pool model hosted in a microcomputer. The study was designed to provide instantaneous dialysis performances (body and dialyzer clearances, dialyzer mass transfer coefficient) and to determine the in vivo functional permeability characteristics of the patient [intercompartment urea mass transfer coefficient (Kc)]. Thirteen end-stage renal disease patients (age 54 +/- 16 years; 12 male and 1 female) were studied during nine consecutive dialysis sessions (3 weeks).
Urea kinetics obtained from the urea monitoring system fitted closely the urea kinetic modeling prediction, confirming the validity of the double-pool model structure. Effective in vivo urea mass transfer coefficient averaged 912 +/- 235 mL/min/1.73 m2, a value close to those reported with more invasive methods. Large variations ranging from 363 to 1249 mL/min were observed among patients, confirming very large interindividual patient permeability differences. Interestingly, the urea mass transfer coefficient was inversely correlated with the postdialysis rebound values. Intraindividual variations were also noted as a function of time denoting functional changes in urea mass transfer coefficient values. The urea distribution volume was 38.1 +/- 7, 8 L (53 +/- 8% body weight). V1 referring to the extracellular volume and V2 to the intracellular volume were 9 +/- 2 L (13 +/- 2% body weight) and 29.2 +/- 6.6 L (41 +/- 1.3% body wt), respectively. The extracellular/intracellular volume ratio was 0.31 (approximately one third) and was not as usually defined by the paradigm 1/2 ratio.
Online double-pool urea kinetic modeling gave a new insight in urea kinetic modeling approach. Urea dynamics fit perfectly a double-compartment model structure. Accessible extracellular volume to hemodialysis is smaller than expected. The in vivo urea mass transfer coefficient must be considered as an individual and variable characteristic of ESRD patients that should be taken into consideration when prescribing the hemodialysis schedule.
“透析剂量”是由萨金特和戈奇基于尿素动力学模型提出的概念，是一种用于量化和优化透析疗效方案的实用且公认的工具。然而，已表明将“透析充分性”概念过度简化为Kt/V指数可能导致严重的透析不充分，并随后对透析患者的发病率和死亡率产生有害影响。从这个角度来看，Kt/V的测定必须非常谨慎，并依赖于透析后尿素浓度的准确测量，并将其作为质量保证过程中的一种工具来综合使用。
在本研究中，我们通过与微型计算机中托管的双池模型接口的血液侧（超滤液）连续在线尿素监测系统分析尿素动力学。该研究旨在提供即时透析性能（身体和透析器清除率、透析器传质系数），并确定患者的体内功能通透性特征[隔室间尿素传质系数（Kc）]。对13例终末期肾病患者（年龄54±16岁；12例男性和1例女性）进行了连续9次透析治疗（3周）的研究。
从尿素监测系统获得的尿素动力学与尿素动力学模型预测结果密切吻合，证实了双池模型结构的有效性。体内有效尿素传质系数平均为912±235 mL/min/1.73 m²，该值与采用更具侵入性方法报道的值相近。患者之间观察到的变化范围很大，从363到1249 mL/min不等，证实了个体间通透性差异非常大。有趣的是，尿素传质系数与透析后反弹值呈负相关。还注意到个体内变化是时间的函数，表明尿素传质系数值的功能变化。尿素分布容积为38.1±7.8 L（53±8%体重）。分别指细胞外液容积的V1和指细胞内液容积的V2为9±2 L（13±2%体重）和29.2±6.6 L（41±1.3%体重）。细胞外/细胞内液容积比为0.31（约三分之一），并非通常由范例1/2比值定义。
在线双池尿素动力学模型为尿素动力学建模方法提供了新的见解。尿素动力学完美符合双室模型结构。血液透析可及的细胞外液容积比预期的小。体内尿素传质系数必须被视为终末期肾病患者的个体和可变特征，在制定血液透析方案时应予以考虑。
