ABSTRACT
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.
ABSTRACT
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.