INTRADIALYTIC INFUSION OF DIALYSATE BOLUS FOR THE ESTIMATION OF ABSOLUTE BLOOD VOLUME IN HAEMODIALYSIS PATIENTS

Objectives: A relatively simple method has recently been proposed for the estimation of absolute blood volume (ABV) in haemodialysis (HD) patients, which involves intradialytic infusion of a dialysate bolus and visual assessment of the subsequent increase in the relative blood volume (RBV) displayed on the screen of the dialysis machine. The aim of this study was to propose an algorithm for an automated and more accurate assessment of such RBV increase, taking into account the possible noise and short-term variability in the RBV signals. Methods: The study was based on data collected during maintenance dialysis in 98 patients of the Vienna General Hospital, Austria performed with Fresenius 5008 machines. After 1 h of treatment, the dialysis was temporarily stopped in order to infuse 240 mL of dialysis fluid at the rate of 200 mL/min using the hemodiafiltration module. The RBV signals were recorded by the Blood Volume Monitor integrated in the dialysis machine. The performance of the algorithm was evaluated on data from patients with relatively undisturbed RBV signals available from two HD sessions from the same week of treatment. Results: We proposed an algorithm consisting of interpolation of the RBV signals and fitting them with 5th degree polynomials for up to 30 min before and after the bolus infusion. The intra-patient spread of the ABV estimated in two sessions from the same week using the fitted RBV curves was 182 mL, thus significantly lower (p < 0.001) compared with the simple two-point approach (462 mL). Conclusions: The proposed algorithm has the potential to be used in clinical practice for an automated estimation of ABV to support the proper ultrafiltration settings, although it needs to be validated on larger datasets and requires some improvements on the technical side of bolus infusion and RBV signal recording.