Lindley Elizabeth J, Chamney Paul W, Wuepper Andreas, Ingles Helen, Tattersall James E, Will Eric J
Department of Renal Medicine, St James's University Hospital, Leeds, UK.
Nephrol Dial Transplant. 2009 Jan;24(1):211-6. doi: 10.1093/ndt/gfn457. Epub 2008 Aug 12.
The availability of haemodialysis machines equipped with on-line clearance monitoring (OCM) allows frequent assessment of dialysis efficiency and adequacy without the need for blood samples. Accurate estimation of the urea distribution volume 'V' is required for Kt/V calculated from OCM to be consistent with conventional blood sample-based methods.
Ten stable HD patients were monitored monthly for 6 months. Time-averaged OCM clearance (K(OCM)) and pre- and post-dialysis blood samples were collected at each monitored session. The second generation Daugirdas formula was used to calculate the single-pool variable volume Kt/V, (Kt/V)(D). Values of V to allow comparison between OCM and blood-based Kt/V were determined from Watson's formula (V(Watson)), bioimpedance spectroscopy (V(BIS)), classical urea kinetic modelling (V(UKM_C)) and a simple computation of V (V(UKM_S)) from the blood-based Kt/V and K(OCM)t.
Comparison of K(OCM)t/V with (Kt/V)(D) shows that using V(Watson) leads to significant systematic underestimation of dialysis dose. K(OCM)t/V(BIS) agrees with (Kt/V)(D) to within +/- 10%. K(OCM)t/V(UKM_S) is, by definition, identical to (Kt/V)(D) when initially calculated. However, if a historical value of V is used, agreement between K(OCM)t/V and (Kt/V)(D) over 6 months varies by 5% for V(BIS) and 10% for V(UKM_S).
When investigating the effect of different treatment strategies on dialysis efficiency, any estimate of V can be used provided it is constant, as K is the relevant parameter. When frequent supervision of actual dialysis dose is required, the greatest consistency between K(OCM)t/V and the reference, Kt/V(D), over time is achieved with V(BIS).
配备在线清除率监测（OCM）的血液透析机的出现，使得无需采集血样就能频繁评估透析效率和充分性。为了使通过OCM计算得到的Kt/V与基于传统血样的方法一致，需要准确估算尿素分布容积“V”。
对10例稳定的血液透析患者进行为期6个月的每月监测。在每次监测期间收集时间平均OCM清除率（K(OCM)）以及透析前和透析后的血样。使用第二代Daugirdas公式计算单池可变容积Kt/V，即(Kt/V)(D)。通过Watson公式（V(Watson)）、生物电阻抗光谱法（V(BIS)）、经典尿素动力学建模（V(UKM_C)）以及根据基于血样的Kt/V和K(OCM)t对V进行的简单计算（V(UKM_S)）来确定V的值，以便比较OCM和基于血样的Kt/V。
将K(OCM)t/V与(Kt/V)(D)进行比较表明，使用V(Watson)会导致透析剂量出现显著的系统性低估。K(OCM)t/V(BIS)与(Kt/V)(D)的一致性在±10%以内。根据定义，最初计算时K(OCM)t/V(UKM_S)与(Kt/V)(D)相同。然而，如果使用V的历史值，在6个月内K(OCM)t/V与(Kt/V)(D)之间的一致性对于V(BIS)而言变化为5%，对于V(UKM_S)而言变化为10%。
在研究不同治疗策略对透析效率的影响时，只要V是恒定的，任何对V的估算都可以使用，因为K是相关参数。当需要频繁监测实际透析剂量时，使用V(BIS)能使K(OCM)t/V与参考值Kt/V(D)在较长时间内保持最大程度的一致性。
