Depner T A
Nephrology Division, University of California, Davis, Sacramento 95817, USA.
Am J Nephrol. 1996;16(1):17-28. doi: 10.1159/000168966.
The interpretation of traditional serum urea and creatinine concentrations as indices of the severity of uremia requires major modifications in hemodialyzed patients. Although high urea concentrations usually signify worsening uremia and inadequate dialysis, low concentrations do not guarantee a good outcome. Urea production as modified by diet and other factors must also be included in a complete description of dialysis quantity and adequacy. The expression 'Kt/V' is a measure of hemodialysis that includes both urea removal and urea generation and is easy to measure from predialysis and postdialysis serum urea concentrations. Kt/V can be most precisely measured with the aid of mathematical models of urea kinetics during and between hemodialyses. Although a reliable measure of the dialysis dose received by most patients, the single-compartment model overestimates serum urea concentrations during hemodialysis and fails to predict the rebound immediately following dialysis. The classic two-compartment model that includes a factor for resistance to diffusion between the compartments, more accurately predicts the BUN profile but fails to account for blood flow-related disequilibrium including cardiopulmonary recirculation. Since solute disequilibrium reduces the effectiveness of hemodialysis, models that incorporate equilibrated urea concentrations both before and after hemodialysis are potentially more accurate tools for quantifying dialysis. Dialysate methods have the potential to accurately measure both solute removal which is the ultimate goal of dialysis, and patient clearance which is considered a better measure of the dialysis effect than dialyzer clearance. Application of these newer techniques requires major changes in sampling methods and changes in analytical equipment that will delay implementation. Meanwhile, analysis of blood-side urea concentrations using the single-compartment, variable volume model provides a reasonable estimate of Kt/V but must be interpreted with due consideration of its well-recognized pitfalls.
将传统的血清尿素和肌酐浓度作为尿毒症严重程度指标进行解读时，需要对血液透析患者进行重大修正。尽管高尿素浓度通常表明尿毒症恶化和透析不充分，但低浓度并不能保证良好的预后。饮食和其他因素对尿素生成的影响，也必须纳入透析量和充分性的完整描述中。“Kt/V”表达式是一种血液透析测量指标，它既包括尿素清除又包括尿素生成，并且可以根据透析前和透析后血清尿素浓度轻松测量。借助血液透析期间及透析之间尿素动力学的数学模型，可以最精确地测量Kt/V。尽管单室模型是大多数患者所接受透析剂量的可靠测量方法，但它高估了血液透析期间的血清尿素浓度，并且无法预测透析后立即出现的反跳。经典的双室模型包括一个隔室间扩散阻力因子，能更准确地预测血尿素氮（BUN）曲线，但无法解释包括心肺再循环在内的与血流相关的不平衡。由于溶质不平衡会降低血液透析的有效性，纳入透析前后平衡尿素浓度的模型可能是更准确的透析量化工具。透析液方法有可能准确测量溶质清除（这是透析的最终目标）以及患者清除率（被认为比透析器清除率更能衡量透析效果）。应用这些新技术需要在采样方法上进行重大改变，并更换分析设备，这将延迟实施。同时，使用单室可变体积模型分析血液侧尿素浓度可对Kt/V进行合理估计，但必须充分考虑其公认的缺陷来进行解读。
