Flanigan M J
Department of Medicine, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242-6040, USA.
Kidney Int Suppl. 2000 Aug;76:S72-8. doi: 10.1046/j.1523-1755.2000.07609.x.
Sodium chloride is the most abundant salt in extracellular fluid. In normal individuals, the tonicity exerted by dissolved sodium chloride determines plasma osmolality and indirectly determines intracellular tonicity and cell volume. Uremic patients retain nitrogenous wastes and have an elevated plasma osmolality. While urea exhibits osmotic activity in serum, no sustained gradient can be established across cell boundaries because it readily diffuses through cell membranes. Thus, sodium remains the major indicator of body tonicity and determines the distribution of water across the intracellular-extracellular boundary, subsequent cell volume, thirst, and, among patients with renal insufficiency, systemic blood pressure. As a result of highly conserved plasma tonicity control systems, uremic subjects demonstrate remarkable stability of their serum sodium. Dialysate is a synthetic interstitial fluid capable of reconstituting extracellular fluid composition through urea extraction and extremely efficient solute and solvent (salt and water) transfer to the patient. Subtle transdialyzer gradients deliver and remove large quantities of trace elements, solvent, and solute to patients, creating a variety of dialysis "disequilibrium" syndromes manifest as cellular and systemic distress. Every dialysis patient uses dialysate, and the most abundant chemicals in dialysate are salt and water. Despite its universal use, no consensus on dialysate composition or tonicity exists. This can only be explained if we believe that dialysate composition is best determined by matching unique dialysis delivery system characteristics to specific patient requirements. Such a paradigm treats dialysate as a drug and the dialysis system as a delivery device. Understanding the therapeutic and toxic profiles of this drug (dialysate) and its delivery device (the dialyzer) is important to safe, effective, goal-directed modifications of therapy. This article explores some of the historical rationale behind choosing specific dialysate tonicities.
氯化钠是细胞外液中含量最丰富的盐。在正常个体中，溶解的氯化钠所产生的张力决定血浆渗透压，并间接决定细胞内张力和细胞体积。尿毒症患者会潴留含氮废物，血浆渗透压升高。虽然尿素在血清中具有渗透活性，但由于它能轻易透过细胞膜，因此无法在细胞边界建立持续的浓度梯度。所以，钠仍然是机体张力的主要指标，决定着水在细胞内外边界的分布、随后的细胞体积、口渴感，以及在肾功能不全患者中还决定着系统血压。由于血浆张力控制系统高度保守，尿毒症患者的血清钠表现出显著的稳定性。透析液是一种合成的细胞间液，能够通过尿素清除以及向患者高效转移溶质和溶剂（盐和水）来重构细胞外液成分。细微的跨透析器梯度会向患者输送和清除大量微量元素、溶剂和溶质，从而引发各种表现为细胞和全身不适的透析“失衡”综合征。每位透析患者都会使用透析液，而透析液中含量最丰富的化学物质就是盐和水。尽管透析液被广泛使用，但对于其成分或张力尚无共识。只有当我们认为透析液成分最好通过将独特的透析输送系统特性与特定患者需求相匹配来确定时，这一点才能得到解释。这种模式将透析液视为一种药物，将透析系统视为一种输送装置。了解这种药物（透析液）及其输送装置（透析器）的治疗和毒性特征对于安全、有效地进行目标导向的治疗调整非常重要。本文探讨了选择特定透析液张力背后的一些历史依据。
