Evaluation of daily fluid balance during continuous hemodialysis and filtration (CHDF)

Introduction

In critical care, accurate assessment of daily fluid balance is both necessary and important. We evaluated the accuracy of the calculated daily fluid balance during continuous hemodialysis and filtration (CHDF) by checking the relationship between two values: (a) daily fluid balance calculated from the balance sheet, and (b) daily body-weight change, a standard way of evaluating daily fluid balance.

Materials and methods

We studied data obtained from patients who underwent CHDF using one of two machines, CHF-1 or JUN-500 (Ube Medical Corporation, Tokyo, Japan). CHDF patients were randomly assigned to one or other of the machines: Group-A (14 patients) to CHF-1 and Group-B (7 patients) to JUN-500. We also studied the relationship between the two values, (a) and (b), above in 10 patients (Group C) not undergoing CHDF. Within each group, the correlation between values (a) and (b) was studied by regression analysis. Significance was defined as P < 0.05.

Results

The number of time-points studied was 32 in Group A, 22 in Group B, and 45 in Group C. Within each group, we saw a significant relationship for (a) versus (b), the coefficient numbers (r²) being 0.400 in Group A, 0.663 in Group B and 0.757 in Group C.

Discussion

JUN-500 has three pumps, providing a stricter regulation of rates of infusion and removal of fluids; this may have given more accurate management under CHDF than that achieved with CHF-1. During CHDF, a large amount of water may be infused and/or removed, and so a slight error in pump calibration can lead to a considerable inaccuracy in the daily fluid balance calculated from the balance sheet. This would result in a fairly low correlation number for (a) versus (b). In our Groups A and B, although we found significant relationships between the two values, the r² numbers were not particularly high. Therefore, using the above reasoning, we would have been unwise to draw conclusions about changes in daily fluid balance using balance-sheet data alone.

Conclusion

During CHDF, daily fluid balance still needs to be based on data obtained by measurement of daily weight change, not solely on data obtained from the fluid-balance sheet.