Lowrie Edmund G, Li Zhensheng, Ofsthun Norma, Lazarus J Michael
Fresenius Medical Care (NA), Incorporated, Lexington, Massachusetts 02420, USA.
Kidney Int. 2002 Nov;62(5):1891-7. doi: 10.1046/j.1523-1755.2002.00642.x.
The normalized treatment ratio, Kt/V derived from urea kinetic models (UKM), is a commonly used measure of dialysis dose. This measure assumes that smaller patients with low volume of urea distribution (V) require proportionately less total treatment (Kt) than larger patients. The conclusion has been questioned because the UKM use assumptions that could make them invalid for accurately predicting a clinical outcome like survival. It is possible that a relationship exists between Kt and body size whereby a different Kt is required for different sizes. This study therefore explored the relationships among body size, Kt, and death risk focusing on possible interactions between Kt and size.
The sample included 43,334 patients treated on January 1, 1999. Survival time was modeled using Kt or body size groups to evaluate the shape of the risk profiles. Kt and the size measures were then evaluated together as continuous functions both in main effects (that is, Kt and size) and interaction models to see if the association of Kt with risk might be different for different sizes. The size measures were body weight, weight adjusted statistically for height, body surface area (BSA), weight divided by height (wt/ht) and the body mass index (BMI).
The log of risk decreased in rough linear fashion for Kt, weight, weight for height, and BSA. The log-risk relationships were "reverse J-shaped" for wt/ht and BMI. The main effects models suggested improved survival with increasing Kt and all of the size measures. Adding an interaction term increased the benefit associated with increasing Kt and for weight, weight for height and BSA at low values of Kt and size. A significant, positive interaction term mitigated those effects at higher values. Thus, the death risk penalties associated with reducing Kt among small patients were as great as or greater than they were among large patients. A similar pattern was observed for V. Adding the interaction to the BMI model destroyed the main effects, so that there was no significant association between risk and either Kt or BMI. A cross-categorical model of BMI and Kt, however, revealed improving survival with increasing Kt among both low and high BMI patients throughout the range of Kt.
Evidence supporting the intuition that smaller patients require proportionately lower dialysis dose than larger patients was not found. To the contrary, smaller patients suffer as much risk as or more risk than larger patients from reducing Kt. Deciding dialysis treatment using a Kt/V based intuition may lead to avoidable under-dialysis particularly among small patients.
源自尿素动力学模型（UKM）的标准化治疗比Kt/V是一种常用的透析剂量衡量指标。该指标假定，尿素分布容积（V）较小的体型较小的患者相比体型较大的患者，所需的总治疗量（Kt）成比例地更少。这一结论受到了质疑，因为UKM所采用的假设可能使其在准确预测诸如生存率等临床结局方面无效。Kt与体型之间可能存在一种关系，即不同体型需要不同的Kt。因此，本研究探讨了体型、Kt和死亡风险之间的关系，重点关注Kt与体型之间可能的相互作用。
样本包括1999年1月1日接受治疗的43334例患者。使用Kt或体型分组对生存时间进行建模，以评估风险曲线的形状。然后将Kt和体型指标作为连续函数在主效应模型（即Kt和体型）以及交互作用模型中进行共同评估，以查看Kt与风险之间的关联对于不同体型是否可能有所不同。体型指标包括体重、根据身高进行统计学调整后的体重、体表面积（BSA）、体重除以身高（wt/ht）以及体重指数（BMI）。
Kt、体重、身高校正体重和BSA的风险对数呈大致线性下降。wt/ht和BMI的对数风险关系呈“倒J形”。主效应模型表明，随着Kt以及所有体型指标的增加，生存率有所提高。添加交互项增加了在Kt和体型值较低时，Kt增加以及体重、身高校正体重和BSA增加所带来的益处。在较高值时，一个显著的正交互项减轻了这些影响。因此，体型较小的患者中降低Kt所带来的死亡风险惩罚与体型较大的患者一样大甚至更大。对于V也观察到了类似模式。将交互项添加到BMI模型中破坏了主效应，因此风险与Kt或BMI之间均无显著关联。然而，BMI和Kt的交叉分类模型显示，在整个Kt范围内，低BMI和高BMI患者中随着Kt增加生存率均有所提高。
未找到支持体型较小的患者相比体型较大的患者需要成比例更低透析剂量这一直觉的证据。相反，体型较小的患者因降低Kt而承受的风险与体型较大的患者一样大甚至更大。基于Kt/V的直觉来决定透析治疗可能会导致可避免的透析不足，尤其是在体型较小的患者中。
