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

To 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.

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.

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.

(1) 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.