CVVH模式下置换液及枸橼酸输注的数学计算模型设计与分析

A mathematical calculation model of replacement fluid and citric acid infusion in continuous veno-venous hemofiltration

目的为便于更好地理解与掌握连续性静脉-静脉血液滤过(CVVH)模式下置换液与枸橼酸抗凝剂输注的数学逻辑,设计一种数学计算模型.方法首先对CVVH模式下各参数进行定义,以滤器前输注的主体置换液称为A液,5%碳酸氢钠为B液,枸橼酸为T液;以滤器后输注的主体置换液称为a液,5%碳酸氢钠为b液.然后进行逻辑转换,将回路终端液体(Z)分为X、Y两部分,X为经过滤器处理后的残留原血浆;Y为在体外循环过程中最终混入原血浆的残留非血浆成分,包括前置换液、枸橼酸流经滤器后的剩余部分及后置换液.根据CVVH原理及滤器对不同物质的筛选系数,列出单位时间内X、Y、Z处的液体容积及电解质浓度的数学公式;再将此公式录入Excel单元格,最后制成数学计算模型,并进行举例模拟计算.结果将所得的X、Y、Z处的容积计算公式、电解质计算公式、总钙计算公式录入Excel单元格建立CVVH计算模型,通过模拟计算显示,非枸橼酸抗凝时,只有保持A、B和(或)a、b同向同比输注时,Y处的Na^+、K^+、Cl^-、HCO3^-与原配方结果一致,且不随血流量等参数的改变而改变;采用其他方式(如同向不同比、同比不同向等)输注时,一旦调整其中任何一个参数(如血流量、置换液量等),Y处的计算结果均有不同程度的变化,进而使Z处的电解质水平也随之改变.枸橼酸抗凝时,调整任何一种模式与参数,均会导致Y、Z处的电解质出现不同的结果.无论采用何种模式及参数配伍,回路的总Ca2+浓度变化不大.结论将CVVH置换液录入Excel计算模型,可以囊括各种输注方式的搭配,并能直观呈现各种搭配方式的结果,有利于医务人员的逻辑分析与风险预估.

Objective To design a mathematical calculation model for better understanding and grasping the logical problem of replacement fluid and citric acid anticoagulant infusion in continuous veno-venous hemofiltration (CVVH). Methods ① Parameter definition: A, B, and T were respectively called the main part of pre-replacement fluid, 5% sodium bicarbonate solution, and 4% sodium citrate infused before filter. And a and b were respectively called the main part of post-replacement fluid, and 5% sodium bicarbonate solution infused after filter.② Logic conversion:The liquid in back terminal (Z) was artificially divided into two parts. One (X) was the original residual plasma after filtration. The second (Y) was the part excluding the plasma, including the left part of pre-replacement fluid with sodium citrate, and the post-replacement fluid.③The mathematical formulas of liquid volume and electrolyte concentration at X, Y and Z in unit time were listed according to the principle of CVVH and the screening coefficient of filter for different substances.④The calculation formulas were entered into Excel form, and a mathematical calculation model was made, and a simulation calculation with examples was carried out. Results An Excel model was established by inserting the calculation formulas of volume, electrolyte, and total calcium at X, Y and Z. And it was found that the concentration of Na^+, K^+, Cl^-, HCO3^- at Y point remained unchanged only when A, B and (or) a, b was kept in same side and proportion even with the change of blood flow and other parameters without sodium citrate as anticoagulant. Once any of the parameters (such as blood flow, replacement fluid volume, etc.) were adjusted in other infusion methods (such as different ratios, different directions of the same year, etc.), the calculation results at Y would vary, and the electrolyte concentration at Z would change accordingly. A change of dilution model or parameter would result in the change of the electrolyte concentration at Y and Z with sodium citrate as anticoagulant. The concentration of total calcium scarcely changed no matter in what model and parameters. Conclusions All kinds of infusion ways could be included in the Excel model. The infusion results of all kinds of infusion matching could be intuitively evaluated. It is helpful for the medical staff to make a logical analysis and risk prediction in CVVH.