连续性静脉-静脉血液滤过模式下置换液输注方式的数学解析

A mathematic analysis of different manners of replacement fluid infusion in continuous veno-venous hemofiltration

目的：建立连续性肾脏替代治疗（CRRT）时选择置换液输注方式的数学公式，为提高治疗效果提供根据。方法以连续性静脉-静脉血液滤过（CVVH）模式下采取不同方式输注置换液时的数学计算公式为例，与标准置换液的结果公式进行对比，分析不同输注方式的效果差异。①比较指标：CRRT回路单位时间内血浆容积（“V回”）及某电解质（若为其他溶质，则筛选系数需为1.0）的血浆浓度（“C回”）。②研究对象：实际置换液（以最为复杂的需要分为A、B两组分的置换液为例）前、后置换模式与标准置换液（即A、B一体）进行比较。③根据标准置换液公式，推导出前、后置换模式下，A、B液同向时同比例与不同比例，以及不同向时同比例与不同比例这4种情况下的公式。结果根据公式可以推算出，无论前、后置换模式，只有在A、B液同向、同比例输注时，“V回”（即静脉端和Return端，不含红细胞比容）与“C回”的结果与标准置换液的结果公式完全相同；其他情况下则存在差异，如在前置换模式和后置换模式下，①A、B液同向、不同比例时：“V回”、“C回”与标准置换液的不同在于，B液的比例发生了变化；②A、B液非同向、同比例时：“V回”与标准置换液是相同的；“C回”与标准置换液的不同之处在于，整个计算公式与标准置换液完全不同，且步骤更为复杂；③A、B液非同向、非同比例时：“V回”与标准置换液的不同在于，B液比例发生了变化，“C回”的不同不仅在于其中B液的比例发生了变化，而且整个计算公式与标准置换液完全不同。结论①当置换液需分组输注时，如碳酸氢盐配方，置换液的不同组分只有在同向、同比例方式的情况下才与原置换液配方的输注效果相同，其输注结果也可在医务人员的预料与掌控之内；否则需要根据公式反复计算，这样就会使医务人员难以掌控与判断置换液对患者血浆电解质及容量的影响趋势，可能导致严重的治疗失误，如脱水量数据不准确，甚至医源性的电解质紊乱。②数字公式可用于分析有类似分组置换液的情况，如使用枸橼酸局部抗凝时，可利用公式分析大量的枸橼酸溶液滤器前输注与置换液不同方向和输注比例所产生的结果。

ObjectiveTo establish a mathematical formula for choosing the manner of replacement fluid infusion in continuous renal replacement therapy （CRRT）, so as to provide the basis for improving the treatment effect. Methods A mathematical formula for choosing the manner of replacement fluid infusion with continuous veno-venous hemofiltration （CVVH） was taken as an example, and it was compared with the result of standard replacement fluid in order to analyze the effect of different manners of infusion.① Comparison parameters： the plasma volume （＂Vreturn＂） and some electrolyte concentration （＂Creturn＂） in back way of CRRT （if other thing was solute, filter coefficient should be 1.0）.② Research objects： the actual replacement fluid （for example, the most complex should be sorted into A and B type） mode （pre or post） was compared with the standard replacement fluid （the A and B in one）.③ Based on the formula of standard replacement, four equations in different conditions were derived： pre-dilution and post-dilution mode; same direction and same ratio; same direction and different ratio; different direction and same ratio; different direction and different ratio.Results The calculated results of ＂Vreturn＂ （except hematocrit） and ＂Creturn＂ were same to the standard only following the rule of same direction and ratio for A and B no matter pre-dilution mode or post-dilution mode, and it was different from the standard in others. In pre-dilution mode and post-dilution mode, it showed：① A and B in same direction and different ratio： ＂Vreturn＂ and ＂Creturn＂ were different from the standard for the alterative ratio of B.② A and B in different direction and same ratio： ＂Vreturn＂ was same to the standard, but ＂Creturn＂ was different from the standard for the completely different and more complex computational formula.③ A and B in different direction and different ratio： both ＂Vreturn＂ and ＂Creturn＂ were different from the standard. The different ＂Vreturn＂ was due to the different ratio of B. The different ＂Creturn＂ was caused by different ratio of B and the completely different computational formula.Conclusions① For parts of replacement fluid which must be separated （ for example, bicarbonate formula ）, the result is same to the standard, and is predicted and mastered only following the rule of same direction and ratio. Otherwise, we need to calculate the two parameters over and over again. The result will run out of our judgment. The wrongness of losing water and electrolyte disorders maybe come out.② Accordingly,the formula could be used to analyze the same case like the separated replacement infusion, for example, a large number of citrates as regional anticoagulation were infused only in the front of filter, while the replacement fluid can be done in varied forms.