Nonlinear Parameter and State Estimation Approach for Intradialytic Measurement of Absolute Blood Volume

Background Managing blood and fluid volumes in chronic kidney disease (CKD) patients plays an essential role in dialysis therapy to replace kidney function. Objective This study aims to develop an estimation approach to provide predictable information on blood and fluid volumes during a regular dialysis routine. Methods The method utilizes a non-linear fluid volume model, an optimization technique, and the Unscented Kalman Filter (UKF). This method does not rely on specific ultrafiltration and dilution protocols and uses the Fisher information matrix to quantify the estimation error. Results The method was applied to 21 data sets of ten patients. A significant moderate correlation was obtained when estimated blood volumes were compared to a different method applied to the same data set. Average specific blood volumes were plausible and in the range of 78.7 and 75.9 mL/kg at the end of the high ultrafiltration rate pulse and above the critical level of 65 mL/kg. Critical blood volumes were only observed in four studies done on three patients. Conclusion The absolute blood volume estimated at the beginning and during every dialysis session offers the opportunity to detect critical blood volumes and to improve fluid management in CKD patients significantly.